Saccade-related activity in the fastigial oculomotor region of the macaque monkey during spontaneous eye movements in light and darkness.

Saccade-related burst neurons were recorded in the caudal part of the fastigial nucleus (fastigial oculomotor region) during spontaneous eye movements and fast phases of optokinetic and vestibular nystagmus in light and darkness from three macaque monkeys. All neurons (n = 47) were spontaneously active and exhibited a burst of activity with each saccade and fast phase of nystagmus. Most neurons (n = 31) only exhibited a burst of activity, whereas those remaining also exhibited a pause in firing rate before or after the burst. Burst parameters varied considerably for similar saccades. For horizontal saccades all neurons, except for three, had a preferred direction with an earlier onset of burst activity to the contralateral side. For contralateral saccades the burst started on average 17.5 ms before saccade onset, whereas the average lead-time for ipsilateral saccades was only 6.5 ms. Three neurons were classified as isotropic with similar latencies and peak burst activity in all directions. None of the neurons had a preferred direction with an earlier onset of burst activity to the ipsilateral side. Burst duration increased with saccade amplitude, whereas peak burst activity was not correlated with amplitude. There was no relationship between peak burst activity and peak eye velocity. In the dark, neurons generally continued to burst with each saccade and fast phase of nystagmus. Burst for saccades in the dark was compared with burst for saccades of similar amplitude and direction in the light. Saccades in the dark had a longer duration and peak burst activity was reduced on average to 62% (range 36-105%).(ABSTRACT TRUNCATED AT 250 WORDS)