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 Episodic memory-related activation in schizophrenia: meta-analysis

2005 ◽  
Vol 187 (6) ◽  
pp. 500-509 ◽  
Author(s):  
Amélie M. Achim ◽  
Martin Lepage
Keyword(s):  
Episodic Memory ◽  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Meta Analysis ◽  
Temporal Cortex ◽  
Neural Correlates ◽  
Brain Regions ◽  
Group Differences ◽  
Memory Encoding ◽  
The Brain

BackgroundNumerous studies have examined the neural correlates of episodic memory deficits in schizophrenia, yielding both consistencies and discrepancies in the reported patterns of results.AimsTo identify in schizophrenia the brain regions in which activity is consistently abnormal across imaging studies of memory.MethodData from 18 studies meeting the inclusion criteria were combined using a recently developed quantitative meta-analytic approach.ResultsRegions of consistent differential activation between groups were observed in the left inferior prefrontal cortex, medial temporal cortex bilaterally, left cerebellum, and in other prefrontal and temporal lobe regions. Subsequent analyses explored memory encoding and retrieval separately and identified between-group differences in specific prefrontal and medial temporal lobe regions.ConclusionsBeneath the apparent heterogeneity of published findings on schizophrenia and memory, a consistent and robust pattern of group differences is observed as a function of memory processes.

scholarly journals Age-Related Compensatory Reconfiguration of PFC Connections during Episodic Memory Retrieval

2020 ◽  
Author(s):  
Lifu Deng ◽  
Mathew L Stanley ◽  
Zachary A Monge ◽  
Erik A Wing ◽  
Benjamin R Geib ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Memory Retrieval ◽  
Medial Temporal Lobe ◽  
Memory Performance ◽  
Functional Integration ◽  
Brain Network ◽  
Age Related ◽  
Connectivity Patterns ◽  
The Brain ◽  
Related Increase

Abstract During demanding cognitive tasks, older adults (OAs) frequently show greater prefrontal cortex (PFC) activity than younger adults (YAs). This age-related increase in PFC activity is often associated with enhanced cognitive performance, suggesting functional compensation. However, the brain is a complex network of interconnected regions, and it is unclear how network connectivity of PFC regions differs for OAs versus YAs. To investigate this, we examined the age-related difference on the functional brain networks mediating episodic memory retrieval. YAs and OAs participants encoded and recalled visual scenes, and age-related differences in network topology during memory retrieval were investigated as a function of memory performance. We measured both changes in functional integration and reconfiguration in connectivity patterns. The study yielded three main findings. First, PFC regions were more functionally integrated with the rest of the brain network in OAs. Critically, this age-related increase in PFC integration was associated with better retrieval performance. Second, PFC regions showed stronger performance-related reconfiguration of connectivity patterns in OAs. Finally, the PFC reconfiguration increases in OAs tracked reconfiguration reductions in the medial temporal lobe (MTL)—a core episodic memory region, suggesting that PFC connectivity in OAs may be compensating for MTL deficits.

scholarly journals Delay-dependent contributions of medial temporal lobe regions to episodic memory retrieval

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Maureen Ritchey ◽  
Maria E Montchal ◽  
Andrew P Yonelinas ◽  
Charan Ranganath
Keyword(s):  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Functional Neuroimaging ◽  
Contextual Information ◽  
Medial Temporal Lobes ◽  
Temporal Lobes ◽  
Pattern Similarity ◽  
Delayed Recognition ◽  
Delay Dependent ◽  
Over Time

The medial temporal lobes play an important role in episodic memory, but over time, hippocampal contributions to retrieval may be diminished. However, it is unclear whether such changes are related to the ability to retrieve contextual information, and whether they are common across all medial temporal regions. Here, we used functional neuroimaging to compare neural responses during immediate and delayed recognition. Results showed that recollection-related activity in the posterior hippocampus declined after a 1-day delay. In contrast, activity was relatively stable in the anterior hippocampus and in neocortical areas. Multi-voxel pattern similarity analyses also revealed that anterior hippocampal patterns contained information about context during item recognition, and after a delay, context coding in this region was related to successful retention of context information. Together, these findings suggest that the anterior and posterior hippocampus have different contributions to memory over time and that neurobiological models of memory must account for these differences.

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 Human hippocampal CA3 damage disrupts both recent and remote episodic memories

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Thomas D Miller ◽  
Trevor T-J Chong ◽  
Anne M Aimola Davies ◽  
Michael R Johnson ◽  
Sarosh R Irani ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Memory Performance ◽  
Functional Integration ◽  
Resting State Fmri ◽  
Model Organisms ◽  
Default Network ◽  
Episodic Retrieval ◽  
Graph Theoretic ◽  
Episodic Memories

Neocortical-hippocampal interactions support new episodic (event) memories, but there is conflicting evidence about the dependence of remote episodic memories on the hippocampus. In line with systems consolidation and computational theories of episodic memory, evidence from model organisms suggests that the cornu ammonis 3 (CA3) hippocampal subfield supports recent, but not remote, episodic retrieval. In this study, we demonstrated that recent and remote memories were susceptible to a loss of episodic detail in human participants with focal bilateral damage to CA3. Graph theoretic analyses of 7.0-Tesla resting-state fMRI data revealed that CA3 damage disrupted functional integration across the medial temporal lobe (MTL) subsystem of the default network. The loss of functional integration in MTL subsystem regions was predictive of autobiographical episodic retrieval performance. We conclude that human CA3 is necessary for the retrieval of episodic memories long after their initial acquisition and functional integration of the default network is important for autobiographical episodic memory performance.

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 Age-related compensatory reconfiguration of PFC connections during episodic memory retrieval

2019 ◽  
Author(s):  
Lifu Deng ◽  
Mathew L. Stanley ◽  
Zachary A. Monge ◽  
Erik A. Wing ◽  
Benjamin R. Geib ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Memory Retrieval ◽  
Medial Temporal Lobe ◽  
Functional Integration ◽  
Brain Network ◽  
Activity Increase ◽  
Age Related ◽  
Functional Brain Network ◽  
Connectivity Patterns ◽  
The Brain

AbstractDuring demanding cognitive tasks, older adults (OAs) frequently show greater prefrontal cortex (PFC) activity than younger adults (YAs). This age-related PFC activity increase is often associated with enhanced cognitive performance, suggesting functional compensation. However, the brain is a complex network of interconnected regions, and it is unclear how network connectivity of PFC regions differs for OAs vs. YAs. To investigate this, we examined the age-related difference in functional brain network mediating episodic memory retrieval. YAs and OAs participants encoded and then recalled visual scenes, and age-related differences in network topology during memory retrieval were investigated as a function of memory performance. We measured both quantitative changes in functional integration and qualitative reconfiguration in connectivity patterns. The study yielded three main findings. First, PFC regions were more functionally integrated with the rest of the brain network in OAs. Critically, this age-related increase in PFC integration was associated with better retrieval performance. Second, PFC regions showed stronger performance-related reconfiguration of connectivity patterns in OAs. Finally, the magnitude of PFC reconfiguration increases in OAs tracked reconfiguration reductions in the medial temporal lobe (MTL) – a core episodic memory region, suggesting that PFC connectivity in OAs may be compensating for MTL deficits.

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.

Children show adult-like hippocampal pattern separation for familiar but not novel events

2020 ◽  
Author(s):  
Susan L. Benear ◽  
Elizabeth A. Horwath ◽  
Emily Cowan ◽  
M. Catalina Camacho ◽  
Chi Ngo ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Developmental Change ◽  
Pattern Separation ◽  
Developmental Changes ◽  
Similarity Analysis ◽  
Separation Processes ◽  
Parahippocampal Cortex ◽  
Pattern Similarity

The medial temporal lobe (MTL) undergoes critical developmental change throughout childhood, which aligns with developmental changes in episodic memory. We used representational similarity analysis to compare neural pattern similarity for children and adults in hippocampus and parahippocampal cortex during naturalistic viewing of clips from the same movie or different movies. Some movies were more familiar to participants than others. Neural pattern similarity was generally lower for clips from the same movie, indicating that related content taxes pattern separation-like processes. However, children showed this effect only for movies with which they were familiar, whereas adults showed the effect consistently. These data suggest that children need more exposures to stimuli in order to show mature pattern separation processes.

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