scholarly journals Episodic memories: how do the hippocampus and the entorhinal ring attractors cooperate to create them?

2020 ◽  
Author(s):  
Krisztián A. Kovács
Keyword(s):  
Episodic Memory ◽  
Entorhinal Cortex ◽  
Clinical Case ◽  
Hippocampal Formation ◽  
New Model ◽  
Spatial Aspect ◽  
Episodic Nature ◽  
Episodic Memories ◽  
The Brain ◽  
Made In

AbstractThe brain is capable of registering a constellation of events, encountered only once, as an episodic memory that can last for a lifetime. As evidenced by the clinical case of the patient HM, memories preserving their episodic nature still depend on the hippocampal formation, several years after being created, while semantic memories are thought to reside in neocortical areas. The neurobiological substrate of one-time learning and life-long storing in the brain, that must exist at the cellular and circuit level, is still undiscovered. The breakthrough is delayed by the fact that studies jointly investigating the rodent hippocampus and entorhinal cortex are mostly targeted at understanding the spatial aspect of learning. Here we present the concept of an entorhinal cortical module, termed EPISODE module, that could explain how the representations of different elements constituting episodic memories can be linked together. The new model that we propose here reconciles the structural and functional observations made in the entorhinal cortex and explains how the downstream hippocampal processing organizes the representations into meaningful sequences.

Episodic memory recognition of the hippocampus using a deep learning method

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Takashi Kuremoto
Keyword(s):  
Deep Learning ◽  
Episodic Memory ◽  
Male Rat ◽  
Support Vector ◽  
Female Rat ◽  
Ca1 Neurons ◽  
Episodic Memories ◽  
Deep Learning Model ◽  
The Brain ◽  
Planning Action

Hippocampus plays an important role in processing episodic memory. The different patterns of multi-unit activity (MUA) of CA1 neurons in hippocampus corresponds to the different high order functions of the brain such as memory, association, planning, action decision, etc. In this paper, a deep learning model, which is a composition of convolutional neural network (CNN) and support vector machine (SVM), is adopted to classify 4 kinds of episodic memories of a male rat: restraint stress (restraint), contact with a female rat (female), contact with a male rat (male), and contact with a novel object (object). In addition, the characteristic patterns of the different events occurred in CA1 neurons are specified by the feature explanation of CNN using Grad-CAM. As the result, this study suggests that it is available to recognize episodic memories by MUA signals and vice versa.

scholarly journals Semantic Memory

Psychology ◽  
2019 ◽  
Author(s):  
Michael N. Jones ◽  
Johnathan Avery
Keyword(s):  
Episodic Memory ◽  
Semantic Memory ◽  
Communication Systems ◽  
Declarative Memory ◽  
Memory Systems ◽  
Brain Regions ◽  
Semantic Knowledge ◽  
World Knowledge ◽  
Episodic Memories ◽  
The Brain

Semantic memory refers to our general world knowledge that encompasses memory for concepts, facts, and the meanings of words and other symbolic units that constitute formal communication systems such as language or math. In the classic hierarchical view of memory, declarative memory was subdivided into two independent modules: episodic memory, which is our autobiographical store of individual events, and semantic memory, which is our general store of abstracted knowledge. However, more recent theoretical accounts have greatly reduced the independence of these two memory systems, and episodic memory is typically viewed as a gateway to semantic memory accessed through the process of abstraction. Modern accounts view semantic memory as deeply rooted in sensorimotor experience, abstracted across many episodic memories to highlight the stable characteristics and mute the idiosyncratic ones. A great deal of research in neuroscience has focused on both how the brain creates semantic memories and what brain regions share the responsibility for storage and retrieval of semantic knowledge. These include many classic experiments that studied the behavior of individuals with brain damage and various types of semantic disorders but also more modern studies that employ neuroimaging techniques to study how the brain creates and stores semantic memories. Classically, semantic memory had been treated as a miscellaneous area of study for anything in declarative memory that was not clearly within the realm of episodic memory, and formal models of meaning in memory did not advance at the pace of models of episodic memory. However, recent developments in neural networks and corpus-based tools for modeling text have greatly increased the sophistication of models of semantic memory. There now exist several good computational accounts to explain how humans transform first-order experience with the world into deep semantic representations and how these representations are retrieved and used in meaning-based behavioral tasks. The purpose of this article is to provide the reader with the more salient publications, reviews, and themes of major advances in the various subfields of semantic memory over the past forty-five years. For more in-depth coverage, we refer the reader to the manuscripts in the General Overviews section.

scholarly journals Time cells in the human hippocampus and entorhinal cortex support episodic memory

2020 ◽  
Author(s):  
Gray Umbach ◽  
Pranish Kantak ◽  
Joshua Jacobs ◽  
Michael Kahana ◽  
Brad E. Pfeiffer ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Entorhinal Cortex ◽  
Cell Activity ◽  
Memory Task ◽  
Temporal Information ◽  
Temporal Organization ◽  
Human Epilepsy ◽  
Human Hippocampus ◽  
Phase Precession ◽  
Episodic Memories

AbstractThe organization of temporal information is critical for the encoding and retrieval of episodic memories. In the rodent hippocampus and entorhinal cortex, recent evidence suggests that temporal information is encoded by a population of “time cells.” We identify time cells in humans using intracranial microelectrode recordings obtained from 27 human epilepsy patients who performed an episodic memory task. We show that time cell activity predicts the temporal organization of episodic memories. A significant portion of these cells exhibits phase precession, a key phenomenon not previously seen in human recordings. These findings establish a cellular mechanism for the representation of temporal information in the human brain needed to form episodic memories.

scholarly journals Metric and chronological time in human episodic memory

2020 ◽  
Author(s):  
Hallvard Røe Evensmoen ◽  
Lars M. Rimol ◽  
Henning Hoel Rise ◽  
Tor Ivar Hansen ◽  
Hamed Nili ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Time Scales ◽  
Entorhinal Cortex ◽  
Medial Temporal Lobe ◽  
Brain Network ◽  
Parahippocampal Cortex ◽  
Temporal Pole ◽  
Episodic Memories ◽  
Short Time ◽  
Chronological Time

The relative contributions of metric and chronological time in the encoding of episodic memories are unknown. One hundred one healthy young adults viewed 48 unique episodes of visual events and were later tested on recall of the order of events (chronological time) and the precise timing of events (metric time). The behavioral results show that metric recall accuracy correlates with chronological accuracy for events within episodes, but does not play a role on larger time-scales across episodes. Functional magnetic resonance imaging during encoding and recall showed that metric time was represented in the posterior medial entorhinal cortex, as well as the temporal pole and the cerebellum, whereas chronological time was represented in a widespread brain network including the anterior lateral entorhinal cortex, hippocampus, parahippocampal cortex and the prefrontal cortex. We conclude that metric time has a role in episodic memory on short time-scales and is mainly subserved by medial temporal lobe structures.

scholarly journals Hippocampal ripples signal contextually-mediated episodic recall

2021 ◽  
Author(s):  
John J Sakon ◽  
Michael J. Kahana
Keyword(s):  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Animal Studies ◽  
Contextual Information ◽  
Ripple Effect ◽  
Active Behavior ◽  
Human Participants ◽  
Episodic Memories ◽  
The Brain ◽  
High Frequency Oscillatory

High-frequency oscillatory events, termed ripples, represent synchrony of neural activity in the brain1. Experiments in animal models have characterized ripples during quiescent and sleep states1 and to a lesser degree during active behavior2-4. Converging evidence from these animal studies5,computational modeling6, and recent examinations in human participants support a link between hippocampal7-9 or medial temporal lobe (MTL)10,11 ripples and memory retrieval. Analyzing direct MTL recordings from 219 neurosurgical participants performing episodic recall tasks, we ask whether ripples specifically reflect the reinstatement of contextual information12-14, a defining property of episodic memory12,15, and are not just a recapitulation of recently-experienced stimuli7,10. Here we find that the rate of hippocampal ripples rises just prior to the free recall of recently-formed memories. This pre-recall ripple effect appears most strongly in the CA1 and dentate gyrus (DG) subfields of hippocampus--regions critical for episodic memory16-18. Neighboring entorhinal and parahippocampal cortices exhibit a significantly weaker effect. The pre-recall ripple effect is strongest prior to the retrieval of semantically- and/or temporally-related recalls, indicating the involvement of ripples in contextual reinstatement, thereby specifically linking ripples with retrieval of episodic memories.

scholarly journals Time cells in the human hippocampus and entorhinal cortex support episodic memory

2020 ◽  
Vol 117 (45) ◽  
pp. 28463-28474 ◽  
Author(s):  
Gray Umbach ◽  
Pranish Kantak ◽  
Joshua Jacobs ◽  
Michael Kahana ◽  
Brad E. Pfeiffer ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Entorhinal Cortex ◽  
Cell Activity ◽  
Memory Task ◽  
Cellular Mechanism ◽  
Temporal Information ◽  
Temporal Organization ◽  
Human Epilepsy ◽  
Human Hippocampus ◽  
Episodic Memories

The organization of temporal information is critical for the encoding and retrieval of episodic memories. In the rodent hippocampus and entorhinal cortex, evidence accumulated over the last decade suggests that populations of “time cells” in the hippocampus encode temporal information. We identify time cells in humans using intracranial microelectrode recordings obtained from 27 human epilepsy patients who performed an episodic memory task. We show that time cell activity predicts the temporal organization of retrieved memory items. We also uncover evidence of ramping cell activity in humans, which represents a complementary type of temporal information. These findings establish a cellular mechanism for the representation of temporal information in the human brain needed to form episodic memories.

DIFFICULTIES IN DIAGNOSING MOYA-MOYA DISEASE (CLINICAL CASE)

2020 ◽  
pp. 48-53
Author(s):  
Novikova I.N. ◽  
Popova T.F. ◽  
Gribacheva I.A. ◽  
Petrova E.V. ◽  
Marushchak A.A. ◽  
...  
Keyword(s):  
Cerebral Angiography ◽  
Neurological Disorders ◽  
Clinical Case ◽  
Carotid Arteries ◽  
Internal Carotid ◽  
Cerebral Arteries ◽  
Moya Moya Disease ◽  
Middle Cerebral Arteries ◽  
Internal Carotid Arteries ◽  
Made In

Moya-Moya disease is a rare progressive chronic cer-ebrovascular disease characterized by a narrowing of the lumen of the intracranial segments of the internal carotid arteries, as well as the initial segments of the anterior and middle cerebral arteries with the devel-opment of a network of small vascular anastomoses. Violations of blood supply due to occlusion lead to the development of ischemic strokes in the correspond-ing pools, and ruptures of vascular anastomoses - to the development of hemorrhagic strokes, causing a variety of neurological disorders. The article presents a clinical case of Moya-Moya disease in a 31-year-old patient. The disease was manifested by acute disorders of cerebral circulation in ischemic and hemorrhagic types. The diagnosis was made in accordance with the diagnostic criteria of the disease based on the data of endovascular cerebral angiography.

scholarly journals Bi-Temporal Anodal Transcranial Direct Current Stimulation during Slow-Wave Sleep Boosts Slow-Wave Density but Not Memory Consolidation

2021 ◽  
Vol 11 (4) ◽  
pp. 410
Author(s):  
Simon Ruch ◽  
Kristoffer Fehér ◽  
Stephanie Homan ◽  
Yosuke Morishima ◽  
Sarah Maria Mueller ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Slow Wave ◽  
Direct Current ◽  
Memory Consolidation ◽  
Transcranial Direct Current Stimulation ◽  
Slow Wave Sleep ◽  
Memory Performance ◽  
Direct Current Stimulation ◽  
Sleep Parameters ◽  
Episodic Memories

Slow-wave sleep (SWS) has been shown to promote long-term consolidation of episodic memories in hippocampo–neocortical networks. Previous research has aimed to modulate cortical sleep slow-waves and spindles to facilitate episodic memory consolidation. Here, we instead aimed to modulate hippocampal activity during slow-wave sleep using transcranial direct current stimulation in 18 healthy humans. A pair-associate episodic memory task was used to evaluate sleep-dependent memory consolidation with face–occupation stimuli. Pre- and post-nap retrieval was assessed as a measure of memory performance. Anodal stimulation with 2 mA was applied bilaterally over the lateral temporal cortex, motivated by its particularly extensive connections to the hippocampus. The participants slept in a magnetic resonance (MR)-simulator during the recordings to test the feasibility for a future MR-study. We used a sham-controlled, double-blind, counterbalanced randomized, within-subject crossover design. We show that stimulation vs. sham significantly increased slow-wave density and the temporal coupling of fast spindles and slow-waves. While retention of episodic memories across sleep was not affected across the entire sample of participants, it was impaired in participants with below-average pre-sleep memory performance. Hence, bi-temporal anodal direct current stimulation applied during sleep enhanced sleep parameters that are typically involved in memory consolidation, but it failed to improve memory consolidation and even tended to impair consolidation in poor learners. These findings suggest that artificially enhancing memory-related sleep parameters to improve memory consolidation can actually backfire in those participants who are in most need of memory improvement.

scholarly journals Effects of Brain Size on Adult Neurogenesis in Shrews

2021 ◽  
Vol 22 (14) ◽  
pp. 7664
Author(s):  
Katarzyna Bartkowska ◽  
Krzysztof Turlejski ◽  
Beata Tepper ◽  
Leszek Rychlik ◽  
Peter Vogel ◽  
...  
Keyword(s):  
Adult Neurogenesis ◽  
Subventricular Zone ◽  
Molecular Mechanisms ◽  
Brain Size ◽  
Hippocampal Formation ◽  
Small Animals ◽  
Suncus Murinus ◽  
The Brain ◽  
Neomys Fodiens ◽  
Migratory Stream

Shrews are small animals found in many different habitats. Like other mammals, adult neurogenesis occurs in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus (DG) of the hippocampal formation. We asked whether the number of new generated cells in shrews depends on their brain size. We examined Crocidura russula and Neomys fodiens, weighing 10–22 g, and Crocidura olivieri and Suncus murinus that weigh three times more. We found that the density of proliferated cells in the SVZ was approximately at the same level in all species. These cells migrated from the SVZ through the rostral migratory stream to the olfactory bulb (OB). In this pathway, a low level of neurogenesis occurred in C. olivieri compared to three other species of shrews. In the DG, the rate of adult neurogenesis was regulated differently. Specifically, the lowest density of newly generated neurons was observed in C. russula, which had a substantial number of new neurons in the OB compared with C. olivieri. We suggest that the number of newly generated neurons in an adult shrew’s brain is independent of the brain size, and molecular mechanisms of neurogenesis appeared to be different in two neurogenic structures.

scholarly journals Molecular Mechanisms of Drug Resistance in Glioblastoma

2021 ◽  
Vol 22 (12) ◽  
pp. 6385
Author(s):  
Maya A. Dymova ◽  
Elena V. Kuligina ◽  
Vladimir A. Richter
Keyword(s):  
Drug Resistance ◽  
Brain Tumor ◽  
Molecular Mechanisms ◽  
Primary Brain Tumor ◽  
Therapeutic Resistance ◽  
Molecular Characteristics ◽  
Blood Brain ◽  
Conventional Radiation ◽  
The Brain ◽  
Made In

Glioblastoma multiforme (GBM) is the most common and fatal primary brain tumor, is highly resistant to conventional radiation and chemotherapy, and is not amenable to effective surgical resection. The present review summarizes recent advances in our understanding of the molecular mechanisms of therapeutic resistance of GBM to already known drugs, the molecular characteristics of glioblastoma cells, and the barriers in the brain that underlie drug resistance. We also discuss the progress that has been made in the development of new targeted drugs for glioblastoma, as well as advances in drug delivery across the blood–brain barrier (BBB) and blood–brain tumor barrier (BBTB).

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