Discharge Characteristics of Single Units in Superior Colliculus of the Alert Rhesus Monkey.

Schiller PH; Koerner F
Journal of Neurophysiology, 1971 Sept., 34:5, 920-35.

Abstract
1. Single-unit activity was studied in the superior colliculus of the alert rhesus monkey. One eye of each animal was immobilized prior to the experiment by transection of the 3rd, 4th, and 6th cranial nerves. Eye-movement electrodes were implanted around the orbit of the moving eye. During recordings the head was restrained, permitting the study of both the receptive fields of collicular units via the immobilized eye and their relation to eye movement as assessed by EOG records of the moving eye.
2. In the superficial layers of the superior colliculus units responded only to visual stimuli. These units were not specific regarding stimulus shape or direction of stimulus movement. They were selective, however, in terms of stimulus size. Two types of such units were discerned; one class responded well both to smoothly moving and stationary, flashing stimuli. The other class failed to respond to smooth movement and discharged most vigorously to rapid, jerky stimulus displacements.
3. In the lower layers of the superior colliculus units associated with eye movements were found. These units fired in sharp bursts prior to saccades. Discharge was specific in terms of both the direction and the size of rapid eye movements and was independent of the initial position of the eye in the orbit. Most of these units had receptive fields which were located in that area of the visual field to which the fovea was directed as a result of a discharge-associated saccade. Some of these units discharged prior to saccades both in the light and dark.
4. Those units related to eye movement which had their visual receptive fields near the center of the fovea discharged both prior to small saccades and during smooth pursuit. These units appear to participate in the correction of retinal-target errors during tracking.
5. The results suggest that the monkey superior colliculus plays an important role in the foveal acquisition and maintenance of visual targets.