Fast-timescale hippocampal processes bridge between slowly unfurling neocortical states during memory search

Michelmann, S.; Dugan, P.; Doyle, W.; Friedman, D.; Melloni, L.; Strauss, C.; Devore, S.; Flinker, A.; Devinsky, O.; Hasson, U.; Norman, K. A.

doi:10.1101/2025.02.11.637471

bioRxiv · 10.1101/2025.02.11.637471

Fast-timescale hippocampal processes bridge between slowly unfurling neocortical states during memory search

Michelmann, S.·Dugan, P.·Doyle, W.·Friedman, D.·Melloni, L.·Strauss, C.·Devore, S.·Flinker, A.·Devinsky, O.·Hasson, U.·Norman, K. A.

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Abstract

Prior behavioral work showed that event structure supports our ability to search through continuous naturalistic memories. We hypothesized that, neurally, this memory search process involves a division of labor between slowly unfurling neocortical states representing event knowledge and fast hippocampal-neocortical communication supporting retrieval of new information at transitions between events. In a sample of ten intracranial EEG patients we tracked slow neural state-patterns as patients viewed a movie and then searched their memories in a structured naturalistic interview. As patients answered questions ("after A, when does B happen next?"), state-patterns from movie-viewing were reinstated in neocortex. During the critical memory-search period, states unfurled in a forward direction, realizing a trajectory from A to B in memory. Punctate moments of state-transition during memory-search were marked by low-frequency power decreases in cortex and preceded by power decreases in hippocampus that correlated with reinstatement. Connectivity-analysis revealed information-flow from hippocampus to cortex underpinning state-transitions.

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Michelmann, S., Dugan, P., Doyle, W., Friedman, D., Melloni, L., Strauss, C., Devore, S., Flinker, A., Devinsky, O., Hasson, U., Norman, K. A.. 2025-02-13. Fast-timescale hippocampal processes bridge between slowly unfurling neocortical states during memory search. https://doi.org/10.1101/2025.02.11.637471

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