Odor Cues During Slow-Wave Sleep Prompt Declarative Memory Consolidation

TLDR

Sleep facilitates memory consolidation, a process thought to involve covert reactivation of newly encoded memories. The study aimed to test whether odor cues during sleep trigger memory reactivation and thereby enhance consolidation. The authors cued memories during slow‑wave sleep by replaying an odor previously paired with learning, demonstrating that such reactivation drives consolidation. Odor re‑exposure during slow‑wave sleep selectively enhanced retention of hippocampus‑dependent declarative memories, elicited hippocampal activation on fMRI, and had no effect during REM, wakefulness, or when the odor was omitted during learning.

Abstract

Sleep facilitates memory consolidation. A widely held model assumes that this is because newly encoded memories undergo covert reactivation during sleep. We cued new memories in humans during sleep by presenting an odor that had been presented as context during prior learning, and so showed that reactivation indeed causes memory consolidation during sleep. Re-exposure to the odor during slow-wave sleep (SWS) improved the retention of hippocampus-dependent declarative memories but not of hippocampus-independent procedural memories. Odor re-exposure was ineffective during rapid eye movement sleep or wakefulness or when the odor had been omitted during prior learning. Concurring with these findings, functional magnetic resonance imaging revealed significant hippocampal activation in response to odor re-exposure during SWS.