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Episodic memories hinge upon our ability to process a wide range of multisensory information and bind this information into a coherent, memorable representation. On a neural level, these 2 processes are thought to be supported by neocortical alpha/beta desynchronization and hippocampal theta/gamma synchronization, respectively. Intuitively, these 2 processes should couple to successfully create and retrieve episodic memories, yet this hypothesis has not been tested empirically. We address this by analyzing human intracranial electroencephalogram data recorded during 2 associative memory tasks. We find that neocortical alpha/beta (8 to 20 Hz) power decreases reliably precede and predict hippocampal "fast" gamma (60 to 80 Hz) power increases during episodic memory formation; during episodic memory retrieval, however, hippocampal "slow" gamma (40 to 50 Hz) power increases reliably precede and predict later neocortical alpha/beta power decreases. We speculate that this coupling reflects the flow of information from the neocortex to the hippocampus during memory formation, and hippocampal pattern completion inducing information reinstatement in the neocortex during memory retrieval.

Original publication

DOI

10.1073/pnas.1914180116

Type

Journal article

Journal

Proc Natl Acad Sci U S A

Publication Date

22/10/2019

Volume

116

Pages

21834 - 21842

Keywords

episodic memory, hippocampus, human, intracranial EEG, neural oscillations, Adult, Electroencephalography, Female, Hippocampus, Humans, Male, Memory, Episodic, Middle Aged, Neocortex, Neural Pathways