Sensorimotor restriction affects sleep-related motor memory consolidation through altered slow oscillation-spindle coupling.

Sleep benefits memory consolidation through periodic sleep spindle activity and associated memory reactivations. The temporal organization of spindles in "trains" is considered a critical sleep mechanism for the timed and repeated reactivation of memories. Also, evidence suggests that a timely phase-locking between slow oscillations (SO) and spindles facilitates learning-related synaptic plasticity. Here, we investigated the contribution of the clustering and coupling of spindles with SO in motor memory consolidation by experimentally promoting local synaptic depression in sensorimotor cortical regions, through upper-limb immobilization, following motor sequence learning. Our results reveal that the cluster-based organization of sleep spindles is independent of daytime sensorimotor experience, while leading to distinct overnight behavioral outcomes. Interestingly, immobilization induced a phase shift in the SO-spindle coupling for spindles occurring in trains but not when isolated outside trains. We demonstrate that spindle trains may promote skill-specific strengthening of motor memories, while isolated spindles may instead create memory-instability conditions leading to enhanced skill transfer.