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

REM sleep remains paradoxical: sub-states determined by thalamo-cortical and cortico-cortical functional connectivity

During paradoxical sleep (PS, aka REM sleep) the cerebral cortex displays rapid electroencephalographic activity similar to that of wakefulness, whereas in the posterior associative thalamus, rapid activity is interrupted by frequent periods of slow-wave (delta) oscillations at 2-3 Hz, thereby dissociating the intrinsic frequency in thalamus and cortex. Here we studied the functional consequences of such a dissociation using intrathalamic and intracortical recordings in 21 epileptic patients, applying coherence analysis to examine changes in functional connectivity between the posterior thalamus (mainly medial pulvinar) and six cortical functional networks, and also between each cortical network with respect to the others. Periods of slow-wave thalamic activity ('delta PS') were more prevalent than phases of 'rapid PS,' and the delta/rapid thalamic alternance did not overlap with the classical tonic/phasic dichotomy based on rapid eye movements. Thalamo-cortical and cortico-cortical functional connectivity significantly decreased during delta PS, relative to both rapid PS periods and to wakefulness. The fact that delta thalamic activity and low thalamo-cortical binding coincided with a suppression of cortico-cortical connectivity supports a crucial role for the posterior associative thalamus, and particularly the medial pulvinar, in ensuring trans-thalamic communication between distant cortical areas. Disruption of such a trans-thalamic communication during delta PS compromises the functional binding between cortical areas, and consequently might contribute to the alteration of perceptual experiences commonly reported during dreams. KEY POINTS: During paradoxical, or REM, sleep (PS), rapid thalamic activity is interrupted by frequent periods of slow delta waves at 2-3 Hz. During these periods of thalamic delta activity there was a drastic drop of functional connectivity between associative thalamus and cortex, and also among different cortical networks. The delta/rapid alternance did not overlap with the classically defined 'tonic/phasic' periods and therefore suggests a distinct dichotomy of functional states in PS. Recurrent decrease in thalamo-cortical and cortico-cortical functional connectivity during PS may compromise the spatio-temporal binding between cortical areas, which in turn could hinder the formation of coherent mental content during dreams.

Impaired attention mechanisms in confabulating patients: A VLSM and DWI study

Attention is one of the most studied cognitive functions in brain-damaged populations or neurological syndromes, as its malfunction can be related to deficits in other higher cognitive functions. In the present study, we aimed at delimiting the attention deficits of a sample of brain-injured patients presenting confabulations by assessing their performance on alertness, spatial orienting, and executive control tasks. Confabulating patients, who present false memories or beliefs without intention to deceive, usually show memory deficits and/or executive dysfunction. However, it is also likely that attention processes may be impaired in patients showing confabulations. Here, we compared confabulating patients' attention performance to a lesion control group and a healthy control group. Confabulating patients' mean overall accuracy was lower than the one of healthy and lesion controls along the three experimental tasks. Importantly, confabulators presented a greater Simon congruency effect than both lesion controls and healthy controls in the presence of predictive spatial cues, besides a lower percentage of hits and longer RTs in the Go-NoGo task, demonstrating deficits in executive control. They also showed a higher reliance on alerting and spatially predictive orienting cues in the context of a deficient performance. Grey and white matter analyses showed that patients' percentage of hits in the Go-NoGo task was related to damage to the right inferior frontal gyrus (pars triangularis and pars opercularis), whereas the integrity of the right inferior fronto-occipital fasciculus was negatively correlated with their alertness effect. These results are consistent with previous literature highlighting an executive dysfunction in confabulating patients, and suggest that some additional forms of attention, such as alertness and spatial orienting, could be selectively impaired in this clinical syndrome.

Exploring Cognitive Impairment in Patients With Bilateral Capsular Genu Lesions

OBJECTIVE

The authors investigated for presence of cognitive impairment after occurrence of bilateral lesions of the genu of the internal capsule (GIC). Clinical and neuropsychological features of unilateral GIC lesions have previously been studied, but the cognitive profile of bilateral lesions of the GIC has not been fully explored.

METHODS

An investigation was conducted of neurocognitive deficits and computerized tomography MRI findings among 4,200 stroke patients with bilateral GIC involvement who were admitted to the hospital between January 2010 and October 2018.

RESULTS

Eight patients with bilateral lesions of the capsular genu were identified and their data analyzed. Overall, behavioral and cognitive dysfunction were characterized by impairment of frontal, memory, and executive functions. Attention and abstraction were present among all eight patients (100%); apathy, abulia, and executive dysfunctions, among seven (87.5%); global mental dysfunction and planning deficits, among six (75.0%); short-term verbal memory deficits and language dysfunctions, among five (62.5%); long-term verbal memory deficits, among four (50.0%); and spatial memory deficits, reading, writing, counting dysfunctions, and anarthria, among two (25.0%). Four of the patients (50.0%) without a history of cognitive disorder showed severe mental deterioration compatible with the clinical picture of dementia. A clinical picture of dementia was still present in these patients 6 months after stroke.

CONCLUSIONS

Bilateral lesions of the capsular genu appearing either simultaneously or at different times were significantly associated with executive dysfunctions.

Confabulation affecting Temporal Consciousness significantly more than Knowing Consciousness

Confabulation, defined as the production of statements and actions that are unintentionally incongruous to the patient's history, background, present and future situation, is a rather infrequent memory disorder, which usually affects patients with significant memory impairment, but may be also observed in patients with normal memory and learning abilities. Confabulation may be selective affecting some cognitive, memory domains while relatively sparing others. In particular, it may affect more Temporal Consciousness, i.e. a specific form of consciousness that allows individuals to remember their personal past, to be oriented in their present world and to predict their personal future, than Knowing Consciousness, i.e. a specific form of consciousness allowing individuals to be aware of past, present and future impersonal knowledge and information. In this study we evaluated confabulations in TC and KC in a group of confabulatory amnesics of various aetiologies. Based on previous studies, it was predicted that confabulations affect significantly more TC than KC. It was also predicted that "Habits Confabulations", i.e. habits and repeated personal events mistaken as specific, unique past and future personal episodes, is the more frequently observed type of confabulation. The results confirmed these predictions and are discussed within the framework of the Memory, Consciousness and Temporality Theory.

Simultaneous Reality Filtering and Encoding of Thoughts: The Substrate for Distinguishing between Memories of Real Events and Imaginations?

Any thought, whether it refers to the present moment or reflects an imagination, is again encoded as a new memory trace. Orbitofrontal reality filtering (ORFi) denotes an on-line mechanism which verifies whether upcoming thoughts relate to ongoing reality or not. Its failure induces reality confusion with confabulations and disorientation. If the result of this process were simultaneously encoded, it would easily explain later distinction between memories relating to a past reality and memories relating to imagination, a faculty called reality monitoring. How the brain makes this distinction is unknown but much research suggests that it depends on processes active when information is encoded. Here we explored the precise timing between ORFi and encoding as well as interactions between the involved brain structures. We used high-density evoked potentials and two runs of a continuous recognition task (CRT) combining the challenges of ORFi and encoding. ORFi was measured by the ability to realize that stimuli appearing in the second run had not appeared in this run yet. Encoding was measured with immediately repeated stimuli, which has been previously shown to induce a signal emanating from the medial temporal lobe (MTL), which has a protective effect on the memory trace. We found that encoding, as measured with this task, sets in at about 210 ms after stimulus presentation, 35 ms before ORFi. Both processes end at about 330 ms. Both were characterized by increased coherence in the theta band in the MTL during encoding and in the orbitofrontal cortex (OFC) during ORFi. The study suggests a complex interaction between OFC and MTL allowing for thoughts to be re-encoded while they undergo ORFi. The combined influence of these two processes at 200-300 ms may leave a memory trace that allows for later effortless reality monitoring in most everyday situations.

Korsakoff's syndrome: a critical review

In this review, we present a survey on Korsakoff's syndrome (KS), a residual syndrome in patients who suffered from a Wernicke encephalopathy (WE) that is predominantly characterized by global amnesia, and in more severe cases also by cognitive and behavioral dysfunction. We describe the history of KS and its definition, its epidemiology, and the lack of consensus criteria for its diagnosis. The cognitive and behavioral symptoms of KS, which include anterograde and retrograde amnesia, executive dysfunction, confabulation, apathy, as well as affective and social-cognitive impairments, are discussed. Moreover, recent insights into the underlying neurocognitive mechanisms of these symptoms are presented. In addition, the evidence so far on the etiology of KS is examined, highlighting the role of thiamine and alcohol and discussing the continuity hypothesis. Furthermore, the neuropathology of KS is reviewed, focusing on abnormalities in the diencephalon, including the mammillary bodies and thalamic nuclei. Pharmacological treatment options and nonpharmacological interventions, such as those based on cognitive rehabilitation, are discussed. Our review shows that thiamine deficiency (TD) is a crucial factor in the etiology of KS. Although alcohol abuse is by far the most important context in which TD occurs, there is no convincing evidence for an essential contribution of ethanol neurotoxicity (EN) to the development of WE or to the progression of WE to KS. Future research on the postmortem histopathological analysis of brain tissues of KS patients is crucial for the advancement of our knowledge of KS, especially for associating its symptoms with lesions in various thalamic nuclei. A necessary requirement for the advancement of studies on KS is the broad acceptance of a comprehensive definition and definite diagnostic criteria. Therefore, in this review, we propose such a definition of KS and draft outlines for prospective diagnostic criteria.

The importance of mammillary body efferents for recency memory: towards a better understanding of diencephalic amnesia

Despite being historically one of the first brain regions linked to memory loss, there remains controversy over the core features of diencephalic amnesia as well as the critical site for amnesia to occur. The mammillary bodies and thalamus appear to be the primary locus of pathology in the cases of diencephalic amnesia, but the picture is complicated by the lack of patients with circumscribed damage. Impaired temporal memory is a consistent neuropsychological finding in Korsakoff syndrome patients, but again, it is unclear whether this deficit is attributable to pathology within the diencephalon or concomitant frontal lobe dysfunction. To address these issues, we used an animal model of diencephalic amnesia and examined the effect of mammillothalamic tract lesions on tests of recency memory. The mammillothalamic tract lesions severely disrupted recency judgements involving multiple items but left intact both recency and familiarity judgements for single items. Subsequently, we used disconnection procedures to assess whether this deficit reflects the indirect involvement of the prefrontal cortex. Crossed-lesion rats, with unilateral lesions of the mammillothalamic tract and medial prefrontal cortex in contralateral hemispheres, were unimpaired on the same recency tests. These results provide the first evidence for the selective importance of mammillary body efferents for recency memory. Moreover, this contribution to recency memory is independent of the prefrontal cortex. More broadly, these findings identify how specific diencephalic structures are vital for key elements of event memory.

Confabulation in children with autism

Some children with high-functioning autistic spectrum conditions (ASC) have been noted clinically to produce accounts and responses akin to confabulations in neurological patients. Neurological confabulation is typically associated with abnormalities of the frontal lobes and related structures, and some forms have been linked to poor performance on source monitoring and executive function tasks. ASC has also been linked to atypical development of the frontal lobes, and impaired performance on source monitoring and executive tasks. But confabulation in autism has not to our knowledge previously been examined experimentally. So we investigated whether patterns of confabulation in autism might share similarities with neurologically-based confabulation. Tests of confabulation elicitation, source monitoring (reality monitoring, plus temporal and task context memory) and executive function were administered to four adolescents with ASC who had previously been noted to confabulate spontaneously in everyday life. Scores were compared to a typically developing (TD) and an ASC control group. One confabulating participant was significantly impaired at reality monitoring, and one was significantly worse at a task context test, relative to both the ASC and TD controls. Three of the confabulators showed impairment on measures of executive function (Brixton test; Cognitive Estimates test; Hayling Test B errors) relative to both control groups. Three were significantly poorer than the TD controls on two others (Hayling A and B times), but the ASC control group was also significantly slower at this test than the TD controls. Compared to TD controls, two of the four confabulating participants produced an abnormal number of confabulations during a confabulation elicitation questionnaire, where the ASC controls and TD controls did not differ from each other. These results raise the possibility that in at least some cases, confabulation in autism may be less related to social factors than it is to impaired source memory or poor executive function.

Medio-dorsal thalamus and confabulations: Evidence from a clinical case and combined MRI/DTI study

The Medio-Dorsal Nuclei (MDN) including the thalamic magnocellular and parvocellular thalamic regions has been implicated in verbal memory function. In a 77 year old lady, with a prior history of a clinically silent infarct of the left MDN, we observed the acute onset of spontaneous confabulations when an isolated new infarct occurred in the right MDN. The patient and five age-matched healthy subjects underwent Magnetic Resonance Imaging (MRI) and Diffusion Tensor Imaging (DTI). The thalamic lesions were localized by overlapping Morel Thalamic Atlas with structural MRI data. DTI was used to assess: i) white matter alterations (Fractional Anisotropy, FA) within fibers connecting the ischemic areas to cortex; ii) the micro-structural damage (Mean Diffusivity) within the thalamic sub-regions defined by their structural connectivity to the Anterior Cingulate Cortex (ACC) and to the temporal lobes. These target regions were chosen because their damage is considered associated with the appearance of confabulations. Thalamic lesions were localized within the parvocellular regions of the right and left MDNs. The structural connectivity study showed that the fiber tracts, connecting the bilaterally damaged thalamic regions with the frontal cortex, corresponded to the anterior thalamic radiations (ATR). FA within these tracts was significantly lower in the patient as compared to controls. Mean diffusivity within the MDNs projecting to Broadman area (BA) 24, BA25 and BA32 of ACC was significantly higher in the patient than in control group. Mean diffusivity values within the MDN projecting to temporal lobes in contrast were not different between patient and controls. Our findings suggest the involvement of bilateral MDNs projections to ACC in the genesis of confabulations and help provide clarity to the longstanding debate on the origin of confabulations.

Fantastic confabulation in right frontal lobe epilepsy

Background

Interictal behavioral symptoms in frontal lobe epilepsy (FLE) are variable and often difficult to discriminate from other localization-related epilepsies.

Methods and results

We report two female patients with right FLE who exhibited fantastic confabulations. One of the patients had a 14-year history of hypermotor seizures, and the other had a 10-year history of dyscognitive seizures with automatism. Their fantastic confabulations arose in the context of moderate-to-severe cognitive impairment and of a variety of behavioral abnormalities, including emotional withdrawal and compulsive behaviors.

Conclusion

Fantastic confabulations are rare but may be a relatively specific behavioral marker for FLE-associated psychosis.

Different patterns of recollection impairment in confabulation reveal different disorders of consciousness: A multiple case study

Recollection is used to refer to the active process of setting up retrieval cues, evaluating the outcome, and systematically working toward a representation of a past experience that we find acceptable. In this study we report on three patients showing different patterns of confabulation affecting recollection and consciousness differentially. All patients confabulated in the episodic past domain. However, whereas in one patient confabulation affected only recollection of events concerning his personal past, present and future, in another patient confabulation also affected recollection of impersonal knowledge. The third patient showed an intermediate pattern of confabulation, which affected selectively the retrieval of past information, both personal and impersonal. We suggest that our results are in favor of a fractionation of processes involved in recollection underling different disorders of consciousness.

A neurophenomenological model for the role of the hippocampus in temporal consciousness. Evidence from confabulation

Confabulation, the production of statements or actions that are unintentionally incongruous to the subject's history, background, present and future situation, is a rather infrequent disorder with different aetiologies and anatomical lesions. Although they may differ in many ways, confabulations show major similarities. Their content, with some minor exceptions, is plausible and therefore indistinguishable from true memories, unless one is familiar with the patient's history, background, present and future situation. They extend through the whole individuals' temporality, including their past, present and future. Accordingly, we have proposed that rather than a mere memory disorder; confabulation reflects a distortion of Temporal Consciousness (TC), i.e., a specific form of consciousness that allows individuals to locate objects and events according to their subjective temporality. Another feature that confabulators share is that, regardless of their lesion's location, they all have a relatively preserved hippocampus (Hip), at least unilaterally. In this article, we review data showing differences and similarities among forms of confabulation. We then describe a model showing that the hippocampus is crucial both for the normal functioning of TC and as the generator of confabulations, and that different types of confabulation can be traced back to a distortion of TC resulting from damage or disconnection of brain areas directly or indirectly connected to the hippocampus. We conclude by comparing our model with other models of memory and confabulation.

Memory in time: electrophysiological comparison between reality filtering and temporal order judgment

Orbitofrontal reality filtering (ORF) denotes a little known but vital memory control mechanism, expressed at 200-300ms after stimulus presentation, that allows one to sense whether evoked memories (thoughts) refer to present reality and can be acted upon, or not. Its failure induces reality confusion evident in confabulations that patients act upon and disorientation. In what way ORF differs from temporal order judgment (TOJ), that is, the conscious knowledge about when something happened in the past, has never been explored. Here we used evoked potential analysis to compare ORF and TOJ within a combined experimental task and within a comparable time frame, close to the experienced present. Seventeen healthy human subjects performed an experiment using continuous recognition tasks that combined the challenges of ORF and TOJ. We found that the two mechanisms dissociated behaviorally: subjects were markedly slower and less accurate in TOJ than ORF. Both mechanisms evoked similar potentials at 240-280ms, when ORF normally occurs. However, they rapidly dissociated in terms of amplitude differences and electrical source from 310 to 360ms and again from 530 to 560ms. We conclude that the task of consciously ordering memories in the immediate past (TOJ) is effortful and slow in contrast to sensing memories' relation with the present (ORF). Both functions invoke similar early electrocortical processes which then rapidly dissociate and engage different brain areas. The results are consistent with the different consequences of the two mechanisms' dysfunction: while failure of ORF has a known clinical manifestation (reality confusion as evident in confabulation and disorientation), the failure of TOJ, as tested here, has no such known clinical correlate.

An Electrophysiological Dissociation between Orbitofrontal Reality Filtering and Context Source Monitoring

Memory influences behavior in multiple ways. One important aspect is to remember in what precise context in the past a piece of information was acquired (context source monitoring). Another important aspect is to sense whether an upcoming thought, composed of fragments of memories, refers to present reality and can be acted upon (orbitofrontal reality filtering). Whether these memory control processes share common underlying mechanisms is unknown. Failures of both have been held accountable for false memories, including confabulation. Electrophysiological and imaging studies suggest a dissociation but used very different paradigms. In this study, we juxtaposed the requirements of context source monitoring and reality filtering within a unique continuous recognition task, which healthy participants performed while high-resolution evoked potentials were recorded. The mechanisms dissociated both behaviorally and electrophysiologically: Reality filtering induced a frontal positivity, absence of a specific electrocortical configuration, and posterior medial orbitofrontal activity at 200–300 msec. Context source monitoring had no electrophysiological expression in this early period. It was slower and less accurate than reality filtering and induced a prolonged positive potential over frontal leads starting at 400 msec. The study demonstrates a hitherto unrecognized separation between orbitofrontal reality filtering and source monitoring. Whereas deficient orbitofrontal reality filtering is associated with reality confusion in thinking, the behavioral correlates of deficient source monitoring should be verified with controlled experimental exploration.

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.

The medial dorsal thalamic nucleus and the medial prefrontal cortex of the rat function together to support associative recognition and recency but not item recognition

In humans recognition memory deficits, a typical feature of diencephalic amnesia, have been tentatively linked to mediodorsal thalamic nucleus (MD) damage. Animal studies have occasionally investigated the role of the MD in single-item recognition, but have not systematically analyzed its involvement in other recognition memory processes. In Experiment 1 rats with bilateral excitotoxic lesions in the MD or the medial prefrontal cortex (mPFC) were tested in tasks that assessed single-item recognition (novel object preference), associative recognition memory (object-in-place), and recency discrimination (recency memory task). Experiment 2 examined the functional importance of the interactions between the MD and mPFC using disconnection techniques. Unilateral excitotoxic lesions were placed in both the MD and the mPFC in either the same (MD + mPFC Ipsi) or opposite hemispheres (MD + mPFC Contra group). Bilateral lesions in the MD or mPFC impaired object-in-place and recency memory tasks, but had no effect on novel object preference. In Experiment 2 the MD + mPFC Contra group was significantly impaired in the object-in-place and recency memory tasks compared with the MD + mPFC Ipsi group, but novel object preference was intact. Thus, connections between the MD and mPFC are critical for recognition memory when the discriminations involve associative or recency information. However, the rodent MD is not necessary for single-item recognition memory.

Spontaneous confabulation, temporal context confusion and reality monitoring: a study of three patients with anterior communicating artery aneurysms

Spontaneous confabulation involves the production of false or distorted memories, and is commonly associated with ventromedial prefrontal damage. One influential theory proposes that the critical deficit is a failure to suppress currently irrelevant memory traces that intrude into ongoing thinking (Schnider & Ptak, 1999). In this study, we report experimental investigations with three spontaneously confabulating patients aimed at exploring this account. Using Schnider and Ptak's (1999) continuous recognition paradigm, we replicated their experimental results with our patients. However, our data suggest that the critical impairment might be more generalized than a failure to suppress currently irrelevant memories. First, a temporal source monitoring task failed to show that previous memory traces intrude into the present. Second, a reality monitoring task revealed that confabulating patients had a tendency to misidentify imagined events as real, a result that cannot be explained in terms of temporal confusion. This error was specific to confabulating patients and was not shared by non-confabulating ACoA patients. Our data therefore suggest a more generalized impairment in source monitoring, not only on the basis of temporality or current relevance, but across a range of contextual domains, including information used to distinguish real memories from imaginings.

Memory monitoring failure in confabulation: evidence from the semantic illusion paradigm

Several prominent models of confabulation characterize the syndrome as a failure in controlled aspects of memory retrieval, such as pre-retrieval cue specification and post-retrieval monitoring. These models have been generated primarily in the context of studies of autobiographical memory retrieval. Less research has focused on the existence and mechanisms of semantic confabulation. We examined whether confabulation extends to the semantic domain, and if so, whether it could be understood as a monitoring failure. We focus on post-retrieval monitoring by using a verification task that minimizes cue specification demands. We used the semantic illusion paradigm that elicits erroneous endorsement of misleading statements (e.g., "Two animals of each kind were brought onto the Ark by Moses before the great flood") even in controls, despite their knowing the correct answer (e.g., Noah). Monitoring demands were manipulated by varying semantic overlap between target and foils, ranging from high semantic overlap to unrelated. We found that semantic overlap modulated the magnitude of semantic illusion in all groups. Compared to controls, both confabulators and non-confabulators had greater difficulty monitoring semantically related foils; however, elevated endorsement of unrelated foils was unique to confabulators. We interpret our findings in the context of a two-process model of post-retrieval monitoring.

Behaviorally spontaneous confabulation in limbic encephalitis: the roles of reality filtering and strategic monitoring

Behaviorally spontaneous confabulation is characterized by a confusion of reality evident in currently inappropriate acts that patients justify with confabulations and in disorientation. Here, we describe a 38-year-old woman lawyer hospitalized because of non-herpetic, presumably autoimmune, limbic encephalitis. For months, she considered herself at work and desperately tried to respect her falsely believed professional obligations. In contrast to a completely erroneous concept of reality, she did not confabulate about her remote personal past. In tasks proposed to test strategic retrieval monitoring, she produced no confabulations. As expected, she failed in tasks of reality filtering, previously shown to have high sensitivity and specificity for behaviorally spontaneous confabulation and disorientation: she failed to suppress the interference of currently irrelevant memories and she had deficient extinction capacity. The observation underscores the special status of behaviorally spontaneous confabulation among confabulatory phenomena and of reality filtering as a thought control mechanism. We suggest that different processes may underlie the generation of false memories and their verbal expression. We also emphasize the need to present theories of confabulation together with experimental tasks that allow one to empirically verify the theories and to explore underlying physiological mechanisms.

Mild cognitive impairment in stroke patients with ischemic cerebral small-vessel disease: a forerunner of vascular dementia?

Ischemic cerebral small-vessel disease accounts for a third of acute cerebral ischemic events and contributes to the development of cognitive decline and dementia. Cerebral small-vessel disease can be visualized on MRI studies as lacunar infarcts, white matter lesions and cerebral microbleeds. In general, the short-term prognosis of ischemic cerebral small-vessel disease compared with other stroke subtypes is more favorable, with almost negligible early mortality, absence of neuropsychological impairment and excellent neurological recovery. However, it has been shown recently that the proportion of dementia caused by small-vessel disease ranges from 36 to 67%. On the other hand, patients with a first-ever lacunar infarction present with cognitive impairment (mainly executive dysfunction) in more than half of cases and more than 55% of patients fulfil the criteria of mild cognitive impairment of the vascular type. Moreover, patients with small-vessel disease have an increase in the mid- and long-term risk of death, stroke recurrence and dementia. Neuropsychological abnormalities in small-vessel disease occurred more frequently than previously recognized. Ischemic cerebral small-vessel disease should be regarded as a potentially severe condition prodrome of subcortical vascular dementia rather than a relatively benign disorder.

Stroke and episodic memory disorders

Memory impairments are common after stroke, and the anatomical basis for impairments may be quite variable. To determine the range of stroke-related memory impairment, we identified all case reports and group studies through the Medline database and the Science Citation Index. There is no hypothesis about memory that is unique to stroke, but there are several important facets of memory impairment after stroke: (1) Every node of the limbic system implicated in memory may be damaged by stroke but very rarely in isolation and the combination of amnesia with the associated deficits often illuminates additional aspects of memory functions. (2) Stroke produces amnesia by damage to critical convergence white matter connections of the limbic system, and stroke is the only etiology of amnesia that can delineate the entire pathway of memory and critical convergence points. (3) Stroke also impairs memory, without causing classical amnesia, by damaging brain regions responsible for cognitive processes, some modality specific and some more generally strategic, that are essential for normal learning and recall.

Disorientation, confabulation, and extinction capacity: clues on how the brain creates reality

BACKGROUND

Disorientation and confabulation often have a common course, independent of amnesia. Behaviorally spontaneous confabulation is the form in which patients act according to a false concept of reality; they fail to abandon action plans (anticipations) that do not pertain to the present situation. This continued enactment of previously valid but meanwhile invalidated anticipations can be conceived as deficient extinction capacity, that is, failure to integrate negative prediction errors into behavior. In this study, we explored whether disorientation and behaviorally spontaneous confabulation are associated with extinction failure.

METHODS

Twenty-five patients hospitalized for neurorehabilitation after first-ever brain injury who either had severe amnesia (n = 17), an orbitofrontal lesion (n = 14), or both (n = 6) were tested regarding disorientation (questionnaire) and performed an experimental task of association learning and extinction. Five patients were also classified as behaviorally spontaneous confabulators.

RESULTS

Extinction capacity explained 66% of the variance of orientation in the whole group of patients (amnesics only, 56%; orbitofrontal group only, 90%), whereas association learning explained only 17% of the variance in the whole group (amnesics only, 7%; orbitofrontal group only, 16%). Also, extinction capacity, but not association learning, significantly distinguished between behaviorally spontaneous confabulators and all other subjects.

CONCLUSIONS

Disorientation and behaviorally spontaneous confabulation are strongly and specifically associated with a failure of extinction, the ability to learn that previously appropriate anticipations no longer apply. Rather than invoking high-level monitoring processes, the human brain seems to make use of an ancient biological faculty-extinction-to keep thought and behavior in phase with reality.

Lacunar stroke

Lacunar infarcts or small subcortical infarcts result from occlusion of a single penetrating artery and account for one quarter of cerebral infarctions. Patients with a lacunar infarct usually present with a classical lacunar syndrome (pure motor hemiparesis, pure sensory syndrome, sensorimotor stroke, ataxic hemiparesis or dysarthria-clumsy hand) and, less frequently, an atypical lacunar syndrome. Hypertension and diabetes mellitus are major risk factors for lacunar stroke. Lacunar infarcts show a paradoxical clinical course with a favorable prognosis in the short term, characterized by a low early mortality and reduced functional disability on hospital discharge, but with an increased risk of death, stroke recurrence and dementia in the mid- and long term. Asymptomatic progression of small-vessel disease is a typical feature of the lacunar infarcts. For this reason, lacunar infarction should be regarded as a potentially severe condition rather than a relatively benign disorder and, therefore, lacunar stroke patients require adequate and rigorous management and follow-up. Antiplatelet drugs, careful blood pressure control, the use of statins and modification of lifestyle risk factors are key elements in secondary prevention after lacunar stroke.

Mammillothalamic functional connectivity and memory function in Wernicke's encephalopathy

There is still debate over the neural mechanisms underlying pathogenic and even recovery processes of Wernicke's encephalopathy. Therefore, we attempted to validate the usefulness of resting-state functional connectivity analysis in assessing memory function and its neural correlation with the mammillothalamic tract in patients recovering from Wernicke's encephalopathy. Seven chronic alcoholics recovering from Wernicke's encephalopathy, 14 alcoholic comparisons without Wernicke's encephalopathy, and 14 healthy comparisons underwent functional connectivity MRI scans, as well as verbal and non-verbal memory tests after at least a 1 month abstinence from alcohol. Resting-state functional connectivity strength between the anterior thalamus and the mammillary bodies was investigated by calculating temporal correlations in magnetic resonance signal levels between the two regions during a 5-min passive viewing task. The mean values of the functional connectivity strength between the left anterior thalamus and the ipsilateral mammillary body differed significantly between Wernicke's encephalopathy patients and healthy comparisons (P = 0.014). This connectivity strength in alcoholic comparisons fell between those of the former two groups, with a significant difference from that of healthy comparisons (P = 0.038). In addition, the strength of this left-sided functional connectivity significantly correlated with delayed verbal recall scores (r = 0.771, P = 0.042) and verbal recognition score (r = 0.825, P = 0.022) in patients with Wernicke's encephalopathy. Our findings indicate that memory function in patients recovering from Wernicke's encephalopathy parallels the level of the mammillothalamic functional connectivity; this supports the usefulness of resting-state functional connectivity analysis as a practical alternative to pathological examination of the mammillothalamic tract in living patients with Wernicke's encephalopathy.

Confabulation in Alzheimer's disease: poor encoding and retrieval of over-learned information

Patients who confabulate retrieve personal habits, repeated events or over-learned information and mistake them for actually experienced, specific unique events. Although some hypotheses favour a disruption of frontal/executive functions operating at retrieval, the respective involvement of encoding and retrieval processes in confabulation is still controversial. The present study sought to investigate experimentally the involvement of encoding and retrieval processes and the interference of over-learned information in the confabulation of Alzheimer's disease patients. Twenty Alzheimer's disease patients and 20 normal controls encoded and retrieved unknown stories, well-known fairy tales (e.g. Snow White) and modified well-known fairy tales (e.g. Little Red Riding Hood is not eaten by the wolf) under three experimental conditions: (i) full attention at encoding and at retrieval; (ii) divided attention at encoding (i.e. performing an attention demanding secondary task) and full attention at retrieval; (iii) full attention at encoding and divided attention at retrieval. We found that confabulations in Alzheimer's disease patients were more frequent for the modified well-known fairy tales and when encoding was weakened by a concurrent secondary task (61%), compared with the other types of stories and experimental conditions. Confabulations in the modified fairy tales always consisted of elements of the original version of the fairy tale (e.g. Little Red Riding Hood is eaten by the wolf). This is the first experimental evidence showing that poor encoding and over-learned information are involved in confabulation in Alzheimer's disease.

[Pure amnesia due to the right capsular genu infarction]

A 77-year-old right-handed woman was admitted to our hospital with memory disturbance. Neurological examination was normal except for amnesia. Neuropsychological tests showed severe impairments in verbal and visual memories. Brain MRI revealed a fresh lacunar infarction in the genu of the right internal capsule. Decreased perfusion in the right thalamus and frontal lobe on (99m)Tc-ECD SPECT was attributable to disconnection of the thalamo-cortical tract by infarction. We consider that the patient's amnesia in this case was induced by infarction of the capsular genu, which includes some fibers from the anterior and inferior thalamic peduncles. Our findings demonstrated that lacunar infarction in the genu of the right internal capsule caused severe and persistent amnesia.

Neuropsychological abnormalities associated with lacunar infarction

The objective of this study was to assess neuropsychological abnormalities in 40 patients with lacunar infarction. Topography of infarction, presence of isolated or multiple silent infarcts and white matter hyperintensities were correlated with results of neuropsychological tests and subtypes of lacunar infarction. Patients were studied within 1 month after stroke. A total of 21 patients were males and the mean age was 70.7 years; 30% had a single infarction (mean number of infarctions was 3.4). Twelve patients had pure motor hemiparesis, 9 pure sensory stroke, 8 dysarthria-clumsy hand/ataxic hemiparesis, 8 atypical lacunar syndrome, and 3 sensorimotor stroke. The mean score of the Mini-Mental State Examination was 28.4. Mild cognitive impairment of subcortical vascular features occurred in 23 patients and isolated executive disturbances in 4. Neuropsychological results showed that patients with atypical lacunar syndrome followed by pure motor hemiparesis showed significantly more cognitive executive disturbances. Patients with dysarthria-clumsy hand/ataxic hemiparesis accounted for the best scores in some tests of visuoconstructive function and visual memory. In summary, mild neuropsychological disturbances (57.5%) are not infrequent in acute lacunar infarcts especially in patients with atypical lacunar syndrome and pure motor hemiparesis. Neuropsychological impairment should be considered as common clinical feature in acute lacunar infarction.

What are confabulators’ memories made of? A study of subjective and objective measures of recollection in confabulation

Confabulating patients claim to remember events that had not actually happened, suggesting a vivid subjective experience of false memories. The present study was aimed at examining the nature of subjective experience of retrieval in confabulators and its relation to the objective ability to recollect qualitative aspects of the original episode. In Experiment 1, 5 confabulators, 7 non-confabulating patients, and 12 control subjects studied words under shallow and deep encoding conditions and underwent a Remember (R)/Know (K) recognition task [Tulving, E. (1985). Memory and consciousness. Canadian Psychology, 26, 1-12]. For recognized words, they additionally indicated two qualitative features of the encoding context. Whereas subjective (i.e. R responses) and objective (i.e. source) measures of recollection were associated in normal controls and non-confabulating patients, they were dissociated in confabulators. In Experiment 2, participants explained the content of their R responses. We found that confabulators' recollections mainly included autobiographical information related to test items, but not to the study encounter. We conclude that remembering states in confabulators may be linked to a deficit in inhibiting irrelevant memories triggered by test items during retrieval attempts.

When true memory availability promotes false memory: evidence from confabulating patients

We explored the extent to which confabulators are susceptible to false recall and false recognition, and whether false recognition is reduced when memory for studied items is experimentally enhanced. Five confabulating patients, nine non-confabulating amnesics--including patients with (F amnesics) and without frontal-lobe dysfunction (NF amnesics)--and 14 control subjects underwent the DRM paradigm [Roediger, H. L., & McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology: Learning, Memory and Cognition, 21, 803-814.] in two experimental conditions. In both conditions participants studied eight lists of semantic associates, and free recall was tested after the presentation of each list. In the Standard condition recognition was tested after the presentation of all the lists, whereas in the Proximal condition patients were administered a six-item recognition task after the presentation of each list. Participants also provided remember or know judgements, and described the content of their recollections. All groups of patients recalled a lower proportion of targets and critical lures than did control subjects, but confabulators recalled more words unrelated to the studied lists than did NF amnesics and controls. All groups of participants improved true recognition across conditions. However, whereas normal controls suppressed false recognition to critical lures in the Proximal compared to the Standard condition, and non-confabulating amnesics showed comparable gist-based false recognition, confabulators showed increased levels of false recognition to critical lures across conditions. Furthermore, NF amnesics significantly reduced false recognition to unrelated lures in the Proximal compared to the Standard condition, whereas confabulators were unable to suppress false recognition to unrelated lures across conditions. Analysis of the phenomenological experience showed that, unlike non-confabulating amnesics, confabulators characterized true and false memories with irrelevant information related to test items. Results are interpreted in light of confabulators' monitoring deficits.

Delusional misidentification

The Capgras syndrome and other forms of delusional misidentification may be encountered frequently in neuropsychiatric settings. DMS can occur in the presence of idiopathic psychiatric illness, in diffuse brain illness such as dementia, and in focal neurologic disease. In patients who have focal lesions, there is evidence that right hemisphere damage is necessary for the production of DMS. Although DMS is associated with a pattern of neuropsychologic impairments in the domains of memory, perception, and executive function, these impairments alone do not account for the selectivity and delusional nature of DMS. Therefore, other factors such as premorbid psychopathology, motivation, and loss of ego functions may be important in determining which vulnerable patients develop DMS and which do not.

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.

Comprehension, encoding, and monitoring in the production of confabulation in memory: a study with schizophrenic patients

INTRODUCTION

The aim of the present study was to test the hypotheses proposed by Nathaniel-James and collaborators (Nathaniel-James & Frith, 1996; Nathaniel-James, Foong, & Frith, 1996) to account for the cognitive deficits involved in the production of confabulations in schizophrenic patients: impairments in comprehension, memory encoding, and memory monitoring.

METHOD

Five patients were investigated in this multiple single-case study. Comprehension abilities were investigated in several tests in which a memory bias was avoided. The encoding deficit hypothesis was tested by manipulating cues at encoding and/or retrieval. "Memory monitoring" abilities were examined in two tasks: the Hayling test for all patients and an AB-AC word pairs learning task for two patients.

RESULTS

Four of the patients produced an abnormal level of confabulations in story and fable learning tests. All patients exhibited encoding deficits and specific comprehension difficulties. However, some demonstrated preserved memory monitoring abilities. Across different tests, it was observed that the more the confabulations occurred, the more severe were the comprehension difficulties.

CONCLUSION

The results are in favour of the hypothesis that verbal comprehension difficulties lead to the production of confabulation. They are inconsistent with the idea that memory monitoring impairment is necessarily involved.

Recall and recognition confabulation in psychotic and bipolar disorders: evidence for two different types without unitary mechanisms

Several forms of confabulation have been identified recently in schizophrenic patients, but it has not yet been investigated whether these forms are specific to schizophrenia. Furthermore, the origin of confabulation is unclear. The present study investigated recall and recognition confabulation and their relations with symptomatology, cognitive domains (abstraction and flexibility, verbal fluency, verbal memory, motor activity, and visual-motor processing/attention), computed tomographic (CT) measures (ventricular, cerebral, and Sylvian fissure size), and auditory event-related potentials (amplitudes and latencies of peak components in oddball paradigms) in 33 schizophrenic patients, 35 bipolar I patients, eight schizoaffective patients, and seven patients with other psychotic disorders. We found that neither type of confabulation was specific of any diagnostic group. Recall confabulation was mainly predicted by the predominance of positive symptoms, while recognition confabulation was predicted by a delay in P300 latency and the doses of antipsychotics used. Our results suggest two different mechanisms for both types of confabulation based on interference with the adequate retrieval of information and slowness in early stimulus detection.

Subcortical loop activation during selection of currently relevant memories

Clinical studies on spontaneous confabulation and imaging studies with healthy subjects indicate that the anterior limbic system, in particular, the orbitofrontal cortex (OFC), is necessary to adjust thought and behavior to current reality. It appears to achieve this by continuously suppressing activated memories that do not pertain to ongoing reality, even before their content is consciously recognized. In the present study, we explored through what anatomical connections the OFC exerts this influence. Healthy subjects were scanned with H(2)(15)O PET as they performed four blocks of continuous recognition tasks, each block composed of a different type of stimuli (meaningful designs, geometric designs, words, nonwords). Within each block, three runs composed of exactly the same picture series, arranged in different order each time, were made. Subjects were asked to indicate item recurrences only within the currently ongoing run and to disregard familiarity from previous runs. In the combined first runs, in which all items were initially new and responses could be based on familiarity judgement (with repeated items) alone, we found medial temporal and right orbitofrontal activation. In the combined third runs, when all items were already known and selection of currently relevant memories was required, we found left orbitofrontal activation contingent with distinct activation of the ventral striatum, head and body of the caudate nucleus, substantia nigra, and medial thalamus. The study indicates that the OFC influences the cortical representation of memories through subcortical connections including the basal ganglia and the thalamus. The data are compatible with a role of the dopaminergic reward system in the monitoring of ongoing reality in thinking.

Long-term prognosis after lacunar infarction

Lacunar infarcts, small deep infarcts that result from occlusion of a penetrating artery, account for about a quarter of all ischaemic strokes. These infarcts have commonly been regarded as benign vascular lesions with a favourable long-term prognosis. However, recent studies have shown that this is only the case early in the disease course. A few years after infarct, there is an increased risk of death, mainly from cardiovascular causes. The risk of recurrent stroke after lacunar infarct is similar to that for most other types of stroke, and patients have an increased risk of developing cognitive decline and dementia. Age, vascular risk factors, high nocturnal blood pressure, and severity of cerebral small-vessel disease at onset have significant prognostic implications for almost all outcomes. More studies on mechanisms, prevention, and treatment are needed to provide specific guidance on the long-term management of patients with lacunar infarcts. Risk-factor modification is likely to play a large part in therapeutic interventions targeted at this stroke subtype.

Neural basis of temporal context memory: a functional MRI study

Temporal context information is crucial to understanding human episodic memory. Human lesion and neuroimaging data indicate that prefrontal regions are important for retrieving temporal context memory, although the exact nature of their involvement is still unclear. We employed functional magnetic resonance imaging (fMRI) to elucidate the neural basis of two kinds of temporal context memory: the temporal order of items between lists and within a list. On the day of the fMRI experiment, subjects memorized a list of 30 pictures in the morning and another list of 30 pictures in the afternoon. During the scanning session, the subjects performed three tasks. In a between-lists task, they were asked to judge the temporal order between two items that had been presented in different lists. In a within-list task, they were asked to judge the temporal order between two items that had been presented in a single list. We found bilateral prefrontal activities during these two temporal context memory tasks compared with a simple item-recognition task. Furthermore, in direct comparison between these two tasks, we found differential prefrontal activities. Thus, right prefrontal activity was associated with temporal order judgment of items between lists, whereas left prefrontal activity was related to temporal order judgment of items within a list. These results indicate that retrieval processes of two kinds of temporal context memory are supported by different, but overlapping, sets of cerebral regions. We speculate that this reflects different cognitive processes for retrieving temporal context memory between separate episodes and within a single episode.

The hippocampus as an olfacto-motor mechanism: were the classical anatomists right after all?

The relations between behavior, olfactory input (monitored by recording the activity of the olfactory mucosa), and the spontaneous field potentials of the dentate gyrus were studied in freely moving rats. Bursts of 30-80 Hz (gamma) waves were elicited in the dentate gyrus when a rat sniffed at a variety of objects but were not elicited by auditory, somesthetic, or visual inputs and were not related to the occurrence of locomotion. The presence of gamma wave activity was associated with an enhancement of the population spike elicited in the dentate gyrus by stimulation of the perforant path. Odorized air blown into a nostril via a cannula, inserted under light urethane anesthesia, elicited a gamma wave response bilaterally in the dentate gyrus. These and other data were reviewed to support the general hypothesis that the hippocampus is primarily an olfacto-motor mechanism and does not play any unique role in learning and memory, cognitive mapping, or emotion. The role of the hippocampus in the control of some forms of motor activity is supported by numerous anatomical and electrophysiological studies, studies of the effect of hippocampal lesions on behavior, and studies of the effects of electrical or chemical stimulation of the hippocampus on behavior.

Extensive metabolic and neuropsychological abnormalities associated with discrete infarction of the genu of the internal capsule

OBJECTIVE

The clinical presentation of capsular genu infarct varies. Prominent faciolingual weakness and subcortical dementia are the rule, but symptoms depend on the precise location and extension of the lesion beyond the genu. The aim was to characterise the radiographic, electroencephalographic, and neuropsychometric abnormalities in a woman who had a history of recurrent transient memory loss.

METHOD

Case report.

RESULTS

Magnetic resonance imaging showed an infarct in the genu of the left internal capsule. Positron emission tomography scan demonstrated decreased metabolic activity in the ipsilateral temporal, occipitotemporal, and contralateral cerebellar hemispheres. Electroencephalography showed intermittent rhythmic delta activity in the left frontotemporal region, and findings on neuropsychometric evaluation were consistent with cognitive impairment. Follow up evaluation 7 months after the stroke showed improvement in some areas of the cognitive domain, but residual neuropsychometric and neurophysiological abnormalities persisted.

CONCLUSION

This case illustrates that cerebral and cerebellar diaschisis may contribute to the symptomatic presentation and recovery from capsular genu infarct, although its precise role remains elusive.

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.