Saccade-related activity of periaqueductal gray matter of the monkey.

Single unit activity was recorded extracellularly from the periaqueductal gray matter (PAG) and the superior colliculus of three monkeys during spontaneous saccades and fixation. Most saccade-related cells were found in the dorsal and lateral regions of the PAG and they paused with saccades. The pause preceded the onset of saccades by 34.5 +/- 6.8 msec (n = 31). In 90% of the 31 PAG cells, the saccade-related modulation in activity occurred in all directions. There was a linear relationship between pause duration and saccade duration with correlation coefficients larger than 0.70 in most cells. Superior colliculus cells showed bursts preceding onset of saccades. The lead times averaged 25.3 msec (n = 35). There was no linear relationship between burst duration and saccade duration. These results suggest that the dorsal and lateral regions of PAG play an important role in the saccadic system, probably through long lead burst units in the deep layer of the superior colliculus and/or pontine reticular formation.