Right temporofrontal cortex as critical locus for the ecphory of old episodic memories

Dissociative Amnesia: Remembrances Under Cover

The existence or questionability of "repressed memories" can be discussed as being a matter of definition. It seems, however, far-fetched to consider all "lost" memories as caused by encoding problems, brain damage, forgetfulness, failure to disclose events, and so on. We argue that dissociative amnesia (DA) (or "psychogenic amnesia," or "functional amnesia," or, as we favor to call it, "mnestic block syndrome") is caused by psychic alterations, but ultimately they can be traced to changes in the physiology of the brain, as we are of the opinion that all memory processes-positive or negative-alter brain functions, sometimes more permanently, sometimes transiently. We have proven this idea using functional imaging techniques, in particular fluoro-deoxy-d-glucose positron emission tomography. Having investigated dozens of patients with severe and long-lasting DA conditions, we believe it to be disrespectful to many (but not to all) of the affected patients to question their disease condition, which can be proven to be not caused by feigning, malingering, or direct brain damage.

Behavioral, neurological, and psychiatric frailty of autobiographical memory

Autobiographical-episodic memory is considered to be the most complex of the five long-term memory systems. It is autonoetic, which means, self-reflective, relies on emotional colorization, and needs the features of place and time; it allows mental time traveling. Compared to the other four long-term memory systems-procedural memory, priming, perceptual, and semantic memory-it develops the latest in phylogeny and ontogeny, and is the most vulnerable of the five systems, being easily impaired by brain damage and psychiatric disorders. Furthermore, it is characterized by its fragility and proneness to distortion due to environmental influences and subsequent information. On the brain level, a distinction has to be made between memory encoding and consolidating, memory storage, and memory retrieval. For encoding, structures of the limbic system, with the hippocampus in its center, are crucial, for storage of widespread cortical networks, and for retrieval again a distributed recollection network, in which the prefrontal cortex plays a crucial role, is engaged. Brain damage and psychiatric diseases can lead to what is called "focal retrograde amnesia." In this context, the clinical picture of dissociative or functional or psychogenic amnesia is central, as it may result in autobiographical-emotional amnesia of the total past with the consequence of an impairment of the self as well. The social environment therefore can have a major impact on the brain and on autobiographical-episodic memory processing. This article is categorized under: Psychology > Memory.

Functional Neural Architecture Supporting Highly Superior Autobiographical Memory

Background: The neural mechanisms of highly superior autobiographical memory (HSAM) are poorly understood. To shed light on the functional magnetic resonance imaging (fMRI)-informed neurobiology of this condition, in this study we characterize for the first time the neurofunctional architecture of a 20-year-old individual (B.B.) with HSAM and no concurrent neurological/psychiatric or other clinical conditions. Materials and Methods: Relying on t-test inferential models comparing a single observation with a control group, we processed B.B.'s resting-state fMRI signal and compared it with the neurofunctional architecture of 16 young adults with normal autobiographical memory. Specifically, we analyzed large-scale brain networks, region-to-region functional connectivity, and connectivity indices informed by graph theory. Results: B.B. showed higher expression of large-scale and region-to-region connectivity, larger segregation of the pallidum and enhanced centrality of the temporal pole, orbitofrontal cortex and cerebellar lobule IX. Conclusion: These findings indicate that HSAM is associated with increased expression of neural pathways that support memory encoding, retrieval, and elaboration, but also with reduced expression of patterns typically involved in information control and metacognition, the use of which would be minimized thanks to automatic and accurate memory processing.

Funny or Angry? Neural Correlates of Individual Differences in Aggressive Humor Processing

Humor has been a hot topic for social cognition in recent years. The present study focused on the social attribute of humor and showed different stories to participants, which were divided into four types according to the model of humor style, to explore the underlying neural mechanism of point-to-self aggressive humor and how individual differences modulated it. Measuring the degree of anger and funniness, results suggested that aggressive humor helped us in social communication by reducing the degree of anger. The neural activities showed that bilateral temporal lobes and frontal lobes played a synergistic role in the point-to-self aggressive humor processing, while point-to-self non-aggressive humor was dominant in the left-side brain. Results from the region of interest (ROI) analysis showed that the individual differences of the self-control level and the self-construal level may influence the neural processing of point-to-self aggressive humor by modulating the activated levels and patterns of the right inferior orbital frontal gyrus, the right superior temporal lobe, and the right superior frontal lobe.

Discrepancy Between Cerebral Structure and Cognitive Functioning: A Review

Neuroscientists typically assume that human mental functions are generated by the brain and that its structural elements, including the different cell layers and tissues that form the neocortex, play specific roles in this complex process. Different functional units are thought to complement one another to create an integrated self-awareness or episodic memory. Still, findings that pertain to brain dysplasia and brain lesions indicate that in some individuals there is a considerable discrepancy between the cerebral structures and cognitive functioning. This seems to question the seemingly well-defined role of these brain structures. This article provides a review of such remarkable cases. It contains overviews of noteworthy aspects of hydrocephalus, hemihydranencephaly, hemispherectomy, and certain abilities of "savants." We add considerations on memory processing, comment on the assumed role of neural plasticity in these contexts, and highlight the importance of taking such anomalies into account when formulating encompassing models of brain functioning.

Functional (dissociative) retrograde amnesia

Retrograde amnesia is described as condition which can occur after direct brain damage, but which occurs more frequently as a result of a psychiatric illness. In order to understand the amnesic condition, content-based divisions of memory are defined. The measurement of retrograde memory is discussed and the dichotomy between "organic" and "psychogenic" retrograde amnesia is questioned. Briefly, brain damage-related etiologies of retrograde amnesia are mentioned. The major portion of the review is devoted to dissociative amnesia (also named psychogenic or functional amnesia) and to the discussion of an overlap between psychogenic and "brain organic" forms of amnesia. The "inability of access hypothesis" is proposed to account for most of both the organic and psychogenic (dissociative) patients with primarily retrograde amnesia. Questions such as why recovery from retrograde amnesia can occur in retrograde (dissociative) amnesia, and why long-term new learning of episodic-autobiographic episodes is possible, are addressed. It is concluded that research on retrograde amnesia research is still in its infancy, as the neural correlates of memory storage are still unknown. It is argued that the recollection of episodic-autobiographic episodes most likely involves frontotemporal regions of the right hemisphere, a region which appears to be hypometabolic in patients with dissociative amnesia.

Traumatic brain injury and cognition

Traumatic brain injury (TBI) is a major cause of death and disability, and therefore an important health and socioeconomic problem for our society. Individuals surviving from a moderate to severe TBI frequently suffer from long-lasting cognitive deficits. Such deficits include different aspects of cognition such as memory, attention, executive functions, and awareness of their deficits. This chapter presents a review of the main neuropsychological and neuroimaging studies of patients with TBI. These studies found that patients evolve differently according to the severity of the injury, the mechanism causing the injury, and the lesion location. Further research is necessary to develop rehabilitation methods that enhance brain plasticity and recovery after TBI. In this chapter, we summarize current knowledge and controversies, focusing on cognitive sequelae after TBI. Recommendations from the Common Data Elements are provided, with an emphasis on diagnosis, outcome measures, and studies organization to make data more comparable across studies. Final considerations on neuroimaging advances, rehabilitation approaches, and genetics are described in the final section of the chapter.

Impairment of semantic memory after basal forebrain and fornix lesion

Semantic memory impairment is classically associated with lesion of the anterior temporal lobe. We report the case of a patient with severe semantic knowledge impairment and anterograde amnesia after bilateral ischemic lesion of the fornix and of the basal forebrain following surgical clipping of an aneurysm of the anterior communicating artery. Fluorodeoxyglucose positron emission tomography (FDG-PET) showed a temporal hypometabolism. Severe semantic impairment is a rare complication after rupture of an anterior communicating artery aneurysm and may result from disconnection of the temporal lobe.

FMRI contributions to addressing autobiographical memory impairment in temporal lobe pathology

Episodic autobiographical memory (AM) allows one, through the recollection of sensory-perceptual details, thoughts and feelings, to become aware of an event as belonging to one’s own past as well as being able to project into one’s future. Because AM provides a sense of self-continuity, contributes to the integrity of the self, and helps predicting future experiences, any deficit of AM may have debilitating consequences for everyday life functioning. Understanding AM failure and the underlying neural mechanisms has the potential to shed light on brain reorganization mechanisms and engagement of compensatory processes. Functional magnetic resonance imaging (fMRI) provides the most promising imaging method to tackle these issues. We reviewed evidence from the few studies that used fMRI to investigate the functionality of the residual tissue, the neural reorganization and compensatory mechanisms in patients with neurological conditions due to impaired medial temporal lobe. Overall, these studies highlight the importance of the left hippocampus, which when atrophied and not functional leads to AM deficits but its residual functionality may support relatively normal AM recollection. When damaged hippocampal tissue is not functional, other brain regions (e.g., the medial prefrontal cortex) may be involved to compensate impairment, but they appear generally ineffective to support detailed episodic recollection.

Memory and self-neuroscientific landscapes

Relations between memory and the self are framed from a number of perspectives-developmental aspects, forms of memory, interrelations between memory and the brain, and interactions between the environment and memory. The self is seen as dividable into more rudimentary and more advanced aspects. Special emphasis is laid on memory systems and within them on episodic autobiographical memory which is seen as a pure human form of memory that is dependent on a proper ontogenetic development and shaped by the social environment, including culture. Self and episodic autobiographical memory are seen as interlocked in their development and later manifestation. Aside from content-based aspects of memory, time-based aspects are seen along two lines-the division between short-term and long-term memory and anterograde-future-oriented-and retrograde-past-oriented memory. The state dependency of episodic autobiographical is stressed and implications of it-for example, with respect to the occurrence of false memories and forensic aspects-are outlined. For the brain level, structural networks for encoding, consolidation, storage, and retrieval are discussed both by referring to patient data and to data obtained in normal participants with functional brain imaging methods. It is elaborated why descriptions from patients with functional or dissociative amnesia are particularly apt to demonstrate the facets in which memory, self, and personal temporality are interwoven.

Focal retrograde amnesia and the attribution of causality: An exceptionally critical view

A detailed critique of the literature on focal retrograde amnesia is provided. Some of the cases commonly cited in this literature had, in fact, severely impaired anterograde memory, most often involving visuospatial material. Other cases showed poor anterograde memory in more moderate or subtle form, begging the question of whether "like" had really been compared with "like" across the retrograde and anterograde domains: there may be alternative explanations for the observed patterns of performance. One suggestion is that these patients suffer an impairment of long-term consolidation, an attractive hypothesis but one which requires much more rigorous testing than has occurred to date and which implies that the underlying problem is not specific to retrograde memory. Moreover, within the literature on cases of focal retrograde amnesia, differing patterns of performance on tests of autobiographical memory or remote semantic knowledge have been reported, and sometimes these may have reflected factors other than the sites of lesions. Many of the most convincing cases in this literature have been those in whom there was an initially severe anterograde amnesia as well as an extensive retrograde loss: in these cases, the critical issue is what determines differential patterns of recovery across these domains-it is likely that both physiological and psychological factors are important. A second, somewhat different, group are patients with semantic dementia, who show a pronounced recency effect in remote memory but, in these cases, the most parsimonious explanation may be in terms of predominantly semantic/linguistic and/or strategic factors. A third group are those with transient epileptic amnesia but, in these cases, the memory gaps may reflect past (anterograde) ictal activity. A fourth group are those in whom psychogenic factors may well be relevant. Although it is difficult to "prove" psychological causation, the logical difficulties in attributing causation where brain lesions are either very subtle or multiple have been considerably underestimated in the neuropsychological literature. Given these problems, in uncertain or equivocal cases, it is as critical to present the relevant psychological data for the reader to evaluate as it is to provide the pertinent memory test scores: this is underemphasised in many of the studies reviewed. Publication of cases in the absence of such data may lead to faulty clinical, neuropsychological, and cognitive conclusions. Abbreviations : AA: anterograde amnesia; AMI: Autobiographical Memory Interview; PTA: posttraumatic amnesia; RA: retrograde amnesia; RMT: Recognition Memory Test; TEA: transient epileptic amnesia; TGA: transient global amnesia; WMS: Wechsler Memory Scale.

The impairment of recollection in functional amnesic states

INTRODUCTION

Functional amnesia refers to various forms of amnesia, which have no direct organic brain basis. Psychological stress and trauma were etiologically linked to its development across various cultures.

METHODS

We have studied several patients with functional amnesia, employing neuropsychological and neuroimaging methods. Herein we provide a review of the current understanding of the phenomenology, neuropsychology and neurobiology of functional amnesia, which we illustrate by reference to five own case descriptions and other cases presented in the literature.

RESULTS

Functional amnesia is mostly of retrograde nature and presents in the form of a memory blockade or repression to recollect episodic-autobiographical events, which may cover the whole past life. Sometimes, the recollection impairment is localized to certain time epochs. In comparison to functional retrograde amnesia, functional isolated anterograde amnesia is much rarer and data on its neurobiology are scant. In patients with functional amnesia with pronounced retrograde episodic-autobiographical memory impairments, we identified changes in brain metabolism, above all reductions in the temporo-frontal regions of the right hemisphere. Recently, even subtle structural changes in the white matter of the (right) frontal cortex were described in functional retrograde amnesia by other researchers.

CONCLUSIONS

The disruption in recollection in functional amnesia is often accompanied by changes in personality dimensions, pertaining to cognition (self-related processing, theory of mind), autonoetic consciousness and affectivity. This suggests that functional amnesia is a multifaceted condition. We hypothesize that the recollection deficit in functional retrograde amnesia primarily reflects a desynchronization between a frontal lobe system, important for autonoetic consciousness, and a temporo-amygdalar system, important for evaluation and emotions. Despite assumptions that functional amnesia can always be reversed, several cases of functional amnesia were found to follow a chronic course, suggesting a need for longitudinal prospective studies to quantify possible global cognitive deterioration over time and its neural underpinnings.

Amygdala in action: relaying biological and social significance to autobiographical memory

The human amygdala is strongly embedded in numerous other structures of the limbic system, but is also a hub for a multitude of other brain regions it is connected with. Its major involvement in various kinds of integrative sensory and emotional functions makes it a cornerstone for self-relevant biological and social appraisals of the environment and consequently also for the processing of autobiographical events. Given its contribution to the integration of emotion, perception and cognition (including memory for past autobiographical events) the amygdala also forges the establishment and maintenance of an integrated self. Damage or disturbances of amygdalar connectivity may therefore lead to disconnection syndromes, in which the synchronous processing of affective and cognitive aspects of memory is impaired. We will provide support for this thesis by reviewing data from patients with a rare experiment of nature - Urbach-Wiethe disease - as well as other conditions associated with amygdala abnormalities. With respect to memory processing, we propose that the amygdala's role is to charge cues so that mnemonic events of a specific emotional significance can be successfully searched within the appropriate neural nets and re-activated.

Amygdalar modulation of frontotemporal connectivity during the inkblot test

Unique and unusual responses to inkblot stimuli evoked by emotionally vulnerable psychiatric patients have been considered as examples of interference of emotion with perceptual processes. However, few studies have investigated the interaction between emotion-related and perception-related neural circuits during performance of the inkblot test. In our recent studies using the inkblot stimuli, enlargement of the amygdala was revealed in association with frequent production of unique responses to the inkblot stimuli. Additionally, our studies demonstrated right temporopolar activation associated with the production of unique responses, as well as left anterior prefrontal and bilateral occipitotemporal activation associated with the production of typical responses. On the basis of these results, we hypothesized that the amygdala is involved in modulation of the connectivity among the frontotemporal regions identified in the activation analysis. To address this issue, we performed a functional connectivity analysis of functional magnetic resonance imaging data, using physiophysiological interaction implemented in Statistical Parametric Mapping 2 (SPM2). This analysis revealed that the amygdala imposed a positive modulation on the connection from the anterior prefrontal region to the temporopolar region, and a negative modulation on the connection from the temporopolar region to the occipitotemporal regions. These results suggest that interference of emotion affects perception during the inkblot test.

Is our brain hardwired to produce God, or is our brain hardwired to perceive God? A systematic review on the role of the brain in mediating religious experience

To figure out whether the main empirical question "Is our brain hardwired to believe in and produce God, or is our brain hardwired to perceive and experience God?" is answered, this paper presents systematic critical review of the positions, arguments and controversies of each side of the neuroscientific-theological debate and puts forward an integral view where the human is seen as a psycho-somatic entity consisting of the multiple levels and dimensions of human existence (physical, biological, psychological, and spiritual reality), allowing consciousness/mind/spirit and brain/body/matter to be seen as different sides of the same phenomenon, neither reducible to each other. The emergence of a form of causation distinctive from physics where mental/conscious agency (a) is neither identical with nor reducible to brain processes and (b) does exert "downward" causal influence on brain plasticity and the various levels of brain functioning is discussed. This manuscript also discusses the role of cognitive processes in religious experience and outlines what can neuroscience offer for study of religious experience and what is the significance of this study for neuroscience, clinicians, theology and philosophy. A methodological shift from "explanation" to "description" of religious experience is suggested. This paper contributes to the ongoing discussion between theologians, cognitive psychologists and neuroscientists.

Retrograde episodic and semantic memory impairment correlates with side of temporal lobe damage

Patients with damage to the mesial and anterior portions of the temporal lobes suffer from a memory impairment involving both anterograde and retrograde amnesia. In the retrograde domain, it has been suggested that the relative severity of autobiographical and nonautobiographical memory impairment may depend on the prevalent side of the temporal damage. Here we present two patients suffering from damage to the mesial and anterior portions of the temporal lobes (hippocampal formation, parahippocampal gyrus and polar cortex) as a result of herpes encephalitis. In the first case, A.S., damage predominantly affected the right temporal lobe, whereas in the second patient, R.S., the damage was bilateral but more severe on the left side. A detailed investigation of the retrograde memory deficit demonstrated a partial double dissociation between the two patients, with A.S. almost exclusively impaired in the autobiographical domain (both episodic and semantic) and R.S. with poor performances in all domains, but much more severe in the nonautobiographical (both public events and general semantic knowledge) than in the autobiographical one. These findings reinforce the view of specialization of right and left temporal lobes in the retrieval of retrograde autobiographical and nonautobiographical memories, respectively.

Right temporopolar activation associated with unique perception

Unique mode of perception, or the ability to see things differently from others, is one of the psychological resources required for creative mental activities. Behavioral studies using ambiguous visual stimuli have successfully induced diverse responses from subjects, and the unique responses defined in this paradigm were observed in higher frequency in the artistic population as compared to the nonartistic population. However, the neural substrates that underlie such unique perception have yet to be investigated. In the present study, ten ambiguous figures were used as stimuli. The subjects were instructed to say what the figures looked like during functional MRI scanning. The responses were classified as "frequent", "infrequent" or "unique" responses based on the appearance frequency of the same response in an independent age- and gender-matched control group. An event-related analysis contrasting unique vs. frequent responses revealed the greatest activation in the right temporal pole, which survived a whole brain multiple comparison. An alternative parametric modulation analysis was also performed to show that potentially confounding perceptual effects deriving from differences in visual stimuli make no significant contribution to this temporopolar activation. Previous neuroimaging and neuropsychological studies have shown the involvement of the temporal pole in perception-emotion linkage. Thus, our results suggest that unique perception is produced by the integration of perceptual and emotional processes, and this integration might underlie essential parts of creative mental activities.

Neuropsychological and psychiatric profiles in acute encephalitis in adults

Acute encephalitis is an inflammation of brain tissue that can result from activity in the central nervous system (CNS) of a number of viruses. Although the neurological and psychiatric effects of encephalitis in the acute phase of the illness are well-known (Caroff, Mann, Gliatto, Sullivan, & Campbell, 2001), larger scale studies of the pattern of neuropsychological and psychiatric impairment following recovery from the acute inflammatory phase are less apparent. This paper reports the results of neuropsychological testing with a range of standardised cognitive measures in a case series of long-term post-acute participants. Psychiatric abnormality is examined using the SCL-90-R self-report scale of distress (Derogatis, 1983). We also examined the role of emerging insight in the aetiology of depression in this population. Two clusters of cognitive dysfunction were observed, one group of primarily herpes simplex cases showing a severe generalised deficit across a number of cognitive domains and a second cluster showing a variety of more isolated disorders of executive function. Abnormally high levels of distress were reported by participants, with depression, obsessive-compulsive symptoms, interpersonal sensitivity and phobic anxiety most significantly increased. Depression was found to be least severe in those with most accurate insight into their problems. Examining the correlations between cognitive and psychiatric test results demonstrates a relationship between depression and interpersonal anxiety and specific cognitive measures. Obsessive-compulsive behaviour and phobic anxiety, however, appear to exist independently of the assessed cognitive deficits.

Neuropsychological sequelae of acute-onset sporadic viral encephalitis

Acute encephalitis is an inflammation of the brain parenchyma. In the USA, by estimation, 20,000 cases occur every year. A variety of cognitive deficits may persist after the acute stage, and they are often the sole cause of disability. Recent literature demonstrates the heterogeneity of both amnestic disorders and the outcome following encephalitis. Herpes simplex virus is the most commonly recognised single aetiology of sporadic encephalitis and it may be the cause of the most severe symptoms. Antiviral medication, however, seems to have improved the cognitive outcome when compared to the historical, untreated cases. The cognitive sequelae following herpes simplex virus encephalitis (HSVE) are best known and most commonly described, e.g., in textbooks, but they do not represent the typical symptomatology of encephalitis in general. Much less is unfortunately known about other types of encephalitis, those that account perhaps up to 80% of all cases, where both mild and severe defects have been observed. This article summarises the current knowledge.

The spatiotemporal dynamics of autobiographical memory: neural correlates of recall, emotional intensity, and reliving

We sought to map the time course of autobiographical memory retrieval, including brain regions that mediate phenomenological experiences of reliving and emotional intensity. Participants recalled personal memories to auditory word cues during event-related functional magnetic resonance imaging (fMRI). Participants pressed a button when a memory was accessed, maintained and elaborated the memory, and then gave subjective ratings of emotion and reliving. A novel fMRI approach based on timing differences capitalized on the protracted reconstructive process of autobiographical memory to segregate brain areas contributing to initial access and later elaboration and maintenance of episodic memories. The initial period engaged hippocampal, retrosplenial, and medial and right prefrontal activity, whereas the later period recruited visual, precuneus, and left prefrontal activity. Emotional intensity ratings were correlated with activity in several regions, including the amygdala and the hippocampus during the initial period. Reliving ratings were correlated with activity in visual cortex and ventromedial and inferior prefrontal regions during the later period. Frontopolar cortex was the only brain region sensitive to emotional intensity across both periods. Results were confirmed by time-locked averages of the fMRI signal. The findings indicate dynamic recruitment of emotion-, memory-, and sensory-related brain regions during remembering and their dissociable contributions to phenomenological features of the memories.

Autobiographical memory, the sense of recollection and executive functions after severe traumatic brain injury

Residual disorders of autobiographical memory long after trauma resulting from head injury are rarely assessed, even though they may affect social adjustment and the resumption of daily life. We conducted a thorough study of autobiographical memory in severe traumatic brain injury (TBI) patients, examined at least one year post-trauma. Twenty-five patients were submitted to a novel and controlled autobiographical procedure specially designed to measure episodic memories (i.e., unique, specific in time and space, and detailed) from their entire life span with two kinds of self-remembering experience. The ability to mentally travel back through time and re-experience the source of acquisition, i.e. autonoetic consciousness, was assessed via the "Remember/Know" paradigm and a checking procedure of sense of remembering. Self-perspective in visual imagery, which is also critically involved in episodic recollection, was assessed by the "Field/Observer perspective" paradigm. In addition, the patients underwent a battery of standardized neuropsychological tests to assess episodic and semantic memory, orientation and executive functions. The results showed that the patients, compared with healthy controls, were significantly impaired in recalling episodic autobiographical memories. This impairment was not related to the life period tested or the patients' ages nor the intellectual impairment. Deficits involved disturbances in sense of remembering, visual imagery self-perspective and recollection of spatiotemporal details. Stepwise-regression analyses carried out in the TBI patients revealed a significant relationship between an abnormal sense of remembering and executive dysfunction covering both anterograde and retrograde components. The novel assessment used in this study provides the first detailed evidence of a more fine-grained deficit of autobiographical memory in TBI patients. Indeed, the results suggest that these patients, long after trauma, present autonoetic consciousness and self-perspective disorders, which include sense of identity (the self) as a continuous entity across time, probably related to frontal dysfunction.

Topographical, autobiographical and semantic memory in a patient with bilateral mesial temporal and retrosplenial infarction

According to Consolidation Theory (Squire, 1992, Psychological Review, 99, 195; Squire & Alvarez, 1995, Current Opinion in Neurobiology, 5, 169), the mesial temporal lobes have a time-limited role in the maintenance, storage and retrieval of retrograde declarative memories, such that they are not necessary for recalling remote memories. In contrast, proponents of the Multiple Trace Theory (Fuji, Moscovitch, & Nadel, 2000, Handbook of neuropsychology, 2nd ed., p 223, Amsterdam, New York: Elsevier; Nadel & Moscovitch, 1999, Current Opinion in Neurobiology, 7, 217) posit that the mesial temporal lobe (MTL) is necessary for remembering detailed autobiographical and topographical material from all time periods. A third theory of hippocampal function, the Cognitive Map Theory (O'Keefe & Nadel, 1978, The hippocampus as a cognitive map. Oxford: Clarendon), states that the hippocampus is involved in the processing of allocentric spatial representations. The precise role of the MTL in remote memory has been difficult to elucidate, as the majority of studies present cases with widespread brain damage that often occurred many years prior to testing. We investigated retrograde autobiographical, semantic and topographical memories in a subject (SG) who had recently sustained infarctions confined to the MTL and retrosplenial region bilaterally. Inconsistent with the predictions of Cognitive Map Theory, memory for spatial maps that were learned in the past was preserved. Additional testing indicated that SG suffered from a landmark agnosia, which affected remotely and recently acquired information equally. SG was also poor at imagining which direction he would have to turn his body to move from one landmark to another. In accordance with Consolidation Theory, SG performed similarly to control subjects for remote time periods on various measures of retrograde autobiographical memory and demonstrated intact knowledge regarding famous faces and vocabulary terms that were acquired in the past. In contrast, memory for remote public events was impaired. The current findings indicate that the mesial temporal and/or retrosplenial regions have little role to play in memory for remotely acquired spatial maps, autobiographical memories, famous faces or vocabulary terms. However, the findings for landmark naming, directional calculations between landmarks and knowledge of public events suggest that the MTL and/or retrosplenial cortices remain important for accessing these types of memories indefinitely.

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.

Co-activation of the amygdala, hippocampus and inferior frontal gyrus during autobiographical memory retrieval

Functional MRI was used to investigate the role of medial temporal lobe and inferior frontal lobe regions in autobiographical recall. Prior to scanning, participants generated cue words for 50 autobiographical memories and rated their phenomenological properties using our autobiographical memory questionnaire (AMQ). During scanning, the cue words were presented and participants pressed a button when they retrieved the associated memory. The autobiographical retrieval task was interleaved in an event-related design with a semantic retrieval task (category generation). Region-of-interest analyses showed greater activation of the amygdala, hippocampus, and right inferior frontal gyrus during autobiographical retrieval relative to semantic retrieval. In addition, the left inferior frontal gyrus showed a more prolonged duration of activation in the semantic retrieval condition. A targeted correlational analysis revealed pronounced functional connectivity among the amygdala, hippocampus, and right inferior frontal gyrus during autobiographical retrieval but not during semantic retrieval. These results support theories of autobiographical memory that hypothesize co-activation of frontotemporal areas during recollection of episodes from the personal past.

Towards a bio-psycho-social model of autobiographical memory

Self-awareness and identity are important cornerstones of thinking in social psychology. On the basis of current knowledge and theories from the social, cultural, and biological sciences, this paper attempts to outline an integrative approach to the phenomena of memory and reminiscence. Reference to psychodynamic argumentation is made in addition, where appropriate. The central topic to our argumentation is autobiographical memory, which we analyse according to evolutionary, neuroscientific, and cultural findings. The emotional context and the ontogenetic development of reminiscences (or memories directly relating to one's own self) provide the preliminary framework for an integrated view which includes interactions between the life span, brain development, the social and cultural environment, and genetic predispositions.

Selective memory impairment for personally familiar colors following encephalitis

A 19-year-old man presented with a peculiar memory impairment following non-herpetic viral encephalitis. He was exclusively impaired in generating images for colors of possessions previously well known to him, and consequently these seemed less familiar. He appeared unable to access personally familiar and autobiographical color attributes. Single-photon emission computed tomography and electroencephalogram findings suggest that the right-sided functional abnormalities, specifically in the frontal and temporal regions, were implicated as the functional locus for the patient's unique problem.

The case of K.C.: contributions of a memory-impaired person to memory theory

K.C. has been investigated extensively over some 20 years since a motorcycle accident left him with widespread brain damage that includes large bilateral hippocampal lesions, which caused a remarkable case of memory impairment. On standard testing, K.C.'s anterograde amnesia is as severe as that of any other case reported in the literature, including H.M. However, his ability to make use of knowledge and experiences from the time before his accident shows a sharp dissociation between semantic and episodic memory. A good deal of his general knowledge of the world, including knowledge about himself, is preserved, but he is incapable of recollecting any personally experienced events. In displaying such "episodic amnesia," which encompasses an entire lifetime of personal experiences, K.C. differs from many other amnesic cases. Here, we document for the first time the full extent of K.C.'s brain damage using MRI-based quantitative measurements. We then review the many investigations with K.C. that have contributed to our understanding not only of episodic and semantic memory but also to the development of other aspects of memory theory. These include the distinction between implicit and explicit memory, the prospect of new learning in amnesia, and the fate of recent and remote memory for autobiographical and public events, people, and spatial locations.

[Episodic memory: from mind to brain]

Episodic memory is a neurocognitive (brain/mind) system, uniquely different from other memory systems, that enables human beings to remember past experiences. The notion of episodic memory was first proposed some 30 Years ago. At that time it was defined in terms of materials and tasks. It was subsequently refined and elaborated in terms of ideas such as self, subjective time, and autonoetic consciousness. This chapter provides a brief history of the concept of episodic memory, describes how it has changed (indeed greatly changed) since its inception, considers criticisms of it, and then discusses supporting evidence provided by (a) neuropsychological studies of patterns of memory impairment caused by brain damage, and (b) functional neuroimaging studies of patterns of brain activity of normal subjects engaged in various memory tasks. I also suggest that episodic memory is a true, even if as yet generally unappreciated, marvel of nature.

'In the course of time': a PET study of the cerebral substrates of autobiographical amnesia in Alzheimer's disease

Neuroimaging studies in healthy subjects have yielded controversial results about the neural substrates of autobiographical memory. Moreover, the neural networks responsible for autobiographical amnesia remain poorly understood. Since autobiographical memory is frequently altered in Alzheimer's disease (AD), we used this degenerative disorder as a model and applied a correlative approach between resting cerebral glucose utilization (CMRGlc) and temporally graded memory scores to identify the cerebral structures whose synaptic dysfunction subserves the impairment in autobiographical memory. To this end, we studied a group of 17 AD patients with mild to moderate dementia in whom autobiographical memory was assessed using a specially designed task from three broad time periods [the previous 5 years (period A); middle age (period B); and teenage and childhood (period C)], and measures of resting CMRGlc were obtained with PET. The patients performed less well than a control group for all three time periods and showed the expected temporal gradient, with the most remote period being best preserved (Ribot's gradient). Qualitative analysis showed that remote memories concerned generic (i.e. semantic) rather than specific (i.e. episodic) events. We found a significant positive correlation between autobiographical scores and the metabolism of the right hippocampus (extending to the lingual gyrus), restricted to period A. In addition, period A scores were significantly correlated with the right middle and inferior frontal gyri and the right middle temporal gyrus. Period B scores correlated chiefly with the prefrontal cortex bilaterally (bilateral superior, bilateral middle and right inferior gyri). Metabolic correlations with period C scores were restricted to the left middle frontal gyrus. These findings show striking differences in metabolic correlations with the autobiographical time period, in agreement with prevalent theories of normal functioning of human memory. Thus, in accordance with theories of long-term memory consolidation, we find the expected implication of the hippocampal region in the recall of recent memories, and a disengagement of this structure when the retention interval is beyond 5 years. Moreover, according to the hemispheric encoding/retrieval asymmetry model based on activation studies in healthy subjects, the fact that recent memories preferentially involved the right prefrontal cortex whereas remote memories involved the left prefrontal cortex supports the notion of semanticization of memories with time interval, such that preserved remote memories in AD have a predominantly semantic character.

Impairments in premorbid knowledge recall in patients with hemispheric and intraventricular brain damage

A total of 104 patients with hemispheric arteriovenous malformations (AVM; in the frontal, parietal, and temporal lobes), along with 21 patients with craniopharyngiomas and 21 patients with aresorptive hydrocephalus, were studied. Impairments of the recall of knowledge acquired before disease onset were found in 12 patients with hemispheric AVM. All had suffered severe intraventricular hemorrhage. Similar memory defects were noted in three patients with craniopharyngiomas and 12 with hydrocephalus. These patients had lesions of the mediobasal (periventricular) parts of the brain (frontal and parietal lobes), predominantly of the right hemisphere, as well as the diencephalic regions. The syndrome of selective retrograde amnesia in lesions of these structures was characterized by impairment of the recall of dates and, less frequently, details of event content and autobiography. It is emphasized that processes of recall of the sequence and selectivity of traces during actualization of "old" knowledge played the greater role in the mechanism of development of these impairments. The possible roles of the right and left hemispheres, as well as the diencephalic area, in the information encoding and decoding are discussed.

A role for prefrontal cortex in memory storage for trace fear conditioning

The prefrontal cortex has been shown to participate in the association of events separated by time. However, it is not known whether the prefrontal cortex stores the memory for these relationships. Trace conditioning is a form of classical conditioning in which a time gap separates the conditioned stimulus (CS) from the unconditioned stimulus (US), the association of which has been shown to depend on prefrontal activity. Here we demonstrate that inhibition of extracellular signal-regulated kinase (Erk) cascade (a biochemical pathway involved in long-term memory storage) in the rat medial prefrontal cortex did not interfere with memory encoding for trace fear conditioning but impaired memory retention. In addition, animals displayed impaired memory for the irrelevancy of the training context. Hippocampal Erk phosphorylation was found to have a later time course than prefrontal Erk phosphorylation after trace fear conditioning, indicating a direct role for the prefrontal cortex in associative memory storage for temporally separated events as well as in memory storage of relevancy.

Cortical Activations during judgments about the self and an other person

Self-related thought and other person related thought have received a great deal of study in recent years, but have seldom been examined in the same experiment. This study used functional magnetic resonance imaging (fMRI) to compare the neural correlates of judgments of ones own preferences with judgments of another person's preferences. Each participant viewed food names and made one of three decisions: self (whether he or she liked the food); other (whether a specific friend liked the food), or letter (whether there were more than two vowels in the food name). Self and other decisions both activated bilateral medial areas of the frontal and parietal lobes and the bilateral insula in comparison to the letter task. Self activated superior medial parietal areas in comparison to other, whereas other led to greater activation in inferior medial parietal and left lateral frontal areas than self. These results indicate that the neural networks underlying self processing and other person processing may share common neural substrates, particularly regions associated with representation of the body and mental states.

Oral fluency and narrative production in children with Turner's syndrome

Despite good verbal skills, children with Turner's syndrome (TS) have been found to perform poorly on oral fluency tasks. Explanations for this impairment were explored in a study of 9-12-year-old children with TS. The children with TS were found, as expected, to have impaired levels of retrieval on initial letter fluency tasks, in comparison to their peers. Children with TS were also found to have receptive vocabularies which were significantly better than controls, indicating that the weak performance on oral fluency cannot be attributed to lower vocabulary levels. Naming skills were normal for children with TS, indicating that oral fluency scores cannot be attributed to generalised problems with lexical access. Analysis of the content of fluency performance indicated clusters of words within sub-categories which were of normal size but there were fewer switches between clusters than for controls and fewer returns to previously successful clusters. Additionally, a significantly larger proportion of the words generated were of low frequency (e.g. Assyrian, antediluvian) and the children with TS did not thereby show a normal frequency effect in word retrieval. One explanation is that these reflect abnormal action of executive language retrieval processes. Within narrative production, picture description was normal. However, in relation to narrative tasks, hypothesised to place greater executive demands, there was impairment which was significantly greater for narratives of yesterday than narratives of organising a party. This impairment within the narrative generation tasks could be attributable to a selective impairment within executive retrieval skills, or could represent an impairment in episodic memory or the executive processes involved in its retrieval.

Two cases of functional focal retrograde amnesia with impairment of object use

We report on two patients, TH and KN, with focal retrograde amnesia (FRA). Their memory loss regarding life events extended to their whole lives, whereas they could acquire and retain new information. They also showed prominent deficits in production and comprehension of common words. In addition, at least in the testing situation, they were impaired in their recognition and use of familiar objects. Although both cases of FRA followed an episode that can cause brain pathology, MRI revealed no structural abnormality in either patient. Stressful situations preceding the onset were evident in KN, but not in TH. We discuss their impairments of object knowledge from a neuropsychological perspective, and we interpret the etiology of their condition as a functional rather than a psychogenic amnesia.

Episodic memory: from mind to brain

Episodic memory is a neurocognitive (brain/mind) system, uniquely different from other memory systems, that enables human beings to remember past experiences. The notion of episodic memory was first proposed some 30 years ago. At that time it was defined in terms of materials and tasks. It was subsequently refined and elaborated in terms of ideas such as self, subjective time, and autonoetic consciousness. This chapter provides a brief history of the concept of episodic memory, describes how it has changed (indeed greatly changed) since its inception, considers criticisms of it, and then discusses supporting evidence provided by (a) neuropsychological studies of patterns of memory impairment caused by brain damage, and (b) functional neuroimaging studies of patterns of brain activity of normal subjects engaged in various memory tasks. I also suggest that episodic memory is a true, even if as yet generally unappreciated, marvel of nature.