[Functional organization of the intermediate and deep layers of the superior colliculus of the monkey]

Single neurons and polispike activity were recorded from the superior colliculus of anesthetized, behaving monkeys. In agreement with previous findings neurons of the superficial layers responded exclusively to visual stimuli. In the intermediate layers most neurons were oculomotor, although some of them showed also a visual receptive field. No neurons responding to tactile or auditory stimuli were found. Occasionally the discharge of an oculomotor neuron increased if the ocular movement was triggered by a visual or an acoustical stimulus. Rare tacticle and auditory neurons were recorded in deep layers. However their receptive fields were difficult to map and their responses lacked the precision of the responses of the specific acoustic and tactile areas. Electrical stimulation of the SC produced contralateral eye and head movements, the threshold being high in the superficial layers and low in the intermediate and deep ones. In the deep layers complex limb and trunk movements could be also elicited. In conclusion, in contrast with carnivores and other mammals, the primate superior colliculus appears to be dominated by the visual modality.