Single unit recording and stimulation in the superior colliculus of the alert rhesus monkey.

Schiller PH; Stryker M
Journal of Neurophysiology, 1972 Nov., 35:6, 915-24.

Abstract
1. The superior colliculus of alert rhesus monkeys was investigated. One eye of each animal was immobilized by transection of the 3rd, 4th, and 6th cranial nerves. The location of receptive fields of single units, their properties, and relation of unit discharge to eye movement were studied at various depths within the superior colliculus. Following recording at each site electrical stimulation was delivered through the same microelectrode and the resulting eye movement was compared with the recording data.
2. The recording data show, in agreement with previous reports, that in the superficial layers units appear to respond exclusively to visual stimuli. In the deeper layers cells related to eye movement predominate. The latter discharge prior to saccades of a specific size and direction.
3. Stimulation of the superior colliculus elicits saccades of particular angular extents and directions that are relatively independent of stimulation parameters and are determined by the site of stimulation. Threshold for eliciting saccades drops from 400 ua in the superficial layer to as low as 1 ua in the deeper layers of the colliculus. Prolonged stimulation elicits a staircase of identical saccades.
4. A close correspondence was obtained between recording and stimulation data. In the superficial layers the size and direction of elicited saccades were such as to bring the foveal projection onto that part of the visual field occupied by the receptive field prior to the initiation of movement.
5. In the deeper layers, stimulation produced saccades which duplicated the characteristics of the spontaneous saccades specifically associated with unit discharge. At each site the motor maps defined by the discharge of single units enclosed those obtained by stimulation.
6. The data are discussed in relation to three hypotheses about collicular function; foveation, orientating (i.e., shifting of attention), and corollary discharge.