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CHARACTERIZATION OF NEAR-DEATH
EXPERIENCES & THEIR EXPERIENCERS
Charlotte Martial
THESE PRESENTEE EN VUE DE L’OBTENTION DU GRADE DE
Docteur en Sciences biomédicales
Année académique 2017-2018
Under the supervision of
Prof Steven LAUREYS,
Coma Science Group,
GIGA-Consciousness
Supervisor
Prof. Steven Laureys, MD, PhD, Liège Université
Assessment committee
Prof. Didier Ledoux (president), MD, PhD, Liège Université
Prof. Pierre Damas, MD, PhD, Liège Université
Prof. Vincent Bonhomme, MD, PhD, Liège Université
Prof. Christophe Phillips, PhD, Liège Université
Prof. Arnaud D’Argembeau, PhD, Liège Université
Prof. Filip Raes, PhD, Leuven Universiteit
Prof. Susan Blackmore, PhD, Plymouth University
Cover design:
© Charlotte Martial, 2018
Original drawing by Philippe Martial
This research was supported by the Belgian National Funds for Scientific Research (F.R.S.-
FNRS), the European Commission (European ICT Programme Projects FP7-247919 DECODER),
BIAL Foundation, Human Brain Project, Luminous project, Fonds Léon Fredericq, the James
McDonnell Foundation, the French Speaking Community Concerted Research Action, Mind
Science Foundation, personal travel grants from F.R.S.-FNRS and the University and University
Hospital of Liège.
To all the near-death experiencers
who have kindly shared with
us their experience.
To all the people with whom I had the pleasure
of having inspiring discussions about
near-death experiences.
Table of content
Acknowledgements .......................................................................................... vii
Scientific publications ....................................................................................... xi
List of abbreviations ........................................................................................xiv
Abstract ........................................................................................................ xviii
Résumé ......................................................................................................... xviii
1 Introduction .................................................................................................1
1.1 Description of the phenomenon ..............................................................4
1.2 Specific phenomenological features ........................................................9
1.3 Identifying near-death experiencers ...................................................... 13
1.4 “Near-death-like” experiences .............................................................. 17
1.5 Distressing near-death experiences ....................................................... 19
1.6 Particularity of the resulting memory .................................................... 21
1.7 Near-death experiencers’ characteristics ............................................... 23
1.8 Explanatory models for near-death experiences .................................... 26
1.9 Research on the topic of near-death experiences ................................... 34
1.10 Objectives & overview of the present work ........................................... 38
2 Study 1: Phenomenological characterization of the NDE memory ............. 39
2.1 Summary .............................................................................................. 40
2.2 Background .......................................................................................... 41
2.3 Material & methods .............................................................................. 45
2.4 Results ................................................................................................. 48
2.5 Discussion ............................................................................................ 52
3 Study 2: Temporality of features in NDE narratives .................................. 56
3.1 Summary .............................................................................................. 57
3.2 Background .......................................................................................... 58
3.3 Material & methods .............................................................................. 60
3.4 Results ................................................................................................. 66
3.5 Discussion ............................................................................................ 74
4 Study 3: False memory susceptibility in NDE experiencers ....................... 79
4.1 Summary .............................................................................................. 80
4.2 Background .......................................................................................... 81
4.3 Material & methods .............................................................................. 85
4.4 Results ................................................................................................. 89
4.5 Discussion ............................................................................................ 97
5 Study 4: Fantasy proneness in NDE experiencers .................................... 103
5.1 Summary ............................................................................................ 104
5.2 Background ........................................................................................ 105
5.3 Material & methods ............................................................................ 107
5.4 Results ............................................................................................... 110
5.5 Discussion .......................................................................................... 113
6 Conclusion & future perspectives ............................................................ 117
7 References ............................................................................................... 132
Acknowledgements
Je tiens à remercier toutes les personnes qui ont participé à
l’accomplissement de ce projet. Je pense que la thèse est loin d'être un
travail solitaire et je n’aurais jamais pu réaliser cette these sans le soutien
d’une multitude de personnes dont l’aide, la motivation et l’intérêt
manifestés à l’égard de mes recherches m’ont permis de progresser.
Je tiens tout d’abord à exprimer mes plus vifs remerciements à mon
promoteur, le Prof. Steven Laureys, pour ses multiples conseils avisés, sa
passion envers la recherche et sa curiosité à l’égard du phénomène des
expériences de mort imminente. Je le remercie également pour m’avoir fait
confiance, pour m’avoir appris à être plus autonome tout au long de ce
travail de recherche et m’avoir enseigné les réflexes du « bon » chercheur.
Je remercie chaleureusement les membres de mon comité
d’accompagnement de thèse, pour votre intérêt envers mes recherches et vos
conseils judicieux lors de mes présentations d’avancement de thèse: le Prof.
Pierre Damas, le Prof. Didier Ledoux, le Prof. Christophe Phillips, le Prof.
Vincent Bonhomme, et tout particulièrement le Prof. Arnaud D’Argembeau
pour sa transmission d’une méthode de travail rigoureuse dans le cadre
d’autres projets de recherche. Ma gratitude va également aux membres
externes du jury, le Prof. Filip Raes et le Prof. Susan Blackmore, merci
d’avoir accepté de prendre le temps de lire ce travail et de l’évaluer.
Je tiens à remercier tout particulièrement mes deux « collègues NDE
»: Héléna Cassol et Vanessa Charland-Verville. Ce travail n’aurait jamais
abouti sans votre aide, votre clairvoyance et vos réflexions. Nos projets
communs ont pu voir le jour grâce aux efforts que vous leur avez consacrés.
Un merci particulier à Héléna: j’aimerais lui dire à quel point j’apprécie
travailler avec elle et à quel point j’admire ses qualités humaines d’écoute et
d’empathie. Parmi bien d’autres qualités, j’apprécie particulièrement sa
capacité de raisonnement et sa pondération, surtout quand ça permet
d’adoucir mon « côté (trop) fonceuse ». On forme une bonne équipe et
« l'aventure NDE » n’est pas finie!
Je voudrais remercier chaleureusement quatre collègues et maintenant
amies précieuses, sans qui mon travail au Coma Science Group n’aurait pas
pu être aussi plaisant. Géraldine Martens, Sarah Wannez, Charlène Aubinet
et Héléna Cassol, merci pour le travail que vous fournissez dans l’équipe.
Plus personnellement, merci pour votre soutien, votre attention, votre écoute
en toutes circonstances et... votre humour. C’est clair et net: la période de
doctorat n’aurait pas pu être si amusante et fructueuse sans nos petites
pauses café journalières.
Je tiens à remercier les « vieilles »: Aurore Thibaut, Audrey
Vanhaudenhuyse, Olivia Gosseries, Camille Chatelle et Athena Demertzi.
Merci pour vos conseils avisés et votre disponibilité malgré votre charge de
travail conséquente. Un merci particulier à Aurore, sans qui je n’aurais peut-
être jamais connu le Coma Science Group.
Je remercie chaleureusement tous les autres membres de l’équipe du
Coma Science Group, toujours présents ou qui sont partis vers d’autres
aventures, pour m’avoir appris plein de choses et aidée dans différents
projets. Un merci particulier à: Lizette Heine (notamment pour
l’apprentissage des analyses fMRI; on a bien rit aussi, n’est-ce pas
Charlène?), Jitka Annen, Carol Di Perri, Stephen Larroque, Manon Carrière,
Yorgos Antonopoulos, Enrico Amico, Olivier Bodart, Andrea Piarulli,
Armand Mensen, Murielle Kirsch, Nicolas Lejeune, Evelyne Melotte,
Maire-Aurélie Bruno, Rajanikant Panda, Audrey Wolff, Severine
Blandiaux, Aldo Camargo, Nicolas Depaye, Alice Barra et Leandro Sanz.
Merci également à nos deux secrétaires médicales, Caroline Simays et
Alexandra Meys, sans qui notre travail clinique et nos recherches ne seraient
pas possible. Merci à elles également pour leur précieuse patience.
J’exprime également ma gratitude aux autres membres du GIGA et tout
spécialement au Prof. Marie-Elisabeth Faymonville, Emma Delhaye, Sarah
François, Marine Manard et Mohamed Ali Bahri. Je tiens aussi à remercier
les membres d’autres équipes avec qui j’ai la chance de collaborer:
notamment Anne-Françoise Donneau, Harald Merckelbach, Hedwige Dehon
et Jean-Pierre Jourdan. Mes remerciements vont également à l’Université de
Liège, aux personnels des services de neurologie, des soins intensifs et
d’imagerie médicale du Centre Hospitalier Universitaire de Liège, qui
fournissent un travail de qualité dans l’évaluation et l’accompagnement des
patients qui vivent un coma et aux patients en état de conscience altéré, ainsi
qu’à leur famille. Votre travail facilite grandement nos recherches.
Un tout grand merci à vous tous, chers « expérienceurs », qui avez
contribué à nos travaux et nous avez fait confiance en partageant un « bout »
de votre vie. Nous ne saurions qu’apprécier votre aide précieuse et
indispensable.
Je tiens à remercier vivement mes ami(e)s et particulièrement, Sarah,
Amandine, Elisa, Fanny et Marie avec qui j’ai souvent pu partager ce que je
vivais tout au long du doctorat. Merci de m’avoir soutenue, pour votre
optimisme et d’avoir toujours cru en moi. J’aimerais vous dire oh combien
j’apprécie votre présence.
Et mes parents... ah mes parents! Je ne sais si un jour je pourrais les
remercier comme il se doit pour tout ce qu’ils ont fait pour moi. Vous avez
toujours cru en moi, vous avez toujours veillé sur moi et m’avez toujours
poussée à aller plus loin dans ma vie professionnelle. Votre fierté et votre
amour me portent et me guident tous les jours.
Et enfin... Merci à toi, Henri! Merci simplement d’être là à mes côtés,
pour ton écoute quand mes projets de recherche envahissent un peu notre vie
privée et pour ta patience quand tu me vois moins car je suis souvent partie
à l’étranger. Merci d’avoir été l’épaule réconfortante et le complice de mes
plus beaux moments. Notre couple grandissant sert en quelques sortes de
support à l’épanouissement de mes projets scientifiques.
Scientific publications
The present thesis is based on the following publications:
Articles:
Martial, C., Cassol, H., Charland-Verville, V., Merckelbach, H. & Laureys, S.
(under review). Fantasy proneness correlates with near-death experiences, but
only when they developed outside a life-threatening context.
Martial, C., Charland-Verville, V., Cassol, H., Didone, V., Van Der Linden, M. &
Laureys, S. (2017). Intensity and memory characteristics of near-death
experiences. Consciousness and Cognition, 56, 120–127.
Martial, C., Cassol, H., Antonopoulos, G., Charlier, T., Herosa, J., Donneau, A.-F.,
Charland-Verville, V.* & Laureys, S.* (2017). Temporality of features in
near-death experience narratives. Frontiers in Human Neuroscience, 11, 311.
Martial, C., Charland-Verville, V., Dehon, H.* & Laureys, S.* (2017). False memory susceptibility in coma survivors with and without a near-death
experience. Psychological Research, 1–13.
Book chapter:
Charland-Verville, V., Martial, C., Cassol, H. & Laureys, S. (2017). Near-death
experiences: actual considerations. In C. Schnakers & S. Laureys (Eds.),
Coma and Disorders of Consciousness, 2nd edition (pp. 235–263), Springer.
Other publications:
Articles (as co-author):
Chatelle, C., Hauger, S., Martial, C., Becker, F., Eifert, B., Boering, D., Giacino,
J., Laureys, S., Lovstad, M. & Maurer-Karattup, P. (in press). Assessment of nociception and pain in participants with unresponsive or minimally
conscious state after acquired brain injury: the relationship between the
Coma Recovery Scale-Revised and the Nociception Coma Scale-Revised.
Archives of Physical Medicine and Rehabilitation
Thibaut, A., Chatelle, C., Vanhaudenhyse, A., Martens, G., Cassol, H., Barra, A.,
Martial, C., Carrière, M., & Laureys, S. (in press). Transcranial direct
current stimulation unveils covert consciousness. Brain Stimulation
Mélotte, E.*, Maudoux, A.*, Delhalle, S., Martial, C., Antonopoulos, G.,
Larroque S., Wannez, S., Faymonville, M-E., Kaux, J-F., Laureys, S.*, Gosserie, O.* & Vanhaudenhuyse, A.* (in press). Is oral feeding compatible
with an unresponsive wakefulness syndrome? Journal of Neurology
Cassol, H.*, Pétré, B.*, Degrange, S., Martial, C., Charland-Verville, V., Bragard,
I., Guillaume, M.* & Laureys, S.* (2018). Qualitative thematic analysis of
the phenomenology of near-death experiences. PLoS One, 13(2), e0193001.
Cassol, H., Aubinet, C., Thibaut, A., Wannez, S., Martial, C., Martens, G. & Laureys, S. (2018). Diagnostic, pronostic et traitements des troubles de la
conscience. Neurologie - Psychiatrie – Gériatrie, 8, 47–49.
Di Perri, C.*, Amico, E.*, Heine, L., Annen, J., Martial, C., Larroque, S., Soddu,
A., Marinazzo, D. & Laureys, S. (2017). Multifaceted brain networks reconfiguration in disorders of consciousness uncovered by co-activation
patterns. Human Brain Mapping, 39, 89–103.
Wannez, S., Heine, L., Thonnard, M., Gosseries, O., Laureys, S. et al. [Coma
Science Group collaborators, including Martial, C.] (2017). The repetition
of behavioral assessments in disorders of consciousness. Annals of
Neurology, 81(6), 883-889.
Wannez, S.*, Hoyoux, T.*, Langohr, T., Bodart, O., Martial, C., Wertz, J.,
Chatelle, C., Verly, J.G., & Laureys, S. (2017). Objective assessment of
visual pursuit in patients with disorders of consciousness: an exploratory
study. Journal of Neurology, 264(5), 928–937.
Wannez, S., Gosseries, O., Azzolini, D., Martial, C., Cassol, H., Aubinet, C.,
Annen, J., Martens, G., Bodart, O., Heine, L., Charland-Verville, V.,
Thibaut, A., Chatelle, C., Vanhaudenhuyse, A., Demertzi, A., Schnakers, C.,
Donneau, A.-F. & Laureys, S. (2017). Prevalence of Coma-Recovery Scale-
Revised signs of consciousness in patients in a minimally conscious state.
Neuropsychological Rehabilitation, 11, 1–10.
Amico, E., Marinazzo, D., Di Perri, C., Heine, L., Annen, J., Martial, C., Dzemidzic, M., Laureys, S.* & Goñid, J.* (2017). Mapping the functional
connectome traits of levels of consciousness. NeuroImage, 148, 201–211.
Amico, E., Bodart, O., Rosanova, M., Gosseries, O., Heine, L., Van Mierlo, P.,
Martial, C., Massimini, M., Marinazzo, D.* & Laureys, S.* (2017).
Tracking dynamic interactions between structural and functional connectivity: a TMS/EEG-dMRI study. Brain Connectivity, 7(2), 84–97.
Cavaliere, C.*, Aiello, M.*, Di Perri, C., Amico, E., Martial, C., Thibaut, A.*,
Laureys S.* & Soddu, A.* (2016). Functional connectivity substrates for tDCS response in Minimally Conscious State patients. Frontiers in Cellular
Neuroscience, 10, 257.
Annen, J.*, Heine, L.*, Ziegler, E., Frasso, G., Bahri, M., Di Perri, C., Stender, J.,
Martial, C., Wannez, S., Amico, E., Antonopoulos, G., Bernard, C.,
Tshibanda, J-F., Hustinx, R., & Laureys, S. (2016). Function-structure
uncoupling in patients with severe brain injury as measured by MRI-DWI and FDG-PET. Human Brain Mapping, 37(11), 3707–3720
Heine, L.*, Castro, M.*, Martial, C., Tillmann, B., Laureys, S.* & Perrin, F.*
(2015). Exploration of functional connectivity during preferred music
stimulation in patients with disorders of consciousness. Frontiers in
Psychology, 6, 1704.
Thibaut, A., Di Perri, C., Chatelle, C., Bruno, M.-A., Ali Bahri, M., Wannez, S.,
Piarulli, A., Bernard, C., Martial, C., Heine, L., Hustinx, R., & Laureys, S.
(2015). Clinical response to tdcs depends on residual brain metabolism and grey matter integrity in patients with minimally conscious state. Brain
Stimulation, 8(6), 1116–1123.
Non-peer-reviewed article:
Stephan, S., Radiguer, F., Martial, C., Franconie, C., Laureys, S., & Wauquiez, G. (2017). États de conscience altérée: quel rôle pour les neuropsychologues?
Neurologies, 20, 288–294.
List of abbreviations
ANOVA Analysis Of Variance
CEI Childhood Experience Inventory
CEQ Creative Experiences Questionnaire
DES Dissociative Experience Scale
DRM Deese–Roediger–McDermott
EEG Electroencephalogram
fMRI Functional magnetic resonance imaging
IANDS International Associations for Near-Death Studies
ICMI Inventory of Childhood Memories and Imaginings
LTS Life-Threatening Situation
MCQ Memory Characteristics Questionnaire
MHVS Mill Hill Vocabulary Scale
NDE Near-Death Experience
NDE-like Near-Death-like Experience
NDE-6 Near-Death Experience Scale-6
NMDA N-Methyl-D-Aspartate
OBE Out-of-Body Experience
REM Rapid-Eye Movement
SEM Standard Error of the Mean
SD Standard Deviation
SMS Self-Memory System
WCEI Weighted Core Experience Index
Abstract
When facing a life-threatening situation –or a situation perceived as such, some
people will report having lived various phenomenological experiences (e.g., out-of-
body experiences –OBEs, encountering deceased relatives) that are intriguing by their
extra-ordinary aspect. These distinct perceptual experiences are commonly referred to
as the phenomenon of “near-death experience” (NDE). To date, the scientific
literature devoted to this phenomenon contains a predominance of opinion and review
articles, while there is a lack of empirical investigations that try to understand its rich
phenomenology. Through four data-driven studies, we had two main objectives: (1) to
better characterize the memory of NDE, as well as (2) to better define the cognitive
profile of their experiencers (i.e., people who have experienced a NDE).
Study 1: We began by testing the hypothesis stating that the phenomenological
characteristics of NDE memory could vary with the reported experience’s intensity.
Using the Memory Characteristics Questionnaire (MCQ) and the Greyson NDE scale,
we compared the phenomenological characteristics of NDE memories with the
intensity of the NDE. Our results suggested that participants who described more
intense NDEs also reported more phenomenological memory characteristics of NDE.
Using MCQ items, our study also showed that the intensity of the NDE is associated
in particular with sensory details, personal importance of the event and reactivation
frequency (i.e., the frequency of subsequently thinking and talking about the event)
variables.
Study 2: Phenomenologically, a NDE can be described as a set of
distinguishable features; however, the actual temporality sequence of NDE core
features remains a poorly expored area. Therefore, we aimed at investigating the
frequency distribution of these features (globally and according to the position of
features) as well as the most frequently reported temporality sequences of features in
freely expressed written NDE narratives. Our analyses highlighted the recurrent
sequences of NDE features reported in narratives but showed that overall NDE
features do not appear in a strict temporal order, but rather in a variable one (i.e., differ
across NDE experiencers).
Study 3: To meet our second main objective of characterizing the cognitive
profile of NDE experiencers, we examined their susceptibility to false memories using
the Deese–Roediger–McDermott (DRM) paradigm and to illusory recollection using
the “Remember/Know/Guess” judgments, as compared to matched volunteers. Our
results demonstrated that NDE experiencers were equally likely to produce false
memories as matched volunteers, but that they recalled them more frequently
associated with compelling illusory recollection. Of particular interest, source
monitoring was less successful in NDE experiencers compared to matched volunteers.
Study 4: In parallel with the hypothesis stating that some specific psychological
factors may play an important role in the generation (or recall) of a NDE, our last
study aimed at assessing fantasy and imaginary involvement of NDE experiencers.
Using the Creative Experiences Questionnaire (CEQ) we assessed fantasy engagement
in individuals who developed NDEs in the presence (i.e., “classical” NDEs) or
absence (i.e., “NDEs-like”) of a life-threatening situation. Our results showed that the
reported intensity of the NDEs was positively correlated with engagement in fantasy
and that fantasy proneness may constitute a psychological predisposition for the
occurrence of NDEs-like.
Two main conclusions can be drawn from the present thesis. In the two first
studies, we observed an association between the reported intensity of the NDE and the
phenomenological characteristics of its resulting memory, and variations in the
chronological order of appearance of the features. Secondly, by investigating the NDE
experiencers’ cognitive profile, the results of the two last studies provide evidence that
some cognitive and personality factors may play a role in the generation (or recall) of
a NDE.
Résumé
Lorsqu’elles sont confrontées à une situation potentiellement mortelle ou à
une situation perçue comme telle, certaines personnes déclarent avoir vécu diverses
expériences phénoménologiques (par exemple, une expérience de décorporation, la
rencontre avec des proches décédés) qui sont intrigantes par leur aspect « extra-
ordinaire ». Ces expériences perceptuelles sont communément appelées «
expérience de mort imminente » (EMI). À ce jour, la littérature scientifique
consacrée à ce phénomène contient une prédominance d'articles d'opinion et
d’articles de synthèse, alors qu’il y a un manque important d’études empiriques qui
tentent de comprendre sa riche phénoménologie. En réalisant quatre études, nos
objectifs principaux sont de mieux caractériser (1) le souvenir d’EMI, ainsi que (2)
le profil cognitif de leurs « expérienceurs » (c'est-à-dire, les personnes ayant vécu
une EMI).
Étude 1: Nous avons tout d’abord testé l'hypothèse selon laquelle les
caractéristiques phénoménologiques du souvenir de l’EMI pourraient varier en
fonction de l'intensité de l'expérience rapportée. À l'aide du « Memory
Characteristics Questionnaire » (MCQ) et de l'échelle « EMI de Greyson », nous
avons comparé les caractéristiques phénoménologiques du souvenir de l’EMI avec
l'intensité rapportée de celle-ci. Nos résultats suggèrent que les participants qui ont
décrit des EMI plus intenses ont également rapporté une quantité plus importante
de caractéristiques phénoménologiques du souvenir de l’EMI. En utilisant les items
du MCQ, notre étude a également montré que l'intensité de l’EMI est associée en
particulier aux variables liées aux détails sensoriels, à l'importance personnelle que
l’expérience a pour eux et à la fréquence de réactivation (c'est-à-dire, la fréquence à
laquelle ils ont repensé ou parlé de l’évènement).
Étude 2: Phénoménologiquement, une EMI peut être décrite comme un
ensemble de dimensions distinctes. Cependant, l’ordre temporel de ces dimensions
demeure un domaine peu exploré. Par conséquent, nous avons voulu étudier la
distribution de fréquence de ces dimensions (de façon globale et en fonction de la
position de chaque dimension) ainsi que les séquences temporelles les plus
fréquemment rapportées dans des récits écrits spontanés d’EMI. Nos analyses ont
mis en évidence les séquences récurrentes de dimensions rapportées dans les récits
mais montrent que, de façon générale, les dimensions n'apparaissent pas dans un
ordre temporel strict, mais plutôt dans un ordre variable (c’est-à-dire, qui varie en
fonction des expérienceurs).
Étude 3: Pour répondre à notre deuxième objectif principal de caractérisation
du profil cognitif des expérienceurs d’EMI, nous avons évalué leur susceptibilité
aux faux souvenirs en utilisant le paradigme « Deese-Roediger-McDermott » et
leur susceptibilité à rapporter des détails illusoires en utilisant les jugements «
Remember/Know/Guess », comparé à des volontaires appariés. Les résultats ont
montré que les expérienceurs d’EMI sont tout autant susceptibles de produire des
faux souvenirs que les volontaires appariés, mais qu’ils les rappellent plus
fréquemment associés à des détails mnésiques illusoires convaincants. De façon
intéressante, les processus de monitoring de source étaient moins efficaces chez les
expérienceurs d’EMI, en comparaison à ceux des volontaires appariés.
Étude 4: En parallèle avec l'hypothèse affirmant que certains facteurs
psychologiques spécifiques pourraient jouer un rôle important dans la génération
(ou le rappel) d'une EMI, notre dernière étude visait à évaluer l’implication
imaginaire et fantaisiste des expérienceurs d'EMI. À l'aide du « Creative
Experiences Questionnaire », nous avons évalué l'engagement fantaisiste
d’individus ayant rappelé une EMI suite à une situation potentiellement mortelle ou
non-mortelle. Nos résultats ont montré que l'intensité rapportée des EMI était
positivement corrélée avec l'engagement fantaisiste et que la personnalité encline à
l’imagination pouvait constituer une prédisposition psychologique à la survenue
d'une EMI rappelée suite à une situation potentiellement non-mortelle.
Deux conclusions principales peuvent être tirées de ce travail de thèse. Dans
les deux premières études, nous avons observé une association entre l’intensité de
l’EMI rapportée et la quantité de caractéristiques phénoménologiques du souvenir
qui en résulte, ainsi que des variations au niveau de l’ordre chronologique
d’apparition des différentes dimensions. Deuxièmement, en étudiant le profil
cognitif des expérienceurs d’EMI, les résultats des deux dernières études
fournissent des preuves que certains facteurs cognitifs et de personnalité peuvent
jouer un rôle dans la génération (ou le rappel) d'une EMI.
1
1 Introduction
Based on the following publication:
Charland-Verville, V.1, Martial, C.1, Cassol, H.1 & Laureys, S.1 (2017). Near-death
experiences: actual considerations. In C. Schnakers S. & Laureys (Eds.), Coma
and Disorders of Consciousness, 2nd edition (pp. 235–263), Springer.
1Coma Science Group, GIGA-Consciousness, University and University Hospital of Liège, Liège, Belgium
3
When facing a life-threatening situation, some people will later report having
lived various phenomenological experiences (e.g., seeing a bright light, having the
sensation of leaving the body, encountering deceased relatives) that are intriguing
by their paranormal appearance or are surprising by their extra-ordinary aspect.
These distinct perceptual experiences are commonly referred to as the phenomenon
of “near-death experience” (NDE). Such subjective experiences can emerge when
people are objectively near to death but also when they simply believe themselves
to be. NDEs are now clearly identifiable psychological and physiological reality of
clinical and scientific significance, as well as highly mediatised. However, this
phenomenon is not yet well understood by the scientific community and its
empirical investigations are rather limited. This introduction presents the
phenomenon, the current state of research and the objectives of the present thesis.
4
1.1 Description of the phenomenon
NDEs can be described as a complex phenomenon consisting of a series of
mental events with self-related, highly emotional, mystical and spiritual aspects,
occurring in an altered state of consciousness that is classically related to a (real or
subjectively felt as) life-threatening condition (e.g., cardiac arrest, trauma,
intracerebral haemorrhage, near-drowning or asphyxia; Greyson, 2000a; Moody,
1975). To illustrate the phenomenon studied through this thesis work, a typical
example, drawn from our own collection of testimonies, is described hereinafter. A
52-year-old man had been admitted to hospital for a heart trouble. Due to
complications, he then had to undergo an emergency quadruple coronary artery
bypass graft surgery. Upon recovery from anaesthesia, he remembered having
observed what happened during his operation from the ceiling of the operating
room. He also reported having wanted to follow a very bright light through a dark
tunnel and having experienced an intense feeling of peacefulness and love. In the
following months, he reported desiring to help others, wanting to improve the way
he lives, and not being afraid of death anymore. In reading this, a reasonable
number of individuals will recognize the meaningful human experience being
described, namely a NDE.
Although the appellation has emerged as such only in the 19th century, there
are numerous accounts and representations since ancient times (e.g., drawings in
prehistoric caves, experiences described in Plato’s tales). In the 13th century, the
Italian writer Dante Alighieri approached the theme of life after death in his long
narrative poem called “The Divine Comedy” (Figure 1). Two centuries later,
another popular representation of the phenomenon has been portrayed by the Dutch
painter Hieronymus Bosch in one of his most famous piece of art (Figure 2). In a
nutshell, the phenomenon of NDEs and the associated question of life after death
have been acknowledged over many centuries. Indeed, these representations match
the phenomenological experiences sometimes reported by individuals when they
5
come close to death. However, at that time, these descriptions were not labelled as
“NDEs”.
Figure 1 – Representation of “The Paradise” from Dante Alighieri (engraving by Gustave Doré in 1868)1.
The expression “NDE” (in French, “expérience de mort imminente”) was
first coined by the French philosopher Victor Egger (Egger, 1896) in the 19th
century, when depicting the perceptions experienced by a group of Swiss alpinists
during an expedition in the Alps. Despite a critical context of impending death,
some of these alpinists reported various perceptual experiences such as a sensation
of calm, an altered time perception, the vision of idyllic landscapes, and auditory
hallucinations (Heim, 1891). A few decades later, following the publication of the
book “Life After Life” written by the American physician and philosopher Raymond
Moody (1975), the phenomenon of NDE and the expression itself have reached an
unprecedented popularity. This effervescence led to an increased interest for these
extra-ordinary experiences in the general public as well as in the scientific community.
1 Image taken from Wikipedia (https://fr.wikipedia.org/wiki/Expérience_de_mort_imminente)
6
Figure 2 – Representation of “Ascent of the Blessed” from Hieronymus Bosch (painted around 1505)2.
Although the description of NDEs provided at the beginning of this section
should be appreciated, it is worth noting that no definition of the phenomenon has
been universally accepted. In the first propositions, Moody (1975) defined a NDE
as “any conscious perceptual experience occurring in individuals pronounced
2 Image taken from Wikipedia (https://en.wikipedia.org/wiki/Near-death_experience)
7
clinically dead or who came very close to physical death”. Some years after, the
psychiatrist Bruce Greyson (2000a) suggested a more detailed definition: “a
profound psychological event including transcendental and mystical elements,
typically occurring to individuals close to death or in situations of intense physical
or emotional danger” (pp. 315-316). Since then, many other (more or less detailed
or inclusive) definitions have been proposed in the literature (e.g., Irwin & Watt,
2007; Nelson et al., 2006) and most of these propositions have two common
threads: the notion of (real or subjective) confrontation with death, and the
presence of subjective perceptions.
In the 1970s, the prevalence of NDEs seemed difficult to apprehend, but
Cassem and Hackett (1978) estimated it to be 2% in cardiac arrest patients. Later,
several studies have attempted to come up with prevalence data in cardiac arrest
survivors as well as in the overall population. The most rigorous studies conducted
(in different countries) among the general public have come to a 4 to 8%
prevalence estimation (Knoblauch et al., 2001; Perera et al., 2005; Schmied et al.,
1999). Considering only cardiac arrest survivors, the prevalence seems higher:
around 10 to 23% of survivors report a NDE (Greyson, 2003; Schwaninger et al.,
2002; van Lommel et al., 2001). However, although these surveys set up a rigorous
protocol, this type of far-reaching studies presents certain limitations. Notably,
these data might not reflect the absolute prevalence, insofar as some NDE
experiencers (i.e., people who have experienced a NDE) may not have been willing
to talk about what they experienced. In addition, although these studies deserve
great interest, the heterogeneous set of tools used by researchers to identify NDEs
and the definition used to describe the phenomenon might greatly influence the
obtained prevalences.
Scientific interest has focused upon the aftereffects of the experience.
Directly after having lived a NDE, most of the experiencers report their experience
as positive and life-enhancing (Moody, 1975; Orne, 1995). Nonetheless, for some
the experience is puzzling, which can discourage them from sharing it with other
8
people (Orne, 1995). In a longer term perspective, although the transformational
effects can vary, the most reported changes seem to be a more altruist and spiritual
attitude, an important personal understanding of life and self, as well as a decreased
fear towards death (Groth-Marnat & Summers, 1998; Knoblauch et al., 2001;
Noyes et al., 2009; Ring, 1980; Schwaninger et al., 2002; van Lommel et al.,
2001). NDE experiencers also tend towards less materialist values (Atwater, 1988;
Flynn, 1986; Groth-Marnat & Summers, 1998; Knoblauch et al., 2001; Ring,
1992). In contrast, some negative aftereffects can be observed: few experiencers
declare encountering difficulties in integrating the experience into their current
lives, leading in some cases, to distress and psychosocial impairment (Bush, 1991;
Greyson, 1997). Moreover, a vast majority of experiencers report to feel frustrated
at not being able to describe the high significance of the experience to others as
they would wish (French, 2005). In this regard, NDEs appear to be ineffable
(Knoblauch et al., 2001). In sum, the current literature rather reports a majority of
positive aftereffects following NDEs, in contrast to their critical circumstances of
occurrence.
9
1.2 Specific phenomenological features
In addition to the life-threatening context, NDE is characterized by its
experienced subjective phenomenology. From a phenomenological point of view,
NDEs can be described as a set of distinct components, known in the current
scientific literature as “features”. Simultaneously to suggest a definition of the
phenomenon, Moody (1975) articulated a list of the 15 most frequently recounted
features based on 150 reports of coma survivors that he recruited in his intensive
care units. In his 15-element model, NDEs notably include a feeling of peace and
quietness, the experience of a bright light, the hearing of oneself pronounced dead, a
life review, or the sensing of a border or limit. Within few years after this book,
other authors have enumerated the different features that are typically reported by
NDE experiencers. Unfortunately, most of these works did not include any ranking
of frequency or precise statistical data. In their quest for scientific rigour, other
researchers have attempted to explore the content of NDEs and their frequency using
reported responses to standardized scales (e.g., Charland-Verville et al., 2014;
Corazza & Schifano, 2010; Greyson, 2003; Parnia et al., 2001; Schwaninger et al.,
2002; Zhi-ying & Jian-xun, 1992; see Table 1 for a list of features commonly
reported in the literature). Overall, most studies seem to agree that the feeling of
peace and well-being and out-of-body experiences (OBEs) are the most frequently
reported features in NDEs (e.g., Charland-Verville et al., 2014; Greyson, 2003; Lai
et al., 2007; Schwaninger et al., 2002). Other features, such as seeing a bright light,
experiencing a tunnel, encountering with people or spirits or experiencing
heightened senses (i.e., experiencing sensations more vivid than usual), appear to be
frequently experienced during NDEs, but less often than the two previous ones (e.g.,
Charland-Verville et al., 2014; Greyson, 2003; Parnia et al., 2001; Schwaninger et
al., 2002; Zhi-ying & Jian-xun, 1992). By contrast, some features are least often
recounted, such as experiencing precognitive visions (i.e., seeing events occurring in
the future) and extrasensory perception (i.e., acquisition of information without the
use of the five well-known physical senses; e.g., telepathy; e.g., Charland-Verville et
10
al., 2014; Greyson, 2003; Zhi-ying & Jian-xun, 1992). In publications related to the
frequency of the occurrence of NDE features, recurrent observations are that no
feature appears in all NDE reports. In addition, some authors have assumed that
these features occur one after another (i.e., the presence of a certain sequentiality)
and hypothesized sequences of stages (Noyes et al., 1977; Ring, 1980). Nonetheless,
to date the temporal scheme of NDE features has not yet been identified.
11
Feature References (non-exhaustive list)
Feeling of peace and quiet Charland-Verville et al., 2014; Greyson, 2003; Greyson & Stevenson, 1980; Moody, 1975;
Schwaninger et al., 2002; Zhi-ying & Jian-xun, 1992
Out-of-body experiences Cassol et al., 2018; Charland-Verville et al., 2014; Greyson, 2003; Greyson & Stevenson, 1980; Moody, 1975; Schwaninger et al., 2002; van Lommel et al.,
2001; Zhi-ying & Jian-xun, 1992
Ineffability Moody, 1975; Schwaninger et al., 2002
A sense of entering a dark region (tunnel-like)
Charland-Verville et al., 2014; Greyson, 2003; Greyson & Stevenson, 1980; Moody, 1975;
Schwaninger et al., 2002; van Lommel et al., 2001; Zhi-ying & Jian-xun, 1992
Seeing, or being enveloped in, light Charland-Verville et al., 2014; Greyson &
Stevenson, 1980; Greyson, 2003; Moody, 1975; Schwaninger et al., 2002; Zhi-ying & Jian-xun, 1992
Encountering a presence/hearing a voice Charland-Verville et al., 2014; Greyson, 2003; Moody, 1975; Schwaninger et al., 2002; Zhi-ying &
Jian-xun, 1992
Encountering visible “spirits” or
(deceased or not) persons
Charland-Verville et al., 2014; Greyson, 2003;
Greyson & Stevenson, 1980; Schwaninger et al., 2002; van Lommel et al., 2001; Zhi-ying & Jian-xun,
1992
Experiencing a life review Charland-Verville et al., 2014; Greyson, 2003; Moody, 1975; Schwaninger et al., 2002; van Lommel
et al., 2001; Zhi-ying & Jian-xun, 1992
Sensing a border or limit Charland-Verville et al., 2014; Greyson, 2003;
Greyson & Stevenson, 1980; Schwaninger et al., 2002; van Lommel et al., 2001; Zhi-ying & Jian-xun,
1992
Hearing oneself pronounced dead Moody, 1980
Awareness of being dead Cassol et al., 2018; Morse et al., 1986; Schwaninger et al., 2002; van Lommel et al., 2001
Perception of a heavenly (or hellish) landscape
Greyson & Bush, 1992; van Lommel et al., 2001
Altered perception of time Cassol et al., 2018; Charland-Verville et al., 2014; Greyson, 2003; Schwaninger et al., 2002; Zhi-ying &
Jian-xun, 1992
Precognitive visions Charland-Verville et al., 2014; Greyson, 2003; Schwaninger et al., 2002; Zhi-ying & Jian-xun, 1992
Experiencing extrasensory perception Charland-Verville et al., 2014; Greyson, 2003; Greyson & Stevenson, 1980; Schwaninger et al.,
2002; Zhi-ying & Jian-xun, 1992
Experiencing heightened senses Charland-Verville et al., 2014; Greyson, 2003; Schwaninger et al., 2002; Zhi-ying & Jian-xun, 1992
Feeling a sense of harmony or unity Charland-Verville et al., 2014; Greyson, 2003; Schwaninger et al., 2002; Zhi-ying & Jian-xun, 1992
Coming back into the body Moody, 1975
Table 1 – Recurring features reported in the literature to described NDE.
12
Of all these NDE features, the OBE appears to be distinctive in that this
feature is very often reported in other conditions (e.g., sleep disturbances, migraine,
schizophrenia, epileptic seizures; Blackmore, 1986; Podoll & Robinson, 1999) than
NDEs. Indeed, this feature, which can occur spontaneously, refers to as an
autoscopic experience of perceiving one's body in an extrapersonal space (i.e., from
a place outside one’s body), typically associated with the feeling of floating outside
one’s own body (Blanke et al., 2004). Individuals usually report to be awake and to
see themselves as a part of the extrapersonal world (Blanke et al., 2004). This
specific experience has been repeatedly described in patients suffering from
psychiatric or neurological disorders (e.g., Brugger et al., 1997; Critchley, 1969;
Dening & Berrios, 1994; Devinsky et al., 1989; Frederiks, 1969; Leischner, 1961;
Lukianowicz, 1958), but also in healthy populations (Blackmore, 1982; Irwin,
1985). Most neurologists agree that the OBE phenomenon relates to a paroxysmal
pathology of body perception and cognition (Blanke et al., 2004). Yet, the specific
cause is still debated. Some researchers have proposed a dysfunction of vestibular
or visual processing or a dysfunction of kinaesthesia and proprioception, as well as
the combination of the two (Blanke et al., 2004). Interestingly, the phenomenon of
autoscopy (including a physical visuo-spatial perspective) is mostly experienced as
unreal, in contrast to the broader phenomenon of OBE (including a parasomatic
visuo-spatial perspective) which appears as veridical to individuals (Blanke et al.,
2004; Blanke & Metzinger, 2008; Irwin, 1985; Rogo, 1982). Some years ago,
Ehrsson (2007) has further demonstrated that the illusory experience –in which
individuals experience that their self is located outside their physical bodies and
that they look at their bodies from another perspective– can be induced in healthy
subjects in laboratory settings.
13
1.3 Identifying near-death experiencers
Insofar as there is no universally accepted definition of the phenomenon
itself, the identification of NDE experiencers is rather tricky. Currently, this
identification is based on the number of features subsequently reported as well as
the experienced intensity of each feature. A few years ago, to minimize the
potential complications caused by scholars adopting different definitions, some
chose to build and validated standard scales including threshold scores. Among
them, Ring (1980) has developed the scale called the Weighted Core Experience
Index (WCEI; Table 2). Its development was based on a set of 102 narratives of
individuals that came close to death. He noted that 48% of them had experienced a
NDE according to the index derived from the 10 arbitrarily weighted items of the
scale. Indeed, according to the author, the addition of the ticked items provides an
index representing the depth of a NDE. An individual is considered as having lived
a “core experience” (i.e., having experienced “enough” components related to this
kind of experience) if he/she obtains more than 6 out of 23. In addition, the scale
permits to conclude if the experience is “moderate” (score between 6 and 9) or
“deep” (score between 10 and 23). However, although his work is considered as
pioneer, his tool has some limitations. First, the 10 items were arbitrarily chosen
(i.e., based on his impression of the most often reported features). Second, the cut-
off points indicating moderate and deep experiences were not based on statistical
analysis and were not tested for internal coherence or reliability. Third, it seems
that this scale can lead to false positives when used to identify NDE experiencers
(Greyson, 1983). Fourth, when the NDE is extremely rich, the total score can be
very high despite the presence of only very few features.
14
Feature Weight
Subjective sense of being dead 1
Feeling of peace, painlessness, pleasantness, etc. 2
Sense of bodily separation 2
Sense of entering a dark region 2
Encountering a presence/ hearing a voice 3
Taking stock of one’s life 3
Seeing, or being enveloped in, light 2
Seeing beautiful colors 1
Entering into the light 4
Encountering visible “spirits” 3
Table 2 – The Weighted Core Experience Index (WCEI; Ring, 1980): features and weights assigned
to each feature.
To address Ring’s scale limitations, another author developed the Greyson
Near-Death Experience scale (the Greyson NDE scale; Greyson, 1983). This
widely used questionnaire is a standardized multiple-choice tool which provides a
cut-off score (i.e., total score ≥ 7/32) allowing a standardized identification of NDE
experiencers. The total score (ranging from 0 to 32) might reflect the overall
intensity of the NDE (Greyson, 1983; Lange et al., 2004) since it is obtained by
considering the amount of ticked experienced dimensions (i.e., 0 = “not present”
or, 1 or 2 for the presence of the item) and the gradation of intensity in the provided
scoring (i.e., 1 = “mildly or ambiguously present,” and 2 = “definitively present”).
The scale contains 16 items among which the individual has therefore three
possibilities of response (Table 3), and can be subdivided into four psychologically
meaningful clusters (cognitive, affective, paranormal, and transcendental
experiences). Initially, this tool was used by the author in a clinical setting, to
distinguish individuals who had experienced a NDE from those who had
experienced something else (Greyson, 1983). In short, he created this scale based
on a list of 80 characteristic components described prominently in the NDE
literature. These 80 components included affective states, thought content and
process, perceptual content and processing, bodily sensations, as well as other
15
specific (not classifiable/atypical) items (e.g., experience a tunnel vision). Thanks
to a pilot study, he reduced the list to 33 items and further developments permitted
to create the final scale. At the moment, this scale is considered as the reference
tool in research notably because of its good internal consistency and test-retest
reliability (Greyson, 1983). A short version of this 16-item scale, called the Near-
Death Experience Scale-6 (NDE-6; Prosnick & Evans, 2003), has also been
proposed but practically not used.
16
17
1.4 “Near-death-like” experiences
In contrast to “classical” NDEs developed inside a life-threatening context
(e.g., severe brain injury), similar phenomenological experiences, termed “NDEs-
like”, have also been reported in situations where there was no genuine threat to the
individuals’ life (Charland-Verville et al., 2014; Facco & Agrillo, 2012). These
experiences have been, for example, reported in situations such as during intense
grief (Kelly, 2001), syncope (Lempert et al., 1994a), anxiety (Kelly, 2001) or
meditation (Beauregard et al., 2009). Epileptic patients also appear to report similar
phenomenological experiences following seizures (Hoepner et al., 2013).
Interestingly, Charland-Verville and colleagues (2014) have found that
NDEs-like experiencers report an equivalent intensity and content than
experiencers recalling classical NDEs. However, other studies have rather shown
some differences regarding the reported features: as compared to individuals
reporting NDEs-like, experiencers recalling classical NDEs tend to report more
frequently OBEs (Gabbard & Twemlow, 1991), seeing a very bright light (Owens
et al., 1990), experiencing enhanced cognitive function (Owens et al., 1990), and
encounters with deceased relatives (Kelly, 2001). Yet, again, all these authors did
not employ the same tool to characterize NDEs and to tick (or not) the presence of
one feature.
Although enigmatic, NDE-like phenomena have been the subject of very few
empirical studies (Charland-Verville et al., 2014; Facco & Agrillo, 2012; Gabbard
& Twemlow, 1991). Notably, there does not appear to be any study about the
prevalence of NDE-like phenomena or assessing their impact on experiencers’ life.
Moreover, it is still not clear to which extent the proximity to death is involved in
the appearance of a subjective NDE phenomenology. Some authors have argued
that the expectancy of an impending death or the strong belief of one’s death felt at
that moment, rather than the actual proximity of death, would suffice to trigger
NDEs (Gabbard & Twemlow, 1991). In fact, some experiencers could have been in
18
apparent life-threatening situations (e.g., accidents), and think that the worst
consequence can happen even though the medical condition finally results in no or
very minor damage (Gabbard & Twemlow, 1991). Yet, given that some NDEs-like
do not include any perceived threat to life (e.g., occurring during a meditative
state), not all experiences from this category can be explained by the expectancy or
the belief in an impending death (Facco & Agrillo, 2012). Reports of such NDE-
like experiences raise several puzzling questions, as it suggests that the NDE
phenomenology might potentially be perceivable in everyday life (Facco &
Agrillo, 2012).
19
1.5 Distressing near-death experiences
By now, positive emotions experienced during the subjective
phenomenology are considered as one of the defining characteristics of NDEs,
notably because the common standardized scale to identify NDE experiencers –the
Greyson NDE scale– includes two questions about positive emotions. Nonetheless,
NDEs can occasionally cause great distress. Greyson and Bush (1992) identified
three types of unpleasant NDEs based on 50 collected testimonies. First, some
NDE experiencers describe the “inverse” experiences (Ring, 1994), including
phenomenological perceptions similar to pleasant NDEs (e.g., seeing a bright light
or a tunnel, encountering spirits or persons), but with the exception that they are
perceived as extremely frightening, and associated to an out of control and very
stressful alien reality. Second, another type of NDE, labelled as “void” experiences,
involves perceptions of nonexistence, aloneness, and eternal void. This category of
experiences seems to contain fewer features of the prototypical pleasant NDEs
(Greyson & Bush, 1992, 2014). A third type is the “hellish” experience, described
as a prototypical experience where subjects encounter hell and threatening entities,
and perceptions of impending torment or judgment. NDE experiencers from this
category appear to report even fewer features of the prototypical pleasant NDEs
(Greyson & Bush, 1992, 2014). The order of categories described here corresponds
to an increasing level of fright, as reported by NDE experiencers (Greyson & Bush,
1992, 2014). Another author suggested a fourth category in which individuals are
highly disturbed by a life review (Rommer, 2002). Nonetheless, this category is
rather considered, according to Bush (2002), as a subset of the “hellish”
experience. Although Greyson and Bush (1992) illustrated their pioneer article
with some experiencers’ verbatim, no study has to date performed a rigorous text
analysis in order to highlight the common themes and criteria that cluster each
category and to ultimately confirm them –or not.
In general, investigators have suggested a proportion for distressing NDEs
that varies from 1 to 18% of their sample (Charland-Verville et al., 2014; Gallup &
20
Proctor, 1982; Groth-Marnat & Summers, 1998; Lindley et al., 1981; Ring, 1984;
Sabom, 1982). The limited available information is probably partly due to the fact
that people might be reluctant to share their (partially or entirely) unpleasant
experiences. As a matter of fact, this kind of experience may result in a post-
traumatic stress reaction (Bush, 2002) or recurrent flashbacks (Greyson & Bush,
1992), and the difficulty of integrating the experience and its consequences appear
to be even greater than for positive NDE (Flynn, 1986; Greyson, 1997; Noyes,
1980; Ring, 1984; Sabom, 1982). Indeed, negative experiencers report heightened
fear towards death (Greyson & Bush, 1992). In addition, contrary to what one
might imagine, distressing NDEs do not appear to more frequently occur in
contexts of suicide attempt (Ring & Franklin, 1981; Greyson & Stevenson, 1980).
Overall, these sporadic experiences and their frequency may be underestimated by
researchers (Greyson & Bush, 1992). Currently, the literature on negative NDEs
remains a very poorly explored area.
21
1.6 Particularity of the resulting memory
In reaction to the (paradoxical) dissociation between the richness of the NDE
memory and the associated trigger event probably occurring during a short moment
of brain dysfunction, some authors have proposed that reports of NDEs are, at least
in part, imagined (e.g., French, 2001). Nonetheless, current research assessing
NDE memories does not support this hypothesis. Using both the 38-item or 15-
item versions of the Memory Characteristics Questionnaire (MCQ; Johnson et al.,
1988), built to assess peculiar characteristics of imagined and real event memories,
some research teams recently assessed the memory of NDE and the subjective
experience associated with remembering this event (Moore & Greyson, 2017;
Palmieri et al., 2014; Thonnard et al., 2013). Using six categories subscores of the
MCQ (i.e., sensory details, memory clarity, self-referential and emotional
information, reactivation frequency, and confidence in their own memory),
Thonnard and colleagues (2013) showed that NDE memories were associated with
more sensory, self-referential and emotional details and a greater memory clarity
(e.g., clearer information about time and location), as compared to other memories
of real and imagined events and memories of a coma period without NDE
(according to the Greyson NDE scale). Overall, these studies suggest that NDE
memory can hardly be considered as typically imagined because they contain a
high amount of qualitative phenomenological characteristics such as contextual and
sensorial details (e.g., remembering what we felt or thought during the event,
where the event took place; Moore & Greyson, 2017; Palmieri et al., 2014;
Thonnard et al., 2013). Indeed, it is this subjective experience when remembering
that gives us the impression that a memory belongs to our own past (Johnson et al.,
1988, 1993; Wheeler et al., 1997) –and is not imagined. Coupled with
electroencephalographic measures, Palmieri and colleagues (2014) have further
investigated the neural markers of these memories when enhanced through
hypnosis. Their results support the above results by suggesting that associated
electroencephalographic measures are suggestive of episodic memories of real
22
events (notably because of the presence of theta activity associated with the recall
of NDE memories) –although not necessarily corresponding to events in the
external (real) physical world. Therefore, to date, available studies suggest that the
resulting memory of NDE is very rich in details. One interesting issue is why such
a clear memory trace is created for this experience and little is known about what
exactly accounts for the enhanced memory.
A further interesting question is how this resulting NDE memory evolves over
time. Only one study has addressed the question of the long-term evolution of NDE
memory. Greyson (2007) found that accounts of NDEs were not modified over a
period of two decades. Nonetheless, although his study is highly interesting, Greyson
(2007) used experiencers’ responses on the Greyson NDE scale which includes closed
questions. To date, no study has yet formally paid attention to the reliability of
testimonies using spontaneous written narratives. In addition, knowing that the
subjective experience during retrieval is an essential property of episodic memory and
gives us the sense that we are remembering an event belonging to our personal past, it
would also be interesting to assess how NDE experiencers retrieve this memory and
their (more general) memory performance (e.g., source monitoring).
23
1.7 Near-death experiencers’ characteristics
To date, it is not clear whether NDEs are a randomly occurring phenomenon
or whether some specific inter-individual differences play an important role in their
generation and/or recall. Up to now, no longitudinal survey has been conducted on
this matter. Rather, available studies have investigated experiencers’ personal
characteristics after a NDE, usually attempting to assess characteristics that might
be associated with some NDE features.
Two wide-ranging studies that were performed among patients with cardiac
arrest have found that the frequency of NDE is higher in individuals younger than
60 years old (Greyson, 2003; van Lommel et al., 2001). This pattern might notably
be explained by a greater vulnerability to amnesia at an advanced age. Van
Lommel and his colleagues (2001) further observed more intense NDEs when
reported by women. However, other studies do not report this difference
(Charland-Verville et al., 2014; Greyson, 2003; Roberts & Owen, 1988; Zhi-ying
& Jian-xun, 1992). Interestingly, NDE accounts have also been reported by
children (Bush, 1983; Morse et al., 1986).
In general, retrospective studies showed that most of people experiencing
NDEs do not present deficits in global cognitive functioning (Greyson, 2003) or
specific pathological troubles (Facco & Agrillo, 2012; Gabbard & Twemlow,
1985; Greyson, 1997; Irwin, 1985). The frequency of NDEs does not appear to be
influenced by factors such as social class, educational level, marital status, or prior
psychiatric disorders or characteristics (Greyson, 2003; Ring, 1980; Roberts &
Owen, 1988; Schwaninger et al., 2002; van Lommel et al., 2001; Wilson & Barber,
1983a; Zhi-ying & Jian-xun, 1992). Nevertheless, some authors have highlighted
that NDE experiencers present specific (non-pathological) characteristics with
regard to cognitive and personality traits. Greyson (2003) found that NDE
experiencers were more likely to report prior “paranormal experiences” (e.g.,
altered state of consciousness, “déjà vu” experiences). In line with these results,
24
Ring (1992) suggested a developmental theory of sensitivity to live extraordinary
experiences. In short, the development of dissociative responses (i.e., a lack of
normal integration of thoughts, feelings or experiences into the stream of
consciousness and memory; Bernstein & Putnam, 1986) as a psychological
“defence” in face of stressful situations would be stimulated notably by childhood
trauma (Ring, 1992). More recently, using the Dissociative Experience Scale
(DES; Bernstein et al., 1986), Greyson (2000b) examined the tendency for
dissociation of NDE experiencers and matched people who came close to death but
did not experience such perceptions, by assessing the frequency and types of
dissociative experiences. NDE experiencers appear to report more dissociative
symptoms than the other group, but their responses on the DES are not consistent
with pathological dissociative experiences. This non-pathological tendency of
dissociative symptoms corroborates clinical observations that this population does
not suffer from distress or impairment found in patients with dissociative disorders
(Greyson, 2000b). In addition, using Rorschach measures, Locke and Shontz
(1983) observed that NDE experiencers are indistinguishable from control
individuals in terms of intelligence, state anxiety, neuroticism, and extroversion.
Around the same time, Twemlow and Gabbard (1984) found that NDE
experiencers scored higher on a measure of absorption (i.e., the propensity to focus
attention on imaginative and selected sensory experiences to the exclusion of
stimuli in the external environment; Tellegen & Atkinson, 1974) than a group of
people reporting “only” an OBE.
A few researchers have also been interested in cognitive and personality
characteristics of people experiencing “only” an OBE (and not a “full” NDE). A
long time ago, Irwin (1981, 1985) reported that OBE experiencers have a greater
capacity of absorption than people who never experience OBEs. More recently,
using the short form (entitled the Inventory of Childhood Memories and
Imaginings –ICMI; Wilson & Barber, 1983a) of The Memory, Imagining, and
Creativity Schedule (Wilson & Barber, 1983b), Gow and collaborators (2004)
25
found that OBE experiencers present a greater capacity to absorb themselves in
fantasy and imaginary activities. Almost 30 years ago, Ring and Rosing (1990) also
investigated imaginary engagement of people reporting “classical” full NDEs using
the Childhood Experience Inventory (CEI; Holeman, 1994), but did not find more
pronounced imaginative involvement in this group than in control subjects who
never have been near-death and have never recalled a NDE. Yet, these inconsistent
observations may be due to different instruments that authors employed to measure
fantasy proneness. Taking a cue from these studies, we thought it would be
worthwhile to reopen the issue of whether fantasy proneness might serve as
predisposing psychological tendencies that would increase the probability of
reporting a NDE. In addition, although certain characteristics or experiences, such
as dissociative experiences, appear to correlate with the emergence of NDEs, the
question of a cause and effect relationship can only be answered by prospective
surveys assessing subjects before and after their NDE. In sum, because it is not
possible to predict who will experience a subjective NDE yet, it would be very
arduous to assess psychological predisposition before. However, it would be very
interesting to know to what extent personal factors affect the emergence of the
experience, in order to better understand the experience per se.
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1.8 Explanatory models for near-death experiences
Various explanatory theoretical approaches have been proposed, in attempts
to explain the whole phenomenon of NDEs or certain distinct feature. For
convenience of the presentation of this section, the (non-mutually exclusive)
models are categorized in three main approaches. It is noteworthy that the
explanatory theories are not independent, but overlap substantially.
1.8.1 Transcendental theories
Overall, this category of theories assumes that a NDE is precisely what it
seems to be to the individual experiencing it: an experience which can be
considered as evidence of a “dualistic” model toward the mind-brain relationship
(Zeman, 2005). In other words, authors hypothesize that the mind (or soul) might
be separated from the physical body (Figure 3) and/or that a spiritual portion of
humans can survive after death (Long & Perry, 2010; Potts, 2002). From this
theoretical point of view, NDEs would be a specific state of transcendental
consciousness in which cognition, emotions and self would operate independently
of the brain (Parnia, 2007; van Lommel, 2004).
Proponents of this theory suggest that the allegedly paranormal nature of
NDEs –and especially OBEs– would be confirmed if the observations and facts
reported by NDE experiencers were real-life experiences. Recently, Parnia and his
colleagues (2014) from different centres set up protocols to test this idea; however,
their results did not confirm their hypotheses. Indeed, they had the ingenious idea
to set up operating and resuscitation rooms in which target objects (i.e., religious or
nationalistic symbols, animals or people) were placed on top of cabinets, hence
possibly perceived from a ceiling perspective only (that is a perspective usually
described by experiencers). Nevertheless, none of their two patients reporting
visual awareness of actual events occurring during their resuscitation reported the
27
target objects. In parallel, quantum physics models of non-local consciousness have
also been proposed to account for the continuation of mental function when the
brain is supposed to be impaired or inactive (Carter, 2010; Greyson, 2010;
Schwartz et al., 2005). While these explanatory models have not been confirmed
by empirical surveys, they appear to be very popular among the general public and
to lead the field of NDE research. Although transcendental theories continue to be
supported by some scholars, many other possibilities are being looked at. The
broader current scientific literature about consciousness rather supposes a close
relationship between mind and brain (Laureys et al., 2015).
Figure 3 – Artistic representation of “The soul leaves the body at the moment of death” from
William Blake (engraving by Schiavonetti in 1808)3.
3 Image taken from Wikipedia (https://fr.wikipedia.org/wiki/Out-of-body_experience)
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1.8.2 Psychological theories
Psychological theories consider NDEs as the result of an altered state of
consciousness induced by a life-threatening context, wherein the phenomenology is
derived from the projection of expectations and beliefs of a supposed afterlife (the
“expectation hypothesis”; Appleby, 1989; Blackmore & Troscianko, 1988; Britton
& Bootzin, 2004; Owens et al., 1990). Decades ago, Noyes and Kletti (1976, 1977)
have stated that they conceive the NDEs as a type of depersonalization (i.e., a sense
of the self as unreal or lacking agency) inducing an altered sensation in one’s sense
of identity. A few years later, Irwin (1993) has put forward the dissociation
hypothesis suggesting an altered sensation in the association of one’s identity with
his/her bodily sensation and emotions. In both cases, the idea is that the NDE
phenomenology would emerge as a defence against the life-threatening conditions.
When facing with a potentially inescapable danger, people would be disconnected
from the environment and focused on their internal states (e.g., pleasurable
fantasies). This detachment would offer them a more intelligible and less
distressing “reality” (Noyes & Slymen, 1978). This reasonable psychological
assumption may be particularly interesting to account for OBEs, but fails to explain
some dimensions of NDEs. In addition, this suggests that the eliciting event is
threatening and thus has difficulties explaining NDEs-like.
Since then, more general theories (not so different from the previous
hypotheses) have been proposed to explain the phenomenology of NDE. NDEs
would be –at least partly– the result of the experiencers’ previous and/or general
knowledge, beliefs, and expectations about the world, imagined information
available during the context of emergence, fantasies and guesses (Blackmore,
1993). All these information originating from internal states would further be
mixed with limited information from the remaining senses. This hypothesis is
largely derived from the idea that a two-way flow of information exists (Huitt,
2003): we constantly use information gathered through the senses (‘bottom-up’
processing) but we also construct meaning about our environment (and our
29
interactions with it) by using information we have already stored in memory (‘top-
down’ processing). Indeed, our brain is constantly trying to make sense of the
world around us and the information it receives by using this general dynamic
process of a two-way flow of information (Huitt, 2003). In the case of NDEs, the
phenomenology would be built in order to create a (more) coherent interpretation
of the confusing experience occurring in an altered state of consciousness
(Braithwaite, 2008; Mobbs & Watts, 2011). An alternative
and more sceptical hypothesis holds that some NDEs may, as a result, reflect false
memories, which would be retrospectively built in order to “fill in the gap” after a
period of unconsciousness (French, 2001). This is based on more general
psychological studies suggesting that simply imagining experiencing a particular
event (that in fact had never happen) may lead to the development of false
memories for this event (e.g., Garry et al., 1996; Loftus, 2001). Except for
available data suggesting some dissociative tendencies in NDE experiencers
(Greyson, 2000b), these psychological models have not been tested rigorously.
1.8.3 Organic/neurobiological theories
The last broad category concerns the organic or neurobiological theories
accounting for the NDE phenomenology in terms of brain function. While a very
large number of organic theories have been proposed, we will present here the most
relevant ones: levels of blood gases; endorphins and other neurotransmitters; and
dysfunction in temporal lobes. Overall, these theories are based on the idea that
clinical core NDE features might provide relevant indications on the
neurophysiological mechanisms underlying their emergence. According to them,
the fact that some NDE features can emerge in non-NDE contexts might provide
direct evidence for particular theories.
Several models have highlighted the potential implication of disturbed levels
of blood gases in the NDE phenomenon. Hypercarbia (i.e., abnormal high levels of
30
carbon dioxide in the blood) appear to produce some NDE features such as OBEs
or bright lights (Klemenc-Ketis et al., 2010; Meduna, 1950; Sabom, 1982). It has
also been advanced that cerebral anoxia (e.g., Robin, 1980) or hypoxia (e.g., Els et
al., 2004; Lempert et al., 1994a,b) might cause the NDE phenomenology.
Particularly, syncopal hallucinations resulting from transient cerebral hypoxia
appear to present some similarities with NDEs (Lempert et al., 1994a). Lempert
and collaborators (1994a,b) reported some years ago that syncopes (induced
through hyperventilation and forceful attempted exhalation against a closed airway,
a method called “Valsalva manoeuvre”) in healthy people can provoke NDE-like
phenomena (e.g., feeling of peace or OBE). Since then, it has been postulated that
impaired cerebral oxygen levels (in contexts ranging from the “simple” syncope to
more serious impairments such as cardiac arrests) can result in a disruption of the
physiological balance between the conscious and unconscious states causing a state
similar to the one experienced during rapid-eye movement (REM) sleep (Nelson et
al., 2006). In this regard, the REM intrusion can disturb wakefulness in the form of
visual hallucinations and give an impression of being dead (Nelson et al., 2006).
Interestingly, a cohort of NDE experiencers have been assessed as particularly
sensitive to REM-sleep intrusions and sleep paralysis associated with hypnagogic
(i.e., when falling asleep) and hypnopompic (i.e., when awakening) experiences
(Britton & Bootzin, 2004; Nelson et al., 2006). Other authors have considered a
neuronal disinhibition in the visual cortex (Blackmore, 1993, 1996; Rodin, 1980;
Saavedra-Aguilar & Gómez-Jeria, 1989; Woerlee, 2005). More specifically,
Blackmore (1996) argued that the perception of bright lights and a tunnel vision
might be related to a random excitation in the organization of cells (devoted to the
center or the periphery of the visual field) in the visual cortex, associated with
anoxia. In line with this hypothesis, based on previous clinical neuroimaging data,
one can envisage that resuscitated patients reporting NDEs have transient ischemic
and/or hypoxic lesions or interferences with bilateral occipital cortex and the optic
radiation (Ammermann et al., 2007; Els et al., 2004; Owens et al., 1990). However,
although it is admissible, this assumption needs to be read with caution because no
31
neurological data support it. Recently, Borjigin and colleagues (2013) conducted an
electrophysiological study investigating cardiac arrest in rats. Their findings
demonstrated evidence of highly organized brain activity and neurophysiologic
states during cardiac arrests. They observed a transient and global surge of
synchronized gamma oscillations, exhibiting increased interregional connectivity.
This study opens the way to a scientific framework attempting to explain the highly
lucid and rich mental experiences reported by experiencers in the same context.
In parallel, theories based upon naturally occurring or drug-induced
neurotransmitter releases have been suggested. Notably, endorphin release has
been considered to account for different aspects of NDEs (Carr, 1982). In
particular, Saavedra-Aguilar and Gomez-Jeria (1989) stated that, because of
increased stress, endorphin release may be responsible for pleasant and blissful
feelings occurring during NDEs. In this respect, administration of endorphin-
blocking drugs would also trigger a negative tone during distressing NDEs (e.g.,
naloxone; Judson & Wiltshaw, 1983). Other authors have suggested the implication
of serotonin to specifically account for OBEs (Morse et al., 1989). Jansen’s (1989,
1997, 2001) theory supplies a convincing framework by suggesting a blockade of
the glutamate N-methyl-D-aspartate (NMDA) receptors to account for the NDE
phenomenology (Curran & Morgan, 2000). He developed his model based on the
observation that most of the core NDE features (e.g., seeing a bright light,
experiencing a tunnel) appear to emerge during the administration of Ketamine.
This dissociative anesthetic drug can produce NDE-like symptoms and is a potent
NMDA antagonist. Similarly, in conditions that appear to precipitate NDEs (e.g.,
decreased brain oxygen, blood flow), an increased level of glutamate is released to
prevent neuronal damage. In turn, it stimulates the release of a Ketamine-like
neurotoxin (Jansen, 1997). Nonetheless, to date, it is not yet clear which
pharmacological cerebral mediators or hallucinogenic agents underlie NDE
features.
32
In parallel to the two above-presented theoretical fields, other models have
considered a significant implication of temporal lobe dysfunctions (Blanke et al.,
2002, 2004; Blanke & Mohr, 2005; Britton & Bootzin, 2004; Hoepner et al., 2013).
Interestingly, both direct cortical stimulation (e.g., Blanke et al., 2002, 2004;
Penfield, 1958) and altered functioning (e.g., due to damage or seizures; Hoepner
et al., 2013) of this brain region appear to produce similar NDE features (e.g.,
OBEs; Britton & Bootzin, 2004) or other mystical experiences (Daly, 1975;
Devinsky et al., 1989; Penfield, 1955). It is worth mentioning that this area is
sensitive to anoxia, and that its seizure threshold can be lowered by an endorphin
release (Frenk et al., 1978). Stimulating the specific area of the right temporo-
parietal junction enables the production of OBE that would result from a deficient
multisensory integration in this area (Blanke et al., 2002, 2004; De Ridder et al.,
2007). Studies in neurological patients appear to corroborate this observation.
Patients with epilepsy or migraine have reported a similar phenomenology after
focal electrical stimulation protocols (Blanke et al., 2002; Jasper & Rasmussen,
1958). Several authors have suggested that hypoxia and/or stress occurring during
life-threatening conditions might hypersensitive neurons and lower seizure
thresholds, especially in the temporal lobe (Benveniste et al., 1984; Britton &
Bootzin, 2004). Interestingly, Britton and Bootzin (2004) found more temporal
lobe epileptiform activity and symptoms in NDE experiencers, as compared to
matched non-experiencers.
Overall, these theories can account for some specific components of NDEs,
but there is no consensual or satisfying scientific explanation for the whole
experience. It seems probable that several factors might trigger a NDE, with each
above-stated factor being just one of them (Blackmore, 1996). In general, theories
have been suggested years or decades ago, but science still lacks empirical
grounds. Although the basis of NDEs remains conjectural at this time, the few
available data support the presence of specific neural correlates associated with
each NDE features, integrated in a broader bio-psycho-social phenomenon.
33
Neuroscientifically, the current theories explaining a NDE and its core features
hypothesize that they occur during an altered state of consciousness, accompanied
by specific brain activities resulting from the interactions between
neuropsychophysiological mechanisms (Vanhaudenhuyse et al., 2009).
34
1.9 Research on the topic of near-death experiences
While the scientific community seems to acknowledge the existence of the
phenomenon as a clearly identifiable psychological and physiological reality, its
origin is still a matter of debate. Transcendental interpretations still appear to lead
the discussion of recent empirical findings (see Braithwaite, 2008 for an example
of a critical discussion about recent publications). In some cases, beliefs stating for
the existence of a life after death appear to slow down the set up of rigorous
empirical protocols to investigate NDEs. Hence, the number of scientific
publications about NDEs is relatively limited, in contrast to non-scholarly and non-
peer-reviewed works which are abundant. In addition, while the scientific literature
contains a predominance of opinion and review papers, there is a lack of empirical
investigations that try to understand the phenomenon and its particularities
(Sleutjes et al., 2014). When looking at publications about NDEs in PudMed (a free
search engine indexing primarily the Medline database of peer-reviewed references
and abstracts on life sciences and biomedical topics), only a total of 185
publications is obtained (see Figure 4). By contrast, when doing the same keyword
research in Google Scholar (a freely web search engine accessing any peer-
reviewed literature, but also non-scholarly and/or non-peer-reviewed material from
any disciplines database including books), a total of 15,600 works is found. In a
recent publication, Sleutjes and colleagues (2014) performed a keyword search
(using “near-death experience”) in the Web of Knowledge database (including
academic journals, conference proceedings and book reviews in all fields of
science) and identified a total of 266 articles published between 1977 and 2013,
and addressing the topic. The authors also showed that publications are centrated in
North America and Western Europe (Sleutjes et al., 2014). Consequently, most of
publications on NDEs appear to have been published in specialised journals (e.g.,
Journal of Near-Death Studies) which are not indexed in the Web of Knowledge or
PubMed. Finally, despite the extensive number of research studies cited in this
thesis work, the area has been characterized by methodological difficulties.
35
Available empirical studies are mostly case studies or have small sample sizes, and
include very rarely control groups (e.g., individuals with identical medical history
but who have never reported a NDE phenomenology). For some years now, more
and more non-profit organizations emerge, whose objectives are to provide
information about NDEs and to support NDE experiencers (e.g., International
Associations for Near-Death Studies –IANDS). In addition to the benefits that
experiencers can draw from them, this emergence can also be beneficial to
research, insofar as larger samples can be gathered.
Figure 4 – Number of publications per year on NDEs (for a total of 185 publications). Medline search performed in February 2018 with the keyword “near-death experiences”.
36
From a traditional scientific perspective, the existence of NDEs might
initially be considered paradoxical and related to paranormal (i.e., a phenomenon
beyond scientific investigation). Notably, the lack of consensus on a definition for
NDEs has slowed down the acceptation of NDE research by the scientific
community. But today, the report of such experiences all around the world
questions and deserves reconsideration. NDE is a particular topic, in the sense that
these experiences touch upon the notion of death, which might represent –for
many– a passing to a heavenly spot where we are reunited with close relatives.
Much of the ambiguity in the definition of NDEs mainly stem from the confusion
over how to define death itself and the failure to distinguish the definition of
“clinical death” (i.e., the cessation of heartbeat and respiration) and “brain death”
(i.e., the permanent cessation of functioning of the entire brain). Certain
publications considering NDEs as evidence for life after death may impart the air
of a pseudoscience to NDE studies. Undeniably, the study of NDEs is challenging,
given the important scientific, philosophical, medical and theological implications
related to them. The current decline of religious convictions and practice in some
parts of the world may favour its investigation.
Studying NDEs might be challenging for other reasons. In retrospective
studies, the interval of time between the age at study enrolment and the occurrence
of the NDE is usually relatively long, partly because they decided to share their
experience belatedly. Accounts are in some cases collected years or even decades
later. In addition, retrospective studies may present a sample-bias because only
including self-reporters. Samples of volunteers might not be representative,
because they possibly have greater knowledge of NDEs, while reluctant people
might hypothetically report different NDEs. Retrospective surveys might provide
an opportunity to study different populations and contexts, and this can be realized
with very large samples of NDE experiencers. Investigators also have the
possibility to select individuals with common features; that is, they have the
possibility to create their desired/required strategy of recruitment. By contrast,
37
prospective designs may present an opportunity to overcome some limitations that
are inherent to retrospective studies. Although the occurrence of a NDE is
unpredictable, it is conceivable to follow over time a cohort of patients that are
susceptible of experiencing a NDE in a medical environment. This would notably
permit obtaining more complete medical information (i.e., objective physiological
measurements) concerning the context of occurrence and reducing the hypothetical
memory bias that might affect retrospective surveys by interviewing experiencers
within a few days following their experience. Such protocol is often more rigorous
but heavy to set up as well. It has been shown that the choice of the study design
might have an impact on collected data. When comparing both types of designs in
studies on NDEs, Charland-Verville and colleagues (2014) found that all NDE
features tend to be more frequently reported by NDE experiencers in retrospective
studies than in prospective ones.
38
1.10 Objectives & overview of the present work
The present work aimed at exploring the NDE memory and the cognitive
characteristics of people reporting memories that are consistent with a NDE,
through a psycho-cognitive approach. To do so, our first objective was to explore
the phenomenological characteristics of NDE memories and the subjective
experience associated with remembering this particular event, according to the
reported experience intensities (Chapter 2, study 1). In a second study, we
investigated the frequency distribution of the features retrospectively reported in
NDE narratives as well as the temporality sequences of those features (Chapter 3,
study 2). While NDEs may have a universal character so that they may exhibit
enough common features to belong to the same phenomenon (Atwater, 1988;
Charland-Verville et al., 2014; Grosso, 1981), we nevertheless wanted to explore a
possible temporal variability within the distribution of reported features. In
addition to study the NDE memory, the two last studies aimed at better defining the
cognitive profile of their experiencers. To achieve this, we tested NDE
experiencers and compared their performance with matched individuals having
identical medical history but who have never reported a NDE phenomenology.
More specifically, in a third study, we investigated inter-individual differences in
the susceptibility to produce false memories in experiencers reporting a NDE
developed inside a life-threatening context through a comparison with people
having reported a life-threatening event without a NDE (Chapter 4, study 3). In
Chapter 5 (study 4), we explored fantasy engagement of experiencers reporting a
subjective NDE in the presence (i.e., classical NDEs) or the absence (i.e., NDEs-
like) of a life-threatening situation, through the comparison with non-experiencers.
Finally, we conclude the present work by discussing the findings and future
perspectives.
39
2 Study 1: Phenomenological
characterization of the NDE memory
Based on the following publication:
Martial, C.1, Charland-Verville, V.1, Cassol, H.1, Didone, V.2, Van Der Linden,
M.3 & Laureys, S.1 (2017). Intensity and memory characteristics of near-
death experiences. Consciousness and Cognition, 56, 120–127.
1Coma Science Group, GIGA-Consciousness, University and University Hospital of Liège, Liège, Belgium 2Psychology Research Unit, Cognition and Behavioral, University of Liège, Liège, Belgium 3Cognitive Psychopathology and Neuropsychology Unit, University of Geneva, Geneva, Switzerland
40
2.1 Summary
At present, there is still no satisfactory explanation for the NDEs’ rich
phenomenology. Here we compared phenomenological characteristics of NDE
memories with the reported experience’s intensity. We included 152 individuals
with a self-reported “classical” NDE (i.e., occurring in life-threatening conditions).
All participants completed a mailed questionnaire that included a measure of
phenomenological characteristics of memories (the MCQ) and a measure of NDE’s
intensity (the Greyson NDE scale). Greyson NDE scale total score was positively
correlated with MCQ total score, suggesting that participants who described more
intense NDEs also reported more phenomenological memory characteristics of
NDE. Using MCQ items, our study also showed that NDE’s intensity is associated
in particular with sensory details, personal importance and reactivation frequency
variables.
41
2.2 Background
For some years now, more and more NDE experiencers’ testimonies have
been compiled which demonstrate the compelling intensity of this experience
(Moody, 1975; Ring, 1980). Because the scientific literature devoted to the
investigation of NDE memories is limited, one may attempt to better understand
their particularities using the broader literature on autobiographical memory. If we
consider autobiographic memory as “memory for the events of one’s life” (Conway
& Rubin, 1993, p. 103; see the Self-Memory System –SMS; Conway & Pleydell-
Pearce, 2000; Conway et al., 2004), we could consider NDE memories as part of
this memory system. More broadly, the SMS (Conway & Pleydell-Pearce, 2000)
consists of two main strongly interconnected components: the working self and the
autobiographical memory knowledge base. According to this view, autobiographic
memory is a reconstructive process that links sensory-perceptual episodic memory
and its context (Conway, 2001; Conway & Pleydell-Pearce, 2000). In this respect,
“episodic information” refers to sensory-perceptual knowledge contained in
episodic memories. When accessed during remembering, this information supports
the “recollective experience” (i.e., the feeling of remembering; Wheeler et al.,
1997). As a rule, sensory-perceptual episodic memories do not anchor in memory
except if they become related to more permanent autobiographical memory
knowledge systems (e.g., if there is an enduring association with one’s current
goals). Thus, not all episodic memories remain accessible in memory and can enter
into the subsequent formation of autobiographic memory (Conway, 2001).
The literature has shown that intensity of an experience affects the properties
of the subsequent autobiographical memories more so than do valence or the age of
the memory (e.g., Holmes, 1970; Talarico et al., 2004). Highly intense events are
firmly anchored and remembered in memory (Bradley, 1994) and this is partly due
to associated emotions. In the literature certain models suggest that the effects of
emotion on memory could be explained without suggesting specific mechanisms
associated with the emotional arousal (e.g., Bradley, 1994). From that perspective,
42
the enhanced memory observed for emotional events might be due to “ordinary”
factors (e.g., enhanced attention and/or increased elaboration) –as it is the case with
non-emotional events. In contrast, other models do suggest the existence of some
additional special mechanisms associated with emotional arousal (e.g., McGaugh,
2000). Neural and hormonal mechanisms specific to emotional stimuli might
influence their memory encoding (e.g., notably because of release of hormones;
Cahill & McGaugh, 1998; McGaugh, 2000), leading to more elaborated memory
representations (Bradley, 1994). Since NDEs are known to imply a great emotional
involvement (generally positive in valence) and to be high intensity (Moody,
1975), we can easily suggest that NDE memories can then benefit from a special
encoding and storage (e.g., strong consolidation) that make them more
phenomenologically detailed and more persistent than other kinds of memories.
Surely, other influencing factors can intervene in the creation of an
exceptionally clear memory trace. As the term itself suggests, NDEs typically
occur in situations in which people are close to death or are perceived as such. This
context might strengthen the intensity of what they perceived and also makes the
event “threatening” for individuals, independently of the associated positive
feelings. Through evolution, human memory has developed the ability to
preferentially retain events that are relevant for survival. Indeed, it would be
adaptive to integrate relevant information on adverse events to be prepared for
them in the future (see Porter & Peace, 2007). To face with those potentially
dangerous situations, humans can develop various adaptive mental and physical
responses, including dissociation. Psychological theories have proposed that NDEs
are dissociative states in which individuals experience a dissociation of the self-
identity from bodily sensations (Irwin, 1993), leading them to experience
pleasurable dimensions and sensations instead of the unpleasant event itself
(Pfister, 1930).
In psychological science, subjective self-report scales and questionnaires
have been developed to collect data on many subjective states and contents of
43
consciousness. However, while a growing number of such scales have been
published on several different topics, there are only a very limited number of scales
developed to collect data about NDEs specifically. To date, the most widely used
standardized tool to identify NDEs in research is the Greyson NDE scale (Greyson,
1983; Table 3). Nonetheless, other scales, but non-specific to NDEs, may be used
to assess the experience and, in particular, its subsequent memory and the
associated “recollective experience”. Notably, some authors have used the MCQ
(e.g., Palmieri et al., 2014; Thonnard et al., 2013) with the aim of assessing
subjective qualities of NDEs’ memory characteristics. In fact, the MCQ has been
constructed, by design, in a more extensive area aiming at assessing all types of
memory –whatever the event or content of the evaluated memory. More
specifically, the MCQ permits to examine qualitative characteristics of memories,
in terms of sensory and contextual details and cognitive processes involved in the
recall of a memory. Nowadays, the Greyson NDE scale (Greyson, 1983) and the
MCQ (Johnson et al., 1988) are the two most commonly used standardized
questionnaires in research to evaluate the NDE and its memory.
Although described as occurring in near-death states where the brain is
thought to be working with altered capacities, NDE experiencers can generally give
a very detailed narrative account of their experience (Moody, 1975) and it seems
that the NDEs can differ in term of experience intensity (Charland-Verville et al.,
2014). We then wondered about the variation of NDE memory details according to
the intensity of the experience. To the best of our knowledge, no study has formally
compared the association of the NDE intensity according to the Greyson NDE
scale (Greyson, 1983) with the phenomenological characterization of this type of
memory according to the MCQ (Johnson et al., 1988) in the same sample of
individuals who have lived a NDE. From a theoretical perspective, although the
subjective experience reported by NDE experiencers does not itself provide an
explanation, it nevertheless can give some indications as to which aspects of the
NDE an explanation should account for. Using the Greyson NDE scale (Greyson,
44
1983) and the MCQ (Johnson et al., 1988), the present study aimed at exploring (1)
the association of both the NDE’s intensity (Greyson NDE scale total score) and
the amount of NDE memory characteristics (MCQ total score) with demographic
data (age at interview, age at NDE and time since NDE); (2) the association of
NDE’s intensity (Greyson NDE scale total score) with the amount of NDE memory
characteristics (MCQ total score) and, more in particular, (3) with the different
phenomenological characteristics of NDE memory (MCQ items).
45
2.3 Material & methods
2.3.1 Participants & procedure
Participants were recruited via the International Associations for Near-Death
Studies (IANDS France and IANDS Flanders) and the Coma Science Group
(University and University Hospital of Liège, Belgium). Participants were mailed a
questionnaire including the Greyson NDE scale (Greyson, 1983), the MCQ
(Johnson et al., 1988), and items about sociodemographic (gender, age at NDE, age
at interview) and clinical (time since NDE, presence of life-threatening event,
etiology of coma, presence of coma –i.e., a period of unconsciousness > 1h; Posner
et al., 2007). Participants whose experience did not meet the standardized criteria
(i.e., Greyson NDE scale total score < 7/32; Greyson, 1983) were not included in
the present study. We assessed the participants’ memories characteristics using a
modified version (see Table 4; D’Argembeau & Van der Linden, 2008) of the
MCQ (Johnson et al., 1988). This version encompasses 16 rating scales assessing
feeling of re-experiencing, visual details, other sensory details (i.e., sounds, smells
and tastes), location, time, coherence, verbal component, emotion while
remembering, belief that the event is real, one’s own actions, words and thoughts,
visual perspective, emotional valence, personal importance, and reactivation
frequency. A MCQ total score was derived summing all the 16 items (each on a 1–
7 points Likert scale) and referred to as the amount of memory characteristics (i.e.,
higher total scores reflect greater amount of memory characteristics). No incentive
was offered for participation. Completion of the anonymous questionnaire was
voluntary and taken as consent for participation in the survey. The study was
approved by the ethics committee of the Faculty of Medicine of the University of
Liège.
46
2.3.2 Statistical analyses
Pearson's correlation tests were used to measure the linear association
between variables. More specifically, correlations were obtained using both the
Greyson NDE scale total score and the MCQ total score with each demographic
variable (age at interview, age at NDE and time since NDE). Then, correlation was
done between the Greyson NDE scale total score and the MCQ total score. Finally,
correlations were obtained using the Greyson NDE scale total score and each of the
16 MCQ items. We used the Shapiro-Wilk test to evaluate the hypothesis that a
given sample was from a normal population. To avoid type I errors, the level of
significance undergoes a Bonferroni adjustment (p < .0021) in all statistical
analyses.
47
48
2.4 Results
2.4.1 Demographic data
The distributions of demographic data and scores follow a normal
distribution. The study sample included 152 individuals who have had a NDE
described experience (i.e., meeting the criteria for NDE: Greyson NDE scale total
score ≥ 7/32; Greyson, 1983) after a life-threatening event (i.e., a severe brain
insult; e.g., cardiac arrest, traumatism). Table 5 shows the demographic
characteristics of the entire study cohort.
Demographics Total
N=152
Gender–female 82 (54%)
Age at interview (Mean in years ± SEM) 56 ± 10
Age at NDE (Mean in years ± SEM) 33 ± 14
Time since NDE (Mean in years ± SEM) 23 ± 14
Scales
Greyson NDE scale total score (Mean ± SEM, range) 16 ± 5 7-30
MCQ total score (Mean ± SEM, range) 86 ± 11 41-110
SEM = Standard Error of the Mean
Table 5 – Participants’ descriptive and demographic data (N = 152). The NDE intensity (Greyson
NDE scale total score) and the amount of memory characteristics (MCQ total score).
2.4.2 Correlations between both scale total scores and
demographic data
There were no significant associations with the time since NDE and total
scores on the Greyson NDE scale and the MCQ, meaning that the intensity of NDE
and the amount of NDE memory characteristics do not appear to vary with the
amount of time that had elapsed since NDE. There were also no significant
49
correlations between variables age at interview and at NDE and the Greyson NDE
and MCQ total scores (see Table 6).
2.4.3 Correlations between Greyson NDE scale total
score, MCQ total score and items
Greyson NDE scale total score was positively correlated with MCQ total
score (r = .29, p < .0005), suggesting that individuals who described more intense
NDEs also reported more phenomenological characteristics of NDEs (see Table 4).
Analyses with MCQ items showed positive correlations between the Greyson NDE
scale total score and 3 of those items: other sensory details (r = .29, p < .0005;
MCQ item 3), personal importance (r = .22, p < .002; MCQ item 15), and
reactivation frequency (r = .28, p < .0005; MCQ item 16). This suggests that
individuals who described more elaborate NDEs also reported more sensory
characteristics (i.e., sounds, smells and tastes), personal importance and
reactivation frequency. No further significant correlations were found between the
Greyson NDE scale total score and the other MCQ items (see Table 6).
51
Greyson NDE scale total score MCQ total score
Demography Age at interview Age at NDE Time since NDE
-.11 (.188) -.14 (.079) .06 (.435)
.02 (.821) .01 (.894)
.005 (.951)
MCQ total score & items MCQ total score .29 (.0003) -
Feeling of re-experiencing .10 (.233) - Visual details .07 (.396) - Other sensory details .29 (.0002) - Location -.09 (.249) - Time .05 (.538) - Coherence .17 (.04) - Verbal component .13 (.122) - Feeling emotions .18 (.026) - Real/imagine .20 (.014) -
One’s own actions -.04 (.581) - One’s own words .14 (.086) - One’s own thoughts .04 (.644) - Visual perspective .10 (.236) - Valence .16 (.05) - Personal importance .22 (.002) - Reactivation frequency .28 (.0004) -
Data are Pearson's correlations (p).
Table 6 – Correlations between demographic data, Greyson NDE scale total score, MCQ total score and MCQ items.
52
2.5 Discussion
This retrospective study showed that the intensity of the NDE (i.e., the
Greyson NDE scale total score) appears to be positively correlated with the
overall amount of retrospective phenomenological characteristics identified with
the MCQ (i.e., the MCQ total score). In other words, participants who scored
higher on the Greyson NDE scale also scored higher on the MCQ. This suggests
that the more intense the NDE is, the more the memory seems to be
phenomenologically detailed when NDE experiencers later recall it. It can then
be hypothesized that the deeper the NDE is, the more the memory seems to be
anchored and to benefit from a special encoding, thereby leading the memory to
contain a greater amount of phenomenological characteristics. Moreover, one
can argue that NDE memory characteristics would vary with the amount of time
that had elapsed since the experience. However, it does not seem to be the case
since we did not find a link between the amount of time that had elapsed since
NDE and the amount of memory characteristics. Furthermore, we also found no
association between the NDE’s intensity and the amount of time that had elapsed
since the NDE. Despite our study is not a test–retest design, our data support the
view that the intensity of NDE does not seem to increase or decrease with the
time that had elapsed since the experience. In fact, except Greyson's (2007)
study, it seems that very little is known about the long-term retention of NDE
memories.
Since NDEs are complex subjective experiences typically including
various features, our study also clarified that the NDE’s intensity is associated in
particular with MCQ items of sensory details (concerning sounds, smells and/or
tastes), personal importance of the event and reactivation frequency.
Interestingly, we found that the presence of sensory details in NDE
experiencers’ memory varies with experience’s intensity. Since some studies
have suggested that emotional valence increases the amount of sensory details in
memory (e.g., Schaefer & Philippot, 2005), it seems reasonable to suggest that
53
the NDE –as highly emotional event (Thonnard et al., 2013)– may be encoded
and stored by a special memory mechanism that typically operates during the
encoding of emotionally arousing events. For example, we can speculate that
intensity could increase attentional mechanisms and then be beneficial for all
reported sensory details.
We also observed a relationship between the NDE’s intensity and the
reactivation frequency item on the MCQ. That is, the more intense the NDE is,
the more frequently the NDE seems to be reactivated in memory. Intense events
are more likely to be rehearsed which in turn can enhance the amount of
phenomenological characteristics in memory (Berntsen, 1996, 1998). Recently,
Thonnard et al. (2013) showed that NDE memories were as likely to be
reactivated in memory as other real and imagined events memories or coma
memories that did not classify as a NDE based on the Greyson NDE scale (i.e.,
total score of Greyson < 7/32; Greyson, 1983). In the present study, we
nevertheless noted the association between intensity and reactivation frequency
variables. On the one hand, experience memories may be intentionally and/or
voluntarily brought into awareness and, on the other hand, experience memories
may be reactivated internally and/or externally –sharing it with other people for
example.
Finally, we found that NDE’s intensity varies with the personal
importance experiencers attached to the experience, suggesting that the more
intense the NDE is, the more the NDE could be considered as an important
episode in experiencer’s life. Personal importance given to the NDE could
possibly enhance the overall perceived phenomenological characteristics of
NDE memories. According to Conway's SMS model (Conway & Pleydell-
Pearce, 2000), autobiographical memories are “the transitory mental
constructions of a complex goal-driven set of control processes collectively
referred to as the working self” (Conway et al., 2004, p. 493). Only a relatively
small part of autobiographical memories may remain accessible in long-term
54
memory and this selection should depend on their given relevance to longer-term
goals and consequently to the future.
Still using MCQ items, intensity variations in reported NDEs did not seem
to be associated with the other memory characteristics (emotional information,
visual details, confidence, visual perspective, feeling of re-experiencing)
assessed by the MCQ. Intriguingly, emotional information (i.e., emotional
valence of the experience, emotion while remembering) did not also appear to
vary the NDE’s intensity. While NDEs appear to include extremely high
emotional content (Thonnard et al., 2013), we found that the presence of
emotional details in NDE experiencers’ memory may fluctuate independently of
intensity variation experienced by NDE experiencers.
While resuscitation techniques are improving and providing more
reported NDE testimonies (van Lommel et al., 2001), only very few scales are
present to investigate the phenomenon. In this study, we observed that
individuals who scored higher on one of the questionnaires also scored higher on
the other one. Then, one can ask to what extent there is an overlap between the
items of the two questionnaires and to what extent they evaluate the same
aspects of the experience. However, although the correlation is highly
significant, we found a relatively weak linear relation. Instead, this suggests that
both questionnaires may be testing different and complementary aspects of the
experience. The Greyson NDE scale focuses on the content of the NDE and its
intensity (only) at a phenomenological level while the MCQ assesses qualitative
characteristics of NDE memories and cognitive processes involved in its recall.
Although the Greyson NDE scale inevitably assesses the NDE memory by
retrospectively questioning the individual about what he is remembering, the
MCQ differs from the Greyson NDE scale by exploring the multimodal aspect
(i.e., separately measuring sensory, perceptual, semantic and spatio-temporal
components) of the memory. This may permit to observe distinct implications of
those aspects specific to NDEs in the investigation of its rich phenomenology.
55
Finally, the MCQ also allows assessing negative emotions and confidence in the
memory –which is currently not possible with the Greyson NDE scale.
There are several perceived limitations to the current study. Although we
found a positive correlation between the intensity of NDE and its amount of
associated memory characteristics, the question of cause and effect remains to be
addressed in further work. In particular, the present results do not allow us to say
whether it is the increasing intensity of NDE that leads to a greater amount of
memory characteristics or the inverse pattern. In addition, another variable could
also explain the associated variations we find in this study. For example, it may
be possible that the way in which individuals encode and recall information is
one variable influencing how they respond to both questionnaires. In addition,
this investigation may be subject to selection bias and hence may not be
representative of NDE experiencers in general. Indeed, NDE experiencers who
do not contact us intentionally may possibly experience NDE memory
differently from those who do. Nevertheless, our study embraced a large sample.
In conclusion, the amount of memory details in a NDE (i.e., the MCQ
total score) appears to be positively associated with the intensity of the lived
experience (i.e., the Greyson NDE scale total score). More specifically, our
results highlighted that sensory details (i.e., sounds, smells and tastes), personal
importance and reactivation frequency seem to vary with the intensity of the
NDE (i.e., the Greyson NDE scale total score). The challenge lies in explaining
how memory formation can occur under life-threatening conditions in which the
individual is thought to be unconscious and at a time when memory formation
would not be expected to operate effectively. Yet, in this study the overall
intensity of the NDE was notably obtained by considering the amount of
experienced features ticked by NDE experiencers (as measured by the Greyson
NDE scale), thereby leading to important questions concerning the frequency
distribution of NDE features.
56
3 Study 2: Temporality of features in NDE
narratives
Based on the following publication:
Martial, C.1, Cassol, H.1, Antonopoulos, G.1, Charlier, T.2, Heros, J.1, Donneau,
A.-F.2, Charland-Verville, V.1* & Laureys, S.1* (2017). Temporality of features in near-death experience narratives. Frontiers in Human
Neuroscience, 11, 311.
1Coma Science Group, GIGA-Consciousness, University and University Hospital of Liège, Liège, Belgium 2Biostatistics, Public Health Department, University of Liège and University Hospital of Liège, Liège, Belgium
57
3.1 Summary
After the occurrence of a NDE, experiencers usually report extremely rich
and detailed narratives. Phenomenologically, a NDE can be described as a set of
distinguishable features. Some authors have proposed regular patterns of NDEs;
however, the actual temporality sequence of NDE core features remains a little
explored area. The aim of the present study was to investigate the frequency
distribution of these features (globally and according to the position of features in
narratives) as well as the most frequently reported temporality sequences of
features. We collected 154 French freely expressed written NDE narratives. A text
analysis was conducted on all narratives in order to infer temporal ordering and
frequency distribution of NDE features. Our analyses highlighted the following
most frequently reported sequence of consecutive NDE features: Out-of-Body
Experience, Experiencing a tunnel, Seeing a bright light, Feeling of peace. Yet,
this sequence was encountered in a very limited number of NDE experiencers.
These findings may suggest that NDE temporality sequences can vary across NDE
experiencers. Exploring associations and relationships among features encountered
during NDEs may complete the rigorous definition and scientific comprehension of
the phenomenon.
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3.2 Background
The first documented attempt to establish a chronological order of NDE
features was made through the observations of Kenneth Ring (1980). Derived from
a sample of 102 individuals with a self-reported NDE, Ring (1980) proposed a 5-
stage temporality sequence of NDEs: (1) “an experience of peace, well-being, and
an absence of pain,” (2) “a sense of detachment from the physical body,
progressing to an OBE,” (3) “entering darkness, a tunnel experience with
panoramic memory, and a predominantly positive effect,” (4) “an experience of
light that is bright, warm, and attractive,” and (5) “entering the light; meeting
persons or figures.” He further suggested the concept of “non-core experiences”
which are other types of features less frequently encountered during NDEs (e.g.,
encountering a presence or loved ones or life review). Although Ring is considered
as pioneer with his work, his scale and the proposed 5-stage sequence have some
limitations. In particular, the cut-off points and this sequence were made through
observations, were not based on statistical analysis, and were not tested for internal
coherence or reliability. Around the same period, Noyes et al. (1977) described 3 –
instead of 5– successive phases: (1) resistance (including a recognition of danger,
the fear of dying, a struggle to live, and acceptance of death), (2) life review, and
(3) transcendence (i.e., a mystical state of consciousness). Some authors have thus
decreased the ambiguity in descriptions of the phenomenological features and their
frequency distribution. However, to date, no temporal structure has yet been
rigorously identified.
While sustained efforts have been made to better understand certain
phenomenological features encountered during NDEs, the scientific literature
devoted to the investigation of temporal structure of NDEs narratives seems rather
limited. To the best of our knowledge, no study has formally and rigorously
investigated whether NDE features follow a fixed order or distribution. Overall, the
notion of temporality is fundamental to human experience. Indeed, temporality is
central to characterizing narratives, because they are regularly developed in a
59
dynamic temporal order when written (Fleischman, 1990) and their coherence
emerges from this order (Trabasso et al., 1995). In the case of NDEs phenomenon,
it can be noted that the temporal structure of narratives is dictated by each feature
encountered by NDE experiencers during the experience and configures those
diverse features into a meaningful whole for the NDE experience (Ring, 1980). The
objective of the present study was to explore the chronology of NDE features in a
sample of self-reported written narratives. In our view, investigating the
temporality of NDE features may permit to highlight relationships and connections
among them and, more generally, address the challenging question as to whether
the patterns of NDEs are regular. Given a set of NDE narratives, the present study
aimed at (1) exploring the frequency distribution of NDE features (overall
frequency distribution of NDE features appearing in narratives, frequency
distribution of the first and the last NDE feature occurrences, and frequency
distribution of NDE features according to their position in the narratives); and (2)
eventually identifying the most frequent stages of temporality sequences.
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3.3 Material & methods
3.3.1 Participants & procedure
Participants were recruited via the IANDS France and the Coma Science
Group (University of Liège and University Hospital of Liège, Belgium).
Completion of the anonymous questionnaire was voluntary. Participants were then
mailed a questionnaire that included items about socio-demographic (gender, age at
NDE, age at interview) and clinical (time since NDE) characteristics. Participants
were then asked to freely write down the detailed narrative of the experience on
blank sheets of paper –without any text size restrictions. Finally, they were asked
to respond to the Greyson NDE scale (Greyson, 1983). Participants whose
experience did not meet the accepted criteria (i.e., total score < 7/32 on the
Greyson NDE scale; Greyson, 1983) were excluded from the present analysis. No
incentive was offered for participation. All subjects gave written informed consent
in accordance with the Declaration of Helsinki. The protocol was approved by the
ethics committee of the Faculty of Medicine of the University of Liège.
3.3.2 Text analysis
The first step consisted of the selection of the recurrent NDE features based
on the literature and the experience of two experts gained by acquiring collecting
and reading NDE testimonies. Before reading narratives, an initial list of the
potential features described in literature (scientific publications and books) and
reported to be characteristic of NDEs, was compiled. Firstly, the 16 key
phenomenological features from the Greyson NDE scale (Greyson, 1983) were
considered. 8 out of 16 Greyson NDE scale’s features were retained because each
of them was clearly distinguished as one clear isolated feature (with a unique
occurrence). The other remaining features were not retained to establish the
chronology since they were considered by the research team as “diffuse” features.
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These words, describing the features, were spread throughout the narrative and a
clear and precise position in the text was difficult to establish (e.g., Altered time
perception, Extrasensory perception, Heightened senses, Unearthly environment).
Then, the WCEI scale’s phenomenological features (Ring, 1980) were considered
and two of them (not already reported in the Greyson NDE scale) were added in
the list: Experiencing a tunnel and Entering the light. Lastly, the phenomenological
feature Returning into the body was included as well for the text analysis, because
it is generally reported by NDE experiencers as a protruding element of NDEs and
considered as a clear isolated feature. Table 7 presents the final 11 NDE isolated
features and the 5 other diffuse features retained to perform the text analysis.
After all written narratives were collected, the anonymous dataset was
created. Some accounts constituted a couple of paragraphs and others spanned
several pages. The average was about 383 words (ranged from 28 to 4411) per
account. Text analysis was identically conducted on all written narratives. Two
researchers (one expert and one novice unfamiliar with the NDE phenomenon)
carefully and separately read all narrative texts from the dataset in order to
understand subjective experiences and highlight each reported NDE feature.
Without consulting each other, they broke narratives into constituent parts that all
play integral roles in the narrative. This text analysis had two steps: (1) each
feature explicitly stated in narrative texts (i.e., descriptive words or words
sequences related to the feature) was isolated and classified into one of 16
categories (see Table 7). An open-vocabulary analysis (i.e., not requiring a
predefined set of NDE keywords with a known correspondence to the NDE
phenomenon) was conducted; (2) an order of appearance was then determined for
each isolated feature –and not for the diffuse ones. All features were thus scored
independently by the two experts. Finally, a dataset indicating whether the NDE
(isolated or diffuse) feature was present or not –was used later to establish
frequency distribution– and a stages temporality sequence for each narrative was
acquired. After that, discrepancies among the analysers (i.e., NDE features
62
sequences without unanimity) were identified and then discussed between them
until a consensus was reached.
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64
3.3.3 Statistical analyses
3.3.3.1 Inter-rater reliability
We used Cohen’s kappa coefficient to measure inter-rater reliability in order to
assess the degree to which both researchers agree on their assessment decisions (the
closer the value to 1, the better the concordance is between the two researchers).
3.3.3.2 Frequency distribution of NDE features
Frequency distribution was calculated from the dataset corresponding to
narratives. Data analysis was carried out using SAS (version 9.3 for Windows)
statistical package. We calculated overall frequency distribution of all NDE
features appearing in narratives. By only using the isolated features, we also
calculated frequency distribution of the first and the last NDE feature occurrences
(i.e., the first and the last feature encountered by NDE experiencers during the
experience), and frequency distribution of NDE features according to their position
in narratives.
3.3.3.3 Frequency distribution of NDE features sequences
Frequency distribution of NDE features sequences was calculated from the
dataset corresponding to narratives. Only isolated features were used for those
analyses.
We first wanted to extract the most frequent sequences of two NDE
consecutive features. For this, we used the four most frequent single features
reported by NDE experiencers –considering the threshold percentage of 50% (i.e.,
features reported in more than half of narratives)– and identified among them
frequency distribution of each sequence of two consecutive features (that is,
ultimately obtaining 6 pairs of two features).
65
We then wanted to extract the most frequent sequence consisting of four
consecutive features –considering the obtained result that the mean number of
NDE features per narrative was four (see Results section). For these analyses, all
temporality sequences were analysed using a MatLab custom code which allowed
us to observe the most frequent sequences of features reported in the narratives –
among all sequences reported by NDE experiencers and thus presented in the
gathered dataset.
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3.4 Results
3.4.1 Participants
We collected 154 French written narratives of NDEs (i.e., meeting the
criteria: Greyson NDE scale total score ≥ 7/32; Greyson, 1983). The demographic
data of the entire study cohort are presented in Table 8.
Total
N = 154
Gender–female 82 (53%)
Age at NDE (Mean in years ± SD)
34 ± 17
Age at interview
(Mean in years ± SD)
55 ± 13
Time since NDE (Mean in years ± SD)
22 ± 15
Greyson NDE scale total score (Mean ± SD)
16 ± 6
SD=standard deviation
Table 8 – Demographic data and Greyson NDE scale total score.
3.4.2 Inter-rater reliability
Results showed an almost perfect agreement of both researchers for the text
analysis with a Cohen’s kappa coefficient equal to 0.95 (95% confidence intervals
0.87–0.98).
3.4.3 Frequency distribution of NDE features
Results were expressed as counts and proportions (%) for feature variables.
This analysis showed that the mean number of NDE isolated features reported per
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narrative was 4 ± 2 (ranged from 1 to 9). The mean number of NDE diffuse
features reported per narrative was 1 ± 1 (ranged from 0 to 4). When considering
isolated and diffuse features, results revealed a mean number of 6 ± 2 (ranged from
1 to 15). The number and percentage of narratives in which each NDE feature
appears –whatever their positions in the narrative text– are presented in Table 9
(see the last column of the table). In all the narratives, the most frequently
encountered NDE features were Feeling of peacefulness (80%) and Seeing a bright
light (69%). The third most frequently reported NDE feature was Encountering
with spirits/people (64%). The two least frequently reported NDE features were
Speeded thoughts (5%) and Precognitive visions (4%).
Table 9 also lists frequency distribution of the first and the last NDE feature
encountered in written narratives. Results showed that the most frequent NDE
feature appearing as the first feature in narrative texts was OBE (35%). The most
frequent NDE feature appearing as the last feature –whatever the number of NDE
features encountered during the experience– in narratives was Returning into the
body (36%).
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NDE features First occurrence
N (%)
Last occurrence
N (%)
Overall frequency
N (%)
Isolated features
Out-of-Body-Experience 54 (35) 5 (3) 81 (53)
Experiencing a tunnel 36 (23) 3 (2) 73 (47)
Feeling of peace 24 (16) 22 (14) 123 (80)
Seeing a bright light 20 (13) 9 (6) 106 (69)
Encountering with spirits/people 8 (5) 17 (11) 99 (64)
Life review 7 (5) 8 (5) 25 (16)
Feeling of harmony 2 (1) 4 (3) 21 (14)
Coming to a border/point of no return 1 (1) 26 (17) 62 (40)
Entering the light 1 (1) 2 (1) 27 (18)
Precognitive visions 1 (1) 1 (1) 6 (4)
Returning into the body 0 (0) 56 (36) 57 (37)
Diffuse features
Unearthly environment - - 57 (37)
Heightened senses - - 56 (36)
Altered time perception - - 54 (35)
Extrasensory perception - - 29 (19)
Speeded thoughts - - 8 (5)
Table 9 – Frequency of the first and the last NDE isolated feature occurrences, and overall frequency of NDE (isolated and diffuse) features appearing in narratives (N = 154) –by decreasing order of
frequency according to the first occurrence in narratives.
Table 10 shows the frequency distribution of NDE features according to
their position in the narratives. At time 1 (i.e., the first NDE feature appearing in
narrative texts –whatever the total number of features encountered during the
NDE), the most frequently reported feature was OBE (35%). At time 2 (i.e., the
second NDE feature appearing in narrative texts –whatever the total number of
features encountered during the NDE), Feeling of peacefulness (31%) was the most
often encountered feature. At time 3 and 4, the most frequently reported features
were, respectively, Seeing a bright light (25%) and Encountering with
spirits/people (24%). At time 5 and 6, the most frequently observed feature was
Coming to a border/point of no return (respectively, 22 and 31%). At time 7,
Returning into the body (56%) was the most often reported feature. At time 8, the
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two most frequently reported features were Coming to a border/point of no return
and Returning into the body (both 37%). Finally, results demonstrated that only
three narratives contain a ninth feature and all three were Returning into the body
(100%). One can also observe in Table 10 the total numbers of narratives contained
at each occurrence time (see the last row of the table).
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71
3.4.4 Frequency distribution of NDE features sequences
Frequency distribution of each sequence of two consecutive features is
presented in Table 11 and Figure 5. Total values represent the total numbers of
narratives containing both NDE features and frequency distribution percentages
were calculated out of those totals. Both orders of occurrence for each pair of
features are reported in Table 11 and Figure 5.
NDE features sequences Frequency
N (%)
Out-of-Body-Experience Encountering with spirits/people 43 (91)
Encountering with spirits/people Out-of-Body-Experience 4 (9)
Total frequency 47 (100)
Seeing a bright light Encountering with spirits/people 60 (85)
Encountering with spirits/people Seeing a bright light 11 (15)
Total frequency 71 (100)
Feeling of peace Encountering with spirits/people 63 (77)
Encountering with spirits/people Feeling of peace 19 (23)
Total frequency 82 (100)
Out-of-Body-Experience Feeling of peace 51 (75)
Feeling of peace Out-of-Body-Experience 17 (25)
Total frequency 68 (100)
Out-of-Body-Experience Seeing a bright light 37 (70)
Seeing a bright light Out-of-Body-Experience 16 (30)
Total frequency 53 (100)
Seeing a bright light Feeling of peace 49 (56)
Feeling of peace Seeing a bright light 39 (44)
Total frequency 88 (100)
Table 11 – Frequency of 2 NDE features sequences in order of occurrence reported in narratives (percentages are calculated out of the total amount of narratives containing both NDE
features). Total frequency of narratives containing both NDE features.
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Our analysis demonstrated that, in 47 narratives containing both OBE and
Encountering with spirits/people, 91% consecutively reported them in this order of
occurrence. By contrast, only 9% reported both features in the opposite order. In 71
narratives containing both Seeing a bright light and Encountering with
spirits/people, 85% encountered them in this order. Results also showed that 77%
of narratives containing Feeling of peace and Encountering with spirits/people
encountered both features in this order of occurrence. In 68 narratives containing
both OBE and Feeling of peace, 75% reported them in this order. In all narratives
containing both OBE and Seeing a bright light, 70% encountered both features in
this order of occurrence and 30% reported them in the opposite order. The analysis
finally showed that in all narrative texts containing both Seeing a bright light and
Feeling of peace, 56% reported them in this consecutive order and 44% in the
opposite order.
Figure 5 – Frequency of 2 NDE features sequences in order of occurrence reported in narratives (values in parentheses are percentages calculated out of the total amount of narratives containing both
NDE features).
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Finally, Figure 6 shows the most frequent sequence of four consecutive NDE
features. 6 (22%) out of the 27 narratives containing those four NDE features had
this order of occurrence: OBE, followed by Experiencing a tunnel, followed by
Seeing a bright light, ending by Feeling of peace. We find 33 other sequences of 4
consecutive features, but appearing in 2 to 5 narratives (the list being too
exhaustive to be listed here).
Figure 6 – The most frequent sequence of four NDE features (22%) appearing in narratives (N = 27; percentage calculated out of the total amount of narratives containing these four NDE features).
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3.5 Discussion
The aim of this study was to examine frequency distribution of NDE features
(frequency distribution of each single feature and according to their position in
narrative texts) and NDE features sequences (i.e., the temporal order of distinct
features) conducting text analysis on written narratives of self-reported NDEs (i.e.,
Greyson NDE scale total score ≥ 7/32; Greyson, 1983).
Firstly, our findings replicated previous research that has observed the
feeling of peacefulness as the most frequently encountered feature during NDEs
and precognitive visions as the less frequently encountered (Charland-Verville et
al., 2014; Greyson, 1990, 2003; Lai et al., 2007; Pacciolla, 1996; Schwaninger et
al., 2002; Zhi-ying & Jian-xun, 1992). Our results diverge, however, on the second
most reported feature, which was Seeing a bright light in the present study. OBE
was here recorded in 53% of the testimonies (i.e., the fourth more frequent feature)
while it is usually reported in the literature as the second most commonly
encountered feature in NDEs (i.e., about 80%; Charland-Verville et al., 2014;
Corazza & Schifano, 2010; Greyson, 1990, 2003; Lai et al., 2007; Schwaninger et
al., 2002). Moreover, we observed that OBE is the most frequently cited feature at
the very beginning of the narratives and Returning into the body at the very end.
This suggests that NDEs seem to be regularly triggered by a sense of detachment
from the physical body and end when returning to one’s body. More generally, we
observed that NDE narratives vary in “richness” of encountered features; more
specifically, some narratives may include one feature while (remarkably rich)
others may include up to 15 features in a single experience. Ultimately, the most
significant features (i.e., occurring > 50%) identified in the present work included
Feeling of peace, Seeing a bright light, Encountering with spirits/people and OBE.
Based on the present results –and consistent with previous literature (e.g.,
Charland-Verville et al., 2014; Lai et al., 2007; Greyson, 2003), it appears that no
NDE feature is universal in its occurrence.
75
Our next goal was to investigate frequency distribution of consecutive NDE
features. Our results showed that the most frequently reported sequence of two
consecutive features was, in order of appearance, Feeling of peace and
Encountering with spirits/people. Interestingly, it also appears that Seeing a bright
light, OBE and Feeling of peace were all the more regularly followed by
Encountering with spirits/people in narratives (see Figure 5). We further observed
that NDE experiencers experience more often an OBE before experiencing a
Feeling of peace –than the opposite pattern. Finally, in contrast to all other pairs of
features, the order of occurrence of both features Seeing a bright light and Feeling
of peace seemed less clearly manifested (i.e., almost similar percentages observed
in both orders) –although the overall occurrence frequency of this pair is higher
than the other pairs. We then suggest that it could be due to a strong association
between those both features. It has been previously suggested that the bright light
spotted by NDE experiencers is regularly associated with a profound feeling of
peace (Corcoran, 1988; Moody, 1975; often described as “light peace” and
extremely pleasant) and/or love (Facco & Agrillo, 2012). Therefore, this may make
it difficult for NDE experiencers to clearly distinguish both features and then
identify a chronological order among them.
Third, the present results highlighted the most frequent temporality core
features sequence reported by NDE experiencers in their narratives: OBE, followed
by Experiencing a tunnel, followed by Seeing a bright light, finally followed by
Feeling of peace. We found nevertheless this sequence in a relatively small number
of accounts (i.e., 6). Actually, no invariable temporal sequence of features (i.e.,
observed in all or at least most narratives) could be established in our sample of
narratives, suggesting that every NDE might report a unique pattern of experience.
We then could consider NDE narratives as a changeable collection of possible
elements differing according to NDE experiencers –and not as a regular pattern.
While NDEs may have a universal character so that they may exhibit enough
common features to belong to the same phenomenon (e.g., Atwater, 1988;
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Charland-Verville et al., 2014; Grosso, 1981), we nevertheless observed in this
study a temporal variability within the distribution of reported features. Indeed, our
findings suggest that NDEs may not feature all elements and elements do not seem
to appear in a fixed order. This raises significant questions about what specific
aspects of NDEs could be considered as universal –and what not.
In parallel, the text analysis highlighted “diffuse” features; that is,
dimensions which are reported using words spread throughout narratives. We
observed that the most frequently encountered diffuse feature is Unearthly
environment and the less frequently one is Speeded thoughts. Moreover, our results
revealed that diffuse features are, in general, less frequently reported than isolated
features. The former were reported by NDE experiencers with a frequency ranging
from 5 to 37%, while the latter were observed in testimonies with a frequency
ranging from 4 to 80%. Interestingly, the text analysis revealed the impossibility of
establishing a clear and precise position for diffuse features because of the
propagation of words through narratives.
Alternatively, we believe that our findings are significant by inferring the
relative order of NDE features reported in narratives so as to observing existing
associations and relationships among them in the whole experience. NDEs include
distinct and specific yet unexplained cognitive experiences (physiologically real
and considered as “features” in the present study), which may possibly underlie
different cerebral mechanisms. Some authors have suggested that the mechanisms
involved during NDEs led to a “cascade of events” resulting in the occurrence of
diverse NDE features (Blanke & Dieguez, 2009). More generally, a better
understanding of the existing relationships among NDE features (i.e., determine
how they are interrelated) might help us to explain the entire phenomenon of NDEs
and its underlying mechanisms. The temporality is fundamental because it
concerns our reported perception of the time passing during experiences, which is
one of the central aspects of consciousness (Arstila, 2012). Indeed, it refers to the
perception of all the different experiences we have lived and how we will later
77
recall them. Phenomenologically, life-threatening situations are commonly
associated with alteration in the experience of time and space (Arstila, 2012;
Baruss, 2003; Tart, 1972) as well as bodily perception (Ataria & Neria, 2013; Tart,
1972). Several (non-exclusive) assumptions suggest that as a result of stress, our
senses could record stimuli at higher density, our brain could process more quickly
stimuli and/or our memory could store stimuli at higher density (Arstila, 2012;
Stetson et al., 2007). By contrast, it has also been postulated that “time appears to
slow down because richer than usual memories are later erroneously interpreted to
have spanned a greater period of time than the experience on which they are based
actually did” (Arstila, 2012, p. 5). Because notions of time and chronology are
constructs closely related to memory and consciousness, the present observation
that NDE features appear in a variable order may be relevant in the refinement of
their definition. NDEs are complex experiences and, in our opinion, it is also
essential to consider the experience as a whole (i.e., explore and capture all its
components and how they are interrelated) for a better comprehension of the
phenomenon. In this paper, we therefore offer a first look at the temporal
dimension of features in NDE accounts. We observed in this study a possible
coexistence of different ways to describe features and their temporality (i.e.,
isolated versus diffuse features) within narrations.
There are some limitations in this study that deserve mentioning. First,
limitation is the extent to which testimonies we received are skewed by a selection
bias. Indeed, these findings might not reflect the absolute frequency since many
NDE experiencers can be uncomfortable sharing their experience. Nevertheless,
our study included a relatively large sample of testimonies. Second, we still do not
know exactly to what extent the accounts we got are influenced by the models and
the representations of the phenomenon through the media and published work (e.g.,
NDE description in Moody’s (1975) book). In general, the question of the
reliability of NDE accounts still remains relatively unexplored. Finally, it should be
stressed that our collection of narratives were written in the same language (in this
78
case, French). It would be very interesting to compare NDE narratives from
different languages in order to better investigate the challenging question of socio-
cultural influence.
The present study highlighted the recurrent sequences of NDE features
reported in narratives and shows that NDE features do not appear in a strict
temporal order, but rather in a variable one (i.e., differ across NDE experiencers).
In our opinion, the presented data emphasizes and grants the uniqueness of NDE
experiencers’ experiences. Nonetheless, it should be kept in mind that in this type
of study we are dealing with reports of events –rather than with the events
themselves. Human memory is inherently a reconstructive process and it would
therefore be interesting to assess NDE experiencers’ memory processes.
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4 Study 3: False memory susceptibility in
NDE experiencers
.
Based on the following publication:
Martial, C.1, Charland-Verville, V.1, Dehon, H.2* & Laureys, S.1* (2017). False
memory susceptibility in coma survivors with and without a near-death
experience. Psychological Research, 1–13.
1Coma Science Group, GIGA-Consciousness, University and University Hospital of Liège, Liège, Belgium 2Cognitive and Behavioral Clinical Psychology Unit, Psychology and Neuroscience of Cognition Research Unit (PsyNCog), University of Liège, Liège, Belgium
80
4.1 Summary
It has been postulated that memories of NDEs could be (at least in part)
reconstructions based on experiencers’ previous knowledge and could be built as a
result of the individual’s attempt to interpret the confusing experience. From the
point of view of the experiencer, NDE memories are perceived as being unrivalled
memories due to its associated rich phenomenology. However, the scientific
literature devoted to the cognitive functioning of NDE experiencers in general, and
their memory performance in particular, is rather limited. This study examined
NDE experiencers’ susceptibility to false memories using the Deese–Roediger–
McDermott (DRM) paradigm. We included 20 NDE experiencers who reported
having had their experience in the context of a life-threatening event (Greyson
NDE scale total score ≥ 7/32) and 20 volunteers (matched for age, gender,
education level, and time since brain insult) who reported a life-threatening event
but without a NDE. Both groups were presented with DRM lists for a recall task
during which they were asked to assign “Remember/Know/Guess” judgments to
any recalled response. In addition, they were later asked to complete a post-recall
test designed to obtain estimates of activation and monitoring of critical lures.
Results demonstrated that NDE experiencers and volunteers were equally likely to
produce false memories, but that NDE experiencers recalled them more frequently
associated with compelling illusory recollection. Of particular interest, analyses of
activation and monitoring estimates suggest that NDE experiencers and volunteers
groups were equally likely to think of critical lures, but source monitoring was less
successful in NDE experiencers compared to volunteers.
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4.2 Background
Some authors have proposed that reports of NDE could be altered memories
of real events and could be comparable to false memories (Braithwaite, 2008;
French, 2001). Nonetheless, to our knowledge, no study has directly examined this
hypothesis; that is, whether or not NDE experiencers are particularly prone to false
memory production. In laboratory settings, such memory distortions can be reliably
elicited with the DRM paradigm (Deese, 1959; Roediger & McDermott, 1995), the
most largely used tool to study the production of false memories (see Gallo, 2006,
2010 for reviews). In this procedure, individuals are presented with lists of
semantically associated words (e.g., thread, pin, eye,…) that converge on an
unstudied semantic associate (e.g., needle), an item called “critical lure” (i.e., the
false memory). Later, when asked to remember the word lists, participants are
highly susceptible to falsely recall or recognize this critical lure as being a word
included in the presented list. The DRM illusion is robust to a variety of
manipulations (e.g., persistence across a variety of encoding tasks, retention
intervals, and test formats) and has been observed in a variety of populations (e.g.,
younger and older participants, patients with neurological impairments, and
participants of different languages and cultures). More relevant for the current
study, DRM illusions are typically accompanied by a compelling subjective
experience. That is, participants are quite confident that the critical lure has been
presented, and are able to recollect details related to its supposed presentation –a
phenomenon called “illusory” (e.g., Gallo & Roediger, 2003) or “phantom” (e.g.,
Brainerd et al., 2001) recollection (see Dehon, 2012 for a recent review). Dehon
(2012) defined this phenomenon as “the subjective detailed feeling of remembering
that sometimes accompanies false remembering of events that never happened” (p.
51). In the DRM paradigm, this can be measured with the “Remember/Know”
procedure (Tulving, 1985). This procedure involves asking participants to
differentiate between words that they actually recall with any specific detail related
to his presentation and those based on a strong feeling of familiarity. It is then
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possible to consider a DRM false memory as a falsely recalled critical lure
associated with illusory recollection (i.e., accompanied by “Remember”
judgements; see Dehon, 2012; Gallo et al., 2001; Gallo & Roediger, 2003), and not
as recalled lures purely based on a strong feeling of familiarity. According to the
activation-monitoring theory (e.g., McDermott & Watson, 2001; Roediger et al.,
2001), false memories result from a two-stage theoretical process: when we hear a
list of words, we think about the critical lure (i.e., an internally derived word)
which was not presented, thus making it more easily accessible through spreading
activation in the semantic network. The heightened activation of the critical lure
can then lead to disruption in the participant’s source monitoring (Johnson et al.,
1993) and this word is finally reported by the participant if he was not able to
correctly attribute it to its actual source. Whereas an activation process enhances
false memory, monitoring reduces it. Nuances of these two processes and their
exact nature are still being investigated, but they seem cognitively distinct (Cabeza
et al., 2001; Roediger et al., 2001; Roediger & Mcdermott, 2000).
The existing literature about false memory susceptibility has revealed that
certain cognitive and personality characteristics may be involved in the occurrence
of committing errors in memory. For example, Clancy and colleagues (2002) have
shown using the DRM paradigm that people who report recovered memories of
traumatic events that are unlikely to have occurred (in the case of this study: alien
abduction) seem to be particularly prone to memory distortion. Moreover, the
previous studies have demonstrated that susceptibility to false memories might be
associated with a personal tendency to dissociation (Heaps & Nash, 1999; Hyman
& Billings, 1999). Dissociation can be described as the detachment of thoughts,
feelings, or experiences from the normal stream of consciousness and memory
(Bernstein & Putnam, 1986), and may reflect a failure to efficiently use monitoring
processes or the use of lax criteria to interpret experiences (Johnson, 2006).
Nonpathological dissociation can be considered as a normally distributed trait in
the population and appears to be related to how people process and integrate
83
experiences (Farina & Liotti, 2013). More specifically, it has been demonstrated
that dissociative tendencies are directly related to reality discrimination difficulties
(e.g., Varese et al., 2012). Several studies have shown a positive correlation
between the DRM illusion and the scores on the Dissociative Experiences Scale
(DES; e.g., Hyman & Billings, 1999; Winograd et al., 1998), suggesting that a
tendency towards dissociative experiences is associated with increased rates of
false recall. Dehon et al. (2008) not only replicated this association between the
DES and the DRM illusion, but also found (through the use of a modified DRM
procedure; Brédart, 2000) that this relationship was mediated by the (source)
monitoring component. In parallel, Greyson (2000b) also used the DES as a
measure of dissociative symptoms but in near-death survivors. His study
demonstrated that dissociative symptoms in NDE experiencers were positively
correlated with the depth of the NDE and could support the view that “NDEs
involve a shifting of attention from the physical environment to an altered state of
consciousness in which perception, cognitive functioning, emotional states, and
sense of identity may be partly or completely disconnected from the mainstream of
conscious awareness” (p. 463). This study suggests that NDE experiencers are
more likely to have high-dissociative personality traits (Greyson, 2000b) and those
specific traits, in return, seem to be linked to a higher tendency to reconstruct
experiences (de Ruiter et al., 2006). Indeed, research has reported memory process
changes in high-dissociative people (e.g., Veltman et al., 2005). We can then ask
whether NDE experiencers have certain cognitive characteristics, such as higher
constructive capacities, that lead them to be more susceptible to creating false
memories, since these capacities may induce failures such as memory distortions or
errors.
To the best of our knowledge, no study has directly examined the influence
of top-down memory processes in NDE experiencers. One of the most effective
ways to observe the implication of top-down cognitive influences, and memory
reconstruction is to investigate false memory production, because it allows
84
observing memory suggestibility and distortion (Loftus, 1996; Roediger &
McDermott, 1995). Thus, the aim of this study was to investigate the susceptibility
of NDE experiencers to report false memories and illusory recollection using the
DRM paradigm, compared to matched volunteers. We then wanted to investigate
activation and monitoring processes using Brédart’s (2000) modified DRM
paradigm procedure. After the free recall test, we added a post-recall test in which
participants were asked to report items that they had thought of but did not recall.
This design allows one to obtain estimates of activation and monitoring of critical
non-presented lures during the task.
85
4.3 Material & methods
4.3.1 Participants
The experimental group consisted of 20 individuals who reported a NDE in
the context of a life-threatening situation and that resulted in a coma of different
etiologies: 9 anoxic, 3 traumatic brain injury, or 8 other (i.e., non-traumatic events
such as an exacerbation of an on-going illness or complication during surgery). A
control group matched for age, gender, education level, and time, since brain insult
was also recruited. It was composed of 20 volunteers who reported having had
similar life-threatening incidents (comparable etiologies leading to a period of
coma: 9 anoxic, 3 traumatic brain injury, or 8 other etiology) but without a NDE.
The presence of a NDE was identified using the Greyson NDE scale (i.e., total
score ≥ 7).
NDE experiencers and matched volunteers were recruited via the Website,
publications, and appearances in local media of the Coma Science Group
(University of Liège, Belgium). All participants were native French speakers and
were screened by the experimenter for any signs of memory or cognitive
impairment. None of the volunteers had a premorbid history of neurological or
psychiatric disorders or previous history of alcohol or drug abuse. No incentive
was offered for participation. Written informed consent was obtained from all the
participants. The study was approved by the ethics committee of the Faculty of
Medicine of the University of Liège.
4.3.2 Materials
4.3.2.1 The DRM false memory task
In the DRM procedure, participants were presented with lists of words (e.g.,
note, instrument, sound,…) converging on associated, non-presented lures (e.g.,
86
music), what is called a “critical lure”. The material contains 12 French DRM word
lists of 15 items each (materials from Dehon, 2006 and Dehon et al., 2011). A
female voice uttering the words was recorded and digitized. Lists were presented in
random order using a computer. DRM list words were controlled for word length,
associative strength, level of arousal, level of imagery, valence rating, and degree
of identifiability.
Participants were also invited to detail the subjective experience, i.e., details
related to the supposed presentation of the item (Lampinen et al., 1998), called
“illusory recollection” (e.g., Dehon, 2012). To do so, they were asked to
distinguish memories that they actually recollect (conscious recollection) from
those based on a strong feeling of familiarity (familiarity processes) using the
“Remember/Know/Guess” judgements procedure (Tulving, 1985). These three
types of judgements reflect qualitatively different forms of memory: a
“Remember” judgement refers to a conscious recollection state (i.e., when they
could consciously recollect details of the actual occurrence of the word), a “Know”
judgement refers to the experience of familiarity in the absence of recollection (i.e.,
when they were confident that the item was presented in the list but could not
remember anything about its presentation), and a “Guess” judgement is invoked in
the case of there is no subjective experience and/or guessed responses based on its
thematic similarity.
Furthermore, we used a modified DRM procedure (Brédart, 2000; Dehon,
2006; Dehon & Bredart, 2004) in which a post-recall test was added after the free
recall test. In this phase, participants were instructed to recall words that they had
thought of but did not state in the recall phase, because those words were not
uttered by the recorded voice. This modification of the procedure permits one to
test whether the critical lure had been activated or not. Specifically, the additional
phase required participants to precisely establish the source of memories and the
recall of non-presented critical lures during this additional phase linked to a list that
87
did not initially produce a false memory, thus allowing one to conclude that source
monitoring succeeded.
4.3.2.2 The Mill Hill Vocabulary test
The French version (Deltour, 1993) of the Mill Hill Vocabulary Scale
(MHVS; Raven et al., 1988) was also administered. The MHVS is a multiple-
choice format test used to assess verbal ability.
4.3.3 Procedure
The same procedure was applied to all participants and each participant
was tested individually in a quiet room with a computer. The testing session began
with oral instructions regarding the recall test and the participant was given written
instructions for the “Remember/Know/Guess” judgements procedure that
accompanied recall. They were told that they would hear an audio recording of 12
lists of words and that they would be tested for each list after they learned all the
lists. The lists were presented in random order for each participant and memory
was tested after each list. The registered words were spoken at a rate of one word
every 1.5 s and the durations of the recorded lists ranged from 34 to 37 s. To avoid
retrieval of items from short-term memory, a 30-s distractor task (a backward digit-
span task) was inserted between the learning and free recall phases. For each recall
phase, participants were instructed to write down as many words as possible from
the list which they had just heard, in no particular order. The experimenter strongly
encouraged the participants to avoid guessing. They were given 90 s to complete
each recall phase. During this recall phase, participants indicated for each word one
of three judgement types (“Remember/Know/Guess”). After having recalled all the
lists, participants were instructed to say if, during the learning phase or during the
recall phase, a word came to their mind, but that they did not write it down during
88
the recall task, because they thought that the recording voice had not produced it
(the post-recall test). Then, participants were asked to complete a French-language
adaptation of the MHVS to assure that both groups were equivalent concerning
lexical network. Finally, they were fully debriefed about the study.
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4.4 Results
4.4.1 Demographic data
The descriptive data are presented in Table 12. For all the following
analyses, the alpha level was set at .05. As can be seen in Table 12, both NDE
experiencers and matched volunteers groups matched for age (t(38) = 1.004, p =
.322), gender (χ²(1) = 0, p = 1), years of education (t(38) = −1.433, p = .160), time
since event (t(38) = 1.631, p = .111), and their mean score on the MHVS (t(38) =
−1.293, p = .204).
NDE experiencers
N=20
Volunteers
N=20
p
Gender–female 9 (45%) 9 (45%) 1
Age 60 ± 6 58 ± 4 .322 (Mean in years ± SEM, range) 46-69 47-70
Education level 14 ± 2 15 ± 2 .160 (Mean in years ± SEM, range) 9-18 2-19
Time since NDE or accident (Mean in years ± SEM, range)
29 ± 14 1-61
21 ± 12 1-43
.111
Mill Hill (Mean score out of 44 ± SEM, range)
26 ± 4 15-32
27 ± 2 22-33
.204
SEM=standard error of the mean
Table 12 – Participants’ descriptive and demographic data (N = 40).
4.4.2 Free recall
The mean proportions of recalled studied items, critical lures, and non-
critical intrusions (i.e., intrusions other than critical lures) were created by
averaging the number of recalled words per category across the 12 lists.
A two-way mixed ANOVA that included Group type (NDE experiencers vs.
volunteers) and Item type (studied, critical lures, and intrusions) with repeated
measures on the last factor was carried out on the mean proportions of recalled
90
items across the lists (Table 13). The main effect of Group type [F(1,38) = 1.30, p
= .261] was not significant, showing that both NDE experiencers and matched
volunteers recalled similar rates of items across all item types. The analysis
revealed a significant main effect of Item type [F(2,76) = 150.21, p < .001].
Justified by our predictions, false recall results were followed up with pairwise
planned comparisons (see Cann et al., 2011; Dehon, 2006). Pairwise planned
comparisons revealed that participants recalled significantly more studied items (M
= .45, SD = .10) and critical lures (M = .45, SD = .20) than intrusions (M = .04, SD
= .03) [F(1,38) = 583.81, p < .001], while proportions of studied items and critical
lures were equivalent [F(1,38) = .004, p = .947]. This comparison between recalled
word responses to studied, critical lures, and intrusions revealed a “false memory
effect” (Roediger & McDermott, 1995), meaning that the DRM paradigm reliably
created false memories in our participants (Figure 7). Finally, the Group type ×
Item type interaction was not significant [F(2,76) = 2.465, p = .092]. Justified by
our predictions, pairwise planned comparisons were conducted and revealed that
NDE experiencers recalled similar mean proportions of studied items than
volunteers [F(1,38) = 0.124, p = .726] (see Table 13). Numerically, NDE
experiencers falsely recalled critical lures more than volunteers in the free recall
phase, but this did not reached significance [F(1,38) = 2.569, p = .117]. The
proportions of intrusions were not significantly different between both groups
[F(1,38) = 0.150, p = .700]. Because the mean proportions of non-critical
intrusions recalled by each participant were very low (≤ .04) (Table 13), they were
not submitted to subsequent statistical analyses.
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92
Figure 7 – Mean proportions of studied items, critical lures, and intrusions recalled at free recall test in all participants. Error bars = standard deviation. *<.05; **<.01
4.4.3 “Remember”, “Know” & “Guess” responses
The mean proportions of “Remember/Know/Guess” judgements assigned to
recalled items were created by averaging the number of recalled words per
category and per judgement across the 12 lists and are presented in Table 13.
A similar two-way mixed ANOVA that included Group type (NDE
experiencers vs. volunteers) and Item type (studied vs. critical lure) with repeated
measures on the last factor was carried out on the mean proportions of
“Remember” judgements assigned to studied items and critical lures (Table 13).
The main effect of Group type was not significant [F(1,38) = 3.709, p = .061],
indicating that NDE experiencers and volunteers made similar proportions of
“Remember” responses across all item types. Results indicated a significant main
effect of Item type [F(1,38) = 7.967, p = .007], showing that “Remember”
responses were more likely to be attributed to studied items (M = .40, SD = .08)
93
than critical lures (M = .30, SD = .20). The Group type × Item type interaction was
not significant [F(1,38) = 3.638, p = .064]. Interestingly, pairwise planned
comparisons revealed that “Remember” proportions assigned to studied items were
similar in both groups [F(1,38) = 0.001, p = .975] (see Table 13). By contrast, NDE
experiencers obtained higher proportions regarding to “Remember” responses
attributed to critical items than those of volunteers [F(1,38) = 4.377, p = .04]
(Figure 8). In the volunteers group, pairwise planned comparisons revealed that
they were more likely to assign “Remember” responses to studied items than
critical items [F(1,38) = 11.187, p < .01]. No other significant differences were
found with planned comparisons.
Figure 8 – Mean proportions of critical lures and studied items recalled with “Remember” responses
at free recall test in each group, NDE experiencers and matched volunteers. Error bars = standard deviation. *<.05; **<.01
Studied item
Critical lure
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Next, the same analysis made on “Know” judgements assigned to recalled
items (Table 13) revealed a significant main effect of Item type [F(1,38) = 25.494,
p < .001], indicating that proportions of “Know” responses attributed to studied
items were significantly smaller than those attributed to critical lures (M = .03, SD
= .03 and M = .11, SD = .11, respectively). The main effect of Group type and the
interaction were not significant [F(1,38) = 0.036, p = .850] and [F(1,38) = 0.283, p
= .597], respectively. Both groups obtained similar proportions of “Know”
judgements for studied items and critical lures, respectively [F(1,38) = 1.223, p =
.276] and [F(1,38) = 0.013, p = .909]. In both groups, pairwise planned
comparisons revealed that they were more likely to assign “Know” responses to
critical lures than studied items [F(1,38) = 15.579, p < .001] for NDE experiencers
group and [F(1,38) = 10.199, p < .01] for volunteers group (see Table 13). No
other significant differences were found with planned comparisons.
Finally, the same analysis was conducted on the proportions of “Guess”
judgements assigned to recalled items (Table 13). Results revealed a significant
effect of Item type [F(1,38) = 7.653, p < .01], demonstrating that proportions of
“Guess” responses attributed to studied items were significantly smaller than those
attributed to critical lures (M = .01, SD = .01 and M = .04, SD = .06, respectively).
The main effect of Group type and the Group type x Item type interaction [F(1,38)
= 0.526, p = .473] and [F(1,38) = 1.058, p = .310], respectively, was not
significant. Planned comparisons revealed that in the volunteers group, “Guess”
judgements assigned to critical lures were significantly higher than those assigned
to studied items [F(1,38) = 7.202, p < .05] (see Table 13). By contrast, those two
proportions were similar in NDE experiencers [F(1,38) = 1.509, p = .227]. No
other significant differences were found with planned comparisons.
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4.4.4 Production of the critical lure during the post‑recall
test
The proportions of critical lures produced during the post-recall test were
computed for both NDE experiencers and volunteers groups across all lists (Table
14). As expected, the analysis showed that volunteers recalled a higher proportion
of critical lures during this phase (t(38) = −2.107, p = .04) than NDE experiencers
(Figure 9).
Tests NDE experiencers
N=20
Volunteers
N=20
p
Free recall test Critical lure .50 (.18) .40 (.21) .117
Post-recall test Critical lure .02 (.07) .12 (.20) .04*
Summed proportions Critical lure
.52 (.19)
.52 (.23)
.998
Table 14 – Mean proportions of critical lures produced by NDE experiencers and matched volunteers in the free recall test and in the post-recall test. Summed proportions of critical lures recalled at free recall test and critical lures produced during the post-recall test in NDE experiencers and matched
volunteers. Standard deviations are presented in brackets. * < .05; ** < .01
Additional analyses were performed to observe activation and monitoring
performance rates in both groups. The summed proportions of critical lures recalled
at free recall test and critical lures produced during the post-recall test were
calculated in both groups for studied items and critical lures (see Brédart, 2000;
Dehon, 2006; Dehon & Brédart, 2004 for more information) to obtain an estimate
of activation rate of critical lures (see Table 14). The analysis showed that mean
proportions of activated critical lures were similar (t(38) = .002, p = .998) in both
groups (see Table 14). This indicates that critical lures were equally often activated
during the experiment in NDE experiencers and volunteers, but NDE experiencers
were less likely to recall them during the post-recall test.
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Figure 9 – Mean proportions of critical lures recalled at free recall test and critical lures produced
during the post-recall test in NDE experiencers and matched volunteers. Error bars = standard deviation. *<.05; **<.01
97
4.5 Discussion
The objective of the present study was to investigate false memory
production using the DRM false memory paradigm in people who have
experienced a NDE and to compare their estimates of monitoring and activation of
critical lures, as compared to a matched cohort without NDEs. We also measured
illusory recollections in both groups in this procedure using the
“Remember/Know/Guess” procedure (Tulving, 1985).
Several findings emerge from this pioneer study. First, the DRM task
reliably created false memories in our participants –the so-called “false memory
effect” (i.e., the rates of false recall of critical lures were far higher than that of
other non-critical intrusions; Roediger & McDermott, 1995). Overall, the rates of
recall of non-critical intrusions were very low (an average of .04) in all our
participants, indicating that recall rates for critical lures were not due to guessing
(see also rates of “Guess” judgements). Therefore, our findings replicate the
previous research that has used the DRM paradigm to induce substantial rates of
compelling false memories (e.g., Dehon, 2012).
Second, we obtained equivalent proportions of correct and false recall
performance in both groups. Yet, if one considers the subjective experience (as
measured with “Remember/Know/Guess” judgements) associated with recalled
items, we observed that judgements assigned to recalled studied items were
equivalent in both groups, suggesting that both groups were also equally confident
that those items had occurred. By contrast, the subjective experience associated
with false recall reveals a different pattern. That is, NDE experiencers more
frequently attributed to false recall a “Remember” response that was associated to a
conscious recollection state to false recall, whereas there was no statistically
significant difference for the rates of false recall between both groups. This
suggests that while NDE experiencers did not produce significantly more false
memories, those that were produced were more often associated with illusory
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recollection. The false memories accompanied with illusory recollection are
compelling, since participants are very confident that the critical lure has occurred,
and are able to give details regarding its presentation, although it was never
presented. Following the “conscious activation” account (e.g., Roediger &
McDermott, 1995), illusory recollection appears, because people may generate the
critical lures during the learning phase and later remember the characteristics of
these generations as justifications that the critical lures were presented in the
previous lists (Lampinen et al., 2008). Alternatively, illusory recollection may
occur due to the integration of misleading retrieval cues (e.g., a voice that did not
correspond to the voice that originally produced the list words; see the
“imagination account”; Dobson, 2007) into the recollective experience (e.g.,
Whittlesea, 2002; Whittlesea & Williams, 1998, 2000). Similarly, illusory
recollection might occur, because the feeling of familiarity leads to a search for
details in memory that corroborate the distractors (see the “familiarity plus
corroboration account”; e.g., Lampinen et al., 2008). In addition, we also observed
that volunteers more frequently attributed a “Guess” response that was associated
to an absence of subjective experience to false recall than correct recall—which
was not the case in NDE experiencers. This is consistent with the above findings,
suggesting qualitatively different forms of memory experiences associated with
false and correct recall in both groups.
Third, we used a variant of the DRM task to separately estimate activation
and monitoring processes (cf. Brédart, 2000). This allowed us to determine, in both
groups, whether false memory production is caused by a higher activation process
or by a reduced monitoring process. We found that NDE experiencers were less
likely to produce critical lures during the post-recall test, while both groups were
equally as likely to recall non-presented critical lures during the initial recall. In
addition, the sum of produced critical lures in the recall test and in the post-recall
test indicated that critical lures were activated during the experiment equally often
in NDE experiencers and volunteers groups. This suggests that NDE experiencers
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were as prone as their matched volunteers to think of the critical lures and that the
monitoring explanation is a likely account for the non-occurrence of a false
memory in volunteers but less so in NDE experiencers. The fact that volunteers
reported critical lures during the post-recall test for presented lists indicates more
efficient source monitoring abilities than those of NDE experiencers. According to
the activation-monitoring account (e.g., McDermott & Watson, 2001; Roediger et
al., 2001), false memories occur, because the critical lure is activated during the
presentation of the associated words in the list or during the subsequent recall of
those. This activation mechanism seems to be equally effective in both groups,
importantly, not more frequent in NDE experiencers. In the case of our
participants, NDE experiencers seem to more often mistakenly attribute the
memory of the word to the list presentation rather than their own thoughts and this
may reflect a bias in the monitoring of internal events that is influenced by top-
down processes (e.g., the individual’s beliefs and expectations).
Several speculative hypotheses may explain the heightened emergence of
illusory recollection and reduction in source monitoring in NDE experiencers. We
observed that NDE experiencers are as likely to encode and reconstruct
information (i.e., identical rate of false memories) than non-NDE experiencers;
however, their cognitive processing style then leads them to recall a greater
detailed subjective feeling of remembering information that was not actually
experienced. One hypothesis could be that NDE experiencers, as high dissociators
(Greyson, 2000b), are characterized by a distinct cognitive processing style
involving enhanced attention and working memory abilities (de Ruiter et al., 2006).
Previous studies have shown that non-pathological individuals with high-
dissociative abilities present an enhanced elaborative encoding (Elzinga et al.,
2003; de Ruiter et al., 2006). This distinct ability could, in turn, lead those
individuals to make illusory recollection of such a kind more likely. Then,
compelling illusory recollection may make it even more difficult to discriminate
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information that they thought of from those that had actually been experienced
(source monitoring abilities).
In addition to this interpretation, another hypothesis could be advanced to
explain our results. It can be envisioned that specific experience such as NDEs
results in a change in processing memory information leading to higher levels of
illusory recollection creation. Notably, the false memory literature has shown that
positive moods and emotions are associated with higher susceptibility to
misinformation than are negative moods (Forgas et al., 2005; in the case of DRM
paradigm: Storbeck & Clore, 2005, 2011). Positive moods are associated with more
general schematic processing, resulting in increasing the semantic activation and
thus producing false memories in the DRM procedure (Roediger et al., 2001). As
NDE experiencers tend to have more positive views of future experiences after
having lived their NDE and persistent positive aftereffects (Atwater, 2001; Ring,
1980), their encoding process may be modified after experiencing a NDE. This
might then explain the observed pattern of results of our study, by admitting that
NDE experiencers likely retain more general information, rather than specific
information (Schacter & Slotnick, 2004).
Some authors have suggested that NDE memories can be comparable to
false memories, based on their beliefs and rich fantasies (e.g., Braithwaite, 2008;
French, 2001). Our study cannot conclude that the subjective experience associated
with NDE is illusory recollection, but the present results do suggest that NDE
experiencers are more likely than non-NDE experiencers to illusory recollect
details associated with the supposed presentation of non-presented items.
Nevertheless, there are some limitations of this study that deserve mention. First,
the extent to which these findings from such laboratory situations are generalizable.
The ecological validity of false memories created by the DRM paradigm has been
discussed (Pezdek, 2007; Wade et al., 2007), because memories of word lists are,
by design, less complex than autobiographical memories. Further studies are
needed to examine the cognitive processing style of NDE experiencers population
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in the context of more complex false and true autobiographical memories. Second,
we must take into account that our participants were a little older than typical
populations in DRM studies. Indeed, partly because NDE experiencers decided to
share their experience belatedly, they are in the range of 40–60 years old. The
susceptibility to DRM false memories has been shown to increase with age (e.g.,
Dehon & Bredart, 2004; Gallo & Roediger, 2003; see Schacter et al., 1997 for a
review). Investigations have generally demonstrated some evidence for impaired
source memory in older adults under conditions in which recollection performance
of both young and old population has been equated experimentally (Schacter et al.,
1994). However, on one hand, compared to research literature on DRM false recall,
our rates of true and false recall seem to be consistent with the previous studies
(e.g., Dehon & Bredart, 2004) and this limit was taken into account when selecting
a matched volunteers group. On the other hand, volunteers were matched for age,
even though one cannot rule out the possibility that this may have masked
differences between our NDE experiencers and volunteers groups.
Finally, another related question concerns the retrospective assessment of
their cognitive functioning. The retrospective design of this study does not allow us
to say whether NDEs occur more frequently in people with increased illusory
recollection or whether such experiences induce increased illusory recollection in
people who were previously not prone to this. The question of cause and effect can
be answered only by a prospective study in which illusory recollection is assessed
in individuals before and after their NDEs.
In conclusion, the present study showed that NDE experiencers and
matched volunteers without a NDE were equally likely to produce false memories,
but that NDE experiencers were more likely to associate them with compelling
illusory recollection (i.e., a detailed subjective feeling of remembering items that
actually were not presented). Moreover, NDE experiencers seem to have more
difficulty in later identifying the source of information that was activated as a
consequence of “intact” semantic activation processes in the DRM paradigm. Since
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the research data on the cognitive processing style in NDE experiencers are still
sparse, this study constitutes a first approach toward understanding their memory
formation and, more generally, their cognitive processing style. It would also be
worth investigating NDE experiencers’ other personal characteristics. Notably, as
source monitoring breakdown is strongly related to fantasy proneness
(Merckelbach et al., 2000), it would also be important to assess fantasy
engagement in NDE experiencers.
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5 Study 4: Fantasy proneness in NDE
experiencers
Based on the following publication:
Martial, C.1, Cassol, H.1, Charland-Verville, V.1, Merckelbach, H.2, & Laureys,
S.1 (under review). Fantasy proneness correlates with near-death
experiences, but only when they developed outside a life-threatening
context.
1Coma Science Group, GIGA-Consciousness, University and University Hospital of Liège, Liège, Belgium 2Forensic Psychology Section, Maastricht University, Maastricht, the Netherlands
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5.1 Summary
Little is known about the personality characteristics of those who have
experienced a NDE. One interesting candidate is fantasy proneness. We studied
this trait in individuals who developed NDEs in the presence (i.e., classical NDEs)
or absence (i.e., NDEs-like) of a life-threatening situation. We surveyed a total of
228 individuals. From those, 108 qualified as NDE experiencers (i.e., Greyson
NDE scale total score 7): 51 had their NDEs in the context of a life-threatening
situation; 57 had their NDEs not related to a life-threatening situation. From those
who did not meet the criteria to be considered “experiencers”, 20 had their NDE in
the absence of a life-threatening situation; 50 had faced death but did not recall a
NDE and finally, 50 healthy people without a history of life threat and/or NDE. All
participants completed a measure of NDE intensity (the Greyson NDE scale) and a
measure of fantasy proneness (the Creative Experiences Questionnaire –CEQ).
People reporting NDEs-like scored higher on fantasy proneness than those
reporting classical NDEs, individuals whose experiences did not meet the NDE
criteria and matched controls. By contrast, individuals reporting classical NDEs
showed similar engagement in fantasy as matched controls. The reported intensity
of the experiences was positively correlated with engagement in fantasy. Our
findings support the view that strong engagement in fantasy by individuals
recalling NDEs-like might make these persons more likely to report such
subjective experiences when exposed to suitable physiological and/or
psychological conditions (e.g., meditation, syncope).
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5.2 Background
The current paper focuses on fantasy proneness (Wilson & Barber, 1983a) as
one potential variable that may shape people’s reports of NDEs and NDEs-like.
Fantasy proneness refers to a habitual engagement in imaginative activities
(Merckelbach et al., 2001). Each individual has (to some extent) imaginative
capacities and can report a range of experiences that are more or less related to
imagination (e.g., daydreaming; Aleman & de Haan, 2004). Yet, even within the
non-psychiatric samples, fantasy can distort perception and memory thereby
leading to reality monitoring errors (Aleman & de Haan, 2004).
Although many humans are exposed to life-threatening situations (i.e., a severe
brain injury) or have the feeling that they have been close to death at some point in
their life, only a limited number of persons recall identifiable NDEs (Greyson, 2003;
van Lommel et al., 2001). Similarly, an important question is why some individuals
experience NDEs-like phenomena, when others do not, although they have been
exposed to physiological and/or psychological conditions that are known to be
associated with NDEs-like (e.g., meditation, syncope). Decades ago, an unpublished
conference presentation discussed preliminary results concerning a potentially greater
investment in fantasy and imaginative processes in experiencers reporting classical
NDEs in comparison with healthy subjects and people reporting an event that brought
them near to death but did not recall a NDE phenomenology (Council J. & Greyson
B., unpublished data, 1985). These authors used the ICMI (Wilson & Barber, 1983a).
This questionnaire might, however, reach limited conclusions due to ambiguity
regarding its psychometric information. Indeed, this questionnaire seems to fail to
assess critical characteristics of the fantasy-proneness construct (e.g., the involvement
in fantasy as a form of coping) and to contain irrelevant and potential confusing items
(Gilmour, 2012). By contrast, this questionnaire extensively overlaps with some other
concepts that are too distant from the description of fantasy proneness (e.g.,
expressions of talent, personality disorders; Dunn et al., 2004; Fuchs et al., 2007;
Klinger et al., 2009; Lack et al., 2003; Merckelbach et al., 2000, 2001; Merritt &
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Waldo, 2000; Sanchez-Bernardos & Avia, 2006; Thomson & Jaque, 2011; Waldo &
Merritt, 2000). In short, this questionnaire is too convoluted to assess a conceptually
consistent measure (Klinger et al., 2009) and little attention has been paid to assess its
validity (Gilmour, 2012).
With this in mind, the present study aimed to assess fantasy engagement using
the CEQ (Merckelbach et al., 2001) (1) in experiencers (i.e., Greyson NDE scale total
score 7/32; Greyson, 1983) reporting NDEs in and (2) outside the context of an
actual threat to life; (3) in individuals reported having had a NDE without a life-
threatening situation but not qualified as experiencers (i.e., Greyson NDE scale total
score < 7/32; Greyson, 1983); (4) in matched control participants who had been
exposed to a life-threatening situation but did not report any kind of NDE; and finally
(5) matched control participants who had neither faced a life threatening situation, nor
had any NDEs. We also looked into the association between fantasy proneness and
self-reported intensity of NDEs (i.e., Greyson NDE scale total score; Greyson, 1983).
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5.3 Material & methods
5.3.1 Participants & procedure
Subjects were recruited from among individuals who contacted us to share
their experience. Initially, they were recruited via the IANDS France and Flanders
and the Coma Science Group (University and University Hospital of Liège,
Belgium). At that time, they were mailed a questionnaire including the Greyson
NDE scale (Greyson, 1983) and items of socio-demographic (gender, age) and
clinical (time since experiences, presence of life-threatening event) data. To gauge
the presence of a life-threatening event (i.e., a severe brain injury), we asked
participants whether they had gone through a period of coma and whether they had
stayed in intensive care. Participants whose experience did not meet the accepted
criteria of a NDE (i.e., total score < 7/32; Greyson, 1983) were included in the
“non-NDE experiencers/non-LTS” group (see below). Control participants were
recruited via announcements by the Coma Science Group.
Participants were invited to participate in a study on creativity. To that end,
they were mailed a questionnaire including the CEQ (Merckelbach et al., 2001).
The term “fantasy proneness” was not used either in the explanatory letter or in the
questionnaire itself. The CEQ (Merckelbach et al., 2001) is a self-report instrument
which is a measure of fantasy proneness including 25 true/false items (Table 15). A
total score is derived from the sum of all the true responses and referred to as a
validated index of propensity towards fantasy (higher scores indicate higher levels
of fantasy proneness; Merckelbach et al., 2001).
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Items
1. “As a child, I thought that the dolls, teddy bears, and stuffed animals that I played with were living creatures.”
2. “As a child, I strongly believed in the existence of dwarfs, elves, and other fairy tale figures.”
3. “As a child, I had my own make believe friend or animal.”
4. “As a child, I could very easily identify with the main character of a story and/or movie.”
5. “As a child, I sometimes had the feeling that I was someone else (e.g., a princess, an orphan, etc.).”
6. “As a child, I was encouraged by adults (parents, grandparents, brothers, sisters) to fully indulge myself in my fantasies and daydreams.”
7. “As a child, I often felt lonely.”
8. “As a child, I devoted my time to playing a musical instrument, dancing, acting, and/or drawing.”
9. “I spend more than half the day (daytime) fantasizing or daydreaming.”
10. “Many of my friends and/or relatives do not know that I have such detailed fantasies.”
11. “Many of my fantasies have a realistic intensity.”
12. “Many of my fantasies are often just as lively as a good movie.”
13. “ I often confuse fantasies with real memories”
14. “I am never bored because I start fantasizing when things get boring.”
15. “Sometimes I act as if I am somebody else and I completely identify myself with that role.”
16. “When I recall my childhood, I have very vivid and lively memories.”
17. “I can recall many occurrences before the age of three.”
18. “When I perceive violence on television, I get so into it that I get really upset.”
19. “When I think of something cold, I actually get cold.”
20. “When I imagine I have eaten rotten food, I really get nauseous.”
21. “I often have the feeling that I can predict things that are bound to happen in the future.”
22. “I often have the experience of thinking of someone and soon afterwards that particular person calls or shows up.”
23. “I sometimes feel that I have had an out of body experience.”
24. “When I sing or write something, I sometimes have the feeling that someone or something outside myself directs me.”
25. “During my life, I have had intense religious experience which influenced me in a very strong manner.”
Table 15 – The Creative Experiences Questionnaire (CEQ; Merckelbach et al., 2001); a true/false response format is available for each item.
The total sample consisted of 128 people who claimed to have experienced a
NDE. 51 participants (40%) described experiences that met the accepted criteria of
NDEs (i.e., Greyson NDE scale total score 7/32; Greyson, 1983) in the context of
a life-threatening situation (“NDE experiencers/LTS” group). 57 (44%) described
experiences that also met the accepted criteria of NDEs (i.e., Greyson NDE scale
total score 7/32; Greyson, 1983) but in the absence of a life-threatening situation
(“NDE experiencers/non-LTS” group). 20 (16%) described experiences in the
109
absence of a life-threatening context but that did not meet the accepted criteria of
NDEs (i.e., Greyson NDE scale total score < 7/32; Greyson, 1983; “non-NDE
experiencers/non-LTS” group). We recruited a cohort of 100 control participants:
50 people who had come close to death at some point in their lives but did not
recall a NDE (“controls/LTS” group) and 50 healthy people who had never
reported to have experienced NDEs (“controls/non-LTS” group). Completion of
the anonymous questionnaire was voluntary and written informed consent was
obtained from all participants enrolled in the study. The study was approved by the
ethics committee of the Faculty of Medicine of the University of Liège.
5.3.2 Statistical analyses
Pearson’s χ² tests were used to assess frequency distributions. One-way
ANOVAs and t-tests were performed to compare age, age at experience, time since
experience, and reported intensity of the NDE within groups. Pairwise planned
comparisons were then conducted to determine which groups differed significantly
from each other. The distribution of CEQ total scores was skewed. For this reason,
non-parametric tests were used. Thus, group differences regarding the CEQ were
evaluated with the Kruskal-Wallis test. Next, we performed post-hoc comparisons
using Bonferroni-corrected (p < .01) Mann-Whitney U tests to examine possible
differences across groups. Spearman’s rank-order correlations were computed to
examine associative strength between CEQ total scores and Greyson NDE scale
total scores and subscale scores. All participants who reported having experienced
a NDE were included, also those who obtained a score of less than 7 on the
Greyson NDE scale. Finally, we calculated Spearman rank-order correlations
between CEQ and Greyson NDE total scores for each of the two experiencer
groups separately. To avoid type I errors, Bonferroni adjustments (p < .007) were
applied.
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5.4 Results
The five groups did not significantly differ with regard to gender and age
distributions (see Table 16). Experiencers groups and the non-NDE experiencers
group did not differ either for age at experience or for time elapsed since the
experience.
Demographics NDE experiencers Non-NDE
experiencers
non-LTS n=20
Controls p η2
LTS n=51
non-LTS n=57
LTS n=50
non-LTS n=50
Gender–female 27 (53%) 36 (63%) 11 (55%) 32 (64%) 29 (58%) .76 -
Age Mean in years ± SD
57 ± 13
57 ± 14
62 ± 14
53 ± 11
55 ± 12
.11
.03
Age at experience
Mean in years ± SD
35 ± 17
28 ± 16
35 ± 20
29 ± 13
-
.14
.03
Time since experience Mean in years ± SD
22 ± 16
28 ± 17
27 ± 20
24 ± 12
-
.16
.03
LTS=life-threatening situation ; SD=standard deviation
Table 16 – Demographic data of subsamples.
As to the intensity (i.e., Greyson NDE scale total score) of reported NDEs,
NDE experiencers/LTS (mean total score = 16 ± 5) and NDE experiencers/non-
LTS (mean total score = 15 ± 6) groups had similar scores (t(106)= .25, d = .20, p
= .79).
Total CEQ scores were significantly different between groups (see Table
17). The NDE experiencers/non-LTS group obtained significantly higher CEQ total
scores than the NDE experiencers/LTS (p < .005, d = .56), non-NDE
experiencers/non-LTS (p < .001, d = .83), and control/non-LTS (p < .0001, d = 1.2)
groups. By contrast, CEQ total scores of NDE experiencers/LTS and controls/LTS
groups were not significantly different (p = .019, d = .47). Finally, non-NDE
111
experiencers/non-LTS and control/non-LTS groups obtained similar CEQ total
scores (p = .39, d = .21).
Scale NDE experiencers Non-NDE
experiencers
non-LTS n=20
Controls p d
LTS n=51
non-LTS n=57
LTS n=50
non-LTS n=50
CEQ total score Median (IQR)
7 (5–11)
11 (7–13)
7 (4–8)
6 (3–9)
6 (2.5–8)
<.0001
.85
LTS=life-threatening situation ; IQR=inter-quartile range
Table 17 – CEQ total scores of subsamples.
Among individuals who claimed to have had a NDE (whether or not they
reached the cut-off of 7/32; i.e., NDE experiencers/LTS, NDE experiencers/non-
LTS and non-NDE experiencers/non-LTS groups), Greyson NDE scale total scores
were positively correlated with total CEQ scores (see Table 18). To investigate
whether the correlational result observed in this analysis effectively reflects an
association between experiencers’ investment in fantasy and the reported intensity
of the NDE, we performed a Spearman’s rank-order correlation between Greyson
NDE scale and CEQ total scores but without including the three CEQ items (item
21, 23, and 25; see Table 15) showing some overlaps with certain items of the
Greyson NDE scale. We observed a similar significant positive correlation
(Spearman r = .26; p < .005).
Total CEQ scores were also positively correlated with affective, paranormal
and transcendental subscale scores but not with cognitive subscale scores (Table
18). Looking at the subsamples, for the NDE experiencers/non-LTS group only, we
found a significant positive correlation (Spearman r = .33; p < .007) between
Greyson NDE scale total scores and total CEQ scores. By contrast, in the NDE
experiencers/LTS group, the correlation between both total scores did not attain
significance (Spearman r = .28; p = .054).
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CEQ total score p
Greyson NDE scale Total score .32 <.0005
Subscale scores Cognitive
.22
.015
Affective .27 <.007 Paranormal .26 <.007 Transcendental .28 <.007
Table 18 – Spearman rank correlations between CEQ total score and Greyson NDE scale scores and
subscale scores for the total sample (N = 128).
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5.5 Discussion
The sample of individuals who reported NDEs-like scored higher on self-
reported measures of fantasy proneness than matched control individuals who had
never experienced NDEs and individuals who had reported similar experiences that
did not meet NDEs criteria. Interestingly, although both groups of experiencers
reported similar intensities of experience (as also reported in previous studies;
Charland-Verville et al., 2014), experiencers recalling NDEs-like showed a greater
engagement in fantasy than those with classical NDEs. Thus, compared with
control participants who exhibited moderate fantasy engagement (in line with
previous non-clinical population studies; Merckelbach et al., 1999, 2001), the CEQ
scores of individuals who reported NDEs-like are suggestive of heightened fantasy
proneness levels.
The retrospective and correlational design of this study does not permit
conclusions to be made about the casual pathway; that is, whether NDEs-like occur
more frequently in individuals with (previously established) high engagement in
fantasy or whether such experiences encourage fantasy proneness in individuals
who were previously not prone to fantasy. Yet it is reasonable to hypothesize that
high engagement in fantasy, as a habitual tendency, makes people more likely to
report subjective NDEs-like when exposed to certain physiological and/or
psychological conditions (e.g., meditation). Indeed, some items of the CEQ allude
to retrospective recall of childhood experiences (Merckelbach et al., 2001; see
Table 15), supporting the idea of an enduring predisposition towards fantasy in
those who score relatively high on the CEQ.
By contrast, we found no indication that individuals with classical NDEs are
more fantasy prone than matched controls, including individuals who had come
close to death without having NDEs. Given the sample size in the current study, we
believe that there is little reason to believe that a NDE per se is the result of fantasy
prone fabrication.
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Interestingly, we found an association between experiencers’ investment in
fantasy and imagination and the reported intensity of the NDE. More specifically,
individuals’ engagement in fantasy were correlated with affective, paranormal, and
transcendental NDE features (as assessed by the Greyson NDE subscale scores;
Greyson, 1983), but not with their cognitive features. Yet, the correlational
analyses performed within each of the two experiencers’ groups revealed
differential patterns depending on whether (or not) a threat to the individual’s life
was experienced. That is, the more individuals described intense NDEs in the
absence of a life-threatening situation, the higher they scored on fantasy proneness,
whereas there was no significant correlation between the intensity of the NDE and
an engagement in fantasy for experiencers whose NDEs occurred in the context of
a life-threatening situation. Again, these correlations (or their absence) do not
imply any form of causality (or the absence thereof). Still, another hypothesis is
that when no life-threatening situation was present, the reported intensity of the
experience depends on how strongly the individual is involved in fantasy and
imaginative processes.
The present findings warrant follow-up investigation. Specifically, it is
important to look into factors (e.g., reality monitoring failures) involved in fantasy
proneness that may generate NDEs-like. One possibility might be that individuals
with NDEs-like are more “open to experiences”, a personality trait of the Five-
Factor Model (McCrae & Costa, 1987). It is likely that the experiencers recalling
NDEs-like are unusually sensitive to internal states and possess a special
propensity to pick up certain perceptual elements that other individuals are blind to.
This formulation is consistent with the notion of a “NDE-prone personality”,
defined as “the capacity to shift into states of consciousness that afford access to
non-ordinary realities coupled with strong tendencies toward psychological
absorption” (Ring & Rosing, 1992, p. 235). In line with this, fantasy prone
individuals’ lives appear to be experientially richer (Rothmann & Coetzer, 2003)
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and as a consequence, their fantasies are “as real as real” (Wilson & Barber,
1983a).
Alternatively, the reality monitoring model (Johnson & Raye, 1981) could
provide a framework for understanding why some individuals may report NDEs-
like accounts. The CEQ (Merckelbach et al., 2001) used in this study specifically
assesses the frequency in which individuals engage in fantasy and their difficulties
in distinguishing fantasy and reality. Thus, it may be the case that these
experiences arise as a consequence of source-monitoring errors, whereby inner
thoughts and feelings are wrongly interpreted as memories of events that occurred
in reality. Fantasy proneness goes along with lenient criteria and is closely related
to suboptimal reality monitoring (Aleman et al., 1999; Johnson & Raye, 1981).
Thus, extreme internal focus in individuals could, in some cases, result in
memories of subjective experiences meeting the identification criteria of NDEs but
occurring without a life-threatening situation (i.e., NDEs-like).
Our study has several methodological constraints. First, participants enrolled
in the study were mostly self-selected and might not be representative due to a
possible selection bias. Second, our study was cross-sectional and relied on self-
report measures.
To date, it is not clear whether NDEs are a randomly occurring phenomenon
or whether some specific psychological factors play an important role in their
generation (or recall). Although much has been learned regarding the NDE
phenomenon per se, considerably less research has been directed at exploring the
psychological mechanisms that might lead to the occurrence of such memories.
Fantasy proneness (Wilson & Barber, 1983a) may constitute a psychological
predisposition for the occurrence of NDEs-like.
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6 Conclusion & future perspectives
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The main focus of this chapter is to discuss more generally what can be
learned about the nature of the NDE phenomenon from studying the
phenomenological characteristics reported in the resulting memory, the temporal
sequences of features retrospectively reported in narratives, and the cognitive
characteristics of their experiencers.
In our first study, NDE experiencers were requested to rate the
phenomenological characteristics of their NDE memories using the MCQ. In short,
we observed that the more intense the NDE was reported by experiencers: (a) the
more frequently the NDE seems to be reactivated (i.e., thought or talked about the
NDE); (b) the more sensory details (concerning sounds, smells and/or tastes) they
report; and (c) the more importance they give to the experience. When
remembering an important experience, we may retrieve the event with considerable
detail, thereby leading to feel a subjective experience of mentally “reliving” the
event (Tulving, 2002). From a broader cognitive perspective, observing NDE
memories that apparently contain considerable sensory-perceptual detail is
interesting as it suggests that humans might be able to recall memories of a
moment characterized by a severely impaired consciousness (e.g., due to severe
brain injury). Yet it is still unclear when exactly these phenomenological
experiences are experienced as well as when their memory encoding precisely
occurs. These experiences are described as occurring in near-death states where the
brain and its associated processes are thought to be working with altered capacities;
however, those ones seem to be firmly anchored in NDE experiencers’ memories.
NDE memories can be distinguished from other autobiographical memories
because of their particularly high significance for experiencers and their emotional
character (Thonnard et al., 2013). It is thus likely that the self-referential nature of
the NDE encourages the retrieval of associated memory details (Conway &
Dewhurst, 1995). In a recent study, we observed that NDE memories can be
considered as “self-defining memories” (i.e., important autobiographical memories
that are highly relevant to personality processes and usually characterized by
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affective intensity, vividness, and linkages to other memories; Cassol et al., in
preparation). A sample of 47 experiencers reporting classical NDEs performed a
“self-defining memory” task requesting to generate two self-defining memories
(Singer & Blagov, 2000, 2001; Thorne & McLean, 2001). We found that 60% of
these NDE experiencers recall their NDE as one of the two self-defining memories,
suggesting that the NDE memory constitutes an important part of NDE
experiencers’ personal identity. In addition, this study also showed that the more
intense (according to the Greyson NDE scale) the NDE is, the more central it will
be to NDE experiencers’ identity (using the Centrality of Event Scale; Berntsen &
Rubin, 2006). The construction and consolidation of one’s narrative identity relies
on a limited number of memories of self-defining (emotionally positive or
negative) events (Wood & Conway, 2006) and for many the NDE memory can be
one of them. It would be further interesting to compare their responses to the ones
of NDE-like experiencers and individuals who have lived a close brush with death
without a NDE. This would notably permit to distinguish the effects of proximity
with death from the impact of the phenomenological features that were
experienced.
In general, autobiographical memories are likely to be subject to distortions
as time goes by (Schacter, 1996). Memories of emotional events (e.g., traumatic
events) may be particularly sensitive to distortions notably due to emotional
influences (Schooler & Eich, 2000). It is then reasonable to question the reliability
of NDE memories (French, 2001; Martens, 1994). Some elements commonly
associated with NDEs may lead to doubts on the reliability of its resulting
memories. For example, the context of occurrence may influence the memory:
cardiac arrests (sometimes leading to amnesia; Parnia et al., 2007), traumatic
situations, or influence of potentially psychoactive medications can alter memories
(Curran, 2000). In addition, the fact that in some cases they are reported long after
the event may reduce vividness and details of memories (Talamini & Goree, 2012).
By contrast, NDE experiencers usually harbour no doubts. Finally, given the
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ineffable nature of the experience itself, it is reasonable to assume that the
subsequent narrative of this particular experience is highly likely to be influenced
by our natural memory process of construction. For example, their testimony may
be different and more coherent when they talk about it, in such a way that other
people could really understand it. In the future, it would be interesting to set up
prospective studies in medical environment to follow memory evolution. Coupled
with neuroimaging techniques, prospective designs will also permit to correlate
physiological and/or pharmacological data with NDE features reported by patients.
In the third chapter, we investigated the temporal chronology of features
reported in NDE narratives. A long time ago, some authors have assumed that
NDEs exhibit a recurrent temporal sequentiality (Noyes et al., 1977; Ring, 1980).
Our analysis of several tens of narratives highlighted that NDE features do not
appear in a strict temporal order though, but rather differ across narratives.
Nevertheless, a limitation inherent to our methodology is the use of retrospective
freely expressed written narratives as supports to highlight the temporality. To
deepen the sequential structure of NDEs, it would be interesting to ask NDE
experiencers to indicate themselves the temporal order of the different features,
notably allowing them the option to indicate two or more features as occurring at a
same time. Nevertheless, given the context of occurrence associated an altered state
of consciousness which often appears to have an effect on time perception –even
resulting in a perception of timelessness (Block, 1979), one might postulate that
their report of temporal structure can be distorted. In our study, altered time
perception is reported by 35% of experiencers in narratives. When using closed
questionnaires, this feature appears to be more frequently recalled (e.g., 78% of
experiencers in Charland-Verville et al., 2014; 65% of experiencers in Wittman et
al., 2017). Thus, while time perception is intricately related to questions of
consciousness (Block, 1979), time perception associated with NDEs is a difficult
issue to study.
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After having experienced an event, people are not able to remember a literal
record of the experience but instead a summary representation of their prior
experience (Conway, 2009). Hence, the memory includes a compression of short-
time slices of the past event (Conway, 2009). This assumption is supported by
empirical evidence suggesting that episodic memories consist of a succession of
slices or moments in a temporally compressed way (Jeunehomme et al., 2017).
Recently, Jeunehomme and colleagues (2017) showed that when remembering
real-life events, people mentally re-experience past events in a temporally
compressed way and these temporal compression rates are modulated depending on
the nature of recalled events (e.g., events that involved goal-directed actions or
spatial displacements). To date, however, it is not yet known how information that
constitutes real-life events is condensed in memory. Then this issue appears to be
even more complicated for memories of NDEs or other internally-generated events.
As NDEs are personal and mentally experienced, it would be difficult to test the
temporal compression encoded in real time.
As for pleasant NDEs, some authors have suggested a recurrent temporality in
distressing NDEs. Grey (1985) has proposed a 5-stage sequence: (1) panic and fear,
(2) experiencing an OBE, (3) entering a black void, (4) feeling an evil force, and
finally (5) entering a hellish environment. One can easily observe similarities with
Ring’s (1980) temporal model suggested for pleasant NDEs. However, as initially
proposed by Greyson and Bush (1992), distressing NDEs appear to embrace different
single types of experiences which include completely unlike features. Grey’s (1985)
temporal sequence has thus little chance of being representative for the whole
distressing experiences and was not based on empirical data and statistical analyses.
Thus, temporality in distressing and pleasant NDEs remains a very poorly explored
area and it is important to exude caution throughout the interpretation of the results of
our second study. Nevertheless, our study addressed certain gaps in the existing
literature by showing differences between self-reported narratives regarding the
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temporality sequences of features. Our findings raise broader questions about which
specific aspects of NDEs could be considered as universal and which could not.
The third objective of this thesis was to explore NDE experiencers’ certain
cognitive factors purported to be related to the fact of reporting a NDE. To achieve
this, in two studies, we tested NDE experiencers and compared their performance
with matched individuals having lived identical medical conditions (e.g., a period of
coma due to a life-threatening event) but who did not report a NDE phenomenology
afterwards. The third study showed that NDE experiencers are as likely to produce
false memories as coma survivors who did not report NDEs; however, their cognitive
processing style leads them to recall a greater detailed subjective feeling of
remembering information that was not actually experienced. In addition, we observed
less successful source monitoring processes in NDE experiencers compared to non-
NDE experiencers. In the last study, we found self-reported stronger engagement in
fantasy in experiencers reporting NDE-like than in those reporting classical NDEs,
individuals whose experiences did not meet the NDE criteria and matched controls. In
contrast, experiencers reporting classical NDEs did not show particularly high
engagement in fantasy. Interestingly, taking into consideration all individuals who
claimed to have had a NDE (whether or not they reached the cut-off of 7/32 on the
Greyson NDE scale), the reported intensity of the experiences was positively
correlated with engagement in fantasy. However, looking at the subsamples, we only
found a positive association between the reported intensity of the experiences and the
level of engagement in fantasy in individuals reporting NDEs-like, but not in
individuals reporting classical NDEs. These results support the view that strong
engagement in fantasy by individuals recalling NDEs-like might make these persons
more likely to report such subjective experiences when exposed to suitable
physiological and/or psychological conditions (e.g., syncope, meditation). Taken
together, these two studies suggest that cognitive factors may be important in the
formation and/or the recall of a subjective NDE phenomenology when exposed to
suitable conditions. However, susceptibility to false memory and illusory recollection,
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and source monitoring efficiency were only investigated in people reporting classical
NDEs. At the time the study was undertaken, we lacked sufficient NDE experiencers
reporting NDEs-like. By now, our sample could permit to assess NDE-like
experiencers in lab for tasks requesting to meet participants in person. In addition, in
our study on fantasy engagement, we did not observe high fantasy proneness in
experiencers reporting classical NDEs. Yet, given the results achieved here, it could
reasonably be assumed that experiencers are likely to have an increased sensitivity to
internally-generated percepts (such as imagery), to be concerned with their mental
processes and possess a special propensity to pick up some perceptual elements that
other individuals are blind to. For some experiencers, mental images might then be
more experienced as perceptual-like (e.g., with regard to sensory, contextual and
semantic details; see Johnson & Raye, 1981), which could lead to confusions between
mental images and percepts. This could explain why some NDE experiencers claim
that they occurred in reality (i.e., perception of reality as experienced in everyday
life).
In that scenario, this type of attentional process could be considered as a form
of absorption. This can be viewed as a personality trait anchored on the capacity for
imaginative involvement (Roche & McConkey, 1990; Tellegen, 1981, 1982) and is
known to be inherent to a heightened sense of the reality of the attentional object. The
event is experienced as real, even when it is constructed from memory or imagination
(Tellegen, 1981, 1982). While further research will be necessary to corroborate this
hypothesis, we noticed in one of our ongoing studies that NDE experiencers appear to
be particularly sensitive to hypnotic states and to present high capacity of
psychological absorption. Indeed, in the context of our study aiming at investigating
the recall of NDE under hypnotic induction (Martial et al., in preparation), 2 out of 7
NDE experiencers were exceptionally highly receptive to hypnotic induction (i.e.,
“hypnosis virtuoso”). This is an unusually high proportion of individuals sensitive to
hypnotic state and absorption which is consistent with the present results, insofar as
absorption and hypnotisability are thought to be characteristics of “fantasy proneness
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personalities” (Wilson & Barber, 1983a). Nevertheless, notably because our sample is
very small, future studies are needed to explore this observation. Furthermore, a long
time ago Twemlow and Gabbard (1984) observed greater absorption in NDE
experiencers than individuals reporting “only” an OBE, but they did not compare it to
other control groups (e.g., people who never experienced a NDE).
One promising direction would be to study top-down influences in NDE
experiencers. Indeed, the common thread to these cognitive factors (heightened
illusory recollection, source monitoring errors, fantasy proneness) and sensitivity to
modified state of consciousness (high hypnotizability) may be a greater tendency to
more automatic top-down processing. Top-down cognitive processes may represent
core vehicles to some types of unusual states or experience (such as hypnosis; see
Crawford, 1994; Egner & Raz, 2007; Raz, 2004). In this view, functions such as
attention or monitoring systems putatively afford individuals the cognitive means to
focus their mental efforts towards internally-generated percepts. In fact, both memory
and perception are constructive processes, influenced by input from our senses
(bottom-up influences) but also by our own knowledge, beliefs and expectations
about the world (top-down influences). Alterations in information processing in
which the system assigns a decisive priority to top-down factors in determining the
final percept, at the expense of bottom-up information, might contribute to the
occurrence of NDEs. Ways to test top-down influences in NDE experiencers would
be to observe whether they are conducive to experiencing altered states of
consciousness or other manipulations of internally-directed attention or to
experimentally induce sensory deprivation permitting to modulate the presence of
sensory inputs and thus to observe the impact of top-down priors.
Top-down mechanisms may also be central in influencing the meaning, form,
and content of NDEs. In support of this reconstructive view, the NDE experiencers’
religiosity and cultural background have been suggested to influence the NDEs’
content and the features’ interpretation (Belanti et al., 2008; Blackmore, 1993). Some
studies have shown a culture-related incidence of certain features (i.e., tunnel vision;
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Belanti et al., 2008; Kellehear, 1993, 2009; Pasricha & Stevenson, 1986). However,
most of the conducted studies are case studies and surveys are mainly conducted in
Western cultures, thus limiting the generalizability and the conclusions that can be
drawn at a cultural level. Future cross-cultural studies are therefore needed.
Obviously, the two last studies of this thesis are limited in terms of conclusions
and future studies are needed to strengthen and complete the exploration of
experiencers’ cognitive profile. While there are a few studies assessing one
personality or cognitive trait in isolation in samples of NDE experiencers, it would
then be valuable to set up an administration protocol including a full battery of tests
(notably including assessments of fantasy and imagination, personality traits such as
openness to experience, paranormal belief, dissociation, absorption) and to observe
which variables are of interest and are correlate with. This would permit to gain a
greater understanding of NDE phenomenon and its relationship with significant
variables of interest. In this thesis work, we wanted to examine experiencers’
cognitive profile, which may not be relevant to the psychological mechanisms
operating at the time of the experiences but still can be indicative as psychological
models. Attempting to explain NDEs may be tested only indirectly by this kind of
study.
An immediate observation, which also constitutes NDEs’ defining criteria, is
that NDEs contain the three features of a hallucination: “any percept-like experience
which (a) occurs in the absence of an appropriate stimulus, (b) has the full force or
impact of the corresponding actual (real) perception, and (c) is not amenable to
direct and voluntary control by the experiencer” (Slade & Bentall, 1998, p. 23).
However, as compared to “typical” hallucinations, NDEs appear during a period of
severely impaired consciousness (e.g., due to severe brain injury). Yet, the report of
NDEs-like makes them more compatible with “typical” hallucinations –although the
state of consciousness in which people are when they live such experiences is not
clear yet. The apparent clear sensorium of some NDE experiencers has very often
been used to argue that NDEs are “real” (i.e., corresponding to appropriate real
126
external stimuli) and not a hallucination. An intense illusion of reality is often
reported by NDE experiencers (i.e., similar phenomenological sense of certainty that
accompanies the everyday perception; Dell’Olio, 2010; Schwaninger et al., 2002) and
subsequent psychological effects may be related in part to the personal conviction of
this “reality”. In its broadest sense, the term “hallucination” can be applied to any
non-voluntary perception that does not match external stimulation (Slade & Bentall,
1998). In the process of perceptions, we actively infer the causes of our sensations
and this can be influenced by our prior experiences or expectations (top-down
influences; Friston, 2005). In some circumstances, even in healthy individuals, the
mismatch between priors and inputs can contribute to belief updating (Blackmore,
1993). These mechanisms appear to be particularly active in situations in which the
perceptive features are ambiguous –similar contexts classically associated with the
emergence of a NDE– to resolve this ambiguity. The erroneous attribution of unreal
stimuli to be real (i.e., source monitoring process) might be caused by a deficit of the
integration of multimodal sensation or by abnormal perceptive information processing
(Aleman et al., 2003). This real perceptual bias may be due to a mix of cognitive and
neurophysiological mechanisms taking place during the event. However, although the
NDE phenomenon meets the definition of hallucinations, the term “hallucination”
may be too vague to convey the essential nature of the experience that is to be
explained. Indeed, this would place NDEs or for example fleeting misperceptions
(e.g., perceiving someone to be behind you when he is not) in the same category as
drug-induced or schizophrenic hallucinations. In both a diagnostic and an everyday
language sense, there is an obvious difference between these instances. It is also
important for NDE experiencers themselves to not merely reduce NDEs to
hallucinations. While the term “hallucination” has a pejorative connotation in the
general public, such reactions could lead them to doubt their own sanity. Indeed,
despite a popular view that hallucinations without associated identifiable cerebral
pathology are symptoms of mental illness, research and clinical settings have
highlighted that a relatively large proportion of the healthy population –who do not
have a diagnosis of mental illness– is prone to experience hallucinations (e.g., non-
127
clinical voice hearers; Badcock & Chhabra, 2013). Interestingly, Greyson and Liester
(2004) found that in a sample of 73 interviewed NDE experiencers, 80% of them
reported auditory hallucinations after their NDE and 20% of them reported auditory
hallucinations both before and after their NDE. They also noted that respondents
reporting subsequent hallucinations are individuals who report more elaborate NDEs
(i.e., scoring very high on the Greyson NDE scale). Nonetheless, any direct causative
role has been highlighted and further studies are needed to understand to what extent
NDEs share phenomenological commonalities and divergences with other types of
hallucinations.
Interestingly, it was noted that conscious states sharing some features with
NDEs can be induced by psychoactive substances (Jansen, 1997; Sanz &
Tagliazucchi, 2018). One substance that could possibly trigger these features is
Ketamine, but many other psychedelics also appear to induce comparable
phenomenological experiences (Corazza & Schifano, 2010; Jansen, 1993; Sanz &
Tagliazucchi, 2018). Experiences under psychedelic drugs are characterized by
marked changes in consciousness that notably include feelings of detachment from
the body, self and environment, perceptual distortions, disinhibited emotions, and
alterations in cognition processes (Schmid et al., 2015; Nichols, 2016). Nonetheless,
in terms of rigorous analysis of the associated phenomenology (i.e., the first-person
perspective of “what it feels like” to have an experience), evidence supporting a
relationship between NDEs and psychedelic experiences is scarcer. In the future, it
would then be highly interesting to perform a large-scale analysis comparing NDE
reports with reports of a wide range of experiences elicited by psychoactive
substances (including hallucinogens or other drugs having less direct impact on the
general quality of conscious experience; e.g., sedatives, stimulants; see Sanz &
Tagliazucchi, 2018 for this type of analysis in dream reports). Such analysis would
aim at determining the semantic similarity between these reports, directly addressing
the hypothesis that some “typical” hallucinatory experiences bear a high resemblance
to NDEs (e.g., Ketamine, Salvia divinorum), while other would bear weaker
128
resemblance (e.g., 3,4-Methylenedioxymethamphetamine). Highlighting these
semantic similarities would ultimately provide common neurophysiological basis for
their phenomenological similarity. Whether both types of experiences (i.e., NDEs
versus “typical” hallucinations) share common neurophysiological bases is to be
determined by future experimental work.
In an attempt to understand the mechanisms underlying NDEs, Saavedra-
Aguilar and Gomez-Jeria (1989) have developed a model that integrate the three
general organic theories proposed in the introduction, namely theories suggesting
dysfunction in temporal lobes, neurotransmitters changes, and fluctuations in levels of
blood gases. According to their model, brain stress –which can notably be caused by
life-threatening events (in reference to psychological theories)– may lead to a release
of endogenous neurotransmitters, producing analgesia or pleasant sensations, and to a
decrease in oxygen tension. These reactions may then provoke discharges notably in
the hippocampus and amygdala, thereby inducing complex visual hallucinations. This
interesting model is plausible, intuitively appealing, and merits attention in future
research. Nonetheless, for now, as scientific observers, we “only” have access to
subsequent reports of NDEs and in principle, authentic “classical” NDEs are
unpredictable (e.g., spontaneously emerging in a context of life-threatening situation),
rendering the simultaneous investigation of the underlying neurophysiological
mechanisms almost impossible. But, protocols can be set up to test the reproducibility
of the subjective experience in controlled laboratory. Recently, we successfully
reproduced certain phenomenological NDEs features by inducing vaso-vagal
syncopes in healthy adults who never experienced a NDE (Charland-Verville et al., in
preparation) –without any adverse effects. In this study, the induction of the different
phases of syncopal episode (i.e., fall down, unconsciousness state, and recovery) was
accomplished with state-of-the-art brain monitoring (high-density
electroencephalogram –EEG) to measure changes in brain activity. Interestingly, 8
(out of 22) participants reported similar phenomenological features than what is
experienced during “genuine” NDEs and scored 7 or more on the Greyson NDE scale
129
suggesting the presence of a NDE phenomenology. It is nevertheless certain that these
laboratory-induced NDEs in naive healthy young adults are a mere “reflection” of
“authentic” NDEs. In addition, strong transformational processes with changing life-
insight and decreased fear towards death should not be reported.
Since this study was completed, we also invited individuals who previously had
experienced a “genuine” NDE to recall their experience under hypnotic induction
(elicited similarly as in patients during surgery; see Faymonville et al., 1994, 1995,
1997, 1999) in our laboratory. Rooted in the psychodynamic tradition, hypnosis can
be regarded as a powerful tool to produce an altered state of consciousness that can
facilitate focus on the recall of any kind of memory (Oakley & Halligan, 2009, 2010).
In this study, we directly assessed the NDE experiencer’ subjective first-person
phenomenological experience in parallel with state-of-the-art brain monitoring (in
two separate sessions, using EEG and functional magnetic resonance imaging –fMRI;
Martial et al., ongoing study). This study will permit a within-subject comparison of
these first-person experiences during laboratory “induced” versus previously
experienced “genuine” NDEs. Finally, in the same vein, immersive virtual reality has
recently been used to induce perceived OBEs in our laboratory in NDE experiencers
and control subjects who never experienced a NDE (Cassol et al., ongoing study).
Previous studies have shown that this technique can provoke a sensed presence
perception (Lenggenhager et al., 2007) and permit to study bodily self-consciousness
(using an embodied fake “avatar body”), like the sense of ownership and self-location
(e.g., Maselli & Slater, 2014), illustrating its potential to elicit an experimentally
induced NDE. Thus, syncope, hypnosis and virtual reality can hence be used to
experimentally induce phenomenological experiences that closely resemble NDEs,
while observing and correlating them with brain changes. It would also be interesting
to investigate brain activity in individuals under Ketamine or other dissociative
anaesthetics, well-known to induce NDE-like experiences (e.g., Corazza & Schifano,
2010; Jansen, 1989). To a certain measure, reproducing NDE features in controlled
laboratory settings will permit to go beyond previous limitations inherent in NDE
130
research (e.g., the lack of real-time medical data and brain monitoring, the passage of
time between the experience and the interview), and to directly test the current
neurobiological hypotheses by objectively mapping brain changes.
Finally, as a more general matter, we believe that NDEs-like phenomena call
for a reappraisal of the (more general) NDE phenomenon. As previously stressed by
few authors (Facco & Agrillo, 2012; French, 2005; Lake, 2017), the label itself –
NDE– does not appear to adequately describe the diversity of experiences. Because
there is no clear universal definition of NDEs, an implicit consensus between
investigators has emerged where NDEs are defined in terms of their commonalities
(Greyson, 1999). However, while similar phenomenal content has been described for
various states of consciousness (e.g., trance states, general anesthesia; Charland-
Verville et al., 2014; Facco & Agrillo, 2012), it appears that the classical features of
the NDE phenomenon are not associated exclusively with actual confrontation with
life-threatening circumstances. We believe that NDE research might benefit from
employing a more fine-grained classification. Insofar, an important issue is that
researchers using different definitions are likely to reach distinct conclusions
concerning the phenomenon and its nature, causes and consequences. In addition, as
the Greyson NDE scale has been proposed in 1983 and research made progress since
then, it would be efficient to create new tools permitting to identify different kinds of
NDEs (e.g., distressing NDEs, NDE-like). While NDEs-like exists, the definitions of
these different phenomena, as well as their identification tools, should state the nature
or cause of the experience in order to distinguish them. Differences and inconsistent
findings in the NDE literature may mainly result from varying definitions and from
inadequate identification tools.
To conclude, although it is reasonable to question the reliability of memories
resulting from NDE, the existence of NDE and NDE-like phenomena is, to date, no
longer debated in the scientific community. Their origin, however, is still a matter of
controversy; transcendental, psychological, and neurobiological models have been
proposed but it is still difficult to draw any firm conclusion about their origin. Their
131
significance and interpretation remain also widely debated, but are not a matter of
science.
132
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