Saccadic burst neurons in the fastigial nucleus are not involved in compensating for orbital nonlinearities.

1. To test whether the cerebellum is involved in compensating for orbital nonlinearities, we recorded discharges of saccadic burst neurons in the fastigial oculomotor region (FOR) during both centrifugal and centripetal saccades in two trained macaque monkeys. 2. We also investigated the metrics of centrifugal and centripetal saccades with the same amplitude while output signals from the fastigial nucleus were blocked by muscimol, an agonist of inhibitory neurotransmitter gamma-aminobutyric acid (GABA), injected into the FOR. 3. We studied discharges of 32 fastigial neurons that were inhibited by microstimulation of the oculomotor vermis. These neurons exhibited unique burst responses during contralaterally and ipsilaterally directed saccades, as shown in our previous report. The discharge pattern, the peak burst frequency, the burst lead time, and the burst duration were consistent, regardless of initial eye position. 4. The muscimol injection produced hypermetric saccades toward the injection side and hypometric saccades to the opposite side, regardless of whether saccade was centripetally or centrifugally directed. 5. These findings suggest that the FOR is not involved in the compensation of saccade metrics for orbital nonlinearities.