Delta Oscillations Coordinate Intracerebellar and Cerebello-Hippocampal Network Dynamics during Sleep

During sleep, the widespread coordination of neuronal oscillations across both cortical and subcortical brain regions is thought to support various physiological functions. However, how sleep-related activity within the brain's largest sensorimotor structure, the cerebellum, is multiplexed with well-described sleep-related mechanisms in regions such as the hippocampus remains unknown. We therefore simultaneously recorded from the dorsal hippocampus and three distinct regions of the cerebellum (Cris I, lobule VI, and lobules II/III) in male mice during natural sleep. Local field potential (LFP) oscillations were found to be coordinated between these structures in a sleep stage-specific manner. During non-REM sleep, prominent delta frequency coherence was observed between lobule VI and hippocampus, whereas non-REM-associated hippocampal sharp-wave ripple activity evoked discrete LFP modulation in all recorded cerebellar regions, with the shortest latency effects in lobule VI. We also describe discrete phasic sharp potentials (PSPs), which synchronize across cerebellar regions and trigger sharp-wave ripple suppression. During REM, cerebellar delta phase significantly modulated hippocampal theta frequency, and this effect was greatest when PSPs were abundant. PSPs were phase-locked to cerebellar delta oscillation peak and hippocampal theta oscillation trough, respectively. Within all three cerebellar regions, prominent LFP oscillations were observed at both low (delta, <4Hz) and very high frequencies (similar to 250Hz) during non-REM and REM sleep. Intracerebellar cross-frequency analysis revealed that delta oscillations modulate those in the very high-frequency range. Together, these results reveal multiple candidate physiological mechanisms to support "offline," bidirectional interaction within distributed cerebello-hippocampal networks.