Phase-amplitude coupling of sleep slow oscillatory and spindle activity correlates with overnight memory consolidation.

Initially independent lines of research suggest that sleep-specific brain activity patterns, observed as electroencephalographic slow oscillatory and sleep spindle activity, promote memory consolidation and underlying synaptic refinements. Here, we further tested the emerging concept that specifically the coordinated interplay of slow oscillations and spindle activity (phase-amplitude coupling) support memory consolidation. Particularly, we associated indices of the interplay between slow oscillatory (0.16-1.25 Hz) and spindle activity (12-16 Hz) during non-rapid eye movement sleep (strength [modulation index] and phase degree of coupling) in 20 healthy adults with parameters of overnight declarative (word-list task) and procedural (mirror-tracing task) memory consolidation. The pattern of results supports the notion that the interplay between oscillations facilitates memory consolidation. The coincidence of the spindle amplitude maximum with the up-state of the slow oscillation (phase degree) was significantly associated with declarative memory consolidation (r = .65, p = .013), whereas the overall strength of coupling (modulation index) correlated with procedural memory consolidation (r = .45, p = .04). Future studies are needed to test for potential causal effects of the observed association between neural oscillations during sleep and memory consolidation, and to elucidate ways of modulating these processes, for instance through non-invasive brain-stimulation techniques.