Introduction to Cognitive Disorders

Introduction to cognitive disorders

Topics covered:

  • Introduction
  • Delirium
  • Dementia
    • Changes in the concept of dementia
    • Cortical dementias
    • Axial and diencephalic dementias
  • Conclusion
  • References


The three terms delirium, dementia, and amnesic syndrome appear together in the classification manuals because they share a common, but not exclusive, organic aetiology. However, these conditions have little in common from a historical, clinical, and psychopathological perspective. Because the notion of ‘organicity' is imprecise, it would perhaps be preferable to use Schneider's term ‘corporeally based manifestations' ( körperlich begründbaren Psychosen). In this article, delirium, dementia, and the amnesic syndrome will be discussed separately from historical and psychopathological perspectives.


Georget introduced the term stupidité (stupor) to replace Esquirol's term acute dementia to indicate a state in which a person appears to have no ideas or cannot express them. The term was adopted by German as well as French authors. Baillarger (1) suggested that patients with this syndrome were melancholic, and the term ‘melancholy with stupor' became widely accepted despite problems with differential diagnoses. According to Griesinger: (2)

Melancholy with stupor has not only a great theoretical importance due to the strongly marked psychic symptoms and characteristic brain injuries existing in some cases, but also due to the fact that they are easily and frequently mixed up with dementia, which can lead to great errors in relation to the prognosis and treatment; for this they have also a great practical interest.

This controversy resembles that surrounding the term ‘depressive pseudodementia' today. Other authors, while accepting that melacholy with stupor existed, thought that most cases of stupor were independent.

Chaslin (3) included stupidité under the term mental confusion. Both the concept and many of the clinical features correspond to Bonhoeffer's exogenous reaction type (die exogenen Reaktionstypus), (4) which he classified into three groups:

  1. characteristic forms, which comprised amentia, delirium, twilight states, and hallucinosis; 
  2. homonymous forms, i.e those with manifestations similar to schizophrenia, mania, and depression;
  3. a residual group including hyperaesthetic, sensory, or neurastheniform disorders together with Korsakoff's syndrome.

Two properties are essential: the manifestations lack specificity, and they share a disturbance of consciousness ( Bewusstsein). Kraepelin (5) attempted to study organic or exogenous psychoses using the medical aetiological model, believing that each aetiology corresponded to a specific aetiopathogenic mechanism and a characteristic symptomatology. This view was contradicted by Bonhoeffer, (4) who pointed out that in the characteristic forms each aetiology could give rise to any syndrome, and each syndrome could be caused by any aetiological factor.

Characteristic forms are characterized by a disorder of the consciousness; amentia, delirium, and twilight states are due to a decrease of consciousness, whereas hallucinosis is due to an increased clarity of consciousness. (6)

All Bonhoeffer's characteristic forms are included in the current classifications under the term delirium, but this is an error. Firstly, the disturbance of consciousness is not sufficiently emphasized and, secondly, syndromes which should be separated because of their different psychopathological characteristics appear together. In amentia, there is little decrease in consciousness; indeed, it may even go unnoticed although it is always present. Amentia is characterized by incoherent thought and severe motor disorder, whereas delirium is characterized by a more severe disturbance of consciousness with oneirism (absentminded dreaming while awake), hallucinations, and delusions (frequently occupational). In a twilight state, the level of consiousness is intense but fluctuating. It may occur with a decrease of the ‘awake' consciousness (Bewustsein), but without any alteration in ‘reflexive' consciousness' (Ey's conscience de soi (7)). Finally, in hallucinosis increased clarity of consciousness is accompanied by anxiety, auditory hallucinations, and a tendency to paranoid ideas.

Some consider that all four syndromes described by Bonhoeffer should be mantained mainly to avoid diagnostic errors. Amentia, with little change of consciousness, is sometimes mistaken for schizophrenia or, in older people, dementia. The patient is perplexed, makes false identification, and is depersonalized. These manifestations of amentia may also be present in acute endogenous disorders such as the cycloid psychoses. Sometimes these subconfusional manifestations are chronic, with a long evolution when it is easy to mistake them with dementia. The possibility that enhanced amentia in the old may be of psychogenic origin (psychogenic unresponsiveness) has to be kept in mind.


The term ‘dementia' refers to patients with chronic brain damage and severe deterioration of intellectual processes. Frequently, psychotic symptoms (hallucinations and delusions) and affective symptoms are also present. This syndrome has a long history; in antiquity it had a meaning similar to that understood today when used in a medical context (Celsus, 150 BC). The term ‘dementia' was recognized by Pinel, (8) and Esquirol(9) distinguished acute dementia (later called mental confusion) and chronic dementia. Georget (10) subdivided the latter into primary dementias, so called because the intellectual disorder appeared first, and secondary dementias, in which other mental manifestations (e.g. mania and dementia praecox) preceded the intellectual disorder.

There are two periods in the subsequent history of dementia. In the first and longest, from the beginning of psychiatry to the 1970s, dementia was considered as an illness. Since then, dementia has been considered to be a syndrome.

The concept of dementia as an illness was based on an anatomical and clinical approach. Three illnesses were characterized:

  1. general paresis of the insane, identified by Bayle (11) and later attributed to syphilis; (12)
  2. vascular dementias as described by Klippel, (13) i.e. dementias that were exclusively vascular in origin; 
  3. parenchymatous dementias.

In 1898 precise knowledge of the structure of the brain became available using the silver impregnation technique developed by Ramón y Cajal. When analysing the dementias, Alzheimer (14) pointed out that not all are due to a vascular aetiology, and in 1911 he described parenchymatous dementias with neurofibrillar degeneration and senile plaques. (15) This finding was soon confirmed by other authors. Kraepelin (5) called this condition senile dementia, and included in it Kahlbaum's presbyophrenia as a form of dementia arising at an earlier age.

In 1906 Alzheimer (16) described a 52-year-old female patient who presented a severe dementia, with neurological symptoms, aphasia, apraxia, and agnosia, initiated with delusions of jealousy, and whose brain showed the histopathology described in senile dementia. He published this case without being able to ascribe a cause. Similar observations were reported by other authors between 1908 and 1910. (17,18,19) Kraepelin (5) called the condition the presenile dementia of Alzheimer.

Between 1892 and 1904 Pick carried studied lesions in the brains of aphasic patients and published several cases including two of persons aged over 50 with clinical features similar to the presenile dementia of Alzheimer but without its characteristic lesions. Subsequently, Ornari and Spatz (20) coined the term presenile dementia of Pick and described the histopathological characteristics of the disorder and the topography of the lesions. They suggested a hereditary-degenerative aetiology.

Some other forms were subsequently added to the four main dementing illnesses, including the spastic pseudosclerosis described by Creutzfeldt and Jakob in 1927. In the 20 years following the Second World War research raised new questions, including the importance and frequency of mixed vascular and parenchymatous forms, (21) the correlation between the amount of anatomical damage and the seriousness of the dementia, (22) and the identification of new clinical manifestations such as ‘mild dysfunction of the memory'. (23) In general, however, the dementias were still thought of as illnesses, each with specific histopathological findings.

Changes in the concept of dementia

In the 1950s two important events occurred which led to new approaches to the concept of dementia.

  1. Forms intermediate between senile dementia and the presenile dementia of Alzheimer were identified. Sjögren (24) described cases of dementia appearing at older ages than those reported for the presenile dementia of Alzheimer, without extrapyramidal signs, strokes, or signs of aphasia, agnosia, and apraxia, but with similar histopathology although the senile plaques and neurofibrillar tangles were less dense. Sjögren called this condition ‘atrophia senilis cerebri'. During these years the Geneva School showed that patients with senile dementia could present, during the evolution of their disorder, with focal manifestations and lesions analogous to the those found in presenile dementia, in what they called ‘Alzheimerized senile dementia'. This finding lead to a unifying thesis, so that parenchymatous dementias were usually referred to as ‘senile dementia of Alzheimer type'.
  2. Studies of lesions of senile dementia and non-age-associated illnesses led to the abandonment of the idea that senile dementia was a severe form of normal ageing (25) and to the view that the lesions of parenchymatous dementias were not due to ageing. In 1970, Sourander and Sjögren (26) described a series of cases in which characteristic lesions of senile dementia were present. Their findings led to the idea of dementia as a syndrome produced by more than one underlying condition. As a consequence, the terms reversible and irreversible dementias appeared, together with tables of conditions that could produce chronic brain disorder.

Gradually another approach, based on understanding of the functioning of the nervous system, was considered, which made the study of dementia as a syndrome more comprehensible. Barcia (27) suggested that the concept of dementia should be based on the organization of the nervous system and that two concepts are important: the functional levels of the nervous system, as proposed by Jackson, (28) and the idea of specialization of the nervous system.

The first of these ideas led to the differentiation of cortical and subcortical dementias. However, a description which better coincides with Jackson's concepts differentiates three types of dementias: cortical, axial, and dementias due to diseases of the basal ganglia and extrapyramidal diseases.

The concept of the specialization of the nervous system leads to the distinction between ‘left brain and right brain', ‘anterior brain' responsible for mental processes, and ‘posterior brain' responsible for perception of the external and internal worlds.

An alternative scheme proposed by the Swedish Consensus (29) refers to three types of degenerative disease of the nervous system: frontotemporal, temporoparietal, and subcortical dementias.

Subcortical dementia was described by Albert et al. (30) and McHugh and Folstein (31) in relation to progressive supranuclear paralysis and Huntington's disease. In fact the term had already been used by von Stocker (32) in 1932 (subcortical Demenz). The clinical features correspond closely to those described by Wilson (33) in his account of hepatolenticular degeneration, and to those of the ‘bradyphrenia' of Naville (34) and of the dementia of the cerebral trunk (Hirnstammdemenz) reported by Sterz. (35) Sterz probably carried out the best study of this condition prior to 1974 when American authors introduced the term ‘subcortical dementia' and encouraged research to differentiate it from cortical dementia.

Cortical and subcortical dementias can be distinguished satisfactorily on anatomical grounds, but it is interesting that they are characterized by different clinical syndromes. Subcortical dementia can be subdivided into an axial syndrome, of which the main model is Korsakoff's syndrome, and a syndrome arising from lesions of the basal ganglia.

Cortical dementias

Cortical dementias are classified into frontotemporal dementias, temporoparietal dementias, and occipital dementias.

Frontotemporal dementias

Frontotemporal dementias are characterized not by a loss of function but by an inability to act. There is apathy, indifference, or in contrast lack of inhibition, and the patient fails to make plans to change from one activity to another, and to select the actions needed to solve a problem. This syndrome is not necessarily due to lesions of the frontal lobe, but may arise from lesions in the frontal projection system and from other subcortical diseases, including Korsakoff's syndrome.

Cummings (37) recognized three complex syndromes of the frontal lobe which he ascribed to prefrontal circuits:

  1. prefrontal dorsolateral syndrome which is characterized by neuropsychological deficits, including decreased verbal fluency, decreased ability to plan, anomalous motor programming, failures of learning and recovery of memories, and inability to solve problems;
  2. orbitofrontal syndrome which is characterized by lack of inhibition, irritability, and alterations of initiative and introspection depending on environmental cues; (38)
  3. anterior cingulate syndrome which is characterized by apathy and reduction of initiative, which in extreme cases manifests as akinetic mutism.
Temporoparietal dementia

Temporoparietal dementia includes Alzheimer's disease. In a series of studies, the Geneva School (39,40) have found that this disease is characterized by a disintegration of psychological functions which occurs in the opposite order to that in which they are acquired in Piaget's scheme. Disintegration starts with abstract functions and extends to concrete functions and finally to a ‘preoperative' level.

When patients are examined with a test battery proposed by these authors, it is possible to diagnose which psychopathological functions are damaged. For example, in a test using different-sized cubes, in which the smaller ones are heavier, patients with Alzheimer's disease generally identify the larger cubes as heavier, indicating a loss in the ability to differentiate volume and weight. In another test an object is brought closer to the patient from behind so that it can be seen in a mirror in front of the patient. When Alzheimer's patients are asked to takethe object, they are unable to do so because they have lost spatial representation. Findings such as these are of interest not only because they increase understanding of cerebral organization but also because they allow Alzheimer's dementia to be differentiated from pseudodementia.

Occipital dementia

Occipital dementia was first reported in 1902 by Dide and Bocazzo, (41) who described a Korsakoff syndrome produced by bilateral occipital injuries. In 1912, Dide and Perzet (42) described the occipital syndrome as characterized by oblivion, fantasizing, temporospatial disorientation, reduction of the visual field, and psychic blindness. This condition is present in a large proportion of patients with occipital tumours: 24 per cent according to Delay (43) and up to 60 per cent according to Allen. (44) The condition is superimposed on the Korsakoff syndrome (see below) and is produced by symmetrical focal lesions in the middle of occipital lobe and lingual gyri. There is destruction of grey and white matter, although not beyond the tapetum and the occipital horn of the ventricles. Although it is a cortical dementia, this condition is related to the diencephalic syndromes. (45)

Axial and diencephalic dementias

The Korsakoff syndrome is the prototype of the axial or diencephalic dementias. It is characterized by anterograde and retrograde amnesia, temporospatial disorientation, confabulation, false recognition, and occasionally euphoria. The main lesions are localized to the structures of the Papez system, especially the mamillary bodies, although there is always some frontal involvement. The amnesia is anterograde as well as retrograde, and it is reported that patients lack insight into it. (46) However, Shimamura and Squire (47) have reported that most patients with Korsakoff syndrome are aware of their amnesia and of their failures on tests. There is dissociation between explicit and implicit memories. The Korsakoff patient can learn, but is unable to remember the learning process, a fact described by Calparede in 1911. (48) For example, if a Korsakoff patient is pricked while shaking hands, he learns not to shake hands again although he is unable to explain why. The Korsakoff syndrome is described in an article about amnesic syndromes.

Another diencephalic syndrome is diencephalic vascular dementia, a condition recognized recently as a result of the study of cerebral lessions using modern radiological techniques. (49,50)

There are other subcortical dementias associated with extrapyramidal syndromes. Although most of their characteristics had been known for a long time, the studies of progressive supranuclear paralysis by Albert et al. (30) and of Huntington's disease by McHugh and Folstein (31) led to increased interest in these disorders and to recognition of the need to differentiate subcortical from cortical dementias.

In general, instrumental processes are preserved, and cognitive failures are generally referred to disturbances of their onset. In Parkinson's disease the motor or visospatial perception is disturbed and there is difficulty in changing attitude or orientation. (51) Dementia in Parkinson's disease is described further here: Dementia in Parkinson's disease.

These forms of subcortical dementia are mainly related to abnormalities in the striate nuclei and the structures commonly involved with them, including the substantia nigra, the subthalamic nuclei, the septal area, the locus coeruleus, and the deep hemispheric tracts of the white matter. These structures have important connections with the limbic system and with the cerebral cortex, especially the frontal lobes. (37,52,53)

These circuits are the motor circuit, the oculomotor circuit, the dorsolateral prefrontal circuit, the lateral orbitofrontal circuit, and the anterior angled circuit. The main neurotransmitters involved are dopamine, noradrenaline (norepinephrine), serotonin, acetylcholine, and g-aminobutyric acid (GABA), which are the mediators for alterations of mood, motivation, movement, and intellectual function in subcortical dementias.


The term ‘dementia' refers to a large number of conditions, specific symptom patterns, and psychopathological changes. To simplify, there is disorganization of functions in senile dementia of the Alzheimer type, an alteration in the programming of tasks in frontal dementia, an alteration in the temporal organization of experiences in Korsakoff's syndrome, an alteration of perceptive and psychomotor tasks in diencephalic dementia, and an alteration in spatial structures in extrapyramidal subcortical dementia.


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