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J. Neurol. 219, 1--13 (1978) Journal of Neurology © by Springer-Verlag 1978 Surveys of Progress Consciousness and Disturbances of Consciousness Detlev von Cramon Max-Planck-Institut ftir Psychiatrie, KraepelinstraBe 10, D-8000 Mfinchen 40, Federal Republic of Germany Summary. The problem of consciousness is discussed briefly, including the contrary views of consciousness as a transcendental phenomenon and as an animistic fiction. Measurement of consciousness is possible only indirectly by means of quantitative assessment of accompanying behavioral deficits. Knowledge of the structural basis of consciousness is incomplete. The ascending reticular activating system (ARAS) is necessary for the main- tenance of the state of consciousness. The monoamine and a great number of descending projections modulate the ARAS. The contents of consciousness depend also on telencephalic structures, primarily on the telencephalic cortex. Certain localized telencephalic lesions bring about disturbances of con- sciousness. The role of the corpus callosum in the problem of consciousness is discussed (one brain--two minds hypothesis). Then a classification of the various disturbances of consciousness is proposed. The term "disturbances of vigilance" is used for all disturbances of consciousness which are caused by a lesion in or a functional disorder of the ARAS or any of its modulating subsystems. The term "disturbances of the contents of consciousness" refers to disturbances of consciousness due to global or localized lesions or functional disorders of telencephalic structures. A list of characteristic features is given for each class of disturbance of consciousness. Key words: Consciousness - Disturbances of consciousness - Level of consciousness - Contents of consciousness - Vigilance. Zusammenfassung. Das Problem BewuBtsein wird kurz skizziert. Dabei werden die gegensMzlichen Auffassungen fiber BewuBtsein als "transzen- dentales Ph~inomen" bzw. als ,,animistische Fiktion" er6rtert. Die ,,Messung" von Bewugtsein ist indirekt nut fiber die Bestimmung des begleitenden Verhaltensdefizits mSglich. Die Kenntnis fiber die strukturellen Grundlagen des BewuBtseins ist lfickenhaft. Ffir die Aufrechterhaltung des BewuBt- seinsgrades kommt dem aufsteigenden retikulfiren aktivierenden System (ARAS) eine notwendige -- wenngleich nicht hinreichende -- Bedeutung zu. 0340-5354/78/0219/0001/$02.60

Consciousness and disturbances of consciousness

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Page 1: Consciousness and disturbances of consciousness

J. Neurol. 219, 1--13 (1978) Journal of

Neurology © by Springer-Verlag 1978

Surveys of Progress

Consciousness and Disturbances of Consciousness

Detlev von Cramon

Max-Planck-Institut ftir Psychiatrie, KraepelinstraBe 10, D-8000 Mfinchen 40, Federal Republic of Germany

Summary. The problem of consciousness is discussed briefly, including the contrary views of consciousness as a transcendental phenomenon and as an animistic fiction. Measurement of consciousness is possible only indirectly by means of quantitative assessment of accompanying behavioral deficits.

Knowledge of the structural basis of consciousness is incomplete. The ascending reticular activating system (ARAS) is necessary for the main- tenance of the state of consciousness. The monoamine and a great number of descending projections modulate the ARAS. The contents of consciousness depend also on telencephalic structures, primarily on the telencephalic cortex. Certain localized telencephalic lesions bring about disturbances of con- sciousness. The role of the corpus callosum in the problem of consciousness is discussed (one brain-- two minds hypothesis).

Then a classification of the various disturbances of consciousness is proposed. The term "disturbances of vigilance" is used for all disturbances of consciousness which are caused by a lesion in or a functional disorder of the ARAS or any of its modulating subsystems. The term "disturbances of the contents of consciousness" refers to disturbances of consciousness due to global or localized lesions or functional disorders of telencephalic structures. A list of characteristic features is given for each class of disturbance of consciousness.

Key words: Consciousness - Disturbances of consciousness - Level of consciousness - Contents of consciousness - Vigilance.

Zusammenfassung. Das Problem BewuBtsein wird kurz skizziert. Dabei werden die gegensMzlichen Auffassungen fiber BewuBtsein als "transzen- dentales Ph~inomen" bzw. als ,,animistische Fiktion" er6rtert. Die ,,Messung" von Bewugtsein ist indirekt nut fiber die Bestimmung des begleitenden Verhaltensdefizits mSglich. Die Kenntnis fiber die strukturellen Grundlagen des BewuBtseins ist lfickenhaft. Ffir die Aufrechterhaltung des BewuBt- seinsgrades kommt dem aufsteigenden retikulfiren aktivierenden System (ARAS) eine notwendige - - wenngleich nicht hinreichende - - Bedeutung zu.

0340-5354/78/0219/0001/$02.60

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Das ARAS wird durch monoaminerge und eine groBe Zahl vom GroBhirn absteigender Projektionssysteme moduliert.

Telenzephale Strukturen und vor allem der telenzephale Kortex scheinen ftir die Entfaltung yon Bewugtseinsinhalten unentbehrlich. Auch umschrie- bene telenzephale Lfisionen kSnnen partielle StSrungen der BewuBtseins- inhalte verursachen. Die Bedeutung des Balkens ffir das BewuBtsein wird diskutiert (one brain-- two minds-Hypothese).

Im letzten Abschnitt wird eine Taxonomie der verschiedenartigen BewuBt- seinsst6rungen versucht. Unter dem Begriff Vigilanzst6rungen werden alle Bewugtseinsst6rungen zusammengefagt, die durch L~ision oder Funktions- st6rungen des aufsteigenden retikul~ren aktivierenden Systems ( A R A S ) - einschlieBlich seiner modulierenden Subsysteme - - bedingt sind. Unter StSrung der Bewugtseinsinhalte werden BewuBtseinsst6rungen verstanden, die durch globale oder lokale L~ision bzw. Funktionsst6rung telenzephaler Strukturen verursacht werden. Ffir beide Klassen yon BewuBtseinsstSrungen wird ein Merkmalskatalog beschrieben.

1. The Problem o f Consciousness

Writers on the topic of consciousness often begin by pointing out that in spite of a great many efforts there is still no satisfactory definition of consciousness. On the other hand, there is hardly an author who has resisted the temptation of adding his own definition to those already in existence. The result is a tremendous number of different equations (Graumann, 1966), descriptions and terminolo- gical discourses (Brain, 1958; Bleuler, 1961; Ey, 1967; Frederiks, 1969). The question of why there is this apparent inability to understand consciousness has been answered in a great many different ways.

1.1 Consciousness and the Body-Mind Relationship

A number of authors--including such prominent brain researchers as Eccles and Hess--hold the view that consciousness cannot be understood a priori since it is a transcendental phenomenon. They hold that it is intrinsically impossible to arrive at valid concepts about processes which are inaccessible to human perception. The connection between neiaral activity and subjective, conscious experience is inaccessible to rational understanding and, in Hess's opinion, will remain a mystery eternally. This could be explained by the fact that the human brain is not organized to analyze itself, although it is able to understand certain results of its own activity. This view is close to a position on the body-mind problem which has been contested among western philosophers for hundreds of years. The sup- porters of the theory of parallelism and interactionism maintain that mind and matter are two separate entities. Leibniz' parallelism assumes that body and mind do not influence each other, although each state of one corresponds to a state of the other in accordance with the rule of prestabilized harmony. Interactionism, on the other hand, postulates interaction between the two entities: physical processes cause psychic processes and vice versa. Supporters of

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the theory of identity--Feigl being the most important among them--regard psychic processes as derivatives of brain processes and postulate a strict psychoneural identity. The hypothesis of isomorphism (K6hler, Metzger) has gained in importance as a scientific model. Brain and psychic processes are understood to be analogue structures which must be described and explained separately but which complement each other insofar as they are related to the same phenomenon (see corpuscular and wave theory of light).

1.2 Consciousness as an Epiphenomenon

In the first half of the 20th century the behaviorists (Watson, Boring) took a radical position. For them the concept of consciousness was an animistic fiction and thus likewise something which a priori was not subject to scientific investigation. The group of behaviorists referred to as cognitive behaviorists (Tolman) soon accepted the old mentalistic (consciousness) position again, but they do not consider the problem of consciousness to be the real problem of psychological research (Casler, 1976). For them consciousness is an epiphe- nomenon which emerges of necessity from the interaction of the basic psychic functions such as attention, perception, motivation and memory. They hold that there is no such thing as independently functioning consciousness. The problem is to elucidate the relationship between brain processes and basic mental functions and in this way to come to a better understanding of the preconditions for consciousness. But the most important contribution of behaviorism has been to add the technics of systematic observation and measurement of behavior to the introspective technic which had been the sole approach of psychology for the study of consciousness (Wundt, 1911). Introspective technics and behavioral measurement are the two main tools of consciousness research today.

1.3 The Neurologist's View

The only compelling reason for the neurologist to think about consciousness is the great variety of disturbed states of consciousness which he sees in connection with a great many different kinds of pathological processes of the central nervous system. In the neuropsychiatric literature the ambiguity about the meaning of consciousness is reflected in the utter terminological confusion one finds. This confusion has developed because philosophers, psychologists, cyberneticists, neurophysiologists, psychiatrists and neurologists have often used the same terms with rather different meanings based on concepts of different complexity. In clinical practice sometimes contradictory uses of the term consciousness and related terms have resulted in a jargon with which one can communicate only vaguely about underlying processes.

1.4 The Problem of Measurement

According to Lhermitte and Gautier (1966), the neurologist has two tasks in his research on consciousness: (a) to analyze the behavior of patients with disturbances of consciousness as exactly as possible and (b) to locate the lesions in the CNS which are responsible for the disturbances.

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The measurement of behavior was clearly neglected for a long time in comparison to the description of behavior. During the past two decades, however, there have been several attempts to evaluate quantitatively the be- havioral deficit in patients with varying degrees of disturbed consciousness (Wieck, 1973; Jouvet, 1969; von Cramon, 1975). Here brain performance is measured following the application of physical, verbal and figural stimuli.

The problem of measuring what a patient with an altered consciousness experiences continues to seem insoluble. The inventories and scales commonly used in clinical psychiatry are of no use, for example, as soon as it becomes impossible to communicate verbally with the patient in a differentiated manner. Questioning the patient after the disturbance of consciousness has subsided usually does not lead to any useful information since the patient cannot remember this period exactly or may even have amnesia for the period.

1.5 The Seat of Consciousness

For Jackson (1931), the prefrontal region of the frontal lobes was the anatomical substrate and thus the seat of consciousness. Penfield (1957) placed great importance on the centrencephalic integrating system. This system includes neural structures in the diencephalon and in the rostral brain stem. Walshe (1957) criticized Penfield's concept. He found it rather unlikely that the reticular formation as a limited and phylogeneticaliy old system of the brain could carry out functions which are as complex as those needed for the maintenance of consciousness.

A holistic neuron theory of consciousness was also developed under the influence of cybernetic models (Rowbotham, 1965). In this model, all active neurons in the CNS are in communication with each other. Every neuron in the CNS always "knows" what every other neuron is doing. In this model con- sciousness as "awareness of environment and self" (Cobb, 1958) can be attributed to even a motor neuron that "is aware of" itself and the surroundings with which it is connected. There is no assumption here of a higher center as the seat of consciousness.

2. Brain and Consciousness

The discussion about the anatomical and physiological correlates of con- sciousness and disturbances of consciousness is facilitated if two aspects of the consciousness system are examined separately. On the one hand there is the problem of determining which neural structures are necessary for the maintenance of the state of consciousness and on the other the problem of localizing those neural systems which are probably necessary for the contents of consciousness.

2.1 The Monamine Projection Systems of the Brain Stem

Four rather large projection systems of the brain stem are involved in the control of the complex processes which regulate the continuum between consciousness and sleep. These are the monaminergic projections from the locus coeruleus

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(norepinephonergic), f rom the raphe nuclei (serotinergic), and from the substantia nigra (dopaminergic) together with the cholinergic tracts which come from the pontine and mesencephalic reticular formation. In spite of the anatomical and, especially, pharmacological differences in these fiber systems, major difficulties arise when one tries to isolate them from one another and to assign a specific function to each subsystem. They interact with each other on various levels and maintain a fine balance between their synergistic and antagonistic actions in both cerebral hemispheres. These non-specific projection systems differ from the spe- cific, unilaterally organized systems in that they interact bilaterally. All four of these subsystems appear to have the same anatomical peculiarity: because of extensive axonal branching they are able simultaneously to influence completely different structures in the brain. The functional effect of the fiber systems mentioned appears to lie in a rather global modulation of neuronal excitability.

2.2 The Ascending Reticular Activating System (ARAS)

Whereas the projection fibers of the raphe nuclei and the locus coeruleus are mainly responsible for the regulation of sleep, it has long been known that tracts ascending from the pontine and mesencephalic reticular formation play a key role in the maintenance of the state of consciousness. The central reticular formation has a role in the arousal reaction. This arousal reaction is characterized by desynchronization of thalamic and cortical slow wave activity and by an increase of the resting discharge of cortical neurons. This effect of the ARAS is also of a rather global nature and can be seen in most of the diencephalic and telencephalic structures. Reticular stimulation results in the inactivation of the local inhibitory circuits at the level of the thalamic relay nuclei. This allows the afferent reticular tracts to control the transfer of impulses in the thalamus in a manner specific to the modality ("gating" function). It has been shown by histochemical and physiological experiments that the cortex, too, is influenced directly via the reticular fibers. However, the mechanism of reticular modulation of the telence- phalic cortex is not understood as yet. A detailed discussion of the reticular control mechanisms can be found in Singer (1977).

The ARAS is modulated by a number of other fiber systems. These include frontofugal fibers and tracts which descend from the amygdala, the hippocampus and the hypothalamus (Brodal, 1965). The interaction of the ARAS with the periaqueductal gray matter plays a role here, but nothing more is known about this. These projections allow a kind of feedback relationship between the processing of specific information by the CNS and the selection of certain information from the total information available at any one time.

The findings of Alema et al. (1966) appear to indicate that the reticular formation is not of importance for the maintenance of consciousness. The injection of sodium amytal into the vertebral artery did result in a ponto- mesencephalic functional disorder with complete paralysis including the 3rd and 4th cranial nerves (and including the parasympathetic component of the 3rd). But the patients did not lose consciousness and there was no change in their responses to visual and acoustic stimuli. On the other hand, the injection of amytal into the carotid artery ipsilateral to the remaining hemisphere in patients who had

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undergone hemispherectomy resulted in immediate loss of consciousness (Obra- dor, 1964). This finding permits the conclusion that the diencephalic reticular projections are the main structures necessary for the maintenance of con- sciousness. Doty (1975) had an idea which fits in well here. In his view, the deleterious effect of midbrain lesions could be due to an interruption of the trophic influences, which are normally maintained by the extensively branched fiber systems of the brain stem in the dependent regions of the brain. Apparently not only do classical electrophysiological mechanisms play a role in the main- tenance of consciousness, but neurohumoral mechanisms also.

2.3 The Role of Telencephalic Structures in Consciousness

There is wide agreement today that the level of functioning of the cerebral cortex has a role in consciousness. Cortical activity is necessary for the contents of consciousness. Since there is no valid concept about how the cerebral cortex works, any ideas about the generation of the contents of consciousness in the cortex are speculative. It is not even clear whether only certain areas of the cortex or all of it are involved.

When there is diffuse destruction of the telencephalic gray matter with relative preservation of the brain stem (neocortical death) this is referred to clinically as the apallic syndrome. The associated disturbance of consciousness is called coma vigil. The term coma is misleading, however. What is meant is a state of unconsciousness combined with a state of wakefulness. Being awake cannot be equated with being conscious. Wakefulness is only one function of the system for the maintenance of the state of consciousness and is apparently possible even without cortical activity. Consequently it is by no means always correlated with rapid EEG activity since it is the EEG which reflects the neural activity of the cerebral cortex.

In order that different kinds of performance by the brain are possible, complicated interactions between different apparatuses within the cerebrum must be established by means of appropriate modulation of neuronal excitability. The cortex is the organ of consciousness but it needs the interactive control system in the rostral brain stem. This system is a precondition for the delicately balanced interplay of cortical actions. It is therefore not surprising to find that certain lesions of the rostral brain stem have the same effect as the diffuse destruction of the telencephalic cortex, as may happen in the case of the apallic syndrome.

Clinical observations have shown that localized telencephalic lesions may lead to loss or alteration of certain contents of consciousness. This can happen in such a specific way that the disturbance of consciousness can help to localize a cerebral lesion. Disorders of body consciousness associated with parietal lesions should be mentioned in this connection as examples of a partial lack of awareness of the body. Disorders of the contents of consciousness such as those which are characteristic of the dreamy states of psychomotor epilepsy can originate in a lesion of the region referred to as the pararhinal region. The pararhinal region involves certain parts of the temoral lobe. It is closely related to the limbic system. Another example is the elusive disturbance of consciousness associated with lesions of the cingulate area.

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2.4 One Brain-Two minds?

The studies on split-brain patients have drawn attention to the importance of the corpus callosum for the regulation of consciousness (Sperry, 1966; Gazzaniga, 1972; Zangwill, 1975). Following commissurotomy there are two coexisting conscious entities. Each hemisphere seems to have its own sensations, ideas and motivations, which may be at cross purposes with those of the other hemisphere. The physical substrate of consciousness appears to exist in the human brain in duplicate. For reasons which remain unclear, in the normal brain the separate consciousness systems are connected to each other by the corpus callosum. Consequently it is the corpus callosum which conveys the information which is responsible for the unity of consciousness. Following midline sectioning the neural system which controls the goals and priorities of the organism--MacKay (1966) called it the metaorganizing system--appears to be preserved, now appearing as two completely independent systems in each cerebral hemisphere. It appears that each hemisphere always has such a metaorganizing system.

Based on his own studies on split-brain patients, Dimond (1976) postulated that the splenium of the corpus callosum "forms the essential bridge of the consciousness system" and that thus the whole consciousness system is probably located in the posterior part of the brain. Other possible anatomical locations might be the posterior part of the cingulate area and the praecuneus. The projections of this system for consciousness reach as far as the parietal lobes and the medial temporal lobes (see Section 2.3). According to Dimond this hypo- thetical consciousness system is like a river which has a great many tributaries. At first the material flows together from many areas of the brain (recruiting phase), then there is "smoothing of the material and the filling of the gaps" (con- structive phase) and finally the material is fed into the fiver of the consciousness system. In this final phase subjective experience occurs, the experiencing of integrated brain activity (work phase).

2.5 The Significance of Somatic Factors for Consciousness

Various general somatic factors influence the functional capability of neural structures and thus consciousness. The following factors are important causal agents of disturbances of consciousness: - - oxygen deficiency - - hypoglycemia - - dehydration and hyperhydration - - disorders of the electrolytes and the acid-base balance - - disorders of the barrier system (blood-brain barrier and blood-CSF barrier) - - disturbances of body temperature - - vitamin deficiency - - disturbances in porphyrin metabolism - - disorders of the liver, kidneys, pancreas, thyroid, adrenal glands - - release of toxic metabolic products from tumors - - ingestion of or abrupt withdrawal of substances with a toxic effect (e.g. alcohol, drugs/narcotics, organic solvents).

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3. Classification of Disturbances of Consciousness

3.1 The Concept of Disturbance of Consciousness

The concept of disturbance of consciousness implies that there is a state of normal, undisturbed consciousness. The establishment of a convention with a sound theoretical basis on what normal consciousness is would be extremely difficult, and not without ethical problems. However, among the population of a given culture there is a seemingly automatic consensus about what is normal and what is a deviation from ordinary consciousness. Of practical significance is the realization that not all deviations of consciousness are signs of a pathological process. A distinction should therefore be made between altered states of consciousness and disturbed states of consciousness. A disturbed state of con- sciousness exists when a pathological process with a physical basis can be found which is causing the deviation. There is no sharp demarcation between the two states, however. Certain drugs and poisons, for example, can first produce an altered state of consciousness and later, depending on the concentration of the toxic substance in the organism, a disturbance of consciousness. In view of our current knowledge, psychogenic stupor cannot be regarded as a disturbance of consciousness, although there are pathological states which mimic these con- ditions (e.g. epileptic twilight state). And arguments could probably be found for calling catatonic and depressive stupor disturbances of consciousness. Assign- ment to one category or the other can be problematical in borderline cases, but a distinction between a altered state of consciousness and a disturbed state of consciousness is useful in clinical practice. Disturbances of consciousness require the attention of the psychiatrist or neurologist, whereas altered states of consciousness (e.g. trance, ecstasy) are primarily of interest to psychologists and anthropologists. But for therapeutic purposes the psychiatrist, too, makes use of technics for altering consciousness (e.g. hypnosis).

3.2 Classification of Disturbances of Consciousness

Considering the structure and functioning of the consciousness system (see Section 2), a division of disturbances of consciousness into two categories suggests itself. (1) Disturbances of consciousness due to damage to those neural structures which guarantee the maintenance of the state of consciousness. The result is a restriction in the state of consciousness, the level of consciousness and the lucidity of consciousness. The term disturbance of vigilance has been suggested for this category of disturbances of consciousness. In this context the term is used as Head used it (1926): vigilance as the expression of the physiological efficiency of the CNS and thus primarily as a measure of the performance of the ARAS in the rostral brain stem, including its modulating subsystems. The current level of vigilance can be determined indirectly through measurement of the degree of differentiation in the responses of the brain. Vigilance cannot be spoken of simply in terms of its presence or absence; rather, it must be regarded as a uni- dimensional continuum from undisturbed consciousness to brain death.

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(2) Disturbances of consciousness due to a change in the functioning of telence- phalic structures, especially cortical structures. The change may be due to an attack on the telencephalic structures themselves by a damaging agent, or it may be secondary to a pathological change affecting the afferent impulses to these structures. Since consciousness is always consciousness of something, the es- sential aspect of this category of disturbances of consciousness is a disturbance of the contents of consciousness. In the more severe degrees of disturbed vigilance, this disturbance of the contents cannot be observed any longer, however.

Here the syndrome known as the locked-in syndrome (de-efferentiation syndrome; Plum and Posner, 1972) and akinetic mutism should be mentioned. The severe reduction of motor functions, including speech, gestures and facial expression found in these syndromes, might be misinterpreted as a primary disturbance of consciousness. Since the locked-in syndrome is due to an infarction of the ventral pons, the assumption that there is a primary disturbance of consciousness is not very likely anyhow. But in the case of akinetic mutism the pattern of lesions is not always the same. However, the fact that this state can disappear and then reappear within the space of a few minutes speaks against the assumption of a major disturbance of consciousness. Because of the continuing immobilization, a secondary alteration of the state of consciousness may result in both syndromes (Ludwig, 1969).

3.2.1 Disturbances of Vigilance

Disturbances of vigilance can be characterized by several features which cannot be regarded as independent variables but at the same time whose interdependence cannot be described clearly. They are more or less pronounced with the different kinds and degrees of disturbed vigilance, and not all of them are found with every disturbance. Each feature can be present to a greater or lesser degree or not at all. The features are described below in terms of a reduction of a facility.

(1) De-differentiation of Brain Performance. There is diminished differentiation of brain performance; brain performance is complex (syncretic) but its preciseness is reduced. (2) Slowed Mental and Motor Activity. Mental and motor processes begin with a delay and proceed at a slowed pace. (3) Receding of the Surroundings. Contact with the emotional surroundings is impaired; the surroundings are experienced as if through a veil. (4) Diminished Personal Control With the loss of personal control, intense and primitive emotions appear. Affect is uninhibited and no longer differentiated. Control of body posture and movement is diminished; this includes control of eyelid movement. The eyes cannot be kept open. (5) Reduction of Ability to Communicate. Verbal communication and communi- cation via facial expression and gestures are impaired. (6) Disturbance of Orientation. There are disturbances of orientation regarding time, place and person. (7) Diminished Responsiveness. The response to external stimuli is reduced.

Not only vigilance but also sleep is an active performance of neural systems which are located close together in the brain stem and interact with the ARAS.

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Therefore the disturbances in the functioning of these two diametrically opposed states of vigilance and sleep should be kept clearly separated terminologically. Pathological disturbances of sleep and disturbances of the sleep-waking cycle thus do not belong a priori to the disturbances of vigilance. Nevertheless, those states must be listed as disturbances of vigilance where a disturbance of the sleep- regulating system is suspected but where there is a reduction in the length of the remaining vigilance phases. In accordance with the list of characteristics given above, a disturbance of vigilance must also be assumed with the various kinds of dementia. Although these etiologically heterogeneous syndromes are not char- acterized adequately in this way, still they should be looked at in terms of the disturbance of consciousness involved. In dementia an irreversible disturbance of consciousness progresses, in slow motion as it were. Certain partial functions of vigilance (e.g. responsiveness, body control, some aspects of orientation) are preserved for a long time. Thus there is a partial disturbance of vigilance. In the early stages, and in later stages as well, disturbances of the contents of consciousness appear (see Section 3.2.2.1).

3.2.1.1 Classification of Disturbances of Vigilance

(A) Global disturbance of vigilance due to temporary loss of functioning of the ascending activating system. - - paroxysmal loss of consciousness/fainting: with grand mal seizures, with

syncopal seizures - - loss of consciousness induced by medication: anesthesia (B) Global disturbances of vigilance due to functional disturbances or structural brain lesions with mesodiencephalic location of primary or secondary origin. - - clouded consciousness ~ - - continuing unconsciousness/coma 1 (C) Partial disturbance of vigilance due to temporary loss of functioning of the ascending activating system

- - absence: with petit mal seizures (D) Partial disturbance of vigilance due to structural brain lesions with diffuse telencephalic location or mesodiencephalic location of primary or secondary origin - - coma vigil: with apallic syndrome - - dementia

akinetic mutism (?) (E) Reduction in length of periods of vigilance due to functional disturbances of the sleep-regulating systems - - narcolepsy - - hypersomnia.

In the literature on coma the term clouded consciousness is often used as a generic term and subdivided into the stages of drowsiness, somnolence, sopor, precoma and coma. The dividing lines between the various stages are rather arbitrary, however. It proves useful to describe the state of diminished vigilance (clouded consciousness) and the state of loss vigilance (continuing unconsciousness/coma) more precisely by means of a quantitative determination of the behavioral deficit (von Cramon, 1975)

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3.2.2 Disturbances of the Contents of Consciousness

This category has general characteristics with limitations expressed in terms of deterioration analogous to those given for disturbances of vigilance (Section 3.2.1). The list below includes only those features which are found very frequently. (a) Altered Meaning. Great insight and enlightenment are experienced, resulting in the eureka feeling. But there is very little connection between the objective truth of the contents of consciousness experienced and the subjective evaluation of these contents. Available language is inadequate to describe the indescribable. (b) Increased Suggestibility. Ideas, feelings and motivation are easily influenced. (c) Altered Affect. Affect is labile, contradictory: anxious-agitated, and some- times euphoric-ecstatic emotions occur. Emotion may be characterized by helplessness and bewilderment but also by complete disinterest. (d) Thought Disorders. The thought process is circuitous, complicated, uncon- centrated; the chain of thoughts disintegrates into unrelated bits and pieces (incoherent thought); things which are obviously contradictory are often not experienced as disturbing; confabulations are introduced; disturbances of content of thought (e.g. delusion of persecution, delusion of grandeur) are rare. (e) False Perceptions. These are found in all sensory modalities. False visual perceptions are particularly frequent; they can have a scenic-dreamlike character or be extremely elementary. (f) Altered Awareness of Body. Distortions and deformations of the body are experienced; parts of the body are ignored or even considered to have been lost. (g) Disturbance of Perception of Time. Time appears to be moving faster or slower than it is; it can seem to stand still (the "feeling of forever"). (h) Increased Distractibility. The response to external stimuli can be increased to the point of a startle response to minor stimuli.

3.2.2.1 Classification of the Disturbances of the Contents of Consciousness

(A) Disturbances of the contents of consciousness due to diffuse functional disturbances of the telencephalic structures (Section 2.5). (B) Disturbances of the contents of consciousness due to localized functional disorder or local structural brain lesions in the telencephalon (Section 2.3) associated with 2

- - lesions of the cingulum - - lesions of the parietal lobes - - functional disorders of lesions of the pararhinal region and parts of the

temporal lobes

'3.2.3 Disturbances of Consciousness Associated with Organic Psychoses

Psychiatric textbooks make distinctions among the following syndromes: (1) hallucinosis, (2) the amnestic syndrome, (3) delirium, (4) confusion and (5) twilight state. One additional syndrome is usually included which on the

2 This is only a partial listing

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c o n t i n u u m between confusion and delirium: the oneiroid state (dreamlike con- fusion), which is labelled as a special form of delirium.

Dis turbances of both vigilance and contents of consciousness are the pr imary features of these syndromes. The individual disturbances are present in differing degrees of severity and are amalgamated so that it is difficult to identify the elements in these alloys. A detailed discussion of these syndromes is not within the scope of this article. The following table is an at tempt to indicate which features of the two categories of dis turbances of consciousness just delineated are present in these five syndromes.

Features present a

Disturbances of Disturbances contents of of vigilance consciousness

Hallucinosis (c) e - -

Amnestic syndrome d 1, 2, 6

Delirium (a), b, c, d, e, f, h 1, (3), 4, (5), 6

Confusion (a), c, d, h 1, 4, (5), 6

Dissociative reaction or state (a), c, ? 3, 5, 6, 7

a Parentheses indicate features which are not always present

References

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Received April 21, 1978