Fig. 2.

Reducing cerebellar output enhances and inhibits the estimated sensory-induced S1–M1 theta- and gamma-band coherence, respectively. (A) Averaged LFP signals in subgranular wS1 and supragranular wM1 following either air-puff stimulation of the contralateral facial whiskers, optogenetic Purkinje cell (PC) stimulation, or a combination of both. In the column on the right, there was a 20-ms delay between the onset of air puff and Purkinje cell stimulation. Purkinje cell stimulation was performed with an optic fiber with a 400-µm diameter placed on the center of crus 1. Traces were derived from channels 10 (wS1) and 3 (wM1), first averaged per mouse (100 trials per condition) and then over 8 mice. (B) Heat maps with the estimated coherence strength for each frequency. Purkinje cell stimulation induced a delayed increase in the lower frequency range, mainly theta band. Sensory stimulation predominantly caused a rapid increase in the lower gamma-band range. This increased coherence in the lower gamma band range could be suppressed by simultaneous optogenetic Purkinje cell stimulation. This suppression was largely absent when the optogenetic stimuli were delayed by 20 ms, indicating the importance of fast cerebellar processing. (C) Heat maps showing Granger causality from wS1 to wM1. (D) Granger causality for wM1 to wS1. (E) Estimated coherence after whisker stimulation (Left) and for optogenetic Purkinje cell stimulation alone (Right). (F) Simultaneous Purkinje cell stimulation enhanced and suppressed the estimated theta- and gamma-band coherence, respectively. These modulations were largely reduced by a 20-ms delay in the onset of Purkinje cell stimulation. The increased theta-band activity may partly reflect a direct effect of Purkinje cell stimulation. Shaded areas indicate SEM (n = 8 mice; *P < 0.05, χ² > 3.84, DoC test; Materials and Methods).