Episodic and Source Memory in Autism

Tanuja PoorunMSc Research Methods

Supervised by Prof. Paul W. BurgessWith G. G. Yaacovi & H. Sugarman

Outline

• Literature Review

• Hypotheses

• Participants

• Procedure

• Possible Results

• Questions

Remembering & Knowing

Awareness of Memory

Autonoetic Consciousness:

[Contextual details of previous events]

Remembering =

Episodic Memory

Noetic Consciousness:

[Abstract awareness of knowledge]

Knowing =

Semantic Memory

Episodic Memory (EM)

• Link between EM deficits and frontal lobe (FL) impairment– Patients with FL damage & those with schizophrenia

experience less “remembering”

• EM may require aspects of executive control – known cognitive deficits in ASD

• Possible impairment of autonoetic experience in adults with ASD– Evidence of EM deficits in adults with Asperger’s

syndrome (Bowler et al., 2000)

Source Memory (SM)

• Defined as ability to recollect contextual information about an event– Possibly a function of EM

• rPFC implicated in SM– See Figure 1 (Turner et al., 2008)

• Possible SM deficits in ASD– Evidence in adolescents & adults with Asperger’s

Syndrome (Bowler et al., 2004)

SM link to rPFC

Figure 1:

Regions of rPFC activated in critical contrasts.

Recollection of perceived/imagined and temporal source versus new items

(Turner et al., 2008)

Theory of Mind (ToM)

• Also known as “mentalising’: The cluster of abilities held to be necessary to understand the mental processes of others (Frith, 1997)

• ToM strongly associated with FL functioning– See Figure 2

• Evidence of impaired ToM in ASD– E.g false belief test

• Possible link to EM & SM deficits– Inability to reflect upon subjective experience & lack of

consciousness of own knowledge

ToM linked to PFL

Figure 2:

Location of peak activations in medial prefrontal regions during tasks where subjects think about their own or others' mental states (carried out by C. Frith, 1999)

Gateway Hypothesis

• Supervisory Attentional Gate (SAG) (Burgess et al., 2007)

– Supported by rPFC, approx. Brodmann’s Area 10– Functional sub-division of rPFC (see Fig. 3)– Mediates attentional switching between external stimuli

(stimulus-oriented, SO cases) and internal representations (stimulus-independent, SI cases)

• Atypical functioning of SAG in autism– fMRI: Atypical recruitment of rPFC in ASD (Gilbert et al., 2008)

– Impairments in mentalising (associated with mrPFC)– Impairments in attentional switching between SO & SI

Differential activation of rPFC

Figure 3: Differential activation of the rostromedial and rostrolateral PFC during attentional orientation to external and internal information, respectively. Center: Brain activation map showing significantly stronger activation of the anterior rostromedial PFC during the orientation of attention to external as compared to internal information (blue), and significantly stronger activation of the rostrolateral PFC during the orientation of attention to internal as compared to external information (red). (Henseler et al. 2010)

Central Coherence (CC) Theory

• Possible weak CC in ASD– Failure to integrate sources of information to establish

meaning– Possibly caused by atypical SAG– Disproportionate attentional focus on external stimuli at

expense of attention to internal representations

• May explain difficulties in retrieving subjective experiences in ASD, i.e. less ‘remembering” (EM) + difficulties in retrieving context in which information was encoded (SM)

Hypotheses

• HFA adults will show impairments in EM & SM

• Prospective Memory (PM) Task– PM deficits in ASD subjects who also show

impairments in EM & SM may contribute towards our understanding of the SAG.

Participants

• 40 participants in total– 20 HFA adults– 20 control

• IQ measures– National Adult Reading Test– Advanced Progressive Matrices

• Autism Questionnaire

Procedure

• Encoding Phase– Participants rate words according to Pleasant or

Unpleasant– Stimuli:

• 30 words (List A) obtained from MRC Linguistic Database• Neutral, high frequency, concrete, 4-7 letters long• E.g. Coat, Surf, Kitchen

– Responses recorded using arrow keys

Procedure

• Remember/Know Task– Adapted from Wheeler & Stuss (2003) memory

paradigm – Stimuli

• 60 words = 30 words from List A + 30 matched new words

– Participants required to determine if word comes from previous task (List A) or if word is new

Procedure

• Instructions for Remember/Know Task

Remember(Press Key 1)

Know(Press Key 2)

New Word(Press Key 3)

You recognise seeing the presented word during the previous task and can remember specific details about it (such as when the word occurred or what you thought about at the time).

You recognise the presented word but can not re-experience something specific that is related to that word (meaning that you simply know or you have a general feeling that it

occurred earlier).

You do not remember seeing the presented word and you think that it is new (meaning that it did not appear in the first task), or you are unsure whether you saw the word or not.

Procedure

Procedure

• Temporal Order Judgement Task– Adapted from Turner et al. (2008) source monitoring

paradigm– Stimuli:

• 60 words from FOILS 1 and 2

– Participants required to determine whether the presented word comes from the 1st R/K Task or the 2nd R/K Task.

– Responses recorded using arrow keys

Analysis

• Encoding Phase– Latencies & Pleasantness ratings

• Remember/Know Task– Latencies– Accuracy– Remember or Know responses

• Temporal Order Judgement Task– Latencies– Accuracy

Possible results

• Deficits in EM in ASD:– More “Remembering” than “Knowing” responses

• Deficits in SM in ASD:– Lower accuracy due to problems in retrieval of context-

specific information

References

• Bowler, D. M., Gardiner, J. M., Grice, S. J. (2000). Episodic Memory and Remembering in Adults with Asperger Syndrome. Journal of Autism and Developmental Disorders, 30 (4), 295-304.

• Burgess, P.W., Dumontheil, I. & Gilbert, S.J. (2008). The gateway hypothesis of rostral prefrontal cortex (area 10) function. Trends in Cognitive Sciences, 11 (7), 290-298

• Frith, U. (1997). The neurocognitive basis of autism. Trends in Cognitive Sciences, 1 (2), 73-77.

• Gilbert, S.J., Bird, G., Brindley, R., Frith, C.D. & Burgess, P.W. (2008). Atypical recruitment of medial prefrontal cortex in autism spectrum disorders: An fMRI study of two executive function tasks. Neuropsychologia, 46 (9), p2281-2291.

• Wheeler, M. A. & Stuss, D. T. (2003). Remembering and knowing in patients with frontal lobe injuries. Cortex, 39, 827-846

Questions?