Abstract
Purkinje cells (PC), the sole output neurons of the cerebellar cortex, encode sensorimotor information, but how they do it remains a matter of debate. Here we show that PCs use a multiplexed spike code. Synchrony/spike time and firing rate encode different information in behaving monkeys during saccadic eye motion tasks. Using the local field potential (LFP) as a probe of local network activity, we found that infrequent pause spikes, which initiated or terminated intermittent pauses in simple spike trains, provide a temporally reliable signal for eye motion onset, with strong phase-coupling to the β/γ band LFP. Concurrently, regularly firing, non-pause spikes were weakly correlated with the LFP, but were crucial to linear encoding of eye movement kinematics by firing rate. Therefore, PC spike trains can simultaneously convey information necessary to achieve precision in both timing and continuous control of motion.
Highlights
Movements are often executed with high precision in timing and trajectory control
Purkinje cells (PC) use linear firing-rate coding with weak PC-to-PC correlations to robustly control continuous movement kinematics, where high signal-to-noise ratio is achieved by averaging the rates of many PCs (Shidara et al, 1993; Thier et al, 2000; Roitman et al, 2005; Medina and Lisberger, 2007; Catz et al, 2008; Herzfeld et al, 2015)
We first estimated the sensitivity of neural signals to eye motion by computing their cross-correlation functions to eye velocity (EV), CCFLFP-EV and CCFSpike-EV for the local field potential (LFP) and simple spikes, respectively (Figure 1B)
Summary
Movements are often executed with high precision in timing and trajectory control. The cerebellum is heavily involved in online motor control and should process sensorimotor information with great accuracy. PCs use linear firing-rate coding with weak PC-to-PC correlations to robustly control continuous movement kinematics, where high signal-to-noise ratio is achieved by averaging the rates of many PCs (Shidara et al, 1993; Thier et al, 2000; Roitman et al, 2005; Medina and Lisberger, 2007; Catz et al, 2008; Herzfeld et al, 2015). Spikes that initiate and terminate pauses often synchronize sharply across nearby PCs (Shin and De Schutter, 2006).
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