Single trial coupling of Purkinje cell activity to speed and error signals during circular manual tracking

The simple spike firing of cerebellar Purkinje cells encodes information on the kinematics of limb movements. However, these conclusions have been primarily based on averaging the discharge of Purkinje cells across trials and time and there is little information on whether Purkinje cell simple spike firing encodes specific motor errors during limb movements. Therefore, this study investigated single-trial correlations between the instantaneous simple spike firing of Purkinje cells with various kinematics and error signals. Purkinje cells (n = 126) were recorded in the intermediate and lateral zones centered on the primary fissure while three monkeys intercepted and tracked a target moving in a circle. Cross-correlation analysis was performed between the instantaneous simple spike firing rate and speed, the directional component of the velocity vector, and error signals during single movement trials. Significant correlations at physiologically relevant lags of +/-250 ms were observed with tracking speed for 37% of Purkinje cells, with the velocity component in 39%, with direction error in 6% and speed error in 25%. Simple spike firing of the majority of Purkinje cells with significant correlation showed a negative lag with respect to speed and a positive lag with respect to error signals. We hypothesize that the cerebellum is involved in movement planning and control by continuously monitoring movement errors and making intermittent corrections that are represented as fluctuations in the speed profile.