Temporal cluster-based organisation of sleep spindles underlies motor memory consolidation

Sleep benefits motor memory consolidation, which is mediated by sleep
spindle activity and associated memory reactivations during non-rapid eye
movement (NREM) sleep. However, the particular role of NREM2 and NREM3
sleep spindles and the mechanisms triggering this memory consolidation
process remain unclear. Here, simultaneous electroencephalographic and
functional magnetic resonance imaging (EEG-fMRI) recordings were collected
during night-time sleep following the learning of a motor sequence task.
Adopting a time-based clustering approach, we provide evidence that
spindles iteratively occur within clustered and temporally organised
patterns during both NREM2 and NREM3 sleep. However, the clustering of
spindles in trains is related to motor memory consolidation during NREM2
sleep only. Altogether, our findings suggest that spindles’ clustering and
rhythmic occurrence during NREM2 sleep may serve as an intrinsic rhythmic
sleep mechanism for the timed reactivation and subsequent consolidation of
motor memories, through synchronised oscillatory activity within a
subcortical-cortical network involved during learning.