scholarly journals Long-term consolidation switches goal proximity coding from hippocampus to retrosplenial cortex

2017 ◽  
Author(s):  
E. Zita Patai ◽  
Amir-Homayoun Javadi ◽  
Jason D. Ozubko ◽  
Andrew O’Callaghan ◽  
Shuman Ji ◽  
...  
Keyword(s):  
Spatial Information ◽  
Hippocampal Formation ◽  
Neural Substrates ◽  
Retrosplenial Cortex ◽  
Long Term Memory ◽  
Hippocampal Activity ◽  
University College London ◽  
Virtual Simulations ◽  
First Time

AbstractRecent research indicates the hippocampus may code the distance to the goal during navigation of newly learned environments. It is unclear however, whether this also pertains to highly familiar environments where extensive systems-level consolidation is thought to have transformed mnemonic representations. Here we recorded fMRI while University College London and Imperial College London students navigated virtual simulations of their own familiar campus (> 2 years of exposure) and the other campus learned days before scanning. Posterior hippocampal activity tracked the proximity to the goal in the newly learned campus, but not in the familiar campus. By contrast retrosplenial cortex tracked the distance to the goal in the familiar campus, but not in the recently learned campus. These responses were abolished when participants were guided to their goal by external cues. These results open new avenues of research on navigation and consolidation of spatial information and help advance models of how neural circuits support navigation in novel and highly familiar environments.Significance StatementHistorically, research on the hippocampal formation has focused on its role in long-term memory and navigation – often in isolation. No study to date has directly compared realistic navigation within familiar with recently learned environments, nor has it been explored how the neural substrates, along with computational codes, may change. In this study, we show for the first time, a shift from hippocampal to cortical coding of distance to a goal during active navigation. This study bridges the gap between memory consolidation and navigation, and paves the way for more functional and realistic understanding of the hippocampus.

The hippocampus, space, and viewpoints in episodic memory

2002 ◽  
Vol 55 (4) ◽  
pp. 1057-1080 ◽  
Author(s):  
Neil Burgess
Keyword(s):  
Episodic Memory ◽  
Large Scale ◽  
Spatial Information ◽  
Functional Neuroimaging ◽  
Hippocampal Formation ◽  
Spatial Context ◽  
Controlled Study ◽  
Long Term Memory ◽  
Long Term Storage

A computational model of how single neurons in and around the rat hippocampus support spatial navigation is reviewed. The extension of this model, to include the retrieval from human long-term memory of spatial scenes and the spatial context of events is discussed. The model explores the link between spatial and mnemonic functions by supposing that retrieval of spatial information from long-term storage requires the imposition of a particular viewpoint. It is consistent with data relating to representational hemispatial neglect and the involvement of the mammillary bodies, anterior thalamus, and hippocampal formation in supporting both episodic recall and the representation of head direction. Some recent behavioural, neuropsychological, and functional neuroimaging experiments are reviewed, in which virtual reality is used to allow controlled study of navigation and memory for events set within a rich large-scale spatial context. These studies provide convergent evidence that the human hippocampus is involved in both tasks, with some lateralization of function (navigation on the right and episodic memory on the left). A further experiment indicates hippocampal involvement in retrieval of spatial information from a shifted viewpoint. I speculate that the hippocampal role in episodic recollection relates to its ability to represent a viewpoint moving within a spatial framework.

scholarly journals The lateral intraparietal sulcus takes viewpoint changes into account during memory-guided attention in natural scenes

2021 ◽  
Vol 226 (4) ◽  
pp. 989-1006
Author(s):  
Ilenia Salsano ◽  
Valerio Santangelo ◽  
Emiliano Macaluso
Keyword(s):  
Spatial Information ◽  
Temporal Cortex ◽  
Independent Effect ◽  
Long Term Memory ◽  
Natural Scenes ◽  
Behavioral Measures ◽  
Attention Network ◽  
Low Contrast ◽  
Dorsal Attention Network

AbstractPrevious studies demonstrated that long-term memory related to object-position in natural scenes guides visuo-spatial attention during subsequent search. Memory-guided attention has been associated with the activation of memory regions (the medial-temporal cortex) and with the fronto-parietal attention network. Notably, these circuits represent external locations with different frames of reference: egocentric (i.e., eyes/head-centered) in the dorsal attention network vs. allocentric (i.e., world/scene-centered) in the medial temporal cortex. Here we used behavioral measures and fMRI to assess the contribution of egocentric and allocentric spatial information during memory-guided attention. At encoding, participants were presented with real-world scenes and asked to search for and memorize the location of a high-contrast target superimposed in half of the scenes. At retrieval, participants viewed again the same scenes, now all including a low-contrast target. In scenes that included the target at encoding, the target was presented at the same scene-location. Critically, scenes were now shown either from the same or different viewpoint compared with encoding. This resulted in a memory-by-view design (target seen/unseen x same/different view), which allowed us teasing apart the role of allocentric vs. egocentric signals during memory-guided attention. Retrieval-related results showed greater search-accuracy for seen than unseen targets, both in the same and different views, indicating that memory contributes to visual search notwithstanding perspective changes. This view-change independent effect was associated with the activation of the left lateral intra-parietal sulcus. Our results demonstrate that this parietal region mediates memory-guided attention by taking into account allocentric/scene-centered information about the objects' position in the external world.

scholarly journals COMPLEXITY-BASED ANALYSIS OF THE ALTERATIONS IN THE STRUCTURE OF CORONAVIRUSES

Fractals ◽  
2021 ◽  
Vol 29 (02) ◽  
pp. 2150123
Author(s):  
HAMIDREZA NAMAZI ◽  
ALI SELAMAT ◽  
ONDREJ KREJCAR
Keyword(s):  
Hurst Exponent ◽  
Complex Structure ◽  
Approximate Entropy ◽  
Sample Entropy ◽  
Long Term Memory ◽  
Complex Structures ◽  
Term Memory ◽  
The World ◽  
First Time

The coronavirus has influenced the lives of many people since its identification in 1960. In general, there are seven types of coronavirus. Although some types of this virus, including 229E, NL63, OC43, and HKU1, cause mild to moderate illness, SARS-CoV, MERS-CoV, and SARS-CoV-2 have shown to have severer effects on the human body. Specifically, the recent known type of coronavirus, SARS-CoV-2, has affected the lives of many people around the world since late 2019 with the disease named COVID-19. In this paper, for the first time, we investigated the variations among the complex structures of coronaviruses. We employed the fractal dimension, approximate entropy, and sample entropy as the measures of complexity. Based on the obtained results, SARS-CoV-2 has a significantly different complex structure than SARS-CoV and MERS-CoV. To study the high mutation rate of SARS-CoV-2, we also analyzed the long-term memory of genome walks for different coronaviruses using the Hurst exponent. The results demonstrated that the SARS-CoV-2 shows the lowest memory in its genome walk, explaining the errors in copying the sequences along the genome that results in the virus mutation.

Does the Body Image Exist in Three Dimensions? The Study of Visual Mental Representation of a Body and a Nonbody Object

2001 ◽  
Vol 92 (1) ◽  
pp. 223-233
Author(s):  
D. P. McCabe ◽  
D. I. Ben-Tovim ◽  
M. K. Walker ◽  
D. Pomeroy
Keyword(s):  
Spatial Information ◽  
Mental Image ◽  
The Body ◽  
Three Dimensions ◽  
Long Term Memory ◽  
Depth Information ◽  
Mental Images ◽  
Term Memory ◽  
3 Dimensional

Do the mental Images of 3-dimensional objects recreate the depth characteristics of the original objects' This investigation of the characteristics of mental images utilized a novel boundary-detection task that required participants to relate a pair of crosses to the boundary of an image mentally projected onto a computer screen. 48 female participants with body attitudes within expected normal range were asked to image their own body and a familiar object from the front and the side. When the visual mental image was derived purely from long-term memory, accuracy was better than chance for the front (64%) and side (63%) of the body and also for the front (55%) and side (68%) of the familiar nonbody object. This suggests that mental images containing depth and spatial information may be generated from information held in long-term memory. Pictorial exposure to views of the front or side of the objects was used to investigate the representations from which this 3-dimensional shape and size information is derived. The results are discussed in terms of three possible representational formats and argue that a front-view 2½-dimensional representation mediates the transfer of information from long-term memory when depth information about the body is required.

scholarly journals Fine Spike Timing in Hippocampal–Prefrontal Ensembles Predicts Poor Encoding and Underlies Behavioral Performance in Healthy and Malformed Brains

2020 ◽  
Vol 31 (1) ◽  
pp. 147-158
Author(s):  
Amanda E Hernan ◽  
J Matthew Mahoney ◽  
Willie Curry ◽  
Seamus Mawe ◽  
Rod C Scott
Keyword(s):  
Working Memory ◽  
Spatial Information ◽  
Spatial Working Memory ◽  
Spike Timing ◽  
Functional Network ◽  
Long Term Memory ◽  
Encode Task ◽  
To Receive ◽  
Task Parameters

Abstract Spatial working memory (SWM) is a central cognitive process during which the hippocampus and prefrontal cortex (PFC) encode and maintain spatial information for subsequent decision-making. This occurs in the context of ongoing computations relating to spatial position, recall of long-term memory, attention, among many others. To establish how intermittently presented information is integrated with ongoing computations we recorded single units, simultaneously in hippocampus and PFC, in control rats and those with a brain malformation during performance of an SWM task. Neurons that encode intermittent task parameters are also well modulated in time and incorporated into a functional network across regions. Neurons from animals with cortical malformation are poorly modulated in time, less likely to encode task parameters, and less likely to be integrated into a functional network. Our results implicate a model in which ongoing oscillatory coordination among neurons in the hippocampal–PFC network describes a functional network that is poised to receive sensory inputs that are then integrated and multiplexed as working memory. The background temporal modulation is systematically altered in disease, but the relationship between these dynamics and behaviorally relevant firing is maintained, thereby providing potential targets for stimulation-based therapies.

scholarly journals Metabolic Impairment in Human Amnesia: A PET Study of Memory Networks

1992 ◽  
Vol 12 (3) ◽  
pp. 353-358 ◽  
Author(s):  
Ferruccio Fazio ◽  
Daniela Perani ◽  
Maria Carla Gilardi ◽  
Fabio Colombo ◽  
Stefano F. Cappa ◽  
...  
Keyword(s):  
Hippocampal Formation ◽  
Cerebral Metabolism ◽  
Human Memory ◽  
Clinical Syndrome ◽  
Long Term Memory ◽  
Positron Emission ◽  
New Information ◽  
Magnetic Resonance Imaging Mri

Human amnesia is a clinical syndrome exhibiting the failure to recall past events and to learn new information. Its “pure” form, characterized by a selective impairment of long-term memory without any disorder of general intelligence or other cognitive functions, has been associated with lesions localized within Papez's circuit and some connected areas. Thus, amnesia could be due to a functional disconnection between components of this or other neural structures involved in long-term learning and retention. To test this hypothesis, we measured regional cerebral metabolism with 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) and positron emission tomography (PET) in 11 patients with “pure” amnesia. A significant bilateral reduction in metabolism in a number of interconnected cerebral regions (hippocampal formation, thalamus, cingulate gyrus, and frontal basal cortex) was found in the amnesic patients in comparison with normal controls. The metabolic impairment did not correspond to alterations in structural anatomy as assessed by magnetic resonance imaging (MRI). These results are the first in vivo evidence for the role of a functional network as a basis of human memory.

scholarly journals Memory for events and their spatial context: models and experiments

2001 ◽  
Vol 356 (1413) ◽  
pp. 1493-1503 ◽  
Author(s):  
Neil Burgess ◽  
Suzanna Becker ◽  
John A. King ◽  
John O'Keefe
Keyword(s):  
Episodic Memory ◽  
Spatial Information ◽  
Functional Neuroimaging ◽  
Real Life ◽  
Neural Representation ◽  
Spatial Context ◽  
Long Term Memory ◽  
Long Term Storage ◽  
General Aspects

The computational role of the hippocampus in memory has been characterized as: (i) an index to disparate neocortical storage sites; (ii) a time–limited store supporting neocortical long–term memory; and (iii) a content–addressable associative memory. These ideas are reviewed and related to several general aspects of episodic memory, including the differences between episodic, recognition and semantic memory, and whether hippocampal lesions differentially affect recent or remote memories. Some outstanding questions remain, such as: what characterizes episodic retrieval as opposed to other forms of read–out from memory; what triggers the storage of an event memory; and what are the neural mechanisms involved? To address these questions a neural–level model of the medial temporal and parietal roles in retrieval of the spatial context of an event is presented. This model combines the idea that retrieval of the rich context of real–life events is a central characteristic of episodic memory, and the idea that medial temporal allocentric representations are used in long–term storage while parietal egocentric representations are used to imagine, manipulate and re–experience the products of retrieval. The model is consistent with the known neural representation of spatial information in the brain, and provides an explanation for the involvement of Papez's circuit in both the representation of heading direction and in the recollection of episodic information. Two experiments relating to the model are briefly described. A functional neuroimaging study of memory for the spatial context of life–like events in virtual reality provides support for the model's functional localization. A neuropsychological experiment suggests that the hippocampus does store an allocentric representation of spatial locations.

Visualization of Cad Objects Using a Stereoscopic Display

1994 ◽  
Vol 38 (19) ◽  
pp. 1295-1299
Author(s):  
Michael E. Brown ◽  
Jennie J. Gallimore
Keyword(s):  
Error Rate ◽  
Spatial Information ◽  
Experimental Finding ◽  
Long Term Memory ◽  
Angular Orientation ◽  
Stereoscopic Display ◽  
Term Memory ◽  
Improved Performance ◽  
Trial Object

Subjects memorized the shape of a static 3-D object displayed on a stereoscopic CRT. In each of a series of trials that followed, single static objects were presented. The angular orientation of each trial object was one of six 36-degree increments relative to the angle of the memorized stimulus. The subject's task was to determine, as quickly and accurately as possible, whether the trial object was the same shape as the memorized object or its mirrored image. One of the two cases was always true. Disparity and interposition were manipulated in a within-subject manner during the initial memorization period and the trials that followed. Subject response time and error rate were evaluated. The experimental objective was to determine the extent to which stereopsis and hidden surface affect subjects' ability to 1) transfer to and retrieve from long-term memory spatial information about a 3-D object, and 2) visualize spatial characteristics in a quick and direct manner. Improved performance due to hidden surface is the most convincing experimental finding. The study also found a significant but limited stereopsis effect.

scholarly journals Acute physical exercise improves memory consolidation in humans via BDNF and endocannabinoid signaling

2017 ◽  
Author(s):  
Blanca Marin Bosch ◽  
Aurélien Bringard ◽  
Maria Grazia Logrieco ◽  
Estelle Lauer ◽  
Nathalie Imobersteg ◽  
...  
Keyword(s):  
Physical Exercise ◽  
Acute Exercise ◽  
Memory Performance ◽  
Long Term Memory ◽  
Hippocampal Activity ◽  
High Exercise Intensity ◽  
Acute Physical Exercise ◽  
Term Performance ◽  
The Impact

AbstractRegular physical exercise enhances memory functions and neurogenesis in the hippocampus, an effect partially mediated by BDNF (Brain Derived Neurotrophic Factor). Acute exercise promotes the release of endocannabinoids (especially anandamide, AEA), which enhance BDNF release and improve hippocampal plasticity in rodents. How acute exercise affects BDNF and AEA levels and influences memory performance in humans remains to date unknown. Here we combined blood biomarkers, behavioral and fMRI measurements to assess the impact of acute physical exercise on associative memory and underlying neurophysiological mechanisms. For each participant, memory was tested after three conditions: rest, moderate or high exercise intensity. A long-term memory retest took place 3 months later. At both test and retest, memory performance increased after moderate but not high intensity exercise or rest. We also show that memory benefited from exercise-related increases in both AEA and BNDF levels: AEA boosted hippocampal activity during memory recall, while BDNF enhanced hippocampal memory representations and long-term performance.

scholarly journals Reactivation of time cell sequences in the hippocampus

2018 ◽  
Author(s):  
Hindiael A. Belchior ◽  
Rodrigo Pavão ◽  
Alan M.B. Furtunato ◽  
Howard Eichenbaum ◽  
Adriano B.L. Tort
Keyword(s):  
Temporal Order ◽  
Spatial Information ◽  
Memory Task ◽  
Fundamental Property ◽  
Long Term Memory ◽  
Potential Mechanism ◽  
Abundant Evidence ◽  
Episodic Memories ◽  
Temporal Sequences

AbstractThe temporal order of an experience is a fundamental property of episodic memories, yet the mechanism for the consolidation of temporal sequences in long-term memory is still unknown. A potential mechanism for memory consolidation depends on the reactivation of neuronal sequences in the hippocampus. Despite abundant evidence of sequence reactivation in the formation of spatial memory, the reactivation of hippocampal neuronal sequences carrying non-spatial information has been much less explored. In this work, we recorded the activity of time cell sequences while rats performed multiple 15-s treadmill runnings during the intertrial intervals of a spatial alternation memory task. We observed forward and reverse reactivations of time cell sequences often occurring during sharp-wave ripple events following reward consumption. Surprisingly, the reactivation events specifically engaged cells coding temporal information. The reactivation of time cell sequences may thus reflect the organization of temporal order required for episodic memory formation.

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