Figure 2. The influence of P-cells on motor output.

A. Analysis of trials in which the error was in the CS-on direction of the P-cell. We measured eye trajectory (velocity vectors as a function of time) during the saccade in the trial in which the error was experienced, as well as the trajectory in the subsequent trial in which saccade was made to the same target. To measure change in behavior, we projected the difference in the 2D sequence of velocity vectors onto the CS-on direction of the P-cell. Following experience of an error, the next trial exhibited an increase in the velocity vector along the direction of error. However, if the P-cell produced a CS, velocity on the next trial was larger in direction CS-on compared to when a CS was absent (mean+SEM across neurons). Distribution of errors for CS present and CS absent trials were comparable (right, shaded region denotes average SD of error distribution across neurons). B. Same as (A) except for trials in which there was no post-saccadic error (|error| < 0.25°). Even without an error, presence of a CS led to increased motor output along direction CS-on of the P-cell that had produced the CS. C. Same as (A), except for trials in which errors were in CS-on+180° of the P-cell under study. Even when the error was opposite the preferred direction, presence of a CS biased behavior in CS-on direction of that cell. D. Trial-to-trial change following any error. We projected the trial-to-trial change in velocity onto direction CS-on (left) and CS-on+90° (right) of the P-cell. When a CS was present, change in motor output was only in direction CS-on. E. A CS during a specific post-saccadic period (~75–150ms) resulted in more learning than earlier or later CS. F. Effect of CS waveform duration. For each P-cell, we split each CS into ‘long’ and ‘short’ with respect to median duration within each cell. At a given CS timing, CS waveform duration did not have a discernable effect on behavior. G. Hypothesized anatomy of the oculomotor vermis P-cells and cerebellar output. Red circles refer to inhibitory neurons; blue circles refer to excitatory neurons. Arrows indicate preferred error vector in sensory space for the inferior olive and P-cells, and direction of force for the motoneurons. The vectors are parallel in the sensory and motor spaces. All error bars are standard error of the mean (SEM)across all neurons (n=67) unless noted.