Abstract
Introduction Surprisingly little is known about neural activity in the sleeping cerebellum.5 17 Using long-term wireless recordings, we have made routine recordings of local field potentials (LFPs) and action potentials for the entirety of natural sleep in non-human primates.
Methods We were able to record simultaneously from the primary motor cortex (M1), the thalamus and the cerebellum using both rigid multi-contact linear electrode arrays and flexible microwires.11 12 Recording for the entirety of the natural sleep was achieved using a custom-made wearable device.
Results We find that the M1 and cerebellum communicate with each other during sleep,13 14 with cerebellum-to-M1 signals passing via the thalamus. We find that both M1 and cerebellar neuronal firings are broadly synchronous and phase-locked to the sleep cycle.7 Additionally, both spikes and LFPs in M1 and cerebellum also show coherence at slow (<1Hz), delta (1-4Hz) and alpha (7–15Hz) frequencies.8 15 16 We also see phase-locking between the spikes of M1 and the LFPs of the cerebellum (and vice versa) at these same frequencies. Using Granger causality analysis on the LFPs we were able to observe directed connectivity from motor cortex to the cerebellum in deep sleep. This suggested a neocortical origin of slow oscillations. By contrast, sleep spindles (in the alpha frequency range) in light sleep revealed a causal influence from the cerebellum to motor cortex, going via the thalamus.
Discussion Our results shed new light on the mechanisms of sleep spindle generation9 and show that the cerebellum is an active participant of sleep. We postulate that the cerebello-thalamo-neocortical pathways is implicated in sleep-dependent consolidation of procedural learning.1-4 6 18-20
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