Reactivation of Hippocampal Ensemble Memories During Sleep

TLDR

Information acquired during active behavior is re‑expressed in hippocampal circuits during sleep, as postulated by memory consolidation theories. The study recorded large ensembles of hippocampal place cells in three rats during spatial tasks and during slow‑wave sleep before and after the tasks. Place cells that co‑fire during behavior also show increased co‑firing during subsequent sleep, a pattern absent in inactive or non‑overlapping cells, and this effect gradually wanes across the sleep session, suggesting synaptic modification during wakefulness.

Abstract

Simultaneous recordings were made from large ensembles of hippocampal "place cells" in three rats during spatial behavioral tasks and in slow-wave sleep preceding and following these behaviors. Cells that fired together when the animal occupied particular locations in the environment exhibited an increased tendency to fire together during subsequent sleep, in comparison to sleep episodes preceding the behavioral tasks. Cells that were inactive during behavior, or that were active but had non-overlapping spatial firing, did not show this increase. This effect, which declined gradually during each post-behavior sleep session, may result from synaptic modification during waking experience. Information acquired during active behavior is thus re-expressed in hippocampal circuits during sleep, as postulated by some theories of memory consolidation.