Reactivated spatial context guides episodic recall

Herweg, Nora A.; Sharan, Ashwini; Sperling, Michael R.; Brandt, Armin; Schulze‐Bonhage, Andreas; Kahana, Michael J.

doi:10.1101/399972

Cited by 13 publications

(15 citation statements)

References 67 publications

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“…In the fMRI literature, it has been shown that hippocampal activity encodes for spatial (63) and abstract representational distances (64) and that hexadirectional modulation of the BOLD signal is observed during mental travel through abstract or imagined spaces (65,66). Several recent studies have suggested that theta power may itself correlate with spatial distances (14,16,17), just as we showed a correlation between theta and representational distances in this paper. If free recall truly constitutes a form of navigation through a semantic-temporal space, might we observe hexadirectionally modulated theta during episodic retrieval?…”

Section: Discussionsupporting

confidence: 76%

“…Hippocampal theta has been associated with spatial navigation in rodents (see ref. 57 for a review) and humans (14)(15)(16) and is seen during spontaneous retrieval of information encountered in a spatial layout (17). Findings during nonspatial memory tasks have been decidedly more mixed, with many studies showing a decrease in MTL theta power during encoding and retrieval (e.g., refs.…”

Section: Discussionmentioning

confidence: 99%

“…Prior studies suggest a fundamental link between hippocampal theta oscillations and the organization of sequential information, such as paths through an environment. In humans, theta power increases as subjects search through a virtual environment (15) or recall trajectories in previously explored spatial layouts (17,18). Here we ask whether theta also supports the retrieval of nearby items in a semantic representational space.…”

Section: B Inset and C And Si Appendix Si Materials And Methods)mentioning

confidence: 99%

“…A recent study by Herweg et al (17) noted that theta power in the PHG predicted the recall of items that occurred nearby in a spatial layout. We therefore asked whether PHG theta power demonstrated the same relationship with interword transition distances.…”

Section: B Inset and C And Si Appendix Si Materials And Methods)mentioning

confidence: 99%

“…Common to studies of spatial navigation in humans and animals is the emergence of a low-frequency oscillation in the hippocampal local field potential (LFP), called the theta rhythm (typically 4 to 8 Hz). Elevated theta spectral power is consistently observed in humans during real-world (13) and virtual navigation (14)(15)(16) and during tasks that require the encoding or retrieval of spatial information (17,18). Theta oscillations appear prominently during rodent navigation (19,20) and relate to neuronal activity, in that the spiking of place-coding cells occurs at drifting phases of the theta rhythm as an animal explores its environment (21,22).…”

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confidence: 99%

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Hippocampal theta codes for distances in semantic and temporal spaces

Solomon

Lega

Sperling

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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113

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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.

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Section: Discussionsupporting

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Section: B Inset and C And Si Appendix Si Materials And Methods)mentioning

confidence: 99%

Section: B Inset and C And Si Appendix Si Materials And Methods)mentioning

confidence: 99%

mentioning

confidence: 99%

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Hippocampal theta codes for distances in semantic and temporal spaces

Solomon

Lega

Sperling

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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113

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Enhancing learning and retention with distinctive virtual reality environments and mental context reinstatement

et al. 2022

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Memory is inherently context-dependent: internal and environmental cues become bound to learnt information, and the later absence of these cues can impair recall. Here, we developed an approach to leverage context-dependence to optimise learning of challenging, interference-prone material. While navigating through desktop virtual reality (VR) contexts, participants learnt 80 foreign words in two phonetically similar languages. Those participants who learnt each language in its own unique context showed reduced interference and improved one-week retention (92%), relative to those who learnt the languages in the same context (76%)—however, this advantage was only apparent if participants subjectively experienced VR-based contexts as “real” environments. A follow-up fMRI experiment confirmed that reinstatement of brain activity patterns associated with the original encoding context during word retrieval was associated with improved recall performance. These findings establish that context-dependence can be harnessed with VR to optimise learning and showcase the important role of mental context reinstatement.

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A learned map for places and concepts in the human MTL

Herweg

Kunz

Brandt

et al. 2020

Preprint

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We examined the information coded by the human medial temporal lobe (MTL) during navigation of a complex virtual environment. Using multivariate decoding, we show that local field potentials in the MTL represent places, their semantic meaning, and the temporal order in which they are visited. These representations strengthen with experience, suggesting that the MTL constructs a learned map of physical and semantic spaces that can be used to predict future trajectories.

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Reactivated spatial context guides episodic recall

Cited by 13 publications

References 67 publications

Hippocampal theta codes for distances in semantic and temporal spaces

Hippocampal theta codes for distances in semantic and temporal spaces

Enhancing learning and retention with distinctive virtual reality environments and mental context reinstatement

A learned map for places and concepts in the human MTL

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