Unimodal and multimodal response properties of neurons in the cat's superior colliculus

Abstract

Cells in the upper layers of the superior colliculus of the cat were found to be exclusively responsive to visual stimuli, whereas neurons responsive to visual or nonvisual stimuli (or both) were encountered in the deeper laminae. Bimodal and trimodal units were located and their response and receptive field properties were described. The response probabilities and receptive field characteristics of neurons located in the deeper laminae differed from those usually encountered in the upper laminae of the superior colliculus and in primary sensory projection nuclei. Visual receptive fields of multimodal units were often large and, in many instances, did not even approach the high response probability to successive identical stimuli, which was characteristic of neurons in the upper laminae. The somatic receptive fields of both unimodal and multimodal units were large, sometimes discontinuous, and appeared to have properties strikingly different from those described in the lemniscal system. The effects of cooling the visual cortex upon unimodal and multimodal unit response properties were investigated and were found to selectively depress responsiveness to visual stimuli while responsiveness to auditory and somatic stimuli remained unaltered.