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Breast Cancer Affects Both the Hippocampus Volume and the Episodic Autobiographical Memory Retrieval  [PDF]
Loretxu Bergouignan, Jean Pierre Lefranc, Marie Chupin, Nastassja Morel, Jean Philippe Spano, Philippe Fossati
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0025349
Abstract: Background Neuroimaging studies show the hippocampus is a crucial node in the neural network supporting episodic autobiographical memory retrieval. Stress-related psychiatric disorders, namely Major Depression and Post Traumatic Stress Disorder (PTSD), are related to reduced hippocampus volume. However, this is not the case for remitted breast cancer patients with co-morbid stress-related psychiatric disorders. This exception may be due to the fact that, consequently to the cancer experience as such, this population might already be characterized by a reduced hippocampus with an episodic autobiographical memory deficit. Methodology We scanned, with a 3T Siemens TRIO, 16 patients who had lived through a “standard experience of breast cancer” (breast cancer and a standard treatment in remission since 18 month) in the absence of any associated stress-related psychiatric or neurological disorder and 21 matched controls. We then assessed their episodic autobiographical memory retrieval ability. Principal Findings Remitted breast cancer patients had both a significantly smaller hippocampus and a significant deficit in episodic autobiographical memory retrieval. The hippocampus atrophy was characterized by a smaller posterior hippocampus. The posterior hippocampus volume was intimately related to the ability to retrieve negative memories and to the past experience of breast cancer or not. Conclusions/Significance These results provide two main findings: (1) we identify a new population with a specific reduction in posterior hippocampus volume that is independent of any psychiatric or neurological pathology; (2) we show the intimate relation of the posterior hippocampus to the ability to retrieve episodic autobiographical memories. These are significant findings as it is the first demonstration that indicates considerable long-term effects of living through the experience of breast cancer and shows very specific hippocampal atrophy with a functional deficit without any presence of psychiatric pathology.
Simulation of Human Episodic Memory by Using a Computational Model of the Hippocampus  [PDF]
Naoyuki Sato,Yoko Yamaguchi
Advances in Artificial Intelligence , 2010, DOI: 10.1155/2010/392868
Abstract: The episodic memory, the memory of personal events and history, is essential for understanding the mechanism of human intelligence. Neuroscience evidence has shown that the hippocampus, a part of the limbic system, plays an important role in the encoding and the retrieval of the episodic memory. This paper reviews computational models of the hippocampus and introduces our own computational model of human episodic memory based on neural synchronization. Results from computer simulations demonstrate that our model provides advantage for instantaneous memory formation and selective retrieval enabling memory search. Moreover, this model was found to have the ability to predict human memory recall by integrating human eye movement data during encoding. The combined approach between computational models and experiment is efficient for theorizing the human episodic memory. 1. Introduction In 1982, Marr [1] argued the importance of computational theory for understanding the information processing in the brain and presented “three levels at which any machine carrying out an information-processing task must be understood (p. 25)” as follows. (i)Computational theory. What is the goal of the computation, why is it appropriate, and what is the logic of the strategy by which it can be carried out? (ii)Representation and algorithm. How can this computational theory be implemented? In particular, what is the representation for the input and output, and what is the algorithm for the transformation? (iii)Hardware implementation. How can the representation and algorithm be realized physically? As an example, consider a brain function of “associative memory of visual stimulus A and B.” In the level of the computational theory, it is asked what relationship between stimulus A and B results in the memory; for example, a correlation coefficient of presentation sequences of A and B will indicate a strength of association between A and B. On the level of representation and algorithm, the visual stimuli can be understood by an -dimensional binary vector pattern where an overlap between stimulus A and B will be an important parameter for their association. A correlation of vector patterns will be represented by a matrix denoting the connection strength between ith and jth units and the matrix will be formed by the Hebb rule with a repetitive presentation of the stimulus. On the level of hardware implementation, it is asked what neuronal activation and dynamics are used for implementing the above algorithm; for example, neuronal synchronization dynamics might play an important
Complementary Roles of Hippocampus and Medial Entorhinal Cortex in Episodic Memory  [PDF]
P. A. Lipton,H. Eichenbaum
Neural Plasticity , 2008, DOI: 10.1155/2008/258467
Abstract: Spatial mapping and navigation are figured prominently in the extant literature that describes hippocampal function. The medial entorhinal cortex is likewise attracting increasing interest, insofar as evidence accumulates that this area also contributes to spatial information processing. Here, we discuss recent electrophysiological findings that offer an alternate view of hippocampal and medial entorhinal function. These findings suggest complementary contributions of the hippocampus and medial entorhinal cortex in support of episodic memory, wherein hippocampal networks encode sequences of events that compose temporally and spatially extended episodes, whereas medial entorhinal networks disambiguate overlapping episodes by binding sequential events into distinct memories.
Perspectives on Episodic-Like and Episodic Memory  [PDF]
Bettina M. Pause,Armin Zlomuzica,Kiyoka Kinugawa,Jean Mariani,Reinhard Pietrowsky,Ekrem Dere
Frontiers in Behavioral Neuroscience , 2013, DOI: 10.3389/fnbeh.2013.00033
Abstract: Episodic memory refers to the conscious recollection of a personal experience that contains information on what has happened and also where and when it happened. Recollection from episodic memory also implies a kind of first-person subjectivity that has been termed autonoetic consciousness. Episodic memory is extremely sensitive to cerebral aging and neurodegenerative diseases. In Alzheimer’s disease deficits in episodic memory function are among the first cognitive symptoms observed. Furthermore, impaired episodic memory function is also observed in a variety of other neuropsychiatric diseases including dissociative disorders, schizophrenia, and Parkinson disease. Unfortunately, it is quite difficult to induce and measure episodic memories in the laboratory and it is even more difficult to measure it in clinical populations. Presently, the tests used to assess episodic memory function do not comply with even down-sized definitions of episodic-like memory as a memory for what happened, where, and when. They also require sophisticated verbal competences and are difficult to apply to patient populations. In this review, we will summarize the progress made in defining behavioral criteria of episodic-like memory in animals (and humans) as well as the perspectives in developing novel tests of human episodic memory which can also account for phenomenological aspects of episodic memory such as autonoetic awareness. We will also define basic behavioral, procedural, and phenomenological criteria which might be helpful for the development of a valid and reliable clinical test of human episodic memory.
The Hippocampus Remains Activated over the Long Term for the Retrieval of Truly Episodic Memories  [PDF]
Caroline Harand, Fran?oise Bertran, Renaud La Joie, Brigitte Landeau, Florence Mézenge, Béatrice Desgranges, Philippe Peigneux, Francis Eustache, Géraldine Rauchs
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0043495
Abstract: The role of the hippocampus in declarative memory consolidation is a matter of intense debate. We investigated the neural substrates of memory retrieval for recent and remote information using functional magnetic resonance imaging (fMRI). 18 young, healthy participants learned a series of pictures. Then, during two fMRI recognition sessions, 3 days and 3 months later, they had to determine whether they recognized or not each picture using the “Remember/Know” procedure. Presentation of the same learned images at both delays allowed us to track the evolution of memories and distinguish consistently episodic memories from those that were initially episodic and then became familiar or semantic over time and were retrieved without any contextual detail. Hippocampal activation decreased over time for initially episodic, later semantic memories, but remained stable for consistently episodic ones, at least in its posterior part. For both types of memories, neocortical activations were observed at both delays, notably in the ventromedial prefrontal and anterior cingulate cortices. These activations may reflect a gradual reorganization of memory traces within neural networks. Our data indicate maintenance and strengthening of hippocampal and cortico-cortical connections in the consolidation and retrieval of episodic memories over time, in line with the Multiple Trace theory (Nadel and Moscovitch, 1997). At variance, memories becoming semantic over time consolidate through strengthening of cortico-cortical connections and progressive disengagement of the hippocampus.
Differential Consolidation and Pattern Reverberations within Episodic Cell Assemblies in the Mouse Hippocampus  [PDF]
Remus O?an,Guifen Chen,Ruiben Feng,Joe Z. Tsien
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0016507
Abstract: One hallmark feature of consolidation of episodic memory is that only a fraction of original information, which is usually in a more abstract form, is selected for long-term memory storage. How does the brain perform these differential memory consolidations? To investigate the neural network mechanism that governs this selective consolidation process, we use a set of distinct fearful events to study if and how hippocampal CA1 cells engage in selective memory encoding and consolidation. We show that these distinct episodes activate a unique assembly of CA1 episodic cells, or neural cliques, whose response-selectivity ranges from general-to-specific features. A series of parametric analyses further reveal that post-learning CA1 episodic pattern replays or reverberations are mostly mediated by cells exhibiting event intensity-invariant responses, not by the intensity-sensitive cells. More importantly, reactivation cross-correlations displayed by intensity-invariant cells encoding general episodic features during immediate post-learning period tend to be stronger than those displayed by invariant cells encoding specific features. These differential reactivations within the CA1 episodic cell populations can thus provide the hippocampus with a selection mechanism to consolidate preferentially more generalized knowledge for long-term memory storage.
Sleep-Dependent Facilitation of Episodic Memory Details  [PDF]
Els van der Helm, Ninad Gujar, Masaki Nishida, Matthew P. Walker
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0027421
Abstract: While a role for sleep in declarative memory processing is established, the qualitative nature of this consolidation benefit, and the physiological mechanisms mediating it, remain debated. Here, we investigate the impact of sleep physiology on characteristics of episodic memory using an item- (memory elements) and context- (contextual details associated with those elements) learning paradigm; the latter being especially dependent on the hippocampus. Following back-to-back encoding of two word lists, each associated with a different context, participants were assigned to either a Nap-group, who obtained a 120-min nap, or a No Nap-group. Six hours post-encoding, participants performed a recognition test involving item-memory and context-memory judgments. In contrast to item-memory, which demonstrated no between-group differences, a significant benefit in context-memory developed in the Nap-group, the extent of which correlated both with the amount of stage-2 NREM sleep and frontal fast sleep-spindles. Furthermore, a difference was observed on the basis of word-list order, with the sleep benefit and associated physiological correlations being selective for the second word-list, learned last (most proximal to sleep). These findings suggest that sleep may preferentially benefit contextual (hippocampal-dependent) aspects of memory, supported by sleep-spindle oscillations, and that the temporal order of initial learning differentially determines subsequent offline consolidation.
Episodic and Semantic Autobiographical Memory in Temporal Lobe Epilepsy  [PDF]
Claudia P. Múnera,Carolina Lomlomdjian,Belen Gori,Verónica Terpiluk,Nancy Medel,Patricia Solís,Silvia Kochen
Epilepsy Research and Treatment , 2014, DOI: 10.1155/2014/157452
Abstract: Autobiographical memory (AM) is understood as the retrieval of personal experiences that occurred in specific time and space. To date, there is no consensus on the role of medial temporal lobe structures in AM. Therefore, we investigated AM in medial temporal lobe epilepsy (TLE) patients. Twenty TLE patients candidates for surgical treatment, 10 right (RTLE) and 10 left (LTLE), and 20 healthy controls were examined with a version of the Autobiographical Interview adapted to Spanish language. Episodic and semantic AM were analyzed during five life periods through two conditions: recall and specific probe. AM scores were compared with clinical and cognitive data. TLE patients showed lower performance in episodic AM than healthy controls, being significantly worst in RTLE group and after specific probe. In relation to semantic AM, LTLE retrieved higher amount of total semantic details compared to controls during recall, but not after specific probe. No significant differences were found between RTLE and LTLE, but a trend towards poorer performance in RTLE group was found. TLE patients obtained lower scores for adolescence period memories after specific probe. Our findings support the idea that the right hippocampus would play a more important role in episodic retrieval than the left, regardless of a temporal gradient. 1. Introduction Cognitive neuroscience over the years has been trying to elucidate which are the basic mechanisms underlying autobiographical memory (AM). Despite the vast amount of studies performed in this area there is still no consensus on the role of medial temporal lobe (MTL) structures. Medial temporal lobe epilepsy (TLE) patients provide a unique opportunity to systematically explore different aspects of AM processing considering the involvement of hippocampal structures on seizure onset and the connectivity to local and distal areas of MTL through the neural network related to epileptic spreading [1]. Epilepsy is a “pathologic model” that allows greater opportunities for research in clinical neuroscience than other neurological disorders, like stroke or dementia, in which massive damage of anatomical structures or a degenerative process is observed. An additional advantage is that most of these patients are young adults, whose illness could have begun in childhood, adolescence, or early adult life periods, giving us the chance to compare their performance at different stages. Furthermore, retrieval in this population has not a distinguished base level performance [2] which is central in the assessment of AM. Two prominent theories
Search-Related Suppression of Hippocampus and Default Network Activity during Associative Memory Retrieval  [PDF]
Emilie T. Reas,Sarah I. Gimbel
Frontiers in Human Neuroscience , 2011, DOI: 10.3389/fnhum.2011.00112
Abstract: Episodic memory retrieval involves the coordinated interaction of several cognitive processing stages such as mental search, access to a memory store, associative re-encoding, and post-retrieval monitoring. The neural response during memory retrieval is an integration of signals from multiple regions that may subserve supportive cognitive control, attention, sensory association, encoding, or working memory functions. It is particularly challenging to dissociate contributions of these distinct components to brain responses in regions such as the hippocampus, which lies at the interface between overlapping memory encoding and retrieval, and “default” networks. In the present study, event-related functional magnetic resonance imaging (fMRI) and measures of memory performance were used to differentiate brain responses to memory search from subcomponents of episodic memory retrieval associated with successful recall. During the attempted retrieval of both poorly and strongly remembered word pair associates, the hemodynamic response was negatively deflected below baseline in anterior hippocampus and regions of the default network. Activations in anterior hippocampus were functionally distinct from those in posterior hippocampus and negatively correlated with response times. Thus, relative to the pre-stimulus period, the hippocampus shows reduced activity during intensive engagement in episodic memory search. Such deactivation was most salient during trials that engaged only pre-retrieval search processes in the absence of successful recollection or post-retrieval processing. Implications for interpretation of hippocampal fMRI responses during retrieval are discussed. A model is presented to interpret such activations as representing modulation of encoding-related activity, rather than retrieval-related activity. Engagement in intensive mental search may reduce neural and attentional resources that are otherwise tonically devoted to encoding an individual’s stream of experience into episodic memory.
The Construction of Semantic Memory: Grammar-Based Representations Learned from Relational Episodic Information  [PDF]
Francesco P. Battaglia,Cyriel M. A. Pennartz
Frontiers in Computational Neuroscience , 2011, DOI: 10.3389/fncom.2011.00036
Abstract: After acquisition, memories underlie a process of consolidation, making them more resistant to interference and brain injury. Memory consolidation involves systems-level interactions, most importantly between the hippocampus and associated structures, which takes part in the initial encoding of memory, and the neocortex, which supports long-term storage. This dichotomy parallels the contrast between episodic memory (tied to the hippocampal formation), collecting an autobiographical stream of experiences, and semantic memory, a repertoire of facts and statistical regularities about the world, involving the neocortex at large. Experimental evidence points to a gradual transformation of memories, following encoding, from an episodic to a semantic character. This may require an exchange of information between different memory modules during inactive periods. We propose a theory for such interactions and for the formation of semantic memory, in which episodic memory is encoded as relational data. Semantic memory is modeled as a modified stochastic grammar, which learns to parse episodic configurations expressed as an association matrix. The grammar produces tree-like representations of episodes, describing the relationships between its main constituents at multiple levels of categorization, based on its current knowledge of world regularities. These regularities are learned by the grammar from episodic memory information, through an expectation-maximization procedure, analogous to the inside–outside algorithm for stochastic context-free grammars. We propose that a Monte-Carlo sampling version of this algorithm can be mapped on the dynamics of “sleep replay” of previously acquired information in the hippocampus and neocortex. We propose that the model can reproduce several properties of semantic memory such as decontextualization, top-down processing, and creation of schemata.
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