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Theta-gamma phase-phase coupling during working memory maintenance in the human hippocampus

Theta-gamma phase-phase coupling during working memory maintenance in the human hippocampus The theta-gamma neural coding theory suggests that multiple items are represented in working memory (WM) by a superposition of gamma cycles on theta oscillations. To enable a stable, non-interfering representation of multiple items, such a theta-gamma neural code may be reflected by phase-phase coupling, i.e., a precise locking of gamma subcycles to specific theta phases. Recent data have indicated that the hippocampus critically contributes to multi-item working memory. Therefore, we investigated phase-phase coupling patterns in the hippocampus based on intracranial EEG recordings in presurgical epilepsy patients performing a variant of the serial Sternberg WM task. In accordance with predictions of the theta-gamma coding theory, we observed increased phase-phase coupling between theta and beta/gamma activity during working memory maintenance compared to inter-trial intervals. These phase-phase coupling patterns were apparent during maintenance of two and four items, but not during maintenance of a single item, where prominent lower coupling ratios occurred. Furthermore, we observed that load-dependent changes of coupling factors correlated with individual WM capacities. Our data demonstrate that multi-item WM is associated with changes in hippocampal phase-phase coupling between theta and beta/gamma activity. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Cognitive Neuroscience Taylor & Francis

Theta-gamma phase-phase coupling during working memory maintenance in the human hippocampus

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References (20)

Publisher
Taylor & Francis
Copyright
© 2015 Taylor & Francis
ISSN
1758-8936
eISSN
1758-8928
DOI
10.1080/17588928.2015.1058254
pmid
26101947
Publisher site
See Article on Publisher Site

Abstract

The theta-gamma neural coding theory suggests that multiple items are represented in working memory (WM) by a superposition of gamma cycles on theta oscillations. To enable a stable, non-interfering representation of multiple items, such a theta-gamma neural code may be reflected by phase-phase coupling, i.e., a precise locking of gamma subcycles to specific theta phases. Recent data have indicated that the hippocampus critically contributes to multi-item working memory. Therefore, we investigated phase-phase coupling patterns in the hippocampus based on intracranial EEG recordings in presurgical epilepsy patients performing a variant of the serial Sternberg WM task. In accordance with predictions of the theta-gamma coding theory, we observed increased phase-phase coupling between theta and beta/gamma activity during working memory maintenance compared to inter-trial intervals. These phase-phase coupling patterns were apparent during maintenance of two and four items, but not during maintenance of a single item, where prominent lower coupling ratios occurred. Furthermore, we observed that load-dependent changes of coupling factors correlated with individual WM capacities. Our data demonstrate that multi-item WM is associated with changes in hippocampal phase-phase coupling between theta and beta/gamma activity.

Journal

Cognitive Neuroscience – Taylor & Francis

Published: Oct 2, 2015

Keywords: Working memory; Intracranial EEG; Hippocampus; n:m phase coupling; Theta activity; Gamma activity

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