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

Reality monitoring and metacognitive judgments in a false-memory paradigm

How well do we distinguish between different memory sources when the information from imagination and perception is similar? And how do metacognitive (confidence) judgments differ across different sources of experiences? To study these questions, we developed a reality monitoring task using semantically related words from the Deese-Roediger-McDermott (DRM) paradigm of false memories. In an orientation phase, participants either perceived word pairs or had to voluntarily imagine the second word of a word pair. In a test phase, participants viewed words and had to judge whether the paired word was previously perceived, imagined, or new. Results revealed an interaction between memory source and judgment type on both response rates and confidence judgments: reality monitoring was better for new and perceived (compared to imagined) sources, and participants often incorrectly reported imagined experiences to be perceived. Individuals exhibited similar confidence between correct imagined source judgments and incorrect imagined sources reported to be perceived. Modeling results indicated that the observed judgments were likely due to an externalizing bias (i.e., a bias to judge the memory source as perceived). Additionally, we found that overall metacognitive ability was best in the perceived source. Together, these results reveal a source-dependent effect on response rates and confidence ratings, and provide evidence that observers are surprisingly prone to externalizing biases when monitoring their own memories.

Interventions for confabulation: A systematic literature review

OBJECTIVE

Confabulations are false memories which are expressedwithout the intention to deceive and arise following brain damage or psychological dysfunction. Confabulations can become a barrier to effective neuropsychological rehabilitation and consequently, intervention is required.The current review aimed to provide a detailed evaluative account of existing interventions for confabulation and their relative effectiveness.

METHOD

The search process found 11 studies conducive with the inclusion and exclusion criteria. A methodological quality assessment was then carried out and the majority of included studies demonstrated poor methodological quality.

RESULTS

Ten types of interventions were identified and the majority of theseled to a reduction or elimination of confabulations.

CONCLUSION

Since methodological quality of many included studies was deemed unsatisfactory, further large-scale experimental research and standardised measures are necessary to adequately compare the relative effectiveness of these interventions. Further research and clinical implications are also highlighted.

The Fornix May Play a Key Role in Korsakoff's Amnesia Secondary to Subcallosal Artery Infarction

BACKGROUND

Subcallosal artery infarction injures the fornix and anterior corpus callosum and sometimes causes Korsakoff's amnesia. We hypothesized that Korsakoff's amnesia might be caused by fornix dysfunction rather than anterior corpus callosum dysfunction in subcallosal artery infarction.

METHODS

A systematic review approach was applied to search PubMed and Google Scholar for articles to compare patients who had both bilateral fornix and corpus callosum infarction due to subcallosal artery territory ischemia (vascular event group; V group) with patients who had undergone anterior corpus callosotomy (callosotomy group; C group).

RESULTS

The V group comprised 10 patients (mean age, 63 years; median, 69 years; standard deviation (SD), 14.5 years; 5 males, 5 females). The C group comprised 6 patients (mean age, 23.7 years; median, 20 years; SD, 7.3 years; 3 males, 3 females). Six of 10 patients (60%) with subcallosal artery infarction exhibited Korsakoff's amnesia. One patient showed neither confabulation nor amnesia. Conversely, no amnesia episodes were seen in any patients from the C group (p = 0.034).

CONCLUSION

Fornix injury, rather than anterior corpus callosum injury, might be the major cause of Korsakoff's amnesia in patients with subcallosal artery infarction.

Neuroimaging correlates of false memory in 'Alzheimer's disease: A preliminary systematic review

Alzheimer's disease (AD) is characterised by episodic memory impairment, but people also experience memory distortions, including false memories, which can impact on safety and reduce functioning. Understanding the neural networks that underpin false memories could help to predict the need for intervention and guide development of cognitive strategies to reduce memory errors. However, there is a relative absence of research into how the neuropathology of AD contributes to false memory generation. This paper systematically reviews the methodology and outcomes of studies investigating the neuroimaging correlates of false memory in AD. Four studies using structural imaging and three studies using functional imaging were identified. Studies were heterogenous in methodology and received mostly 'weak' quality assessment ratings. Combined, and consistent with neuroimaging findings in non-AD populations, results from identified studies provide preliminary support for the hypothesis that medial temporal lobe and prefrontal cortex dysfunction may lead to generation of false memories in AD. However, the small number of studies and significant heterogeneity within them means further study is necessary to assess replicability of results.

In search of the moral-psychological and neuroevolutionary basis of political partisanship

In many countries, a radical political divide brings several socially relevant decisions to a standstill. Could cognitive, affective and social (CAS) neuroscience help better understand these questions? The present article reviews the moral-psychological and neuroevolutionary basis of the political partisanship divide. A non-systematic literature review and a conceptual analysis were conducted. Three main points are identified and discussed: 1) Political partisan behavior rests upon deep moral emotions. It is automatically processed and impervious to contradiction. The moral motifs characterizing political partisanship are epigenetically set across different cultures;2) partisanship is linked to personality traits, whose neural foundations are associated with moral feelings and judgement;3) Self-deception is a major characteristic of political partisanship that probably evolved as an evolutionary adaptive strategy to deal with the intragroup-extragroup dynamics of human evolution. CAS neuroscience evidence may not resolve the political divide, but can contribute to a better understanding of its biological foundations.

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.

A boost of confidence: The role of the ventromedial prefrontal cortex in memory, decision-making, and schemas

The ventromedial prefrontal cortex (vmPFC) has been implicated in a wide array of functions across multiple domains. In this review, we focus on the vmPFC's involvement in mediating strategic aspects of memory retrieval, memory-related schema functions, and decision-making. We suggest that vmPFC generates a confidence signal that informs decisions and memory-guided behaviour. Confidence is central to these seemingly diverse functions: (1) Strategic retrieval: lesions to the vmPFC impair an early, automatic, and intuitive monitoring process ("feeling of rightness"; FOR) often associated with confabulation (spontaneous reporting of erroneous memories). Critically, confabulators typically demonstrate high levels of confidence in their false memories, suggesting that faulty monitoring following vmPFC damage may lead to indiscriminate confidence signals. (2) Memory schemas: the vmPFC is critically involved in instantiating and maintaining contextually relevant schemas, broadly defined as higher level knowledge structures that encapsulate lower level representational elements. The correspondence between memory retrieval cues and these activated schemas leads to FOR monitoring. Stronger, more elaborate schemas produce stronger FOR and influence confidence in the veracity of memory candidates. (3) Finally, we review evidence on the vmPFC's role in decision-making, extending this role to decision-making during memory retrieval. During non-mnemonic and mnemonic decision-making the vmPFC automatically encodes confidence. Confidence signal in the vmPFC is revealed as a non-linear relationship between a first-order monitoring assessment and second-order action or choice. Attempting to integrate the multiple functions of the vmPFC, we propose a posterior-anterior organizational principle for this region. More posterior vmPFC regions are involved in earlier, automatic, subjective, and contextually sensitive functions, while more anterior regions are involved in controlled actions based on these earlier functions. Confidence signals reflect the non-linear relationship between first-order, posterior-mediated and second-order, anterior-mediated processes and are represented along the entire axis.

Neural correlates of malingering in mild traumatic brain injury: A positron emission tomography study

The detection of malingering in cognitive performance is a challenge in clinical and legal environments. Neuroimaging may provide an objective method to determine the source of failure on tests of symptom validity. Participants comprised 45 combat veterans, 31 with mild traumatic brain injury (mTBI), not seeking medical or legal compensation, who completed the Tombaugh Test of Memory Malingering (TOMM) and a positron emission tomography (PET) scan. Based on TOMM performance (i.e., less than 45 of 50 total correct, suggesting suboptimal effort or malingering), subjects were separated into poor TOMM score (PT; n=10) and good TOMM score (GT; n=35) groups. Voxel-based multiple regression analysis with Group (GT/PT) predicting uptake of fluorodeoxyglucose revealed decreased brain metabolism in the ventromedial prefrontal cortex of poor performers. The current findings may suggest that poor TOMM performance in those with combat trauma and mTBI may be related to ventromedial prefrontal cortical dysfunction. These findings have important implications for the disentanglement of feigned versus actual memory impairment, where the latter may be secondary to neural mechanisms not consistent with forgetting or deception.

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.

Puzzling Confabulations – An Overview of Classifications and Theories

Abstract. Confabulations comprise a puzzling collection of false statements, produced without conscious intent to deceive. They have been classified according to the mode of elicitation (spontaneous vs. provoked), the content (fantastic vs. plausible), the memory domain in which they become manifest (episodic vs. semantic), their stability (stable vs. ephemeral), or their selectivity (monothematic vs. multithematic). All classifications appear to be problematic, because there are no clear-cut dichotomies, and confabulations often seem to fall into overlapping categories. There are, in fact, many theories, presumably explaining different kinds of confabulations; the best bet is to regard them as complementary rather than competing.

Psychedelic symptoms of cannabis and cocaine use as a function of trait impulsivity

Trait impulsivity has been linked to addiction in humans. It has been suggested that drug users with high trait impulsivity levels are more sensitive to subjective drug intoxication. This study assessed whether subjective response to drugs differs between drug users with normal or high levels of trait impulsivity. Regular drug users (N = 122) received doses of cocaine HCl, cannabis, and placebo in a three-way crossover study. Their mood, dissociative state, and psychedelic symptoms were measured with subjective rating scales (CADDS, Bowdle, POMS). Trait impulsivity was assessed with the Barratt Impulsiveness Scale. Cannabis increased dissociation and psychedelic state, as well as fatigue, confusion, depression and anxiety, and decreased arousal, positive mood, vigor, friendliness, and elation. Cocaine increased dissociation, psychedelic state, vigor, friendliness, elation, positive mood, anxiety and arousal, while decreasing fatigue. Only a few subjective items revealed a drug × trait impulsivity interaction, suggesting that psychedelic symptoms were most intense in high impulsivity subjects. Trait impulsiveness ratings were negatively correlated with ratings of vigor (r = -.197) and positively correlated with ratings of loss of thought control (r = .237) during cannabis intoxication. It is concluded that a broad association between trait impulsivity and psychedelic subjective drug experience appears to be absent.

Orientation and disorientation: lessons from patients with epilepsy

Orientation in time, space, and person is a fundamental cognitive faculty and the bedrock of neurological and psychiatric mental status examination. Nevertheless, research in orientation and disorientation is neglected in both cognitive science and neuropsychiatry. Specifically, it is still unclear whether disorientations in time, space, and person represent a failure of the same system or merely share a common nomenclature and whether these three domains of orientation depend on different psychological and neural systems. Here, we analyzed descriptions of patients with specific orientation failures associated with circumscribed cortical lesions, with a primary focus on epilepsy. The form of disorientation is analyzed according to its specific domain, the underlying neuropsychiatric disorder, and its anatomical correlate. Disorientations in the different domains are classified as self-referenced (incorrect self-localization) or nonself-referenced (incorrect localization or knowledge of other places, events, and people). Analysis of the cognitive and neural systems disturbed in these patients suggests that disorientation in one or several domains may be related to a failure in a specific brain mechanism localized mostly in the right hemisphere, partially overlapping with the default mode network (mostly the medial and lateral parietal, medial temporal, and lateral prefrontal cortices), which processes essential self-related cognitive faculties such as orientation.

Enhanced power within the default mode network in normal subjects with elevated scores on an egocentric scale

Integrated global power from the primary structures that composed the Default Mode Network (DMN) and from a random collection of other structures were measured by sLORETA (standardized low-resolution electromagnetic tomography) for young university volunteers who had completed an inventory that contained a subscale by which egocentricity has been inferred. Subjects who exhibited higher scores for egocentricity displayed significantly more power within the DMN structures relative to comparison areas. This was not observed for individuals whose egocentricity scores were lowest where the power differences between the DMN and comparison structures were not significant statistically. DMN power was greater in the right hemisphere than the left for men but greater in the left hemisphere than the right for women. The results are consistent with our operating metaphor that elevation of power or activity within the DMN is associated with greater affiliation with the self and its cognitive contents.

Dreams, reality and memory: confabulations in lucid dreamers implicate reality-monitoring dysfunction in dream consciousness

INTRODUCTION

Dreams might represent a window on altered states of consciousness with relevance to psychotic experiences, where reality monitoring is impaired. We examined reality monitoring in healthy, non-psychotic individuals with varying degrees of dream awareness using a task designed to assess confabulatory memory errors - a confusion regarding reality whereby information from the past feels falsely familiar and does not constrain current perception appropriately. Confabulatory errors are common following damage to the ventromedial prefrontal cortex (vmPFC). Ventromedial function has previously been implicated in dreaming and dream awareness.

METHODS

In a hospital research setting, physically and mentally healthy individuals with high (n = 18) and low (n = 13) self-reported dream awareness completed a computerised cognitive task that involved reality monitoring based on familiarity across a series of task runs.

RESULTS

Signal detection theory analysis revealed a more liberal acceptance bias in those with high dream awareness, consistent with the notion of overlap in the perception of dreams, imagination and reality.

CONCLUSIONS

We discuss the implications of these results for models of reality monitoring and psychosis with a particular focus on the role of vmPFC in default-mode brain function, model-based reinforcement learning and the phenomenology of dreaming and waking consciousness.

Ketamine effects on memory reconsolidation favor a learning model of delusions

Delusions are the persistent and often bizarre beliefs that characterise psychosis. Previous studies have suggested that their emergence may be explained by disturbances in prediction error-dependent learning. Here we set up complementary studies in order to examine whether such a disturbance also modulates memory reconsolidation and hence explains their remarkable persistence. First, we quantified individual brain responses to prediction error in a causal learning task in 18 human subjects (8 female). Next, a placebo-controlled within-subjects study of the impact of ketamine was set up on the same individuals. We determined the influence of this NMDA receptor antagonist (previously shown to induce aberrant prediction error signal and lead to transient alterations in perception and belief) on the evolution of a fear memory over a 72 hour period: they initially underwent Pavlovian fear conditioning; 24 hours later, during ketamine or placebo administration, the conditioned stimulus (CS) was presented once, without reinforcement; memory strength was then tested again 24 hours later. Re-presentation of the CS under ketamine led to a stronger subsequent memory than under placebo. Moreover, the degree of strengthening correlated with individual vulnerability to ketamine's psychotogenic effects and with prediction error brain signal. This finding was partially replicated in an independent sample with an appetitive learning procedure (in 8 human subjects, 4 female). These results suggest a link between altered prediction error, memory strength and psychosis. They point to a core disruption that may explain not only the emergence of delusional beliefs but also their persistence.

Comparative study on the inhibitory effect of caffeic and chlorogenic acids on key enzymes linked to Alzheimer's disease and some pro-oxidant induced oxidative stress in rats' brain-in vitro

This study sought to investigate and compare the interaction of caffeic acid and chlorogenic acid on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and some pro-oxidants (FeSO(4), sodium nitroprusside and quinolinic acid) induced oxidative stress in rat brain in vitro. The result revealed that caffeic acid and chlorogenic acid inhibited AChE and BChE activities in dose-dependent manner; however, caffeic acid had a higher inhibitory effect on AChE and BChE activities than chlorogenic acid. Combination of the phenolic acids inhibited AChE and BChE activities antagonistically. Furthermore, pro-oxidants such as, FeSO(4), sodium nitroprusside and quinolinic acid caused increase in the malondialdehyde (MDA) contents of the brain which was significantly decreased dose-dependently by the phenolic acids. Inhibition of AChE and BChE activities slows down acetylcholine and butyrylcholine breakdown in the brain. Therefore, one possible mechanism through which the phenolic acids exert their neuroprotective properties is by inhibiting AChE and BChE activities as well as preventing oxidative stress-induced neurodegeneration. However, esterification of caffeic acid with quinic acid producing chlorogenic acid affects these neuroprotective properties.

Substitutional reality system: a novel experimental platform for experiencing alternative reality

We have developed a novel experimental platform, referred to as a substitutional reality (SR) system, for studying the conviction of the perception of live reality and related metacognitive functions. The SR system was designed to manipulate people's reality by allowing them to experience live scenes (in which they were physically present) and recorded scenes (which were recorded and edited in advance) in an alternating manner without noticing a reality gap. All of the naïve participants (n = 21) successfully believed that they had experienced live scenes when recorded scenes had been presented. Additional psychophysical experiments suggest the depth of visual objects does not affect the perceptual discriminability between scenes, and the scene switch during head movement enhance substitutional performance. The SR system, with its reality manipulation, is a novel and affordable method for studying metacognitive functions and psychiatric disorders.

Olfactory impairment is correlated with confabulation in alcoholism: towards a multimodal testing of orbitofrontal cortex

BACKGROUND

Olfactory abilities are now a flourishing field in psychiatry research. As the orbitofrontal cortex appears to be simultaneously implicated in odour processing and executive impairments, it has been proposed that olfaction could constitute a cognitive marker of psychiatric states. While this assumption appears promising, very few studies have been conducted on this topic among psychopathological populations. The present study thus aimed at exploring the links between olfaction and executive functions. These links were evaluated using two tasks of comparable difficulty, one known to rely on orbitofrontal cortex processing (i.e., a confabulation task), and one not associated with this area (i.e., Stop-Signal task).

METHODOLOGY/PRINCIPAL FINDINGS

Twenty recently detoxified alcoholic individuals and twenty paired controls took part in an experiment evaluating olfactory abilities and executive functioning (i.e., Stop-Signal task and confabulation task). Comorbidities and potential biasing variables were also controlled for. Alcoholic individuals exhibited impaired performance for high-level olfactory processing and significant confabulation problems as compared to controls (but no deficit in Stop-Signal task), even when the influence of comorbidities was taken into account. Most importantly, olfactory abilities and confabulation rates were significantly correlated in both groups.

CONCLUSIONS/SIGNIFICANCE

Alcoholism jointly leads to olfactory and memory source impairments, and these two categories of deficits are associated. These results strongly support the proposition that olfactory and confabulation measures both index orbitofrontal functioning, and suggest that olfaction could become a reliable cognitive marker in psychiatric disorders. Moreover, it underlines the need to take into account these olfactory and source memory impairments in a clinical context.

Glutamatergic model psychoses: prediction error, learning, and inference

Modulating glutamatergic neurotransmission induces alterations in conscious experience that mimic the symptoms of early psychotic illness. We review studies that use intravenous administration of ketamine, focusing on interindividual variability in the profundity of the ketamine experience. We will consider this individual variability within a hypothetical model of brain and cognitive function centered upon learning and inference. Within this model, the brains, neural systems, and even single neurons specify expectations about their inputs and responding to violations of those expectations with new learning that renders future inputs more predictable. We argue that ketamine temporarily deranges this ability by perturbing both the ways in which prior expectations are specified and the ways in which expectancy violations are signaled. We suggest that the former effect is predominantly mediated by NMDA blockade and the latter by augmented and inappropriate feedforward glutamatergic signaling. We suggest that the observed interindividual variability emerges from individual differences in neural circuits that normally underpin the learning and inference processes described. The exact source for that variability is uncertain, although it is likely to arise not only from genetic variation but also from subjects' previous experiences and prior learning. Furthermore, we argue that chronic, unlike acute, NMDA blockade alters the specification of expectancies more profoundly and permanently. Scrutinizing individual differences in the effects of acute and chronic ketamine administration in the context of the Bayesian brain model may generate new insights about the symptoms of psychosis; their underlying cognitive processes and neurocircuitry.

Toward a neurobiology of delusions

Delusions are the false and often incorrigible beliefs that can cause severe suffering in mental illness. We cannot yet explain them in terms of underlying neurobiological abnormalities. However, by drawing on recent advances in the biological, computational and psychological processes of reinforcement learning, memory, and perception it may be feasible to account for delusions in terms of cognition and brain function. The account focuses on a particular parameter, prediction error--the mismatch between expectation and experience--that provides a computational mechanism common to cortical hierarchies, fronto-striatal circuits and the amygdala as well as parietal cortices. We suggest that delusions result from aberrations in how brain circuits specify hierarchical predictions, and how they compute and respond to prediction errors. Defects in these fundamental brain mechanisms can vitiate perception, memory, bodily agency and social learning such that individuals with delusions experience an internal and external world that healthy individuals would find difficult to comprehend. The present model attempts to provide a framework through which we can build a mechanistic and translational understanding of these puzzling symptoms.

Confabulation and delusion: a common monitoring framework

Confabulations and delusions both involve the production of false claims. Although they may have different types of content, they share several characteristics. For example, they are often held with considerable conviction and are resistant to counter evidence, they may be acted upon, and they may be accompanied by a lack of concern about the false claim or its implications. Confabulations and delusions may initially arise from failures in different systems (e.g., mnemonic vs. perceptual or affective). However, their shared characteristics raise the possibility that the monitoring deficits involved might be the same, resulting in failure to reject the confabulatory or delusional ideas. In this paper we will focus on the nature of these common monitoring deficits. Critically, we argue that monitoring in confabulation and delusion involves both unconscious and conscious processes. We propose that an unconscious process is responsible for tagging suspect content which needs to be checked for veracity by a separate set of conscious evaluative processes. Failure of these monitoring processes would allow ideas which ought to be checked and rejected to instead be uncritically accepted: This would result in the production of confabulations or delusions. Importantly, inclusion of both unconscious and conscious monitoring stages allows the model to account for both "endorsement" and "explanation" delusions, and both "primary" and "secondary" confabulations. Our hope is that this model may provide a theoretical framework to guide empirical investigation of the commonalities and differences between the conditions.

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.

Memory loss in Alzheimer's disease: implications for development of therapeutics

Alzheimer's disease (AD) is a progressive neurodegenerative disease marked by a constellation of cognitive disturbances, the earliest and most prominent being impaired episodic memory. Episodic memory refers to the memory system that allows an individual to consciously retrieve a previously experienced item or episode of life. Many recent studies have focused on characterizing how AD pathology impacts particular aspects of episodic memory and underlying mental and neural processes. This review summarizes the findings of those studies and discusses the effects of current and promising treatments for AD on episodic memory. The goal of this review is to raise awareness of the strides that cognitive neuroscientists have made in understanding intact and dysfunctional memory. Knowledge of the specific memorial processes that are impaired in AD may be of great value to basic scientists developing novel therapies and to clinical researchers assessing the efficacy of those therapies.

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.

Functional neuroimaging of belief, disbelief, and uncertainty

OBJECTIVE

The difference between believing and disbelieving a proposition is one of the most potent regulators of human behavior and emotion. When one accepts a statement as true, it becomes the basis for further thought and action; rejected as false, it remains a string of words. The purpose of this study was to differentiate belief, disbelief, and uncertainty at the level of the brain.

METHODS

We used functional magnetic resonance imaging (fMRI) to study the brains of 14 adults while they judged written statements to be "true" (belief), "false" (disbelief), or "undecidable" (uncertainty). To characterize belief, disbelief, and uncertainty in a content-independent manner, we included statements from a wide range of categories: autobiographical, mathematical, geographical, religious, ethical, semantic, and factual.

RESULTS

The states of belief, disbelief, and uncertainty differentially activated distinct regions of the prefrontal and parietal cortices, as well as the basal ganglia.

INTERPRETATION

Belief and disbelief differ from uncertainty in that both provide information that can subsequently inform behavior and emotion. The mechanism underlying this difference appears to involve the anterior cingulate cortex and the caudate. Although many areas of higher cognition are likely involved in assessing the truth-value of linguistic propositions, the final acceptance of a statement as "true" or its rejection as "false" appears to rely on more primitive, hedonic processing in the medial prefrontal cortex and the anterior insula. Truth may be beauty, and beauty truth, in more than a metaphorical sense, and false propositions may actually disgust us.

Evolution of Neurological, Neuropsychological and Sleep-Wake Disturbances After Paramedian Thalamic Stroke

Background and Purpose— The clinical features and natural course of paramedian thalamic stroke is poorly known. The aim of this study was to characterize the evolution of neurological, neuropsychological, and sleep–wake deficits after paramedian thalamic stroke.

Methods— Forty-six consecutive patients, aged 48.4±16.6 years, were studied. Fourteen had bilateral, 16 left-sided, and 16 right-sided lesions. Assessment included neurological examinations, estimation of sleep needs, formal neuropsychological tests (n=27), and polysomnographies (n=31). Functional outcome was followed up over 1 year in 31 patients with the modified Rankin Scale and Barthel index.

Results— Oculomotor palsy (76% of patients), mild gait ataxia (67%), deficits of attention (63%), fluency and error control (59%), learning and memory (67%), and behavior (67%) were common in the acute stroke phase. Outcome was excellent with right-sided infarcts but mostly incomplete with bilateral and left-sided lesions. This was mainly related to persistent frontal lobe-related and cognitive deficits found in 100% bilateral and 90% left-sided, but only 33% right-sided strokes. Initially, hypersomnia was present in all patients associated with increased stage 1 sleep, reduced stage 2 sleep, and reduced sleep spindles. Sleep needs improved in patients with bilateral and almost disappeared with unilateral lesions after 1 year. Sleep architecture remained abnormal with the exception of sleep spindles that increased.

Conclusions— Whereas neurological deficits and hypersomnia recover to large extent in patients with paramedian thalamic stroke, the frontal lobe-related and cognitive deficits, which are mainly linked with bilateral and left-sided lesions, often persist. As such, stroke outcome is better in right-sided than bilateral or left-sided infarcts.

Intrusion errors in explicit memory: their differential relationship with clinical and social outcome in chronic schizophrenia

INTRODUCTION

Memory deficits might account for clinical and adaptive differences between groups of patients with chronic schizophrenia. We investigated the qualitative factors of memory that influence clinical and social status.

METHODS

Psychosocial functioning, clinical symptoms, and memory function were assessed in 99 patients at four time points over a 16-month period using recall scores for semantically related words, unrelated words, paired associated learning, and word span. An initial cluster analysis using symptom assessment data from all four time points divided the sample into three groups: patients with low symptoms ratings that remained stable throughout the study period (low symptom-stable group - LSSG; N=51); patients with initially high symptoms ratings that subsequently improved (high symptom-improved group - HSIG; N=32); and patients with initially high symptoms ratings that deteriorated during the follow-up (high symptom-deteriorated group - HSDG; N=16).

RESULTS

Memory was better preserved in LSSG compared to HSIG and HSDG patients. Recall performance was generally better for semantically related words than for unrelated words but the difference between LSSG and the two other groups was more constant over time for semantically related words. Extra-list errors variable was positively correlated with three PANSS measures (r=.25-.47). Also, the extra-list errors scores were correlated with the Magical Ideation Scale (r=.34-.39). Memory scores (global explicit, unrelated, related) were significantly and positively correlated with independent living skills (r=.26-.55) and the extra-list errors were negatively correlated with both social support and independent living skills (r=-.29 and r=-.46, respectively). All groups showed a reduction in extraneous false recognition errors/intrusions (FRIs) over time with the HSIG showing the greater change. HSIG and HSDG patients committed slightly more FRIs in recall tasks (extraneous information) than LSSG patients.

CONCLUSION

Memory performance is better in patients presenting with less severe symptomatology. The extent to which FRIs reduce over time in patients with schizophrenia is a novel finding.

Dissociating the past from the present in the activity of place cells

It has been proposed that declarative memories can be dependent on both an episodic and a semantic memory system. While the semantic system deals with factual information devoid of reference to its acquisition, the episodic system, characterized by mental time travel, deals with the unique past experience in which an event took place. Episodic memory is characteristically hippocampus-dependent. Place cells are recorded from the hippocampus of rodents and their firing reflects many of the key characteristics of episodic memory. For example, they encode information about "what" happens "where," as well as temporal information. However, when these features are expressed during an animal's behavior, the neuronal activity could merely be categorizing the present situation and could therefore reflect semantic memory rather than episodic memory. We propose that mental time travel is the key feature of episodic memory and that it should take a form, in the awake animal, similar to the replay of behavioral patterns of activity that has been observed in hippocampus during sleep. Using tasks designed to evoke episodic memory, one should be able to see memory reactivation of behaviorally relevant sequences of activity in the awake animal while recording from hippocampus and other cortical structures.

Multiple sclerosis presenting with fantastic confabulation

Multiple sclerosis (MS) is the most common inflammatory, demyelinating disease of the central nervous system. Besides neurological signs and symptoms, the disease may be associated with various psychiatric manifestations, and uncommonly, psychiatric manifestations may be the presenting symptom. On the other hand, confabulation is defined as falsification of memory occurring in clear consciousness in association with an organically derived amnesia or as spontaneous narrative reports of events that never happened. We report an unusual association of confabulation with MS. A 23-year-old man was admitted to a hospital, telling unusual stories. After evaluation and a detailed workup, the patient was given the diagnosis of MS with fantastic confabulations. Neuropsychological evaluation revealed mild frontal lobe dysfunction. Confabulation has been reported after frontal lobe lesions and is also hypothesized to be associated with a deficit primarily in the retrieval of more than one of the following: encoding, consolidation or storage. Clinicians' awareness of this kind of rare association may further enlighten the neural basis of confabulation.

A cognitive neuroscience perspective on psychopathy: evidence for paralimbic system dysfunction

Psychopathy is a complex personality disorder that includes interpersonal and affective traits such as glibness, lack of empathy, guilt or remorse, shallow affect, and irresponsibility, and behavioral characteristics such as impulsivity, poor behavioral control, and promiscuity. Much is known about the assessment of psychopathy; however, relatively little is understood about the relevant brain disturbances. The present review integrates data from studies of behavioral and cognitive changes associated with focal brain lesions or insults and results from psychophysiology, cognitive psychology and cognitive and affective neuroscience in health and psychopathy. The review illustrates that the brain regions implicated in psychopathy include the orbital frontal cortex, insula, anterior and posterior cingulate, amygdala, parahippocampal gyrus, and anterior superior temporal gyrus. The relevant functional neuroanatomy of psychopathy thus includes limbic and paralimbic structures that may be collectively termed 'the paralimbic system'. The paralimbic system dysfunction model of psychopathy is discussed as it relates to the extant literature on psychopathy.

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.

Knowing "what" and knowing "when"

The ability to situate autobiographical memories accurately in the "time-line" of one's own life is a particular aspect of retrograde memory that has received little attention in well-controlled, systematic studies. Here, we addressed this issue by testing the hypothesis that patients with basal forebrain damage would be impaired in their ability to place various autobiographical memories accurately on a 'time-line' of their life. Seven such subjects were contrasted with 11 medial temporal lobe subjects, 8 brain-damaged comparison subjects, and 18 normal comparison subjects, using a procedure in which subjects placed autobiographical events on a time-line of their life. The basal forebrain group was very impaired in this task, relative to the other groups, and on average, misplaced events by more than five years. Although the basal forebrain group was also impaired in retrieving the contents of autobiographical memory, they did not differ statistically from the medial temporal lobe group in this regard (and the medial temporal lobe group did not have impaired time placement of memories). The results indicate an intriguing dissociation between "knowing what" and "knowing when," and suggest that the basal forebrain contains structures that are especially important for "knowing when." Our findings are compatible with the view that the basal forebrain participates critically in retrieval strategies important for memory chronology, which contrasts with the medial temporal lobe's critical role in relational memory per se.

Frontal lobe contributions to recognition and recall: linking basic research with clinical evaluation and remediation

The role of the human frontal lobes in episodic memory is becoming better understood, thanks mainly to focal lesion and neuroimaging studies. Here we review some recent findings from basic research on the frontal lobes in memory encoding, search, and decision-making at retrieval. For each of these processes, researchers have uncovered cases in which frontal memory impairments can be attenuated by various task manipulations. We suggest ways in which these findings may inform clinical evaluation and rehabilitation of memory problems following frontal damage.

The cognitive neuroscience of memory distortion

Memory distortion occurs in the laboratory and in everyday life. This article focuses on false recognition, a common type of memory distortion in which individuals incorrectly claim to have encountered a novel object or event. By considering evidence from neuropsychology, neuroimaging, and electrophysiology, we address three questions. (1) Are there patterns of neural activity that can distinguish between true and false recognition? (2) Which brain regions contribute to false recognition? (3) Which brain regions play a role in monitoring or reducing false recognition? Neuroimaging and electrophysiological studies suggest that sensory activity is greater for true recognition compared to false recognition. Neuropsychological and neuroimaging results indicate that the hippocampus and several cortical regions contribute to false recognition. Evidence from neuropsychology, neuroimaging, and electrophysiology implicates the prefrontal cortex in retrieval monitoring that can limit the rate of false recognition.

What's in a Name for Memory Errors? Implications and Ethical Issues Arising From the Use of the Term "False Memory" for Errors in Memory for Details

The term "false memories" has been used to refer to suggestibility experiments in which whole events are apparently confabulated and in media accounts of contested memories of childhood abuse. Since 1992 psychologists have increasingly used the term "false memory" when discussing memory errors for details, such as specific words within lists. Use of the term to refer to errors in details is a shift in language away from other terms used historically (e.g., "memory intrusions"). We empirically examine this shift in language and discuss implications of the new use of the term "false memories." Use of the term presents serious ethical challenges to the data-interpretation process by encouraging over-generalization and misapplication of research findings on word memory to social issues.

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.