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Memory Traces (memory + traces)
Selected AbstractsElements of a neurobiological theory of hippocampal function: the role of synaptic plasticity, synaptic tagging and schemasEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2006R. G. M. MorrisArticle first published online: 8 JUN 200 Abstract The 2004 EJN Lecture was an attempt to lay out further aspects of a developing neurobiological theory of hippocampal function [Morris, R.G.M., Moser, E.I., Riedel, G., Martin, S.J., Sandin, J., Day, M. & O'Carroll, C. (2003) Phil. Trans. R. Soc. Lond. B Biol. Sci., 358, 773,786.] These are that (i) activity-dependent synaptic plasticity plays a key role in the automatic encoding and initial storage of attended experience; (ii) the persistence of hippocampal synaptic potentiation over time can be influenced by other independent neural events happening closely in time, an idea with behavioural implications for memory; and (iii) that systems-level consolidation of memory traces within neocortex is guided both by hippocampal traces that have been subject to cellular consolidation and by the presence of organized schema in neocortex into which relevant newly encoded information might be stored. Hippocampal memory is associative and, to study it more effectively than with previous paradigms, a new learning task is described which is unusual in requiring the incidental encoding of flavour,place paired associates, with the readout of successful storage being successful recall of a place given the flavour with which it was paired. NMDA receptor-dependent synaptic plasticity is shown to be critical for the encoding and intermediate storage of memory traces in this task, while AMPA receptor-mediated fast synaptic transmission is necessary for memory retrieval. Typically, these rapidly encoded traces decay quite rapidly over time. Synaptic potentiation also decays rapidly, but can be rendered more persistent by a process of cellular consolidation in which synaptic tagging and capture play a key part in determining whether or not it will be persistent. Synaptic tags set at the time of an event, even many trivial events, can capture the products of the synthesis of plasticity proteins set in train by events before, during or even after an event to be remembered. Tag,protein interactions stabilize synaptic potentiation and, by implication, memory. The behavioural implications of tagging are explored. Finally, using a different protocol for flavour,place paired associate learning, it is shown that rats can develop a spatial schema which represents the relative locations of several different flavours of food hidden at places within a familiar space. This schema is learned gradually but, once acquired, enables new paired associates to be encoded and stored in one trial. Their incorporation into the schema prevents rapid forgetting and suggests that schema play a key and hitherto unappreciated role in systems-level memory consolidation. The elements of what may eventually mature into a more formal neurobiological theory of hippocampal memory are laid out as specific propositions with detailed conceptual discussion and reference to recent data. [source] Enhanced mismatch negativity brain response after binaural word presentationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Tanja Endrass Abstract An oddball paradigm was used to investigate brain processes elicited by spoken words and pseudowords played monaurally, to the left or right ear, or simultaneously to both ears of human subjects instructed to ignore acoustic stimuli but watch a silent video film. The mismatch negativity (MMN), a neurophysiological index of the automatic activation of cortical memory traces, was calculated as the difference between the event-related potential elicited by an infrequent deviant stimulus and the event-related potential to the same item presented as a frequent standard stimulus. Consistent with earlier reports, the MMN to words was larger than that to pseudowords, possibly reflecting the existence of memory traces for spoken words. Bilateral redundant stimulus presentation led to a further increase of the MMN to words relative to both unilateral stimulation modes. This bilateral redundancy gain was absent for pseudowords. We interpret the neurophysiological manifestation of a word-specific bilateral redundancy gain as evidence for interhemispheric cooperation in the automatic access to memory traces for spoken words. Accordingly, word-related cortical networks distributed over both hemispheres allow summation of neural activity between and within hemispheres, thereby potentiating the word-related MMN. [source] A single-trace dual-process model of episodic memory: A novel computational account of familiarity and recollectionHIPPOCAMPUS, Issue 2 2010Andrea Greve Abstract 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. [source] Striatal synaptic plasticity: Implications for motor learning and Parkinson's diseaseMOVEMENT DISORDERS, Issue 4 2005Antonio Pisani MD Abstract Changing the strength of synaptic connections between neurons is widely assumed to be the mechanism by which memory traces are encoded and stored in the central nervous system. Plastic changes appear to follow a regional specialization and underlie the specific type of memory mediated by the brain area in which plasticity occurs. Thus, long-term changes occurring at excitatory corticostriatal synapses should be critically involved in motor learning. Indeed, repetitive stimulation of the corticostriatal pathway can cause either a long-lasting increase or an enduring decrease in synaptic strength, respectively referred to as long-term potentiation (LTP), and long-term depression, both requiring a complex sequence of biochemical events. Once established, LTP can be reversed to control levels by a low-frequency stimulation protocol, an active phenomenon defined "synaptic depotentiation," required to erase redundant information. In the 6-hydroxydopamine rat model of Parkinson's disease (PD), striatal synaptic plasticity has been shown to be impaired, although chronic treatment with levodopa was able to restore it. Of interest, a consistent number of L -dopa,treated animals developed involuntary movements, resembling human dyskinesias. Strikingly, electrophysiological recordings from the dyskinetic group of rats demonstrated a selective impairment of synaptic depotentiation. This survey will provide an overview of plastic changes occurring at striatal synapses. The potential relevance of these findings in the control of motor function and in the pathogenesis both of PD and L -dopa,induced motor complications will be discussed. © 2005 Movement Disorder Society [source] The eyewitness post-identification feedback effect: What is the function of flexible confidence estimates for autobiographical events?APPLIED COGNITIVE PSYCHOLOGY, Issue 8 2009Gary L. Wells Suggesting to eyewitnesses who mistakenly identify someone from a lineup that they identified the right person leads them to recall having been more certain, having a better view during witnessing, and having paid closer attention during witnessing. The post-identification feedback effect is robust and has profound forensic implications because the courts relay on witnesses' answers to these questions to make decisions about the reliability of the identification. The effect seems to occur because there is not an accessible memory trace formed about these retrospective judgments, thereby making witnesses rely on an inference process that responds to the feedback. We speculate on the function served by a cognitive system that does not form accessible memory traces for these judgments. Copyright © 2009 John Wiley & Sons, Ltd. [source] Fronto-temporal dysregulation in remitted bipolar patients: an fMRI delayed-non-match-to-sample (DNMS) studyBIPOLAR DISORDERS, Issue 4 2009Jennifer L Robinson Objectives:, Bipolar disorder is associated with working memory (WM) impairments that persist during periods of symptomatic remission. However, the neural underpinnings of these deficits are not well understood. Methods:, Fifteen clinically remitted bipolar patients and 15 demographically matched healthy controls underwent functional magnetic resonance imaging while performing a novel delayed-non-match-to-sample (DNMS) task. This nonverbal DNMS task involves two conditions, one requiring the organization of existing memory traces (,familiarity'), and one involving the formation of new memory traces (,novelty'). These processes are thought to differentially engage the prefrontal cortex and medial temporal lobe, respectively. Results:, Although behavioral performance did not differ between groups, bipolar patients and controls exhibited significantly different patterns of neural activity during task performance. Patients showed relative hyperactivation in the right prefrontal gyrus and relative hypoactivation in visual processing regions compared to healthy subjects across both task conditions. During the novelty condition, patients showed a pattern of hypoactivation relative to controls in medial temporal regions, with relative hyperactivation in the anterior cingulate. Conclusions:, These findings suggest that disruption in fronto-temporal neural circuitry may underlie memory difficulties frequently observed in patients with bipolar disorder. [source] | |||||||||||||