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 coup...

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Bibliographic Details
Published in:Cognitive neuroscience 2015, Vol.6 (4), p.149-157
Main Authors: Chaieb, Leila, Leszczynski, Marcin, Axmacher, Nikolai, Höhne, Marlene, Elger, Christian E, Fell, Juergen
Format: Article
Language:English
Subjects:
Adult
Electroencephalography
Facial Recognition - physiology
Female
Hippocampus - physiology
Humans
Male
Memory, Short-Term - physiology
Signal-To-Noise Ratio
Theta Rhythm - physiology
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Summary: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.
ISSN:1758-8928
1758-8936
DOI:10.1080/17588928.2015.1058254