Response characteristics of single cells in the monkey superior colliculus following ablation or cooling of visual cortex.

ELECTROPHYSIOLOGICAL STUDIES have shown that the characteristics of single cells in the superior colliculus depend to a considerable extent on cortical input. In the cat, the majority of studies reveal a dramatic loss of binocularity and direction selectivity in superficial collicular units following ablation of the visual cortex (1, 18, 25). In the ground squirrel, removal of the visual cortex renders most cells in the intermediate and deep layers of the superior colliculus unresponsive to visual stimuli (14); this also appears to apply to the cat (22). Work on the rabbit, however, indicates that in this species, ablation of visual cortex produces no discernible effects on collicular function (10). The present study has been undertaken to investigate the contribution of visual cortex to collicular function in the rhesus monkey (Macaca mulatta), a species whose visual svstem is believed to be rather similar to that of man. Neuroanatomical work has indicated that in the monkey, as in the cat, retina and visual cortex project densely on the superior colliculus (8). In the monkey, a foveate animal, an interesting specialization has been reported: anterograde-degeneration and autoradiographic studies indicate that the anterior part of the colliculus, representing the central 5” of the visual field, receives extremely sparse or no terminations from the retina and, conversely, heavy projections from visual cortex (5, 9, 26) Single-unit studies of the superior colliculus of the intact monkey have disclosed that, as in the cat, most cells have binocular