Modulating sleep: slow oscillation and spindle stimulation effects onphysiology 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 the effects of closed-loop auditory stimulation of slow oscillations have been well studied, no prior research has successfully targeted sleep spindles to assess their impact on memory. This study investigates the effects of SO and SP stimulation; and an additional condition in which stimulation was delivered 450 ms after spindle detection, on neurophysiology, and declarative, procedural, and complex memory consolidation. Healthy young adults (N = 102) engaged in tasks assessing simple declarative and procedural learning, and a complex piano task designed to require integrated use of multiple memory systems in a naturalistic fashion. Subjects were randomly assigned to one of the experimental conditions or sham stimulation control group, for a 2 hr nap opportunity, or an equivalent period of wakefulness. Using auditory stimulation, we modulated SOs and, for the first time, directly targeted sleep spindles. Results confirmed successful modulation of sleep neurophysiology. However, behavioural outcomes were complex: regardless of condition, declarative memory declined, motor sequence learning improved, and piano task performance varied between pre- and post-testing. Follow-up analysis showed modest links between evoked spindle activity and some tasks, while evoked SO strength had no clear relationship with performance change. Our findings demonstrate the feasibility and effectiveness of manipulating sleep events via precisely-timed stimulation, yet highlight the variability of behavioural outcomes.