scholarly journals Longitudinal Differences in Human Hippocampal Connectivity During Episodic Memory Processing

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Kyuwan Choi ◽  
Lisa Bagen ◽  
Linley Robinson ◽  
Gray Umbach ◽  
Michael Rugg ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Right Hemisphere ◽  
Human Subjects ◽  
Human Memory ◽  
Memory Systems ◽  
Memory Encoding ◽  
Hemispheric Differences ◽  
Data Set ◽  
Human Hippocampus ◽  
Hippocampal Networks

Abstract The question of longitudinal hippocampal functional specialization is critical to human episodic memory because an accurate understanding of this phenomenon would impact theories of mnemonic function and entail practical consequences for the clinical management of patients undergoing temporal lobe surgery. The implementation of the robotically assisted stereo electroencephalography technique for seizure mapping has provided our group with the opportunity to obtain recordings simultaneously from the anterior and posterior human hippocampus, allowing us to create an unparalleled data set of human subjects with simultaneous anterior and posterior hippocampal recordings along with several cortical regions. Using these data, we address several key questions governing functional hippocampal connectivity in human memory. First, we ask whether functional networks during episodic memory encoding and retrieval are significantly different for the anterior versus posterior hippocampus (PH). We also examine how connections differ across the 2–5 Hz versus 4–9 Hz theta frequency ranges, directly addressing the relative contribution of each of these separate bands in hippocampal–cortical interactions. While we report some overlapping connections, we observe evidence of distinct anterior versus posterior hippocampal networks during memory encoding related to frontal and parietal connectivity as well as hemispheric differences in aggregate connectivity. We frame these findings in light of the proposed AT/PM memory systems. We also observe distinct encoding versus retrieval connectivity patterns between anterior and posterior hippocampal networks, we find that overall connectivity is greater for the PH in the right hemisphere, and further that these networks significantly differ in terms of frontal and parietal connectivity. We place these findings in the context of existing theoretical treatments of human memory systems, especially the proposed AT/PM system. During memory retrieval, we observe significant differences between slow-theta (2–5 Hz) and fast-theta (4–9 Hz) connectivity between the cortex and hippocampus. Taken together, our findings describe mnemonically relevant functional connectivity differences along the longitudinal axis of the human hippocampus that will inform interpretation of models of hippocampal function that seek to integrate rodent and human data.

A Scene-Based Episodic Memory System for a Simulated Autonomous Creature

2013 ◽  
Vol 4 (1) ◽  
pp. 32-64 ◽  
Author(s):  
Elisa C. Castro ◽  
Ricardo R. Gudwin
Keyword(s):  
Episodic Memory ◽  
Navigation System ◽  
Cognitive Architecture ◽  
Human Memory ◽  
Memory Systems ◽  
Memory Module ◽  
The Past ◽  
3D Environment ◽  
Main Ideas

In this paper the authors present the development of a scene-based episodic memory module for the cognitive architecture controlling an autonomous virtual creature, in a simulated 3D environment. The scene-based episodic memory has the role of improving the creature’s navigation system, by evoking the objects to be considered in planning, according to episodic remembrance of earlier scenes testified by the creature where these objects were present in the past. They introduce the main background on human memory systems and episodic memory study, and provide the main ideas behind the experiment.

Individual Differences in Value-Directed Remembering

2019 ◽  
Author(s):  
Blake L. Elliott ◽  
Samuel M. McClure ◽  
Gene Arnold Brewer
Keyword(s):  
Working Memory ◽  
Individual Differences ◽  
Episodic Memory ◽  
Structural Equation ◽  
Working Memory Capacity ◽  
Human Memory ◽  
Memory Capacity ◽  
Equation Modeling ◽  
Memory Encoding ◽  
Capacity Limits

Prioritized encoding and retrieval of valuable information is an essential component of human memory due to capacity limits. Individual differences in value-directed encoding may derive from variability in stimulus valuation, memory encoding, or from strategic abilities related to maintenance in working memory. We collected multiple cognitive ability measures to test whether variation in episodic memory, working memory capacity, or both predict differences in value-directed remembering among a large sample of participants (n=205). Confirmatory factor analysis and structural equation modeling was used to assess the contributions of episodic and working memory to value sensitivity in value-directed remembering tasks. Episodic memory ability, but not working memory capacity, was predictive of value-directed remembering. These results suggest that cognitive processes may be differentially related to value-based memory encoding.

scholarly journals Dentate gyrus somatostatin cells are required for contextual discrimination during episodic memory encoding

2019 ◽  
Author(s):  
Cristian Morales ◽  
Juan Facundo Morici ◽  
Nelson Espinosa ◽  
Agostina Sacson ◽  
Ariel Lara-Vasquez ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Dentate Gyrus ◽  
Granule Cells ◽  
Molecular Layer ◽  
Memory Systems ◽  
Pattern Separation ◽  
Activity Levels ◽  
Memory Encoding ◽  
Somatostatin Cells ◽  
Somatostatin Neurons

AbstractEpisodic memory establishes and stores relations among the different elements of an experience, which are often similar and difficult to distinguish. Pattern separation, implemented by the dentate gyrus, is a neural mechanism that allows the discrimination of similar experiences by orthogonalizing synaptic inputs. Granule cells support such disambiguation by sparse rate coding, a process tightly controlled by highly diversified GABAergic neuronal populations, such as somatostatin-expressing cells which directly target the dendritic arbor of granule cells, massively innervated by entorhinal inputs reaching the molecular layer and conveying contextual information. Here, we tested the hypothesis that somatostatin neurons regulate the excitability of the dentate gyrus, thus controlling the efficacy of pattern separation during memory encoding in mice. Indeed, optogenetic suppression of dentate gyrus somatostatin neurons increased spiking activity in putative excitatory neurons and triggered dentate spikes. Moreover, optical inhibition of somatostatin neurons impaired both contextual and spatial discrimination of overlapping episodic-like memories during task acquisition. Importantly, effects were specific for similar environments, suggesting that pattern separation was selectively engaged when overlapping conditions ought to be distinguished. Overall, our results suggest that somatostatin cells regulate excitability in the dentate gyrus and are required for effective pattern separation during episodic memory encoding.Significance statementMemory systems must be able to discriminate stored representations of similar experiences in order to efficiently guide future decisions. This is solved by pattern separation, implemented in the dentate gyrus by granule cells to support episodic memory formation. The tonic inhibitory bombardment produced by multiple GABAergic cell populations maintains low activity levels in granule cells, permitting the process of pattern separation. Somatostatin-expressing cells are one of those interneuron populations, selectively targeting the distal dendrites of granule cells, where cortical multimodal information reaches the dentate gyrus. Hence, somatostatin cells constitute an ideal candidate to regulate pattern separation. Here, by using optogenetic stimulation in mice, we demonstrate that somatostatin cells are required for the acquisition of both contextual and spatial overlapping memories.

scholarly journals Replay of cortical spiking sequences during human memory retrieval

Science ◽  
2020 ◽  
Vol 367 (6482) ◽  
pp. 1131-1134 ◽  
Author(s):  
Alex P. Vaz ◽  
John H. Wittig ◽  
Sara K. Inati ◽  
Kareem A. Zaghloul
Keyword(s):  
Episodic Memory ◽  
Memory Retrieval ◽  
Medial Temporal Lobe ◽  
Single Unit ◽  
Temporal Order ◽  
Human Memory ◽  
Memory Encoding ◽  
Human Cortex ◽  
Past Experiences ◽  
Specific Sequences

Episodic memory retrieval is thought to rely on the replay of past experiences, yet it remains unknown how human single-unit activity is temporally organized during episodic memory encoding and retrieval. We found that ripple oscillations in the human cortex reflect underlying bursts of single-unit spiking activity that are organized into memory-specific sequences. Spiking sequences occurred repeatedly during memory formation and were replayed during successful memory retrieval, and this replay was associated with ripples in the medial temporal lobe. Together, these data demonstrate that human episodic memory is encoded by specific sequences of neural activity and that memory recall involves reinstating this temporal order of activity.

scholarly journals Episodic memory and common sense: how far apart?

2001 ◽  
Vol 356 (1413) ◽  
pp. 1505-1515 ◽  
Author(s):  
Endel Tulving
Keyword(s):  
Episodic Memory ◽  
Common Sense ◽  
Memory Retrieval ◽  
Critical Role ◽  
Human Memory ◽  
Memory Systems ◽  
Perceptual Information ◽  
Subjective Time ◽  
Retrieval Processes ◽  
Past Experiences

Research has revealed facts about human memory in general and episodic memory in particular that deviate from both common sense and previously accepted ideas. This paper discusses some of these deviations in light of the proceedings of The Royal Society's Discussion Meeting on episodic memory. Retrieval processes play a more critical role in memory than commonly assumed; people can remember events that never happened; and conscious thoughts about one's personal past can take two distinct forms—‘autonoetic’ remembering and ‘noetic’ knowing. The serial—dependent—independent (SPI) model of the relations among episodic, semantic and perceptual memory systems accounts for a number of puzzling phenomena, such as some amnesic patients' preserved recognition memory and their ability to learn new semantic facts, and holds that episodic remembering of perceptual information can occur only by virtue of its mediation through semantic memory. Although common sense endows many animals with the ability to remember their past experiences, as yet there is no evidence that humanlike episodic memory—defined in terms of subjective time, self, and autonoetic awareness—is present in any other species.

scholarly journals Direct brain recordings identify hippocampal and cortical networks that distinguish successful versus failed episodic memory retrieval

2020 ◽  
Author(s):  
Ryan Joseph Tan ◽  
Michael D. Rugg ◽  
Bradley C. Lega
Keyword(s):  
Prefrontal Cortex ◽  
Free Recall ◽  
Episodic Memory ◽  
Memory Retrieval ◽  
Right Hemisphere ◽  
Brain Regions ◽  
Angular Gyrus ◽  
Data Set ◽  
Functional Connections ◽  
Left Angular Gyrus

AbstractHuman data collected using noninvasive imaging techniques have established the importance of parietal regions towards episodic memory retrieval, including the angular gyrus and posterior cingulate cortex. Such regions comprise part of a putative core episodic retrieval network. In free recall, comparisons between contextually appropriate and inappropriate recall events (i.e. prior list intrusions) provide the opportunity to study memory retrieval networks supporting veridical recall, and existing findings predict that differences in electrical activity in these brain regions should be identified according to the accuracy of recall. However, prior iEEG studies, utilizing principally subdural grid electrodes, have not fully characterized brain activity in parietal regions during memory retrieval and have not examined connectivity between core recollection areas and the hippocampus or prefrontal cortex. Here, we employed a data set obtained from 100 human patients implanted with stereo EEG electrodes for seizure mapping purposes as they performed a free recall task. This data set allowed us to separately analyze activity in midline versus lateral parietal brain regions, and in anterior versus posterior hippocampus, to identify areas in which retrieval–related activity predicted the recollection of a correct versus an incorrect memory. With the wide coverage afforded by the stereo EEG approach, we were also able to examine interregional connectivity. Our key findings were that differences in gamma band activity in the angular gyrus, precuneus, posterior temporal cortex, and posterior (more than anterior) hippocampus discriminated accurate versus inaccurate recall as well as active retrieval versus memory search. The left angular gyrus exhibited a significant power decrease preceding list intrusions as well as unique phase-amplitude coupling properties, whereas the prefrontal cortex was unique in exhibiting a power increase during list intrusions. Analysis of connectivity revealed significant hemispheric asymmetry, with relatively sparse left– sided functional connections compared to the right hemisphere. One exception to this finding was elevated connectivity between the prefrontal cortex and left angular gyrus. This finding is interpreted as evidence for the engagement of prefrontal cortex in memory monitoring and mnemonic decision–making.

scholarly journals The intrinsic neonatal hippocampal network: rsfMRI findings

2019 ◽  
Author(s):  
Athena L. Howell ◽  
David E. Osher ◽  
Jin Li ◽  
Zeynep M. Saygin
Keyword(s):  
Human Memory ◽  
Memory Systems ◽  
Cortical Networks ◽  
Animal Data ◽  
Human Connectome Project ◽  
Hippocampal Network ◽  
Hippocampal Networks ◽  
Insight Into ◽  
Differential Connectivity ◽  
Anterior Posterior

AbstractMany adults cannot voluntarily recall memories before the ages of 3-5, a phenomenon referred to as “infantile amnesia” The development of the hippocampal network likely plays a significant part in the emergence of the ability to form long-lasting memories. In adults, the hippocampus has specialized and privileged connections with certain cortical networks, which presumably facilitate its involvement in memory encoding, consolidation, and retrieval. Is the hippocampus already specialized in these cortical connections at birth? And are the topographical principles of connectivity (e.g. long-axis specialization) present at birth? We analyzed resting-state hippocampal connectivity in neonates scanned within one week of birth (Developmental Human Connectome Project) and compared them to adults (Human Connectome Project). We explored the connections of the whole hippocampus and its long-axis specialization to seven canonical cortical networks. We found that the neonatal hippocampal networks show clear immaturity at birth: adults showed hippocampal connectivity that was unique for each cortical network, whereas neonates showed no differentiation in hippocampal connectivity across these networks. Further, neonates lacked long-axis specialization (i.e., along anterior-posterior axis) of the hippocampus in its differential connectivity patterns to the cortical networks. This immaturity in connectivity may contribute to immaturity in memory formation in the first years of life.“New and Noteworthy”While animal data, and anatomical and behavioral human data from young children suggest that the hippocampus is immature at birth, to date, there are no direct assessments of human hippocampal functional connectivity (FC) very early in life. Our study explores the FC of the hippocampus to the cortex at birth, allowing insight into the development of human memory systems.

Human Memory Systems: A Framework for Understanding Dementia

ASHA Leader ◽  
2007 ◽  
Vol 12 (16) ◽  
pp. 8-11 ◽  
Author(s):  
Nidhi Mahendra ◽  
Allegra Apple
Keyword(s):  
Human Memory ◽  
Memory Systems

scholarly journals Are visual working memory and episodic memory distinct processes? Insight from stroke patients by lesion-symptom mapping

2021 ◽  
Author(s):  
Selma Lugtmeijer ◽  
◽  
Linda Geerligs ◽  
Frank Erik de Leeuw ◽  
Edward H. F. de Haan ◽  
...  
Keyword(s):  
Working Memory ◽  
Episodic Memory ◽  
Visual Working Memory ◽  
Visual Memory ◽  
Right Hemisphere ◽  
Memory Task ◽  
Stroke Patients ◽  
Lesion Symptom Mapping ◽  
Criterion Setting ◽  
The Right

AbstractWorking memory and episodic memory are two different processes, although the nature of their interrelationship is debated. As these processes are predominantly studied in isolation, it is unclear whether they crucially rely on different neural substrates. To obtain more insight in this, 81 adults with sub-acute ischemic stroke and 29 elderly controls were assessed on a visual working memory task, followed by a surprise subsequent memory test for the same stimuli. Multivariate, atlas- and track-based lesion-symptom mapping (LSM) analyses were performed to identify anatomical correlates of visual memory. Behavioral results gave moderate evidence for independence between discriminability in working memory and subsequent memory, and strong evidence for a correlation in response bias on the two tasks in stroke patients. LSM analyses suggested there might be independent regions associated with working memory and episodic memory. Lesions in the right arcuate fasciculus were more strongly associated with discriminability in working memory than in subsequent memory, while lesions in the frontal operculum in the right hemisphere were more strongly associated with criterion setting in subsequent memory. These findings support the view that some processes involved in working memory and episodic memory rely on separate mechanisms, while acknowledging that there might also be shared processes.

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