Delta oscillations coordinate intra-cerebellar 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, including memory consolidation. However, how sleep-related activity within the brains largest sensorimotor structure, the cerebellum, is multiplexed with well described sleep-related mechanisms in regions such as the hippocampus remains unknown. To address this gap in knowledge, we simultaneously recorded from the dorsal hippocampus and three distinct regions of the cerebellum (Crus I, lobule VI and lobules II/III) during natural murine sleep. We found that LFP oscillations are coordinated between the two structures in a sleep-stage specific manner. Particularly during non-REM sleep, prominent delta frequency coherence was observed between lobule VI and hippocampus. We additionally observed that non-REM associated hippocampal sharp wave ripple activity can drive discrete LFP modulation in all the recorded cerebellar regions, with the shortest latency effects observed in lobule VI. We also describe discrete phasic sharp potentials, synchronized across cerebellar regions, which were strongly phase locked to the peak of ongoing cerebellar delta oscillations and found in greatest numbers during REM. These phasic sharp potentials recorded within the cerebellar cortex were found to be phase-locked to the trough of the hippocampal theta oscillation, further suggesting cross-structural coordination. During REM, cerebellar delta oscillation phase significantly modulated hippocampal theta frequency, and this effect was greatest when phasic sharp potentials were most abundant. Within all three cerebellar regions, prominent LFP oscillations were observed at both low (delta, <4 Hz) and very high frequencies (~ 250 Hz) during non-REM and REM sleep. Intra-cerebellar cross-frequency analysis revealed that delta frequency oscillations strongly modulate those in the very high frequency range. Together, these results reveal multiple candidate physiological mechanisms to support offline, bi-directional interaction within distributed cerebello-hippocampal networks. In particular, we describe a prominent cerebellar delta oscillation, which appears to act as a temporal coordinator of cerebellar activity at both local (intra-cerebellar) and distributed (cerebello-hippocampal) network levels.