Memory consolidation is linked to spindle-mediated information processing during sleep

Abstract

How are brief encounters transformed into lasting memories? Previous research has established the role of non-rapid eye movement (NREM) sleep, along with its electrophysiological signatures of slow oscillations (SOs) and spindles, for memory consolidation. More recently, experimental manipulations have demonstrated that NREM sleep provides a window of opportunity to selectively strengthen particular memory traces via the delivery of sensory cues. It has remained unclear, however, whether experimental memory cueing triggers the brains endogenous consolidation mechanisms (linked to SOs and/or spindles) and whether those mechanisms in turn mediate effective processing of the cue information. Here we devised a novel paradigm in which associative memories (adjective-object and adjective-scene pairs) were selectively cued during a post-learning nap, successfully stabilising next-day retention relative to non-cued memories. First, we found that compared to novel control adjectives, memory cues were accompanied by an increase in fast spindles coupled to SO up states. Critically, EEG pattern decodability of the associated memory category (object vs. scene) was temporally linked to cue-induced spindles and predicted next-day retrieval performance across participants. These results provide highly controlled empirical evidence for an information processing role of sleep spindles in service of memory consolidation.