Reduced specificity of autobiographical memory and aging: Do the executive and feature binding functions of working memory have a role?

Autobiographical memory (AM) is built up from various kinds of knowledge, from general to specific, via generative processes. Aging seems to particularly affect the episodic autobiographical information while preserving information that is more semantic. However, the mechanism of this deficit has not yet been thoroughly tested in relation to working memory. This study is designed to investigate, in a group of 100 subjects, the relationships between age, accessibility to different levels of AM specificity, and two main components of working memory: the central executive and the episodic buffer. We used a new task composed of four embedded verbal autobiographical fluencies (VAF) - from low to highest specificity levels - exploring lifetime periods, general events, specific events, and details, plus tasks exploring free recall of episodic AM and updating, shifting, inhibition, and feature binding in working memory. The results demonstrate that age-related difficulties increase with level of specificity of autobiographical knowledge, i.e., from semantic to episodic aspects. Moreover, regression analyses mainly show that increase in age-related deficit with level of specificity of AM is largely mediated by performance on executive functions (updating and inhibition) and to a lesser extent feature binding in working memory. The results confirm in episodic AM the executive/working memory aging hypothesis, and for the first time highlight the role of episodic buffer in associating the various different details of specific events that elicit the conscious recollection.     

The functional dissociation of posterior parietal regions during multimodal memory formation

The incidental acquisition of multimodal associations is a key memory function for everyday life. While the posterior parietal cortex has been frequently shown to be involved for these memory functions, ventral and dorsal regions revealed differences in their functional recruitment and the precise difference in multimodal memory processing with respect to the associative process has not been differentiated. Using an incidental multimodal learning task, we isolated the associative process during multimodal learning and recollection. The result of the present functional magnetic resonance imaging (fMRI) study demonstrated that during both learning and recollection a clear functional differentiation between ventral and dorsal posterior parietal regions was found and can be related directly to the associative process. The recruitment of a ventral region, the angular gyrus, was specific for learning and recollection of multimodal associations. In contrast, a dorsal region, the superior parietal lobule, could be attributed to memory guided attentional processing. Independent of the memory stage, we assumed a general role for the angular gyrus in the generation of associative representations and updating of fixed association, episodic memory.     

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.     

Hippocampal contributions to recollection in retrograde and anterograde amnesia

Lesions restricted to the hippocampal formation and/or extended hippocampal system (hippocampal formation, fornix, mammillary bodies, and anterior thalamic nuclei) can disrupt conscious recollection in anterograde amnesia, while leaving familiarity-based memory relatively intact. Familiarity may be supported by extra-hippocampal medial temporal lobe (MTL) structures. Within-task dissociations in recognition memory best exemplify this distinction in anterograde amnesia. The authors report for the first time comparable dissociations within recognition memory in retrograde amnesia. An amnesic patient (A.D.) with bilateral fornix and septal nuclei lesions failed to recognize details pertaining to personal past events only when recollection was required, during recognition of episodic details. His intact recognition of generic and semantic details pertaining to the same events was ascribed to intact familiarity processes. Recollective processes in the controls were reflected by asymmetrical Receiver's Operating Characteristic curves, whereas the patient's Receiver's Operating Characteristic was symmetrical, suggesting that his inferior recognition performance on episodic details was reliant on familiarity processes. Anterograde and retrograde memories were equally affected, with no temporal gradient for retrograde memories. By comparison, another amnesic person (K.C.) with extensive MTL damage (involving extra-hippocampal MTL structures in addition to hippocampal and fornix lesions) had very poor recognition and no recollection of either episodic or generic/semantic details. These data suggest that the extended hippocampal system is required to support recollection for both anterograde and retrograde memories, regardless of their age.     

Retrieval mechanisms for autobiographical memories: insights from the frontal variant of frontotemporal dementia

Very few studies have investigated autobiographical memory in the frontal variant of frontotemporal dementia (fv-FTD). The aim of this study was therefore to unravel the mechanisms of autobiographical memory disruption in general and in the anterograde and retrograde components of amnesia in particular, in patients suffering from fv-FTD. An autobiographical memory task assessing overall (AM) and strictly episodic memories (EM) from five lifetime periods covering the entire lifespan revealed the absence of a temporal gradient for both scores, suggesting the existence of a retrieval deficit. An analysis of the correlation between these two scores and a general cognitive assessment of executive function, working, episodic (i.e. new learning ability) and semantic memory, and behavioural changes highlighted the considerable involvement of executive function, semantic memory and, to a lesser degree, episodic memory and behavioural changes. Moreover, step-wise regression analyses performed on the EM score revealed that the executive function was a better predictor of the retrograde component than of the anterograde component, which was linked principally to new episodic learning ability. All these results confirm the impact of executive dysfunction on autobiographical deficits in fv-FTD, and suggest that the mechanisms at the root of autobiographical memory disruption may also involve difficulties in new episodic learning and semantic storage, though this may be due to the fact that we studied an advanced form of fv-FTD.     

Episodic memory, frontal functioning, and aging

Episodic memory is commonly defined as the kind of memory that renders possible conscious recollection of personal happenings and events from one's personal past. Although it is classically assumed that episodic memory is subserved by a distinct neurocognitive system including mediotemporal cortex and hippocampus, recent evidence also supports the idea of a close relationship between episodic memory and frontal cortex. This view assumes that the frontal cortex plays a critical supervisory role in empowering encoding and retrieval episodic memory operations. In recent years, this view had significantly influenced research in the field of normal memory aging. Indeed, different data have highlighted that age-related cognitive differences, most particularly age-related memory differences, might be explained by the decline of executive-frontal functioning that accompanies aging. In this article, we provide studies on aging and episodic memory that, in support of the executive hypothesis of aging episodic memory, have provided evidence that age-related differences in strategies implemented at encoding and retrieval in this type of memory are mediated by the executive functioning difficulties of older adults.     

Reliving lifelong episodic autobiographical memories via the hippocampus: a correlative resting PET study in healthy middle-aged subjects

We aimed at identifying the cerebral structures whose synaptic function subserves the recollection of lifetime's episodic autobiographical memory (AM) via autonoetic consciousness. Twelve healthy middle-aged subjects (mean age: 59 years +/- 2.5) underwent a specially designed cognitive test to assess the ability to relive richly detailed episodic autobiographical memories from five time periods using the Remember/Know procedure. We computed an index of episodicity (number of Remember responses justified by the recall of specific events and details) and an index of retrieval spontaneity, and additionally an index of semanticized memories (number of Know responses). The regional cerebral blood flow (rCBF) was measured in the resting state, with H(2)O(15) as part of an activation PET study. The indexes were correlated with blood flow using volumes of interest in frontotemporal regions, including hippocampus and voxel-wise analyses in SPM. With both analyses, significant correlations were mainly found between the index of episodicity and rCBF in the medial temporal lobe, including hippocampus, across the five time periods (unlike the index of semanticized memories) and between the spontaneity index and rCBF in the prefrontal areas. These results highlight, in healthy subjects, the distinct role of these two structures in AM retrieval and support the view that the hippocampus is needed for reexperiencing detailed episodic memories no matter how old they are.     

Behavioral and functional neuroanatomical correlates of anterograde autobiographical memory in isolated retrograde amnesic patient M.L.

Patient M.L. [Levine, B., Black, S. E., Cabeza, R., Sinden, M., Mcintosh, A. R., Toth, J. P., et al. (1998). Episodic memory and the self in a case of isolated retrograde amnesia. Brain, 121, 1951-1973], lost memory for events occurring before his severe traumatic brain injury, yet his anterograde (post-injury) learning and memory appeared intact, a syndrome known as isolated or focal retrograde amnesia. Studies with M.L. demonstrated a dissociation between episodic and semantic memory. His retrograde amnesia was specific to episodic autobiographical memory. Convergent behavioral and functional imaging data suggested that his anterograde memory, while appearing normal, was accomplished with reduced autonoetic awareness (awareness of the self as a continuous entity across time that is a crucial element of episodic memory). While previous research on M.L. focused on anterograde memory of laboratory stimuli, in this study, M.L.’s autobiographical memory for post-injury events or anterograde autobiographical memory was examined using prospective collection of autobiographical events via audio diary with detailed behavioral and functional neuroanatomical analysis. Consistent with his reports of subjective disconnection from post-injury autobiographical events, M.L. assigned fewer “remember” ratings to his autobiographical events than comparison subjects. His generation of event-specific details using the Autobiographical Interview [Levine, B., Svoboda, E., Hay, J., Winocur, G., & Moscovitch, M. (2002). Aging and autobiographical memory: dissociating episodic from semantic retrieval. Psychology and Aging, 17, 677-689] was low, but not significantly so, suggesting that it is possible to generate episodic-like details even when re-experiencing of those details is compromised. While listening to the autobiographical audio diary segments, M.L. showed reduced activation relative to comparison subjects in midline frontal and posterior nodes previously identified as part of the autobiographical memory network. Reductions were also evident in M.L. in association with personal semantic stimuli (e.g., recordings describing personal habits and routines). These data suggest an association between M.L.’s impoverished recollection of autobiographical material and reduced activation in midline sectors of the autobiographical memory network that support the autonoetic, first-person element of episodic memory.     

The relationship between working memory and episodic memory disorders in transient global amnesia

In a previous study, we investigated the relationship between the disorders of both episodic memory and working memory in the acute phase of transient global amnesia (TGA). Since executive functions were spared, another dysfunction may be responsible for the binding and maintenance of multimodal informations and contribute to the encoding disorders observed in some patients [Quinette, P., Guillery, B., Desgranges, B., de la Sayette, V., Viader, F., &; Eustache, F. (2003). Working memory and executive functions in transient global amnesia. Brain, 126, 1917–1934.]. The aim of this present study was to assess the functions of binding and maintenance of multimodal information during TGA and explore their involvement in episodic memory disorders. We therefore conducted a more thorough investigation of working memory in 16 new patients during the acute phase of TGA using two tasks designed to assess the binding process and both dimensions of the maintenance, namely the active storage and the memory load ability. We also investigated the nature of the episodic memory impairment in distinguishing between the performance of patients with preferential encoding deficits and those of patients with preferential storage disorders on the episodic memory task. This distinction was closely related to the severity of amnesia, i.e. an encoding disorder was observed rather in the early phase of TGA. The results showed that while the functions of binding and maintenance of multimodal information were intact in patients with storage disorders, they were impaired in the case of encoding deficits. These results are interpreted in the recent framework of episodic buffer proposed by Baddeley [Baddeley, A. D. (2000). The episodic buffer: A new component of working memory? Trends in Cognitive Sciences, 4, 417–423] that represents an interface between working memory and episodic memory.     

Amnesia as an impairment of detail generation and binding: Evidence from personal, fictional, and semantic narratives in K.C.

Autobiographical episodic recall involves active simultaneous generation and binding of various elements that were present during the initial experience. Deficits in this reconstructive process may account for some aspects of retrograde amnesia (RA) for personally experienced events. Constructive and reconstructive processes may involve similar mechanisms. If so, patients with extensive anterograde amnesia (AA) and RA should show deficits in non-recollective cognitive domains, such as imagining events that had never been experienced and recounting non-personal narratives, that presumably rely on constructive and re-constructive processes, respectively. To test these possibilities, patient K.C., who has severe AA and RA for personal episodes, was asked to generate fictional events and to recall and recognize details of well-known fairy tales and bible stories. K.C.’s performance on both tasks was better than expected given his severely impaired autobiographical episodic memory (AM), but significantly worse than that of control participants. K.C. was able to create a skeletal outline for both types of narratives, providing sufficient information to convey their gist, but the narratives were fragmented and lacking in detail. This deficit cannot be explained as resulting entirely from deficient stored semantic knowledge, because K.C. was able to discriminate between true and false details of non-personal semantic narratives on a recognition test, which he cannot do for personal events [Gilboa, A., Winocur, G., Rosenbaum, R.S., Poreh, A., Gao, F., Black, S.E., Westmacott, R., & Moscovitch, M. (2006a). Hippocampal contributions to recollection in retrograde and anterograde amnesia. Hippocampus, 16, 966-980]. Thus, retrograde AM impairment may be viewed as both a loss of information as well as a deficit in reconstructive processes that hamper or prevent the binding of information to generate a cohesive, detail-rich memory.     

In search of autobiographical memories: A PET study in the frontal variant of frontotemporal dementia

Patients suffering from frontal variant of frontotemporal dementia (fv-FTD) undergo autobiographical amnesia encompassing all time periods. We previously demonstrated in a group of 20 fv-FTD patients that this impairment involved deficits in executive function and semantic memory for all periods as well as new episodic learning and behavioural changes for the most recent period covering the last 12 months [Matuszewski, V., Piolino, P., de la Sayette, V., Lalevée, C., Pélerin, A., Dupuy, B., et al. (2006). Retrieval mechanisms for autobiographical memories: Insights from the frontal variant of frontotemporal dementia, Neuropsychologia, 44, 2386-2397]. The aim of the present study was to unravel the neural bases of this impairment by mapping in a subgroup of patients correlations between resting-state brain glucose utilization measured by FDG-PET and measures of autobiographical memory (AM) using the TEMPau task which is designed to gauge personal event recollection across five life time periods. Like in our previous report, the group of patients was impaired regardless of time periods compared to healthy subjects providing generic memories instead of event specific sensory-perceptual-affective details, i.e., episodic memories. New data showed that the patients were also impaired in sense of reliving and self-perspective during retrieval. The cognitivo-metabolic correlations between the AM score and resting normalized FDG-Uptake were computed using statistical parametric mapping (SPM2) and controlling for age and dementia severity. They revealed that AM deficits were mainly subserved by the dysfunction of left-sided orbitofrontal and also temporal neocortical areas whatever the period. Additional analysis showed that specific memories were associated with left orbitofrontal areas whereas generic memories were mainly associated with the left temporal pole. This study supports the view that fv-FTD patients undergo a breakdown of generative processes which relies regardless of the remoteness on the left orbitofrontal cortex and temporal neocortex to gain access to AM.     

Semantic memory recognition is supported by intrinsic recollection-like processes: “The butcher on the bus” revisited

Dual-process models suggest that recognition memory is independently supported by recollection and familiarity. Current theories attribute recollection solely to hippocampally mediated episodic memory (EM), and familiarity to both episodic and semantic memory (SM) supported by medial temporal lobe cortex (MTLC) and prefrontal cortex. We tested whether, contrary to this view, recollection-like processes also intrinsically support SM recognition and whether MTL structures are involved in their execution. A semantic Process Dissociation Procedure (PDP) with famous and non-famous names was used in three experiments. Experiment 1 revealed that recollection-like processes in semantic memory were not associated with episodic memory for the public events, were predicted by performance on standard SM tasks and were independent of EM tasks, suggesting they are intrinsic to SM. Experiment 2 demonstrated the independence of the two process estimates by showing only familiarity was affected by shifting response criterion while only recollection estimates were significantly altered under divided-attention. Finally experiment 3 tested amnesic patients with varying degrees of hippocampal and MTLC damage. Despite normal overall fame recognition performance, recollection estimates were specifically affected by MTL damage. When damage was primarily hippocampal, only retrograde recollection estimates were reduced, while more extensive MTLC damage led to both retrograde and anterograde recollection deficits. We conclude that recognition of semantic information is supported by at least two independent processes akin to the ones that support EM recognition. Recollection-like processes are intrinsic to SM and likely do not reflect EM contribution to SM performance. Together with previous studies of recollection in remote memory, these data suggest that recollection is not a unitary phenomenon. In EM it involves autonoetic re-experiencing, and is supported by interaction of fronto-temporal networks; in EM and SM it supports retrieval of contextual/associative information regardless of consciousness type, and is dependent on intact MTL function. Familiarity processes and neural substrates may also differ between lifetime familiarity and within-session familiarity.     

The neural correlates of recollection: hippocampal activation declines as episodic memory fades

Memories for certain events tend to linger in rich, vivid detail, and retrieval of these memories includes a sense of re-experiencing the details of the event. Most events, however, are not retained in any detailed way for more than a few days. According to one theory, the hippocampus plays a specific role in supporting episodic retrieval, that is, the re-experiencing of an event as part of one's personal past. This theory predicts that as episodic memories fade over time and are reduced to feelings of familiarity, activity in the hippocampus should no longer be associated with retrieval. We used high-resolution functional imaging to explore neural activity in medial temporal lobe subregions while participants performed a recognition task at both a short (10-min) and long (1-week) study-test delay. For each recognized item, subjects made "Remember/Know" judgments, allowing us to distinguish between items that were consistently episodic across the two tests and items that were initially episodic, but later became merely familiar. Our results demonstrate that activity in the subiculum is specifically associated with episodic recollection. Overall, recollected items were associated with higher activity in the subiculum than other items. For transiently recollected items, there was a decrease in subicular activity across the 1-week delay as memory faded from recollection to familiarity, whereas consistently recollected items were associated with enhanced subicular activity at both delays. These results provide evidence of a link between subicular activation and recollective experience.     

Profiles of recent autobiographical memory retrieval in semantic dementia, behavioural-variant frontotemporal dementia, and Alzheimer's disease

Episodic autobiographical memory (ABM) comprises recollection for events that are grounded within a specific spatiotemporal context, and usually accompanied by perceptual and emotional information. The neural substrates mediating ABM retrieval are those harbouring significant pathology in semantic dementia (SD) and behavioural-variant frontotemporal dementia (bvFTD), the most common subtypes of FTD. Relatively little is known, however, regarding the differential patterns of contextual details during episodic ABM retrieval across these dementia syndromes. This study investigated episodic ABM retrieval under free and probed recall conditions from 4 time periods with the aim to identify disease-specific profiles of episodic ABM contextual details. Episodic ABM was measured in 25 SD and 15 bvFTD patients and their performance contrasted to that of 17 Alzheimer's disease (AD) patients and 19 age-matched controls. Critically, SD patients showed relatively preserved recent ABM in comparison with remote epochs. In contrast, bvFTD and AD patients showed a reduced capacity to recall specific and contextually rich ABMs across all life epochs, in both free and probed recall conditions. Analyses of the recent period (last 12 months) provided evidence for different profiles of contextual episodic details recalled in dementia syndromes. Following probing, SD patients’ recall deficits emanated exclusively from compromised Emotion/Thoughts and Spatiotemporal details. In contrast, bvFTD patients were significantly impaired across all categories of contextual details whereas AD patients showed deficits for Event and Emotion/Thoughts details only. As the largest study of ABM in FTD to date, these findings emphasise the differential impairment of recent ABM contextual details contingent on the underlying disease pathology. In addition, these results point towards the importance of investigating the constituent elements of emotion processing and strategic retrieval processes as potential variables mediating recent episodic ABM retrieval.     

Patterns of verbal learning and memory in traumatic brain injury.

CVLT and WMS-R Digit Span variables were used to calculate indexes of seven specific short- and long-term memory processes: working memory span and central executive functions, and long-term memory encoding, consolidation, retention, retrieval, control abilities. Scores on these indexes were then cluster-analyzed to determine whether subtypes of memory performance exist that correspond to deficits in these theoretical memory constructs. Parallel analyses were conducted with two large samples (N = 150 and N = 151) of individuals who had sustained a traumatic brain injury (TBI). Findings showed that TBI results in subgroups of memory disorders with specific deficits in consolidation, retention, and retrieval processes. Control problems (keeping track of list versus non-list items) only appeared in conjunction with retrieval deficits. Working memory span and central executive functioning (i.e., the ability to manipulate information in working memory) do not appear to be deficits characteristic of TBI as no such clusters emerged in the analyses. By using specific indexes of memory processes, and in contrast to previous studies, patterns of memory dysfunction were found that correspond to deficits in theoretically meaningful memory constructs.     

A single‐trace dual‐process model of episodic memory: A novel computational account of familiarity and recollection

Dual‐process theories of episodic memory state that retrieval is contingent on two independent processes: familiarity (providing a sense of oldness) and recollection (recovering events and their context). A variety of studies have reported distinct neural signatures for familiarity and recollection, supporting dual‐process theory. One outstanding question is whether these signatures reflect the activation of distinct memory traces or the operation of different retrieval mechanisms on a single memory trace. We present a computational model that uses a single neuronal network to store memory traces, but two distinct and independent retrieval processes access the memory. The model is capable of performing familiarity and recollection‐based discrimination between old and new patterns, demonstrating that dual‐process models need not to rely on multiple independent memory traces, but can use a single trace. Importantly, our putative familiarity and recollection processes exhibit distinct characteristics analogous to those found in empirical data; they diverge in capacity and sensitivity to sparse and correlated patterns, exhibit distinct ROC curves, and account for performance on both item and associative recognition tests. The demonstration that a single‐trace, dual‐process model can account for a range of empirical findings highlights the importance of distinguishing between neuronal processes and the neuronal representations on which they operate. © 2009 Wiley‐Liss, Inc.     

The functional neuroanatomy of autobiographical memory: a meta-analysis

Autobiographical memory (AM) entails a complex set of operations, including episodic memory, self-reflection, emotion, visual imagery, attention, executive functions, and semantic processes. The heterogeneous nature of AM poses significant challenges in capturing its behavioral and neuroanatomical correlates. Investigators have recently turned their attention to the functional neuroanatomy of AM. We used the effect-location method of meta-analysis to analyze data from 24 functional imaging studies of AM. The results indicated a core neural network of left-lateralized regions, including the medial and ventrolateral prefrontal, medial and lateral temporal and retrosplenial/posterior cingulate cortices, the temporoparietal junction and the cerebellum. Secondary and tertiary regions, less frequently reported in imaging studies of AM, are also identified. We examined the neural correlates of putative component processes in AM, including, executive functions, self-reflection, episodic remembering and visuospatial processing. We also separately analyzed the effect of select variables on the AM network across individual studies, including memory age, qualitative factors (personal significance, level of detail and vividness), semantic and emotional content, and the effect of reference conditions. We found that memory age effects on medial temporal lobe structures may be modulated by qualitative aspects of memory. Studies using rest as a control task masked process-specific components of the AM neural network. Our findings support a neural distinction between episodic and semantic memory in AM. Finally, emotional events produced a shift in lateralization of the AM network with activation observed in emotion-centered regions and deactivation (or lack of activation) observed in regions associated with cognitive processes.     

Reminders activate the prefrontal‐medial temporal cortex and attenuate forgetting of event memory

Replicas of an aspect of an experienced event can serve as effective reminders, yet little is known about the neural basis of such reminding effects. Here we examined the neural activity underlying the memory‐enhancing effect of reminders 1 week after encoding of naturalistic film clip events. We used fMRI to determine differences in network activity associated with recently reactivated memories relative to comparably aged, non‐reactivated memories. Reminders were effective in facilitating overall retrieval of memory for film clips, in an all‐or‐none fashion. Prefrontal cortex and hippocampus were activated during both reminders and retrieval. Peak activation in ventro‐lateral prefrontal cortex (vPFC) preceded peak activation in the right hippocampus during the reminders. For film clips that were successfully retrieved after 7 days, pre‐retrieval reminders did not enhance the quality of the retrieved memory or the number of details retrieved, nor did they more strongly engage regions of the recollection network than did successful retrieval of a non‐reminded film clip. These results suggest that reminders prior to retrieval are an effective means of boosting retrieval of otherwise inaccessible episodic events, and that the inability to recall certain events after a delay of a week largely reflects a retrieval deficit, rather than a storage deficit for this information. The results extend other evidence that vPFC drives activation of the hippocampus to facilitate memory retrieval and scene construction, and show that this facilitation also occurs when reminder cues precede successful retrieval attempts. The time course of vPFC‐hippocampal activity during the reminder suggests that reminders may first engage schematic information meditated by vPFC followed by a recollection process mediated by the hippocampus.     

Patterns of autobiographical memory loss in medial-temporal lobe amnesic patients

The issue of whether the hippocampus and related structures in the medial-temporal lobe (MTL) play a temporary or permanent role in autobiographical episodic memory remains unresolved. One long-standing belief is that autobiographical memory (AM), like semantic memory, is initially dependent on the MTL but ultimately can be retained and recovered independently of it. However, evidence that hippocampal amnesia results in severe loss of episodic memory for a lifetime of personally experienced events suggests otherwise. To test the opposing views, we conducted detailed investigations of autobiographical episodic memory in people with amnesia resulting from MTL lesions of varying extent. By combining precise quantification of MTL and neocortical volumes with sensitive measures of recollection of one's personal past, we show that the severity of episodic, but not semantic, AM loss is best accounted for by the degree of hippocampal damage and less likely related to additional neocortical compromise.     

The perceptual richness of complex memory episodes is compromised by medial temporal lobe damage

Perceptual richness, a defining feature of episodic memory, emerges from the reliving of multimodal sensory experiences. Although the importance of the medial temporal lobe (MTL) to episodic memory retrieval is well documented, the features that determine its engagement are not well characterized. The current study assessed the relationship between MTL function and episodic memory's perceptual richness. We designed a laboratory memory task meant to capture the complexity of memory for life episodes, while manipulating memory's perceptual content. Participants encoded laboratory episodes with rich (film clips) and impoverished (written narratives) perceptual content that were matched for other characteristics such as personal significance, emotionality and story content. At retrieval, participants were probed to describe the stories' perceptual features and storyline. Participants also recalled autobiographical memories (AMs) in a comparison condition. We compared the performance of patients with unilateral medial temporal lobe epilepsy (mTLE) and healthy controls to assess how damage to the MTL affects retrieval in these conditions. We observed an overall decrease in detail count in the mTLE group, along with a disproportionate deficit in perceptual details that was most acute in the AM and the perceptually enriched film clip conditions. Our results suggest that the impaired sense of reliving the past that accompanies MTL insult is mediated by a paucity of perceptual episodic memory details. We also introduce a new protocol that successfully mimics naturalistic memories while benefiting from the experimental control provided by using laboratory stimuli. © 2014 Wiley Periodicals, Inc.