Modulating sleep: slow oscillation and spindle stimulation effects on physiology and memory

Sleep plays a role in memory consolidation, with slow oscillations (SO) and sleep spindles (SP) in non-rapid eye movement sleep being central to this process. While closed-loop auditory stimulation of slow oscillations has been well studied, precise real-time targeting of individual sleep spindles to assess their memory impact has remained technically challenging. This study investigates the effects of SO and SP stimulation, plus delayed stimulation (450 ms after spindle detection), on neurophysiology and declarative, procedural, and complex memory consolidation. Healthy young adults (N = 102) engaged in simple declarative and procedural learning tasks, plus a complex piano task requiring integrated use of multiple memory systems. Participants were randomly assigned to five groups (~20 each): wake control, undisturbed sleep, slow oscillation stimulation, immediate spindle stimulation, or delayed spindle stimulation. Results confirmed successful modulation of sleep neurophysiology. However, behavioural outcomes were complex: regardless of condition, declarative memory declined, motor sequence learning improved, and piano performance varied. Follow-up analyses showed modest links between evoked spindle activity and some tasks, while evoked SO strength had no clear relationship with performance change, highlighting behavioural outcome variability.