Discharges of Purkinje cells and mossy fibres in the cerebellar vermis of the monkey during saccadic eye movements and fixation.

1. Discharges of Purkinje cells and of presumed mossy fibres were extracellularly recorded from vermal lobules VI and VII of two monkeys during saccadic eye movements and fixation. Among the units showing changes in activity in relation to either saccades or eye position, eighty-four units were identified as mossy fibres and ninety-one units were Purkinje cells.2. Based on the discharge patterns associated with saccades, mossy fibre units were classified into long-lead burst, burst, and burst-tonic units. The long-lead burst units (twenty-eight units) started firing long before the saccades, the discharge consisting of a prelude (average lead time: 160 msec) and a burst (average lead time: 16 msec). In twenty-two units the saccade-related bursts showed a directional preference. The burst units (thirty-seven units) started firing slightly before the saccade onset (average lead time: 7.4 msec) and thirteen units showed directional preference. The bursts in burst-tonic units (thirteen units) had an average lead time of 0.2 msec.3. Among the ninety-one Purkinje cells, eighty-eight cells showed bursts associated with saccades. Three units paused for all directions of saccades.4. Seventy-one units out of the eighty-eight burst Purkinje cells showed bursts beginning approximately at the saccade onset (average lead time: 0.6 msec) and lasting throughout the saccade. The durations of bursts and saccades were highly correlated (correlation coefficients ranging from 0.70 to 0.88).5. In the remaining seventeen burst Purkinje cells, the bursts followed the saccade onset (average delay: 32 msec). The bursts started approximately 40 msec before the end of a saccade and persisted on the average 70 msec after its completion. Peak firing rate occurred with a close temporal relation to the end of the saccade.6. The tonic activity in nineteen mossy fibres and five Purkinje cells changed with eye positions. In the nineteen mossy fibres, there were thirteen burst-tonic and six tonic units. The activity in the five Purkinje cells was a linear function of horizontal eye position.