Effects of superior colliculus removal on receptive-field properties of neurons in lateral suprasylvian visual area of the cat

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Abstract
The influence of inputs from the tectothalamic pathway on receptive-field properties of cells in the cat''s lateral suprasylvian visual area of cortex (LS area) was investigated. Bilateral aspiration lesions of the superior colliculus were made, and single-cell recording was carried out in the LS cortex 10-115 days later. Following removal of superior colliculus, many of the receptive-field properties of LS cortex cells appeared normal. The cells continued to respond to small stimuli and to show spatial summation to increases in stimulus size. About 80% of the cells were direction selective, just as in normal LS cortex, and their directional tuning was normal. In addition, most of the LS cortex cells were binocularly driven. Receptive-field size and visuotopic organization also were unaffected by the superior colliculus lesions. Three important response properties were altered by removal of the tectothalamic inputs: there was an increased strength of response to stationary flashing stimuli. There was an increased response to slowly moving stimuli among movement-sensitive and direction-selective cells. Although the proportion of cells with internal and surround inhibition did not change following removal of superior colliculus, the spatial distribution of the inhibition differed from normal for many of the LS cortex cells. The tectothalamic inputs to LS cortex are perhaps primarily inhibitory in nature. They include symmetrical internal and surround spatial inhibition, inhibition of responses to slow stimulus movement and inhibition of responses to stationary stimuli. Removal of the superior colliculus produced effects in LS cortex that are very different from the effects of visual cortex removal. The effects of visual cortex removal on LS cortex are largely independent of the superior colliculus and tectothalamic pathway. The multiple pathways that converge on LS cortex provide different spatial and temporal aspects of the receptive-field properties that are formed there. The integrative processes that occur at the LS cortex cells appear to involve the inhibition or masking of some input properties (e.g., orientation selectivity and response to slow movement) and the elaboration of others (e.g., direction selectivity, combining inputs from the contralateral and ipsilateral eyes).

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