A study of confabulation

Relationship between confabulation and measures of memory and executive function

Confabulation has traditionally been attributed to a combination of memory impairment and executive dysfunction, but recent models propose that confabulation can result from executive dysfunction alone. One hundred and ten patients with diverse neurologic and psychiatric diagnoses were subdivided into high-, low-, and non-confabulator groups based upon the ratio of confabulations to total responses produced during story recall. Consistent with the combined deficit model, high-confabulators performed significantly worse than the low- and non-confabulators on measures of memory and measures of executive function that assess sustained attention, mental tracking, and set-shifting ability. However, there were no differences between groups on measures of problem-solving, concept formation, and verbal fluency, suggesting a dissociation in executive functions that contribute to confabulation.

Memory without context: amnesia with confabulations after infarction of the right capsular genu

OBJECTIVE

To explore the mechanism of an amnesia marked by confabulations and lack of insight in a patient with an infarct of the right inferior capsular genu. The confabulations could mostly be traced back to earlier events, indicating that the memory disorder ensued from an inability to store the temporal and spatial context of information acquisition rather than a failure to store new information.

METHODS

To test the patient's ability to store the context of information acquisition, two experiments were composed in which she was asked to decide when or where she had learned the words from two word lists presented at different points in time or in different rooms. To test her ability to store new information, two continuous recognition tests with novel non-words and nonsense designs were used. Recognition of these stimuli was assumed to be independent of the context of acquisition because the patient could not have an a priori sense of familiarity with them.

RESULTS

The patient performed at chance in the experiments probing knowledge of the context of information acquisition, although she recognised the presented words almost as well as the controls. By contrast, her performance was normal in the recognition tests with non-words and nonsense designs.

CONCLUSION

These findings indicate that the patient's amnesia was based on an inability to store the context of information acquisition rather than the information itself. Based on an analysis of her lesion, which disconnected the thalamus from the orbitofrontal cortex and the amygdala, and considering the similarities between her disorder, Wernicke-Korsakoff syndrome, and the amnesia after orbitofrontal lesions, it is proposed that contextual amnesia results from interruption of the loop connecting the amygdala, the dorsomedial nucleus, and the orbitofrontal cortex.

Confabulation and the control of recollection

It is argued that current models of memory do not adequately account for the confabulations that are found in the recall of certain neurological patients. A model of the relation between control processes and memory involved in recalling autobiographical episodes is put forward. It is based on detailed analysis of the protocols of healthy volunteers' autobiographical recollections of recent everyday events. It is held that damage to different components of the model fits with the different patterns of performance found in confabulators, and examples of the errors that confabulators make are discussed in terms of those made by normal subjects.

Neuropsychiatric and neuropsychological correlates of delusions in Alzheimer's disease

We examined the prevalence, phenomenology, and clinical correlates of delusions in a consecutive series of 103 patients with probable Alzheimer's disease (AD). Patients were examined with the Present State Exam and the Dementia-Psychosis Scale. Twenty-one patients (20%) met DSM-III-R criteria for a delusional disorder. The most frequent delusion type was paranoid (71%), followed by hypochondriacal (67%), the Capgras syndrome (29%), house misidentification (29%), and grandiose delusions (29%). Out of the 21 AD patients with delusions, 76% had three or more different types of delusions simultaneously. The frequency of delusions was not significantly associated with age, education, or age at dementia onset, and the type and severity of cognitive impairments was similar for AD patients with and without delusions. However, AD patients with delusions had significantly higher mania and anosognosia scores.

Neuropsychological and neuroanatomical correlates of confabulation

In the present exploratory investigation we report nine confabulatory patients of comparable age, education, and general level of intelligence in the acute epoch of recovery after rupture and clipping of ACoA aneurysms. Five of the nine cases had "spontaneous" confabulation, severe anterograde amnesia, markedly poor attentional and executive functions, and denial of illness. These patients all had multiple lesions that involved basal forebrain, ventral frontal lobe, and striatum. The other four patients manifested only "momentary" or "provoked" confabulations. These patients also had severe anterograde amnesia but showed relatively mild deficits in executive functions. These patients had lesions restricted to the basal forebrain except for one who had additional orbital frontal damage. Analysis of these two groups of confabulatory patients suggests that there is a common profile of deficits and anatomic foundation associated with confabulation; "spontaneous" confabulation appears to require extensive, simultaneous disruption of medial basal forebrain and frontal cognitive systems resulting in profound executive and memory deficits, whereas more limited lesions to the basal forebrain or orbital frontal cortex will result in "transient" or "provoked" confabulatory responses and a more restricted profile of cognitive deficits.

Aneurysm of the anterior communicating artery: a review of neuroanatomical and neuropsychological sequelae

For over 100 years, the study of amnesia in humans has been limited primarily to subjects with either diencephalic or mesial temporal lobe lesions. However, over the last 30 years, it has been reported that individuals who survived aneurysms of the anterior communicating artery (ACoA) often displayed an amnestic syndrome, despite the fact that diencephalic and mesial temporal structures were intact. This article presents a comprehensive review of the ACoA literature concerning the neurobehavioral and neuroanatomical substrates of what has been termed the "ACoA syndrome". Various theoretical models regarding the neural substrates of amnesia are discussed. Possible directions for future research are outlined.

False recognition and misidentification of faces following right hemisphere damage

We report two patients who, following massive damage to the right hemisphere, showed a striking tendency for false recognition and misidentification of faces. Neuropsychological investigations revealed that excessive reliance on a feature-based left hemisphere strategy in face processing, combined with an inability to evaluate critically the output generated by the dysfunctional face recognition system, played a major role in the recognition errors and misidentifications. Our findings suggest that the feature based left hemisphere face recognition system is potentially error-prone, presumably because component facial features are likely to be shared among several different individuals, and that reliable recognition and identification of faces is critically dependent upon the efficient processing of configurational facial information by the right hemisphere. We propose further that decision making and monitoring functions relevant to the operations of the face recognition system are primarily lateralized to the right frontal lobe.

Different patterns of confabulation

In this study we investigated the amnesic-confabulatory condition of two patients, M.B. and S.D., exhibiting different patterns of confabulation. Neuropsychological examination showed in M.B. a normal intellectual efficiency and a selective deficit of episodic memory, whereas S.D. was impaired in tests of intellectual efficiency, episodic memory, semantic knowledge and frontal functions. The relation of confabulation to retrieval conditions and the degree of impairment of the semantic memory system was investigated with a set of questions involving the retrieval of various kinds of information. In M.B. confabulation was restricted to episodic memory tasks, whereas in S.D. it also affected the retrieval of semantic information. S.D.'s confabulatory reports were 'semantically anomalous', whereas the semantic structure of M.B.'s confabulations was appropriate. Further investigation using the encoding specificity paradigm showed an interaction of encoding/retrieval conditions in M.B. but not in S.D. This pattern of results is discussed in terms of a different level of disruption of processes that normally monitor the retrieval of information. It is further argued that the confabulation content must be considered in terms of its semantic structure and relies on the level of integrity of semantic knowledge.

Unawareness of illness and neuropsychological performance in chronic schizophrenia

This research attempts to explore empirically the relationship between lack of awareness of illness and neuropsychological performance in a group of chronic schizophrenic subjects. Thirty one chronic schizophrenics were administered the recently developed Scale to Assess Unawareness of Mental Disorder (SUMD) and 3 neuropsychological tests that have demonstrated ability to assess frontal lobe performance: the Wisconsin Card Sorting Test (WCST, Verbal Fluency Test and Trials A and B. The number of categories completed and the percent perseverative responses on the WCST were found to significantly correlate with lack of illness awareness as measured by the SUMD. These two WCST variables were also able to significantly discriminate between subjects of high versus low awareness. A discriminant function analysis found that a linear combination of WCST percent perseverative responses and symptom severity could successfully categorize 84% of the aware versus unaware subjects. These results are taken to support the hypothesis that at least in some of its manifestations lack of awareness among chronic schizophrenics has an organic etiology probably mediated by the frontal lobes.

Confabulation in Alzheimer's disease

Confabulation is present when memory is disturbed, but does it occur in Alzheimer's disease (AD) where memory abnormalities are often severe? In this study, confabulation was assessed prospectively in 26 AD patients and 15 normal elderly (NE) controls using a neuropsychological battery specifically designed to assess different types of memory errors. The results indicated that the AD group made significantly more verbal intrusions than the NE group. These findings provide evidence for the feasibility of eliciting confabulatory-type behavior during clinical assessment and support previous reports which have documented verbal intrusions as a common accompaniment of the memory impairment manifested by AD patients.

Confabulation following aneurysm of the anterior communicating artery

Nine subjects with aneurysms of the anterior communicating artery (ACoA) and 17 subjects with other intracranial hemorrhages (ICH) were evaluated for confabulatory responses under two naturally occurring conditions: (1) when subjects were not oriented to person, place, month and year, (2) when subjects were fully oriented. Confabulation was observed in all 9 of ACoA patients both during disoriented and oriented periods. In contrast, 7/17 of the other ICH patients showed signs of confabulation while disoriented, whereas only one continued to display confabulatory tendencies while fully oriented. Confabulation was more severe in the ACoA group. These data suggest that the confabulation observed in the other ICH group may be secondary to an acute confusional state while the prolonged confabulation in ACoA patients may be a manifestation of a more primary cerebral disorder.

Autobiographical memory loss and confabulation in Korsakoff's syndrome: a case report

A patient with Korsakoff's syndrome is presented, who showed a selective loss of Autobiographical Memory along with a preserved Semantic Memory. Confabulations were a prominent feature. They only involved Autobiographical Memory and were persistent in time and consistent in content. The implications of these findings for understanding the nature of Autobiographical Memory impairment are discussed.

Autobiographical and text recall in the elderly: an investigation of a processing resource deficit

This study examined different explanations of age-related impairments in recall of details from text and autobiographical events. An interpretation of Central Executive Capacity Deficit was supported and explored further. This suggests that details are more demanding of capacity than main points, and that ability to appropriately integrate details with context is likely to be impaired. An implication was that irrelevant and false information may occur, and this was supported in both autobiographical and text recall. The effects were then examined in relation to various measures of ability. The aim was to determine whether declining capacity (as indicated by "Fluid Intelligence" measures) predicted ability to recall in a detailed manner. The difficulty with details was predicted independently by chronological age and by measures of fluid (e.g. AH4 intelligence test) and the more crystallized verbal ability (Mill Hill vocabulary test). Only a measure of the specificity of autobiographical recall was predicted solely by measures of fluid intelligence. Decreased specificity was not a result of faster decay of memory for details, as there was little difference across the lifespan. The resource deficit appears to affect retrieval and appropriate implementation of detail. It was concluded that lower-ability elderly subjects have decreased Central Executive resources, which leads to poor (often inappropriate) integration of details with central thematic points, but that subjects' verbal ability, which does not decline with age, still has an important part to play.

[Current concept of pseudodementia]

The concept of pseudodementia was coined in the late XIXth century to refer to a syndrome mimicking dementia, but without underlying neurological lesions. Depressive disorders represent the main etiological factor and may present under two different forms, either "depressive cognitive disorders", or the more severe feature of "Wernicke's pseudodementia". The main issue remains diagnosing pseudodementia form organic dementia, especially from cortical degenerations of the Alzheimer type. Thus, the recognition of this clinical syndrome represents an alternative to the diagnosis of dementia which may lead to earlier and more effective psychiatric treatment. Recently, diagnostic criteria have been proposed to facilitate this distinction. Such criteria include clinical history, neuropsychological features, biological findings (dexamethasone suppression test and plasma MHPG) and electroencephalographic sleep studies. Finally, from a theoretical point of neurological conception of depression as well as for current hypotheses on the relationship of this last one with dementia.

Brain white-matter lesions and psychosis

In a prospective study of late-life onset psychosis, five of the first 27 patients studied had extensive white-matter lesions demonstrated by MRI and/or CT. None of 60 age-matched psychiatrically healthy controls demonstrated such lesions. All five patients had a mild dementia and a frontal behavioural syndrome. In addition, every patient performed poorly on neuropsychological tests of frontal function. Dysfunction of the frontal cortex associated with white-matter lesions appears to contribute to the clinical picture of some cases of late-life psychosis.

Unawareness of deficits in neuropsychological syndromes

Damage to different regions of the brain can cause a variety of neuropsychological deficits, including specific disturbances of language, memory, perception and motor function. A significant number of brain-damaged patients are unaware of their deficits, even when they are profound and have debilitating effects on patients' performance. This article reviews clinical observations and experimental investigations concerning unawareness of deficits, considers methodological issues, and critically evaluates different interpretations of the phenomenon. An integrative theoretical framework is proposed to account for unawareness of deficits in diverse neuropsychological syndromes. Possible directions for future research are outlined.

Confabulation in aphasia

We describe a brain-damaged patient who produced two distinctive forms of confabulation, typical and atypical (aphasic), both of which were associated with perseveration, poor self-monitoring, and denial of deficit. We propose that the typical confabulations are triggered by gaps in memory for the period surrounding the onset of his illness, while the aphasic (fantastic) confabulations are triggered by gaps in semantic representation. These observations suggest that confabulations may comprise a portion of the language deficit in patients with other varieties of fluent aphasia.

Confabulation and delusional denial: frontal lobe and lateralized influences

Various forms of confabulation, including denial of illness (e.g., paralysis, blindness), and conditions that often give rise to these disorders, such as cerebral disconnection, disinhibitory states, incomplete information reception, and "gap filling" are discussed. On the basis of clinical observation and a review of a number of studies, it appears that confabulatory states frequently are associated with cerebral damage that involves the right hemisphere, notably, the frontal (often bilaterally) and parietal lobes--areas intimately involved in arousal, attention, information regulation, and integration. With certain forms of injury, initially there appear disturbances in the organization, integration, and assimilation of ideas and associations, such that large gaps appear in the information transmitted to and received by the language axis of the left hemisphere. It is argued that in these instances, the language areas act so as to fill these "gaps" with information that, although inappropriate, is linked in some manner to the fragments received. In contrast, frontal lobe damage sometimes results in gross disinhibition and cortical overresponsiveness and, thus, speech release due to the flooding of the language axis (and other cortical regions) with tangential, fantastical, and grandiose associations. Other forms of confabulation also are reviewed briefly.

Presbyophrenia: clinical aspects

Fifteen cases meeting the diagnostic criteria for presbyophrenia are reported and compared with a control sample of patients suffering from dementia. The presbyophrenic patients exhibited more elevated mood, more hyperactivity, more disorientation, and had lower information scores than the controls. Traditional explanations of 'presbyophrenic behaviour' such as delirium, pathoplastic effect of personality, or superimposed cerebrovascular disease are not adequate. Instead, presbyophrenia may constitute a sub-type of dementia characterised by severe atrophy of the locus coeruleus, marked impairment of noradrenergic transmission, and uninhibited behaviour.

"I don't know" responses in elderly depressives and in dementia

"I don't know" responses were recorded during administration of the Mini-Mental State Examination in elderly patients with primary degenerative dementia and primary major depression. More "I don't know" responses were given by patients with degenerative dementia; however, demented patients did not differ overall from depressives in the proportion of Not Correct responses consisting of "I don't know" responses. These responses were positively correlated with age and with Hollingshead education and social class scores in depressives but not in demented patients. A higher proportion of Not Correct responses consisting of "I don't know" responses needs to be demonstrated in depressive pseudomentia than in degenerative dementia if this clinical sign is to be used in helping to differentiate the two disorders.