Visual signals in the dorsolateral pontine nucleus of the alert monkey: Their relationship to smooth-pursuit eye movements

Summary The visual properties of 77 dorsolateral pontine nucleus (DLPN) cells were studied in two alert monkeys. In 41 cells, presentation of a moving random dot background pattern, while the monkeys fixated a stationary spot, elicited modulations in discharge rate that were related either to (i) the velocity of background motion in a specific direction or to (ii) only the direction of background movement. Thirty-six DLPN cells exhibited responses to small, 0.6–1.7 deg, visual stimuli. Nine such cells exhibited non-direction selective receptive fields that were eccentric from the fovea. During fixation of a stationary bluish spot, the visual responses of 27 DLPN cells to movement of a small, white test spot were characterized by two components: (1) as the test spot crossed the fovea in a specific direction, transient velocity-related increases in discharge rate occurred and (2) a maintained, smaller increase in activity was observed for the duration of test spot movement in the preferred direction. This DLPN activity associated with small visual stimuli was also observed during smooth-pursuit eye movements when, due to imperfect tracking, retinal image motion of the target produced slip in the same direction. These preliminary results suggest that the DLPN could supply the smooth-pursuit system with signals concerning the direction and velocity of target image motion on the retina.This study was supported by NSF Grant BNS-8107111, NIH Grant R01 EY04552-01, and the Smith-Kettlewell Eye Research FoundationDedication. This paper is dedicated to Dr. Kitsuya Iwama, Emeritus Professor of Osaka University Medical School, on his retirement. The first author is grateful for the inspiration and guidance that Dr. Iwama provided during the early part of the author's education in neurophysiology.