scholarly journals Reactivated spatial context guides episodic recall

2018 ◽  
Author(s):  
Nora A. Herweg ◽  
Ashwini D. Sharan ◽  
Michael R. Sperling ◽  
Armin Brandt ◽  
Andreas Schulze-Bonhage ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Spatial Information ◽  
Memory Task ◽  
Spatial Context ◽  
Parahippocampal Gyrus ◽  
Spatial Coding ◽  
Episodic Information ◽  
Neurophysiological Mechanisms ◽  
Hippocampal Theta

AbstractThe medial temporal lobe (MTL) is known as the locus of spatial coding and episodic memory, but the interaction between these cognitive domains, as well as the extent to which they rely on common neurophysiological mechanisms is poorly understood. Here, we use a hybrid spatial-episodic memory task to determine how spatial information is dynamically reactivated in sub-regions of the MTL and how this reactivation guides recall of episodic information. Our results implicate theta oscillations across the MTL as a common neurophysiological substrate for spatial coding in navigation and episodic recall. We further show that spatial context information is initially retrieved in the hippocampus (HC) and subsequently emerges in the parahippocampal gyrus (PHG). Finally, we demonstrate that hippocampal theta phase modulates parahippocampal gamma amplitude during retrieval of spatial context, suggesting a role for cross frequency coupling in coding and transmitting retrieved spatial information.

scholarly journals Theta and gamma hippocampal-neocortical oscillations during the episodic-like memory test: impairment in epileptogenic rats

2021 ◽  
Author(s):  
Anton E Malkov ◽  
Ludmila Shevkova ◽  
Alexandra Latyshkova ◽  
Valentina Kitchigina
Keyword(s):  
Episodic Memory ◽  
Memory Task ◽  
Gamma Oscillations ◽  
High Amplitude ◽  
Memory Test ◽  
Interictal Spikes ◽  
Paroxysmal Activity ◽  
Cortical Oscillations ◽  
Gamma Rhythms ◽  
Hippocampal Theta

Cortical oscillations in different frequency bands have been shown to be intimately involved in exploration of environment and cognition. Here, the local field potentials in the hippocampus, the medial prefrontal cortex (mPFC), and the medial entorhinal cortex (mEC) were recorded simultaneously in rats during the execution of the episodic-like memory task. The power of hippocampal theta (~4-10 Hz), slow gamma (~25-50 Hz), and fast gamma oscillations (~55-100 Hz) was analyzed in all structures examined. Particular attention was paid to the theta coherence between three mentioned structures. The modulation of the power of gamma rhythms by the phase of theta cycle during the execution of the episodic-like memory test by rats was also closely studied. Healthy rats and rats one month after kainate-induced status epilepticus (SE) were examined. Paroxysmal activity in the hippocampus (high amplitude interictal spikes), excessive excitability of animals, and the death of hippocampal and dentate granular cells in rats with kainate-evoked SE were observed, which indicated the development of seizure focus in the hippocampus (epileptogenesis). One month after SE, the rats exhibited a specific impairment of episodic memory for the what-where-when triad: unlike healthy rats, epileptogenic SE animals did not identify the objects during the test. This impairment was associated with the changes in the characteristics of theta and gamma rhythms and specific violation of theta coherence and theta/gamma coupling in these structures in comparison with the healthy animals. We believe that these disturbances in the cortical areas play a role in episodic memory dysfunction in kainate-treated animals. These findings can shed light on the mechanisms of cognitive deficit during epileptogenesis.

scholarly journals Egocentric Navigation Abilities Predict Episodic Memory Performance

2020 ◽  
Vol 14 ◽  
Author(s):  
Giorgia Committeri ◽  
Agustina Fragueiro ◽  
Maria Maddalena Campanile ◽  
Marco Lagatta ◽  
Ford Burles ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Semantic Memory ◽  
Path Integration ◽  
Medial Temporal Lobe ◽  
Declarative Memory ◽  
Memory Performance ◽  
Memory Task ◽  
Recognition Task ◽  
Future Research ◽  
Egocentric Navigation

The medial temporal lobe supports both navigation and declarative memory. On this basis, a theory of phylogenetic continuity has been proposed according to which episodic and semantic memories have evolved from egocentric (e.g., path integration) and allocentric (e.g., map-based) navigation in the physical world, respectively. Here, we explored the behavioral significance of this neurophysiological model by investigating the relationship between the performance of healthy individuals on a path integration and an episodic memory task. We investigated the path integration performance through a proprioceptive Triangle Completion Task and assessed episodic memory through a picture recognition task. We evaluated the specificity of the association between performance in these two tasks by including in the study design a verbal semantic memory task. We also controlled for the effect of attention and working memory and tested the robustness of the results by including alternative versions of the path integration and semantic memory tasks. We found a significant positive correlation between the performance on the path integration the episodic, but not semantic, memory tasks. This pattern of correlation was not explained by general cognitive abilities and persisted also when considering a visual path integration task and a non-verbal semantic memory task. Importantly, a cross-validation analysis showed that participants' egocentric navigation abilities reliably predicted episodic memory performance. Altogether, our findings support the hypothesis of a phylogenetic continuity between egocentric navigation and episodic memory and pave the way for future research on the potential causal role of egocentric navigation on multiple forms of episodic 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.

Object, Space, and Object-Space Representations in the Primate Hippocampus

2005 ◽  
Vol 94 (1) ◽  
pp. 833-844 ◽  
Author(s):  
Edmund T. Rolls ◽  
Jianzhong Xiang ◽  
Leonardo Franco
Keyword(s):  
Episodic Memory ◽  
Spatial Information ◽  
Hippocampal Formation ◽  
Memory Task ◽  
Memory System ◽  
Important Advance ◽  
Object Space ◽  
Place Memory ◽  
Human Hippocampus ◽  
Spatial View

A fundamental question about the function of the primate including human hippocampus is whether object as well as allocentric spatial information is represented. Recordings were made from single hippocampal formation neurons while macaques performed an object-place memory task that required the monkeys to learn associations between objects and where they were shown in a room. Some neurons (10%) responded differently to different objects independently of location; other neurons (13%) responded to the spatial view independently of which object was present at the location; and some neurons (12%) responded to a combination of a particular object and the place where it was shown in the room. These results show that there are separate as well as combined representations of objects and their locations in space in the primate hippocampus. This is a property required in an episodic memory system, for which associations between objects and the places where they are seen are prototypical. The results thus provide an important advance by showing that a requirement for a human episodic memory system, separate and combined neuronal representations of objects and where they are seen “out there” in the environment, is present in the primate hippocampus.

scholarly journals Hippocampal theta codes for distances in semantic and temporal spaces

2019 ◽  
Vol 116 (48) ◽  
pp. 24343-24352 ◽  
Author(s):  
Ethan A. Solomon ◽  
Bradley C. Lega ◽  
Michael R. Sperling ◽  
Michael J. Kahana
Keyword(s):  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Dynamic Range ◽  
Recall Performance ◽  
Spatial Navigation ◽  
Mapping Function ◽  
Cognitive Maps ◽  
Free Recall Task ◽  
Neurosurgical Patients ◽  
Hippocampal Theta

The medial temporal lobe (MTL) is known to support episodic memory and spatial navigation, raising the possibility that its true function is to form “cognitive maps” of any kind of information. Studies in humans and animals support the idea that the hippocampal theta rhythm (4 to 8 Hz) is key to this mapping function, as it has been repeatedly observed during spatial navigation tasks. If episodic memory and spatial navigation are 2 sides of the same coin, we hypothesized that theta oscillations might reflect relations between explicitly nonspatial items, such as words. We asked 189 neurosurgical patients to perform a verbal free-recall task, of which 96 had indwelling electrodes placed in the MTL. Subjects were instructed to remember short lists of sequentially presented nouns. We found that hippocampal theta power and connectivity during item retrieval coded for semantic distances between words, as measured using word2vec-derived subspaces. Additionally, hippocampal theta indexed temporal distances between words after filtering lists on recall performance, to ensure adequate dynamic range in time. Theta effects were noted only for semantic subspaces of 1 dimension, indicating a substantial compression of the possible semantic feature space. These results lend further support to our growing confidence that the MTL forms cognitive maps of arbitrary representational spaces, helping to reconcile longstanding differences between the spatial and episodic memory literatures.

A Neuroanatomical Construct for the Amnesic Effects of Propofol

2002 ◽  
Vol 97 (2) ◽  
pp. 329-337 ◽  
Author(s):  
Robert A. Veselis ◽  
Ruth A. Reinsel ◽  
Vladimir A. Feshchenko ◽  
Ann M. Dnistrian
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Episodic Memory ◽  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Regional Cerebral Blood Flow ◽  
Memory Task ◽  
Statistical Parametric Mapping ◽  
Regional Cerebral Blood ◽  
Word Memory

Background This study was designed to identify neuroanatomical locations of propofol's effects on episodic memory by producing minimal and maximal memory impairment during conscious sedation. Drug-related changes in regional cerebral blood flow (rCBF) were located in comparison with rCBF increases during a simple word memory task. Methods Regional cerebral blood flow changes were assessed in 11 healthy volunteers using H215O positron emission tomography (PET) and statistical parametric mapping (SPM99) at 600 and 1,000 ng/ml propofol target concentrations. Study groups were based on final recognition scores of auditory words memorized during PET scanning. rCBF changes during propofol administration were compared with those during the word memory task at baseline. Results Nonoverlapping memory effects were evident: low (n = 4; propofol concentration 523 +/- 138 ng/ml; 44 +/- 13% decrement from baseline memory) and high (n = 7; 829 +/- 246 ng/ml; 87 +/- 6% decrement from baseline) groups differed in rCBF reductions primarily in right-sided prefrontal and parietal regions, close to areas activated in the baseline memory task, particularly R dorsolateral prefrontal cortex (Brodmann area 46; x, y, z = 51, 38, 22). The medial temporal lobe region exhibited relative rCBF increases. Conclusions As amnesia becomes maximal, rCBF reductions induced by propofol occur in brain regions identified with working memory processes. In contrast, medial temporal lobe structures were resistant to the global CBF decrease associated with propofol sedation. The authors postulate that the episodic memory effect of propofol is produced by interference with distributed cortical processes necessary for normal memory function rather than specific effects on medial temporal lobe structures.

scholarly journals Electrical stimulation in hippocampus and entorhinal cortex impairs spatial and temporal memory

2017 ◽  
Author(s):  
Abhinav Goyal ◽  
Jonathan Miller ◽  
Andrew J. Watrous ◽  
Sang Ah Lee ◽  
Tom Coffey ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Entorhinal Cortex ◽  
Temporal Lobe ◽  
Cognitive Processes ◽  
Brain Stimulation ◽  
Medial Temporal Lobe ◽  
Memory Task ◽  
Temporal Organization ◽  
Electrical Brain Stimulation ◽  
Neurosurgical Patients

AbstractThe medial temporal lobe (MTL) is widely implicated in supporting episodic memory and navigation, but its precise functional role in organizing memory across time and space remains elusive. Here we examine the specific cognitive processes implemented by MTL structures (hippocampus and entorhinal cortex) to organize memory by using electrical brain stimulation, leveraging its ability to establish causal links between brain regions and features of behavior. We studied neurosurgical patients of both sexes who performed spatial-navigation and verbal-episodic memory tasks while brain stimulation was applied in various regions during learning. During the verbal memory task, stimulation in the MTL disrupted the temporal organization of encoded memories such that items learned with stimulation tended to be recalled in a more randomized order. During the spatial task, MTL stimulation impaired subjects’ abilities to remember items located far away from boundaries. These stimulation effects were specific to the MTL. Our findings thus provide the first causal demonstration in humans of the specific memory processes that are performed by the MTL to encode when and where events occurred.Significance StatementNumerous studies have implicated the medial temporal lobe (MTL) in encoding spatial and temporal memories, but they have not been able to causally demonstrate the nature of the cognitive processes by which this occurs in real-time. Electrical brain stimulation is able to demonstrate causal links between a brain region and a given function with high temporal precision. By examining behavior in a memory task as subjects received MTL stimulation, we provide the first causal evidence demonstrating the role of the MTL in organizing the spatial and temporal aspects of episodic memory.

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 Hippocampal theta codes for distances in semantic and temporal spaces

2019 ◽  
Author(s):  
Ethan A. Solomon ◽  
Bradley C. Lega ◽  
Michael R. Sperling ◽  
Michael J. Kahana
Keyword(s):  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Dynamic Range ◽  
Recall Performance ◽  
Spatial Navigation ◽  
Mapping Function ◽  
Cognitive Maps ◽  
Free Recall Task ◽  
Neurosurgical Patients ◽  
Hippocampal Theta

ABSTRACTThe medial temporal lobe (MTL) is known to support episodic memory and spatial navigation, raising the possibility that its true function is to form “cognitive maps” of any kind of information. Studies in humans and animals support the idea that the hippocampal theta rhythm (4-8 Hz) is key to this mapping function, as it has been repeatedly observed during spatial navigation tasks. If episodic memory and spatial navigation are two sides of the same coin, we hypothesized that theta oscillations would also reflect relations between explicitly nonspatial items, such as words. We asked 189 neurosurgical patients to perform a verbal free-recall task, of which 96 had indwelling electrodes placed in the MTL. Subjects were instructed to remember short lists of sequentially-presented nouns. We found that hippocampal theta power and connectivity during item retrieval coded for semantic distances between words, as measured using word2vec-derived subspaces. Additionally, hippocampal theta indexed temporal distances between words after filtering lists on recall performance, to ensure adequate dynamic range in time. Theta effects were only noted for semantic subspaces of 1-dimension, indicating a substantial compression of the possible semantic feature space. These results lend further support to our growing confidence that the MTL forms cognitive maps of arbitrary representational spaces, reconciling longstanding differences between the spatial and episodic memory literatures.

scholarly journals Functional wiring of the human medial temporal lobe

2018 ◽  
Author(s):  
E. A. Solomon ◽  
J. M. Stein ◽  
S. Das ◽  
R. Gorniak ◽  
M. R. Sperling ◽  
...  
Keyword(s):  
Functional Connectivity ◽  
Episodic Memory ◽  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Memory Task ◽  
Memory Processing ◽  
High Frequencies ◽  
Functional Connections ◽  
Brain Functions ◽  
Encoding And Retrieval

AbstractThe medial temporal lobe (MTL) is a locus of episodic memory in the human brain. It is comprised of cytologically distinct subregions that, in concert, give rise to successful encoding and retrieval of context-dependent memories. However, the functional connections between these subregions are poorly understood. To determine functional connectivity among MTL subregions, we had 126 subjects fitted with indwelling electrodes perform a verbal memory task, and asked how encoding or retrieval correlated with interregional synchronization. Using phase-based measures of connectivity, we found that synchronous theta (4-8 Hz) activity underlies successful episodic memory, whereas high-frequencies exhibit desynchronization. Moreover, theta functional connectivity during encoding aligned with key anatomic connections, including critical links between the entorhinal cortex, dentate gyrus, and CA1 of the hippocampus. Retrieval-associated networks demonstrated enhanced involvement of the subiculum, reflecting a substantial reorganization of the encoding-associated network. We posit that coherent theta activity within the MTL marks periods of successful memory, but distinct patterns of connectivity dissociate key stages of memory processing.Significance StatementThe brain functions through the interaction of its distinct parts, but little is known about how such connectivity dynamics relate to learning and memory. We used a large dataset of 126 human subjects with intracranial electrodes to assess patterns of electrical connectivity within the medial temporal lobe – a key region for memory processing – as they performed a memory task. We discovered that unique networks of time-varying, low-frequency interactions correlate with memory encoding and retrieval, specifically in the theta band. Simultaneously, we observed elevated spectral power at high frequencies in these same regions. The result is a complete map of physiological dynamics within the MTL, highlighting how a reorganization of theta networks support distinct memory operations.

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