Intrusions and provoked and spontaneous confabulations on memory tests in Korsakoff’s syndrome

Introduction: Intrusions on verbal memory tests have been used as an index for clinical confabulation. Severe memory impairments in combination with executive dysfunction have been suggested to be the underlying mechanism of confabulation, but to date, this relation is unclear. The aim of this study was (a) to examine the relation between (different types of) intrusions and confabulations in a large sample of confabulating patients with Korsakoff’s syndrome (KS) and (b) to investigate whether different measures of executive functioning and memory performance are related to provoked and spontaneous confabulation. Method: The Dutch version of the California Verbal Learning Test (CVLT) and various executive function and memory tests were administered to a group of 51 confabulating patients with KS. Professional caregivers rated the severity of provoked and spontaneous confabulation behavior of the patients using the Nijmegen–Venray Confabulation List–20 (NVCL–20). Results: The total number of intrusions on the CVLT was not related to either provoked or spontaneous confabulation scores. None of the CVLT intrusion scores correlated significantly with any of the confabulation scores, but we did find small-to-medium, positive correlations between unrelated intrusions and both provoked confabulations and spontaneous confabulation. Provoked confabulation behavior was associated with executive dysfunction and poorer memory performances. Spontaneous confabulation was not related to performance on measures of executive function and memory. Conclusions: The total number of intrusions on verbal memory tests and clinical confabulations appear to be different phenomena. Only unrelated intrusions produced on the CVLT might possibly be related to confabulations. The production of provoked, but not spontaneous, confabulation is associated with executive dysfunction and memory deficits.     

Assessment of Confabulation in Patients with Alcohol-Related Cognitive Disorders: The Nijmegen–Venray Confabulation List (NVCL-20)

Objective: Even though the first awareness of confabulations is often based on observations, only questionnaires and structured interviews quantifying provoked confabulations are available. So far, no tools have been developed to measure spontaneous confabulation. This study describes and validates an observation scale for quantifying confabulation behavior, including spontaneous confabulations, in clinical practice. Method: An observation scale consisting of 20 items was developed, the Nijmegen–Venray Confabulation List-20 (NVCL-20). This scale covers spontaneous confabulation, provoked confabulation, and memory and orientation. Professional caregivers completed the NVCL-20 for 28 Korsakoff (KS) patients and 24 cognitively impaired chronic alcoholics (ALC). Their ratings were related to the Dalla Barba Confabulation Battery (DBCB), Provoked Confabulation Test (PCT), and standard neuropsychological tests. Results: The categories of the NVCL-20 have “good” to “excellent” internal consistency and inter-rater agreement. The KS patients confabulated more (both spontaneously and provoked), and more memory and orientation problems were observed. Correlations with neuropsychological test scores showed that confabulations were associated with memory deficits, but not with intrusions or tests of executive dysfunction. Conclusions: The NVCL-20 is the first instrument that includes items addressing spontaneous confabulation. Administration is reliable, valid and feasible in clinical practice, making it a useful addition to existing confabulating measures.     

Forms of confabulation: Dissociations and associations

Confabulation denotes the emergence of memories of experiences and events which never took place. Whether there are distinct forms with distinct mechanisms is still debated. In this study, we explored 4 forms of confabulation and their mechanisms in 29 amnesic patients. Patients performed tests of explicit memory, executive functions, and two test of orbitofrontal reality filtering (memory selection and extinction capacity in a reversal learning task) previously shown to be strongly associated with confabulations that patients act upon and disorientation. Results indicated the following associations: (1) Intrusions in a verbal memory test (simple provoked confabulations) dissociated from all other forms of confabulation and were not associated with any specific cognitive measure. (2) Momentary confabulations, defined as confabulatory responses to questions and measured with a confabulation questionnaire, were associated with impaired mental flexibility, a tendency to fill gaps in memory, and with one measure of reality filtering. Momentary confabulations, therefore, may emanate from diverse causes. (3) Behaviourally spontaneous confabulation, characterized by confabulations that the patients act upon and disorientation, was strongly associated with failure in the two reality filtering tasks. Behaviourally spontaneous confabulation may be seen as a specific instance of momentary confabulations with a distinct mechanism. (4) A patient producing fantastic confabulations with nonsensical, illogical content had wide-spread cognitive dysfunction and failed in the reality filtering tasks. The results support the presence of truly or partially dissociable types of confabulation with different mechanisms.     

Recovery from spontaneous confabulations parallels recovery of temporal confusion in memory

BACKGROUND: In previous studies, the authors found that patients with spontaneous confabulation differ from those with nonconfabulating amnesia by 1) temporal context confusion (TCC) in memory based on an inability to suppress intrusions of currently irrelevant memory traces into ongoing thinking; and 2) lesions involving the orbitofrontal cortex, basal forebrain, or amygdala and perirhinal cortex. OBJECTIVES: To study the long-term clinical course of spontaneous confabulations, determine whether TCC in memory also parallels the clinical course of spontaneous confabulations, and study the impact of lesion site on clinical course. METHODS: Eight patients with spontaneous confabulation were re-examined 18 months after onset. Tests of memory and executive functioning and measurement of TCC in memory were again applied. MRI according to a standard protocol was performed to determine areas of permanent damage. RESULTS: Seven patients eventually stopped confabulating. TCC, but not common memory or executive tests, precisely paralleled the course of spontaneous confabulations. Patients with isolated, less extensive, orbitofrontal lesions stopped confabulating first and had the best neuropsychological outcome. Patients with basal forebrain lesions continued to confabulate for several months and remained amnesic. One patient with extensive orbitofrontal damage and perirhinal cortex damage continues to confabulate after more than 3 years, continuing to confuse memory traces. CONCLUSIONS: Temporal context confusion in memory is not only the sole feature reliably separating patients with spontaneous confabulation from those with nonconfabulating amnesia in the acute stage, it is also the only feature that precisely parallels the clinical course of spontaneous confabulations. Most patients eventually stop confabulating but duration of confabulations depends on the lesion site.     

Disturbance of time orientation,attention, and verbal memory in amnesic patients with confabulation

Confabulation is often observed in amnesic patients after brain damage. However, evidence regarding the relationship between confabulation and other neuropsychological functions is scarce. In addition, previous studies have proposed two possibilities of the relationship between confabulation and false memory, in which patients with confabulation are likely to retrieve false memories, or confabulations are relatively independent of false memories. The present study investigated how confabulation is related to various cognitive functions, including orientation, attention, frontal lobe function, memory, and mental status, and to false memories, as assessed by the Deese–Roediger–Mcdermott (DRM) paradigm. Patients with organic amnesia participated, and confabulations were evaluated using the Confabulation Battery. Amnestic patients were classified into two groups: confabulating (CP) and nonconfabulating patients (NCP). The CP group was significantly impaired in time orientation, attention, and verbal memory, compared to the NCP group and age-matched healthy controls (HC). Results of the DRM paradigm revealed no significant difference in false memory retrieval induced by critical lures across CP, NCP, and HC groups. Confabulating responses in organic amnesia could be in part induced by disturbance of time consciousness and attention control in severe impairment of verbal memories, and confabulation and false memory could be modulated by different cognitive systems.     

Confabulation: damage to a specific inferior medial prefrontal system

Confabulation, the pathological production of false memories, occurs following a variety of aetiologies involving the frontal lobes, and is frequently held to be underpinned by combined memory and executive deficits. However, the critical frontal regions and specific cognitive deficits involved are unclear. Studies in amnesic patients have associated confabulation with damage to the orbital and ventromedial prefrontal cortices. However, neuroimaging studies have associated memory-control processes which are assumed to underlie confabulation with the right lateral prefrontal cortex. We used a confabulation battery to investigate the occurrence and localisation of confabulation in an unselected series of 38 patients with focal frontal lesions. Twelve patients with posterior lesions and 50 healthy controls were included for comparison. Significantly higher levels of confabulation were found in the frontal group, confirming previous reports. More detailed grouping according to lesion location within the frontal lobe revealed that patients with orbital, medial and left lateral damage confabulated in response to questions probing personal episodic memory (PEM). Patients with orbital, medial and right lateral damage confabulated in response to questions probing orientation to time (OT). Performance-led analysis revealed that all patients who produced a total number of confabulations outside the normal range had a lesion affecting either the orbital region or inferior portion of the anterior cingulate. These data provide striking evidence that the critical deficit for confabulation has its anatomical location in the inferior medial frontal lobe. Performance on tests of memory and executive functioning showed considerable variability. Although a degree of memory impairment does seem necessary, performance on traditional executive tests is less helpful in explaining confabulation.     

Confabulation: a spontaneous and fantastic review

Confabulation can be of two types: provoked or spontaneous. The former is the more common and can occur on challenge to an amnesic patient's memory. Spontaneous confabulation involves an unprovoked outpouring of unbelievable autobiographical claims. The purpose of the present paper is to synthesize the current literature on confabulation for the use of treating clinicians. There is a focus on the spontaneous form, which is less common, but more memorable when encountered. In this paper the history, phenomenology, incidence, anatomical underpinnings and theoretical mechanisms of spontaneous confabulations will be reviewed, and then the paper will conclude by addressing prognostic and treatment issues. A systematic literature review of electronic databases was conducted to identify the key articles, reviews and books that have shaped the understanding of spontaneous confabulation.     

Two types of confabulation.

Examples of confabulation in Korsakoff patients, Alzheimer-type dementing patients, and healthy subjects are discussed. It is argued that there may be two types of confabulation: spontaneous confabulation, which may result from the superimposition of frontal dysfunction on an organic amnesia, and provoked confabulation, which may reflect a normal response to a faulty memory. In the present study, instances of provoked confabulation, given by Korsakoff and Alzheimer patients in story recall, were compared with those produced by healthy subjects at a prolonged retention interval.     

Confabulation and memory in patients with Alzheimer's disease

Confabulation occurs in many brain diseases and concomitant with various cognitive disturbances. The purpose of the present study was to describe semantic features of confabulation and to investigate the relationship between these features and aspects of memory in Alzheimer's disease (AD). A group of 15 AD patients were asked questions aiming to evoke confabulations. The answers were analyzed with focus on semantic remoteness to the target answers into four different categories that made it possible to study the genesis of confabulation. Cognitive tests measuring episodic and semantic memory, priming as well as global cognitive functioning were performed, and the results were related to semantic features of confabulation. Results showed that semantic remoteness to the target answers was positively related to poor performance on Mini Mental State Examination but not to item recall, word fluency, or priming. It appears that difficulties with retrieval of recent autobiographical memories may have resulted in substitution of correct information with remote autobiographical memories, that is primary dysdeictic confabulations.     

Spontaneous confabulation, reality monitoring, and the limbic system — a review

Patients with anterior limbic damage may present a distinct syndrome, spontaneous confabulation: they fail in common memory tests, act on the basis of previous habits rather than currently relevant memories, produce confabulations composed of elements of past true events, are disorientated, and are absolutely convinced about the veracity of their perceived reality. Spontaneous confabulation is independent of other false memories, such as, provoked confabulations or illusory recognition. Studies showed that spontaneous confabulators fail to suppress (inactivate) evoked memories that do not pertain to ongoing reality. Rehabilitation differs from other memory failures. Prognosis depends on the lesion site, but recovery is always associated with recovery of this suppression capacity. Lesions typically involve the posterior medial orbitofrontal cortex or its connections in the basal forebrain. Imaging and evoked potential studies in healthy subjects support the idea that the anterior limbic system provides a reality monitoring mechanism which selects memories of current relevance by suppressing (inactivating) currently irrelevant memories. This mechanism appears to adjust the cortical representation of activated memories before their content is recognised and consolidated. Comparison with animal studies suggests that human reality monitoring is a property of the brain’s reward system.     

Isolated prospective confabulation in Wernicke–Korsakoff syndrome: a case for reality filtering

A 57-year-old man suffered severe amnesia and disorientation, accompanied by content-specific confabulation, due to an alcoholic Wernicke–Korsakoff syndrome. For months, he was deeply concerned about a single obligation that he thought he had to respond to, but which he had already assumed 20 years previously. This monothematic, prospective confabulation was associated with failures of reality filtering as previously documented in behaviorally spontaneous confabulation and disorientation: the patient failed to suppress the interference of currently irrelevant memories and to abandon anticipations that were no longer valid (impaired extinction capacity). Magnetic resonance imaging showed damage to the mamillary bodies and the dorsomedial thalamic nucleus. Positron emission tomography (FDG-PET) showed extended orbitofrontal hypometabolism. We suggest that isolated prospective confabulation shares the core feature (acts and thoughts based on currently irrelevant memory), mechanism (failure of reality filtering), and anatomical basis (orbitofrontal dysfunction) with behaviorally spontaneous confabulations.     

Confabulation, but not executive dysfunction discriminate AD from frontotemporal dementia

We examined confabulation and performance on frontal/executive tasks in Alzheimer's disease (AD) patients and patients with a diagnosis of probable frontotemporal dementia (FTD). Twenty-two patients with probable AD, 10 patients with probable FTD and 32 normal control subjects entered the study. Executive functions were assessed with the Modified Card Sorting test; a verbal fluency test; the Cognitive Estimation test; and the Stroop test. Confabulations were assessed with a modified version of the Confabulation Battery. The Confabulation Battery included 10 questions tapping each of the following domains: Episodic Memory (memories of personal past episodes), Semantic Memory (knowledge of famous facts and famous people), and Personal Future (personal plans). The results revealed that both AD patients and FTD patients were clearly and equally impaired on tests of executive functions. Both patients' groups confabulated across the three tasks of the Confabulation Battery, but FTD patients confabulated significantly more than AD patients on Episodic Memory and Personal Future. The results failed to provide any evidence of a correlation between the performance on frontal/executive tasks and the tendency to produce confabulatory reports. According to our results, confabulation, more than a deficit of frontal/executive functions, discriminate between AD and FTD. Therefore, screening for confabulation and, possibly, for other types of memory distortions may constitute a useful additional clinical tool in order to discriminate AD from FTD.     

The mechanisms of confabulation in schizophrenia

Abstract

Confabulation is a newly described abnormality in schizophrenia, but its mechanisms are as yet unclear. Here we describe a detailed investigation of three cases who were previously identified as confabulators. The patients were administered experimental tasks as well as standard neuropsychological tests of memory and executive function in an attempt to elucidate the possible mechanisms. It was found that the severity of cognitive impairment reflects the severity of confabulation, but that memory impairment is neither necessary nor sufficient to account for confabulation. This suggests that confabulation and memory have different substrates. Within the spectrum of executive deficits, impairments in response suppression and response monitoring, but not planning or generation, were consistently associated with confabulation. It is suggested that the stages of this form of confabulation are unlike those previously reported in other patients since faults occur at both input and output. At the input stage, narrative material is encoded in a disorganized manner, while at the output stage this disorganization is compounded by faulty editing processes. This observation highlights the importance of the interaction between encoding and retrieval in schizophrenia confabulation. Impaired plausibility judgements and confabulation are more likely to occur with complex material which requires organization at the input stage.     

Self-enhancing Confabulation: Revisiting the Motivational Hypothesis

We report a patient who developed spontaneous confabulation following surgical clipping of an anterior communicating artery aneurysm. An autobiographical memory test was used to measure the emotional valence of the patient's self-representations in true and false memories. We found that his confabulations included significantly more positive self-representations than his true memories and that the overall valence of his confabulations was more positive than that of his true memories and than that of the memories of five healthy control participants of the same age and educational attainment. It is proposed that while cognitive dysfunction may explain how confabulations are formed, emotional factors may explain which specific confabulations are constructed.     

Provoked confabulations in Alzheimer's disease

Confabulation in Alzheimer's disease (AD) has been the subject of limited investigation. When studied, the phenomenon has been found to share characteristics with memory distortions produced by neurologically intact individuals. Previous studies that have investigated confabulation in AD have failed to take into account the characteristics of the disease and the presence of confabulations in the retrieval of recent autobiographical memory (ABM). The aim of this study was to develop a test that could investigate the tendency to confabulate in recent autobiographical memory that was specifically created for eliciting confabulatory behaviours in patients with AD. Four experiments have been carried out. In Experiment 1, AD patients who have yet to show confabulatory behaviour were compared to elderly adults. The results revealed that AD patients produced significantly more confabulations on the new test compared to elderly adults. Experiment 2 investigated if the results of the initial experiment were due to AD patients having limited working memory capacity that would lead to difficulties in performing the test compared with elderly adults as AD patients would be in a condition of memory overload. The results showed that even when compared with the performance of elderly individuals under memory overload condition, AD patients still produced more confabulations than elderly adults. Using a correlational approach Experiments 3 and 4 revealed that a high production of provoked confabulatory answers were associated with poor scores on personal episodic memory measures but not with other measures of cognitive functioning such as working memory and/or executive function.     

Self-enhancing confabulation: revisiting the motivational hypothesis

We report a patient who developed spontaneous confabulation following surgical clipping of an anterior communicating artery aneurysm. An autobiographical memory test was used to measure the emotional valence of the patient's self-representations in true and false memories. We found that his confabulations included significantly more positive self-representations than his true memories and that the overall valence of his confabulations was more positive than that of his true memories and than that of the memories of five healthy control participants of the same age and educational attainment. It is proposed that while cognitive dysfunction may explain how confabulations are formed, emotional factors may explain which specific confabulations are constructed.     

Mechanism of disorientation: Reality filtering versus content monitoring

Disorientation is frequent after brain damage. It is a constituent component of post-traumatic amnesia and was part of the original definition of the Korsakoff syndrome, together with amnesia and confabulations. Orbitofrontal reality filtering is a pre-conscious memory control process that has been held accountable for disorientation and a specific type of confabulations that patients act upon. A recent study questioned the specificity of this process and suggested that confabulating patients who failed in orbitofrontal reality filtering similarly failed to monitor the precise content of memories, a critical step within the strategic retrieval account, which describes a series of processes leading up to the recollection of memories. In the present study we combined the proposed experimental requirements of both processes in a single continuous recognition task and tested a group of 21 patients with a matched deficit of delayed free recall. We found that only deficient reality filtering, but not content monitoring, significantly correlated with disorientation and distinguished between confabulators and non-confabulators. Thus, reality confusion, as evident in disorientation and behaviourally spontaneous confabulation, primarily reflects an inability to monitor memories' relation with ongoing reality rather than to monitor their precise content.     

Susceptibility to false memories in patients with ACoA aneurysm

We examined ACoA patients regarding their susceptibility to a range of false memory phenomena. We targeted provoked confabulation, false recall and false recognition in the Deese-Roediger-McDermott-paradigm (DRM-paradigm) as well as false recognition in a mirror reading task. ACoA patients produced more provoked confabulations and more false recognition in mirror reading than comparison subjects. Conversely, false recall/false recognition in the DRM-paradigm were similar in patients and controls. Whereas the former two indices of false memories were correlated, no relationship was revealed with the DRM-paradigm. Our results suggest that rupture of ACoA aneurysm leads to an increased susceptibility to a subset of false memories types.