Phase-amplitude coupling of slow oscillations and sleep spindles as neural marker of gross motor sequence learning and its modulation by motor imagery practice

STUDY OBJECTIVES: The precise temporal coupling between slow oscillations (SOs) and sleep spindles is considered a key mechanism of sleep-dependent memory consolidation. While well-established for declarative and fine motor sequence learning, its role in gross motor sequence learning remains unclear. Here, we assessed whether SO-spindle coupling supports gross motor memory consolidation and whether motor imagery (MI), the mental rehearsal of movements, induces task-specific modulation of this coupling. METHODS: group, n = 40), and again after a 12- and 24-h retention interval. Ambulatory polysomnography was recorded during a baseline and a learning night. RESULTS: Immediate sleep, compared to wakefulness, enhanced motor memory consolidation. Importantly, SO-spindle coupling phase during the learning night, defined as the preferred SO phase at which spindle amplitudes peaked, was associated with overnight performance improvement. Furthermore, for participants who engaged in MI practice prior to sleep, a stronger shift in coupling phase toward the SO up-state from the baseline to the learning night was linked to greater overnight performance gains. CONCLUSIONS: We provide first evidence that SO-spindle coupling phase supports sleep-dependent consolidation of gross motor sequences. Furthermore, we propose that coupling phase may serve a dual role as general marker of motor memory ability and as dynamic mechanism reflecting individual performance differences in response to task-specific MI- practice.