scholarly journals Hierarchical organization of context in the hippocampal episodic code

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Susumu Takahashi
Keyword(s):  
Episodic Memory ◽  
Large Scale ◽  
Spatial Navigation ◽  
Activity Patterns ◽  
Task Demands ◽  
Hierarchical Organization ◽  
Pattern Separation ◽  
Visually Guided ◽  
Neuronal Ensembles ◽  
External Events

The hippocampal system appears to be critically important in establishing episodic memory of both internal and external events within contexts as well as spatial memory, which enables flexible spatial navigation. However, the neuronal substrates that function across different memories in the hippocampal system are poorly understood. I monitored large-scale activity patterns of hippocampal neuronal ensembles in rats performing a novel, continuous task that combined one visually guided and two memory-guided types of navigations in a constant environment. I found that the activity patterns of the hippocampal ensemble represent spatiotemporal contexts (journeys) constructed by temporally ordered past, present and expected future places in tandem with visually or mnemonically guided non-spatial contexts (task-demands) to form episodes. This finding therefore suggests that the hierarchical organization of contexts based on pattern separation and completion enables the hippocampus to play a dual role in spatial navigation and recall of episodic memory.

scholarly journals A Scale-Dependent Neural System for Human Spatial Navigation

2021 ◽  
Author(s):  
Weihua Dong ◽  
Shengkai Wang ◽  
Yu Liu ◽  
Xiaohong Wan ◽  
Jia Liu ◽  
...  
Keyword(s):  
Human Brain ◽  
Large Scale ◽  
Spatial Scales ◽  
Spatial Navigation ◽  
Activity Patterns ◽  
Neural System ◽  
Neural Mechanisms ◽  
Parahippocampal Gyrus ◽  
Small Scale ◽  
Neural Activation

Abstract It is currently unclear whether the human brain processes navigation tasks at different scales in the same way. According to the classical view, humans process navigation information using a hierarchical representation system in a unified way. Other theories, such as the dual and multiple systems theories, suggest that the processing of navigation tasks differs between spatial scales. In addition, previous human navigation studies have mainly focused on scales ranging from rooms to small neighborhoods. However, the neural mechanisms underlying the processing of large-scale spatial navigation tasks in the human brain, and the ways in which neural activation changes with scale, have not been examined in detail. In this study, we conducted a functional magnetic resonance imaging (fMRI) based multi-scale mental navigation experiment across six spatial scales. On the basis of cortical activity patterns, we discovered a scale-dependent neural system that included the parahippocampal gyrus, cingulate gyrus, parietal gyrus and temporal gyrus, revealing neural-based divisions based on spatial scale: small scale (room), medium scale (building), large scale (block), and huge scale (city, country and continent). In contrast, scale-free characteristics were observed in middle occipital gyrus. The current findings provide new insight into the neural mechanisms of scale-driven spatial navigation in humans.

scholarly journals Striatal activity reflects cortical activity patterns

2019 ◽  
Author(s):  
Andrew J Peters ◽  
Nicholas A Steinmetz ◽  
Kenneth D Harris ◽  
Matteo Carandini
Keyword(s):  
Large Scale ◽  
Activity Patterns ◽  
Dorsal Striatum ◽  
Cortical Activity ◽  
Task Engagement ◽  
Visually Guided ◽  
Cortical Inputs ◽  
Cortical Regions ◽  
The Relationship ◽  
Different Parts

The dorsal striatum is organized into domains that drive characteristic behaviors1–7, and receive inputs from different parts of the cortex8,9 which modulate similar behaviors10–12. Striatal responses to cortical inputs, however, can be affected by changes in connection strength13–15, local striatal circuitry16,17, and thalamic inputs18,19. Therefore, it is unclear whether the pattern of activity across striatal domains mirrors that across the cortex20–23 or differs from it24–28. Here we use simultaneous large-scale recordings in the cortex and the striatum to show that striatal activity can be accurately predicted by spatiotemporal activity patterns in the cortex. The relationship between activity in the cortex and the striatum was spatially consistent with corticostriatal anatomy, and temporally consistent with a feedforward drive. Each striatal domain exhibited specific sensorimotor responses that predictably followed activity in the associated cortical regions, and the corticostriatal relationship remained unvaried during passive states or performance of a task probing visually guided behavior. However, the task’s visual stimuli and corresponding behavioral responses evoked relatively more activity in the striatum than in associated cortical regions. This increased striatal activity involved an additive offset in firing rate, which was independent of task engagement but only present in animals that had learned the task. Thus, striatal activity largely reflects patterns of cortical activity, deviating from them in a simple additive fashion for learned stimuli or actions.

scholarly journals Human brain function during pattern separation follows hippocampal and neocortical connectivity gradients

2020 ◽  
Author(s):  
Qiongling Li ◽  
Shahin Tavakol ◽  
Jessica Royer ◽  
Sara Larivière ◽  
Reinder Vos De Wael ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Activity Patterns ◽  
Resting State Fmri ◽  
Pattern Separation ◽  
External Information ◽  
Separation Performance ◽  
Activation Patterns ◽  
Cortical Organization ◽  
Functional Reorganization ◽  
Learning Techniques

AbstractEpisodic memory is our ability to remember past events accurately. Pattern separation, the process of of orthogonalizing similar aspects of external information into nonoverlapping representations, is one of its mechanisms. Converging evidence suggests a pivotal role of the hippocampus, in concert with neocortical areas, in this process. The current study aimed to identify principal dimensions of functional activation associated with pattern separation in hippocampal and neocortical areas, in both healthy individuals and patients with lesions to the hippocampus. Administering a pattern separation fMRI paradigm to a group of healthy adults, we detected task-related activation in bilateral hippocampal and distributed neocortical areas. Capitalizing on manifold learning techniques applied to parallel resting-state fMRI data, we could identify that hippocampal and neocortical activity patterns were efficiently captured by their principal gradients of intrinsic functional connectivity, which follows the hippocampal long axis and sensory-fugal cortical organization. Functional activation patterns and their alignment with these principal dimensions were altered in patients. Notably, inter-individual differences in the concordance between task-related activity and intrinsic functional gradients were correlated with pattern separation performance in both patients and controls. Our work outlines a parsimonious approach to capture the functional underpinnings of episodic memory processes at the systems level, and to decode functional reorganization in clinical populations.

Large Scale Neurocognitive Networks Underlying Episodic Memory

2000 ◽  
Vol 12 (1) ◽  
pp. 163-173 ◽  
Author(s):  
Lars Nyberg ◽  
Jonas Persson ◽  
Reza Habib ◽  
Endel Tulving ◽  
Anthony R. McIntosh ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Large Scale ◽  
Functional Neuroimaging ◽  
Brain Activity ◽  
Activity Patterns ◽  
Brain Regions ◽  
Target Density ◽  
Functional Connections ◽  
Positron Emission ◽  
Episodic Encoding

Large-scale networks of brain regions are believed to mediate cognitive processes, including episodic memory. Analyses of regional differences in brain activity, measured by functional neuroimaging, have begun to identify putative components of these networks. To more fully characterize neurocognitive networks, however, it is necessary to use analytical methods that quantify neural network interactions. Here, we used positron emission tomography (PET) to measure brain activity during initial encoding and subsequent recognition of sentences and pictures. For each type of material, three recognition conditions were included which varied with respect to target density (0%, 50%, 100%). Analysis of large-scale activity patterns identified a collection of foci whose activity distinguished the processing of sentences vs. pictures. A second pattern, which showed strong prefrontal cortex involvement, distinguished the type of cognitive process (encoding or retrieval). For both pictures and sentences, the manipulation of target density was associated with minor activation changes. Instead, it was found to relate to systematic changes of functional connections between material-specific regions and several other brain regions, including medial temporal, right prefrontal and parietal regions. These findings provide evidence for large-scale neural interactions between material-specific and process-specific neural substrates of episodic encoding and retrieval.

scholarly journals Age- and reserve-related increases in fronto-parietal and anterior hippocampal activity during episodic encoding predict subsequent memory

2019 ◽  
Author(s):  
Abdelhalim Elshiekh ◽  
Sivaniya Subramaniapillai ◽  
Sricharana Rajagopal ◽  
Stamatoula Pasvanis ◽  
Elizabeth Ankudowich ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Brain Activity ◽  
Activity Patterns ◽  
Brain Regions ◽  
Task Demands ◽  
Aging Brain ◽  
Older Individuals ◽  
Age Related ◽  
Brain Responses ◽  
Encoding And Retrieval

AbstractRemembering associations between encoded items and their contextual setting is a feature of episodic memory. Although this ability deteriorates with age in general, there is substantial variability in how older individuals perform on episodic memory tasks. This variability may stem from genetic and/or environmental factors related to reserve, allowing some individuals to compensate for age-related decline through differential recruitment of brain regions. In this fMRI study, we tested predictions related to reserve and compensation in a large adult lifespan sample (N=154). We used multivariate Behaviour Partial Least Squares (B-PLS) analysis to examine how age, retrieval accuracy, and a proxy measure of reserve, impacted brain activity patterns during spatial and temporal context encoding and retrieval. Reserve modulated age-related compensatory brain responses in ventral visual, temporal, and fronto-parietal regions during memory encoding as a function of task demands. Activity in inferior parietal, medial temporal, and ventral visual regions were strongly impacted by age at encoding and retrieval, but were also related to individual differences in reserve. Our findings are consistent with the concepts of reserve and compensation and suggest that reserve may mitigate age-related decline by modulating compensatory brain responses in the aging brain.

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.

scholarly journals Modulation of human intracranial theta oscillations during freely moving spatial navigation and memory

2019 ◽  
Author(s):  
Zahra M. Aghajan ◽  
Diane Villaroman ◽  
Sonja Hiller ◽  
Tyler J. Wishard ◽  
Uros Topalovic ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Spatial Memory ◽  
High Frequency ◽  
Medial Temporal Lobe ◽  
Spatial Navigation ◽  
Grid Cell ◽  
Cell System ◽  
Theta Oscillations ◽  
Neural Basis ◽  
Freely Moving

SummaryHow the human brain supports accurate navigation of a learned environment has been an active topic of research for nearly a century1–5. In rodents, the theta rhythm within the medial temporal lobe (MTL) has been proposed as a neural basis for fragmenting incoming information and temporally organizing experiences and is thus widely implicated in spatial and episodic memory6. In addition, high-frequency theta (~8Hz) is associated with navigation, and loss of theta results in spatial memory deficits in rats 7. Recently, high-frequency theta oscillations during ambulatory movement have been identified in humans8,9, though their relationship to spatial memory remains unexplored. Here, we were able to record MTL activity during spatial memory and navigation in freely moving humans immersed in a room-scale virtual reality (VR) environment. Naturalistic movements were captured using motion tracking combined with wireless VR in participants implanted with an intracranial electroencephalographic (iEEG) recording system for the treatment of epilepsy. We found that prevalence of theta oscillations across brain sites during both learning and recall of spatial locations during ambulatory navigation is critically linked to memory performance. This finding supports the reinstatement hypothesis of episodic memory—thought to underlie our ability to recreate a prior experience10–12—and suggests that theta prevalence within the MTL may act as a potential representational state for memory reinstatement during spatial navigation. Additionally, we found that theta power is hexadirectionally modulated13–15 as a function of the direction of physical movement, most prominently after learning has occurred. This effect bears a resemblance to the rodent grid cell system16 and suggests an analog in human navigation. Taken together, our results provide the first characterization of neural oscillations in the human MTL during ambulatory spatial memory tasks and provide a platform for future investigations of neural mechanisms underlying freely moving navigation in humans.

scholarly journals Research on Efficacy Evaluation of Large-Scale Networked Intelligent Perception System

2022 ◽  
Vol 2022 ◽  
pp. 1-11
Author(s):  
Suqiong Ge ◽  
Xiaopeng Huang
Keyword(s):  
Evaluation System ◽  
Large Scale ◽  
Task Demands ◽  
Prototype System ◽  
Engineering System ◽  
Conceptual System ◽  
Efficacy Evaluation ◽  
Perception System ◽  
Service Oriented ◽  
Evaluation Platform

Under the smart engineering system (SES), there is a huge demand for evaluating the efficacy of a large-scale networked intelligent perception system (IPS). Considering the large-scale, distributed, and networked system characteristics and perception task demands, this paper proposes a conceptual system for IPS efficacy evaluation and, on this basis, designs the architecture of the efficacy evaluation system. A networked IPS model is constructed based on domain ontology, an index system is quickly established for efficacy evaluation, the evaluation methods are assembled automatically, and adaptive real-time organization strategies are generated for networked perception based on efficacy estimate. After exploring these key technologies, a prototype system is created for the service-oriented integrated efficacy evaluation platform and used to verify and integrate research results. The research provides support for the efficacy evaluation theories and methods of large-scale networked IPS.

scholarly journals Predictive control of electrophysiological network architecture using direct, single-node neurostimulation in humans

2018 ◽  
Author(s):  
Ankit N. Khambhati ◽  
Ari E. Kahn ◽  
Julia Costantini ◽  
Youssef Ezzyat ◽  
Ethan A. Solomon ◽  
...  
Keyword(s):  
Network Architecture ◽  
Large Scale ◽  
Diffusion Tensor ◽  
Brain Structures ◽  
Network Control ◽  
Single Node ◽  
Neuronal Ensembles ◽  
Subcortical Brain Structures ◽  
Drug Resistant Epilepsy ◽  
Intracranial Recordings

AbstractChronically implantable neurostimulation devices are becoming a clinically viable option for treating patients with neurological disease and psychiatric disorders. Neurostimulation offers the ability to probe and manipulate distributed networks of interacting brain areas in dysfunctional circuits. Here, we use tools from network control theory to examine the dynamic reconfiguration of functionally interacting neuronal ensembles during targeted neurostimulation of cortical and subcortical brain structures. By integrating multi-modal intracranial recordings and diffusion tensor imaging from patients with drug-resistant epilepsy, we test hypothesized structural and functional rules that predict altered patterns of synchronized local field potentials. We demonstrate the ability to predictably reconfigure functional interactions depending on stimulation strength and location. Stimulation of areas with structurally weak connections largely modulates the functional hubness of downstream areas and concurrently propels the brain towards more difficult-to-reach dynamical states. By using focal perturbations to bridge large-scale structure, function, and markers of behavior, our findings suggest that stimulation may be tuned to influence different scales of network interactions driving cognition.

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