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Engram review

Ji-Song Guan, Jun Jiang, Hong Xie, Kai-Yuan Liu
Episodic memory in human brain is not a fixed 2-D picture but a highly dynamic movie serial, integrating information at both the temporal and the spatial domains. Recent studies in neuroscience reveal that memory storage and recall are closely related to the activities in discrete memory engram (trace) neurons within the dentate gyrus region of hippocampus and the layer 2/3 of neocortex. More strikingly, optogenetic reactivation of those memory trace neurons is able to trigger the recall of naturally encoded memory...
2016: Frontiers in Neural Circuits
Ji-Il Kim, Hye-Yeon Cho, Jin-Hee Han, Bong-Kiun Kaang
During past decades, the formation and storage principle of memory have received much attention in the neuroscience field. Although some studies have attempted to demonstrate the nature of the engram, elucidating the memory engram allocation mechanism was not possible because of the limitations of existing methods, which cannot specifically modulate the candidate neuronal population. Recently, the development of new techniques, which offer ways to mark and control specific populations of neurons, may accelerate solving this issue...
April 2016: Experimental Neurobiology
Sheena A Josselyn, Stefan Köhler, Paul W Frankland
Many attempts have been made to localize the physical trace of a memory, or engram, in the brain. However, until recently, engrams have remained largely elusive. In this Review, we develop four defining criteria that enable us to critically assess the recent progress that has been made towards finding the engram. Recent 'capture' studies use novel approaches to tag populations of neurons that are active during memory encoding, thereby allowing these engram-associated neurons to be manipulated at later times...
September 2015: Nature Reviews. Neuroscience
Freddy Jeanneteau
If the engram of long-term memory is encoded by structural changes of neuronal circuits, they are expected to be present at distant time points after learning, to be specific of circuits activated by learning, and sensitive to behavioral contingencies. In this review we present new concepts that emerged from in vivo imaging studies that tracked the structural bases of the memory trace. A fine balance of spine formation and spine elimination needed for behavioral adaptation to new experience is regulated by glucocorticoids, which are secreted in synchrony with circadian rhythms and in response to stress...
April 2015: Médecine Sciences: M/S
Hiroto Kojima, Tetsuya Sakaguchi, Yuji Ikegaya
How are memories stored in the brain and retrieved on demand? This is a frequently asked question. Indeed, we acquire new memories daily and remember old ones. However, how we can memorize one-time experiences is yet to be investigated. Here, we review possible mechanisms by which memories are maintained in neural networks.
May 2015: Brain and Nerve, Shinkei Kenkyū No Shinpo
Johan J Bolhuis, Sanne Moorman
In his pioneering research on the neural mechanisms of filial imprinting, Gabriel Horn has gone a long way to fulfilling Karl Lashley's dream of finding the 'engram' or memory trace in the brain. Here we review recent research into the engram(s) of song learning in songbirds, particularly zebra finches. When juvenile songbirds learn their songs from a tutor, they form and alter a central representation of the tutor song, known as the 'template'. Secondary auditory regions in the caudal medial pallium are likely to contain the neural substrate for the representation of tutor song, but the roles of the different regions remain to be elucidated...
March 2015: Neuroscience and Biobehavioral Reviews
M W Brown, P J Banks
A large body of data from human and animal studies using psychological, recording, imaging, and lesion techniques indicates that recognition memory involves at least two separable processes: familiarity discrimination and recollection. Familiarity discrimination for individual visual stimuli seems to be effected by a system centred on the perirhinal cortex of the temporal lobe. The fundamental change that encodes prior occurrence within the perirhinal cortex is a reduction in the responses of neurones when a stimulus is repeated...
March 2015: Neuroscience and Biobehavioral Reviews
Jean-Jacques Orban de Xivry, Reza Shadmehr
Learning to control our movements is accompanied by neuroplasticity of motor areas of the brain. The mechanisms of neuroplasticity are diverse and produce what is referred to as the motor engram, i.e., the neural trace of the motor memory. Transcranial direct current stimulation (tDCS) alters the neural and behavioral correlates of motor learning, but its precise influence on the motor engram is unknown. In this review, we summarize the effects of tDCS on neural activity and suggest a few key principles: (1) Firing rates are increased by anodal polarization and decreased by cathodal polarization, (2) anodal polarization strengthens newly formed associations, and (3) polarization modulates the memory of new/preferred firing patterns...
November 2014: Experimental Brain Research. Experimentelle Hirnforschung. Expérimentation Cérébrale
Steve Ramirez, Susumu Tonegawa, Xu Liu
With the accumulation of our knowledge about how memories are formed, consolidated, retrieved, and updated, neuroscience is now reaching a point where discrete memories can be identified and manipulated at rapid timescales. Here, we start with historical studies that lead to the modern memory engram theory. Then, we will review recent advances in memory engram research that combine transgenic and optogenetic approaches to reveal the underlying neuronal substrates sufficient for activating mnemonic processes...
2013: Frontiers in Behavioral Neuroscience
Tomonori Takeuchi, Adrian J Duszkiewicz, Richard G M Morris
The synaptic plasticity and memory hypothesis asserts that activity-dependent synaptic plasticity is induced at appropriate synapses during memory formation and is both necessary and sufficient for the encoding and trace storage of the type of memory mediated by the brain area in which it is observed. Criteria for establishing the necessity and sufficiency of such plasticity in mediating trace storage have been identified and are here reviewed in relation to new work using some of the diverse techniques of contemporary neuroscience...
January 5, 2014: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
Kathy L Ruddy, Richard G Carson
Cross education is the process whereby training of one limb gives rise to enhancements in the performance of the opposite, untrained limb. Despite interest in this phenomenon having been sustained for more than a century, a comprehensive explanation of the mediating neural mechanisms remains elusive. With new evidence emerging that cross education may have therapeutic utility, the need to provide a principled evidential basis upon which to design interventions becomes ever more pressing. Generally, mechanistic accounts of cross education align with one of two explanatory frameworks...
2013: Frontiers in Human Neuroscience
Aryeh Routtenberg
It is here proposed that the evanescent network derived from malleable or supple synapses is the substrate for long-lasting memory. The subjective sense of memory permanence is not derived, as suggested by Bain and others, from the stabilization of synaptic structure which gives rise to consolidated distributed networks. This generally held wisdom that synapses are activated and ultimately stabilized to reflect the long-lasting substrate of memory is reinforced by increased interest in the importance of sparse coding in memory consolidation...
March 2013: Hippocampus
Masanori Sakaguchi, Yasunori Hayashi
Memories are stored within neuronal ensembles in the brain. Modern genetic techniques can be used to not only visualize specific neuronal ensembles that encode memories (e.g., fear, craving) but also to selectively manipulate those neurons. These techniques are now being expanded for the study of various types of memory. In this review, we will summarize the genetic methods used to visualize and manipulate neurons involved in the representation of memory engrams. The methods will help clarify how memory is encoded, stored and processed in the brain...
2012: Molecular Brain
Hyo Jung De Smet, Sebastiaan Engelborghs, Philippe F Paquier, Peter P De Deyn, Peter Mariën
Apraxic agraphia is a writing disorder due to a loss or lack of access to motor engrams that program the movements necessary to produce letters. Clinical and functional neuroimaging studies have demonstrated that the neural network responsible for writing includes the superior parietal region and the dorsolateral and medial premotor cortex. Recent studies of two cases with atypical lesion localisations in the left thalamus and the right cerebellum support the hypothesis that the written language network is larger than previously assumed...
August 2011: Brain and Cognition
Sheena A Josselyn
The goal of my research is to gain insight using rodent models into the fundamental molecular, cellular and systems that make up the base of memory formation. My work focuses on fear memories. Aberrant fear and/or anxiety may be at the heart of many psychiatric disorders. In this article, I review the results of my research group; these results show that particular neurons in the lateral amygdala, a brain region important for fear, are specifically involved in particular fear memories. We started by showing that the transcription factor CREB (cAMP/Ca(2+) response element binding protein) plays a key role in the formation of fear memories...
July 2010: Journal of Psychiatry & Neuroscience: JPN
Chia-Lin Wu, Ann-Shyn Chiang
One of the formidable challenges in modern neuroscience is to identify the physical basis of long-term memory (LTM) storage−the engram. Cellular and molecular experiments have suggested that the engram for a particular behavioral task is encoded as changes in synaptic structure and function, yet distributed in an unknown fashion across an ill-defined neural circuit or network. Accumulating genetic and circuitry information has provided some clues toward resolving this engram puzzle.This review will focus on recent discoveries of genes and circuits involved in the formation of olfactory-associated LTM in Drosophila...
2008: Journal of Neurogenetics
Galina F Molodtsova
This review summarizes our research examining the role of serotonergic mechanisms in memory processes. Analysis of serotonin (5-HT) metabolism and specific binding of radioligand [(3)H]5-HT in various brain structures at different stages of a conditioned passive avoidance response in rats has demonstrated that 5-HT is involved in the processes of memory retrieval rather than in acquisition. The process of retrieving a conditioned response formed to a new conditioned stimulus is accompanied by a reduction in postsynaptic 5-HT receptor binding in the amygdala, periacqueductal gray matter, and striatum, while no changes have been seen in the hippocampus or prefrontal cortex...
December 16, 2008: Behavioural Brain Research
André Fiala
The olfactory system of Drosophila resembles that of vertebrates in its overall anatomical organization, but is considerably reduced in terms of cell number, making it an ideal model system to investigate odor processing in a brain [Vosshall LB, Stocker RF: Molecular architecture of smell and taste in Drosophila. Annu Rev Neurosci 2007, 30:505-533]. Recent studies have greatly increased our knowledge about odor representation at different levels of integration, from olfactory receptors to 'higher brain centers'...
December 2007: Current Opinion in Neurobiology
Aryeh Routtenberg
The prevailing textbook view that de novo protein synthesis is required for memory (e.g., [Bear, M. F., Connors, B., & Paradiso, M. 2006. Neuroscience. Lippincott, New York]) is seriously flawed and an alternative hypothesis has been proposed in which post-translational modification (PTM) of proteins already synthesized and already present within the synapse is 'the' substrate for long-lasting memory. Protein synthesis serves a replenishment role. The first part of this review discusses how long-lasting memory can be achieved with 'only' PTM of existing synaptic proteins...
March 2008: Neurobiology of Learning and Memory
Pamela S Hunt, Michael S Fanselow, Rick Richardson, Michael D Mauk, John H Freeman, Mark E Stanton
This article summarizes the proceedings of a symposium organized by Mark Stanton and Pamela Hunt and presented at the annual meeting of the International Society for Developmental Psychobiology. The purpose of the symposium was to review recent advances in neurobiological and developmental studies of fear and eyeblink conditioning with the hope of discovering how neural circuitry might inform the ontogenetic analyses of learning and memory, and vice versa. The presentations were: (1) Multiple Brain Regions Contribute to the Acquisition of Pavlovian Fear by Michael S...
November 2007: Developmental Psychobiology
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