Responses of visual, somatosensory, and auditory neurones in the golden hamster's superior colliculus

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Abstract
As in other mammalian species, a distinct difference between the functional organizations of the superficial and deeper layers of the superior colliculus in the golden hamster was observed. Neurons in the superficial layers were exclusively visual, with small receptive fields, and generally did not show response decrements with repeated stimulation. The sizes of the receptive fields did not vary appreciably as a function of retinal eccentricity. In the deeper layers, visual receptive fields were large or could not be accurately delimited, and response habituation was often evident. Many cells in the deeper layers of the colliculus responded only to somatosensory stimuli. Far fewer cells, which appeared to be confined to the caudal portions of the colliculus, responded to auditory stimuli. Polymodal cells were also encountered. Selectivity to opposing directions of movement was tested for 94 visual cells. Using a null criteron, 27.7% of these cells were judged to be directionally selective. A distribution of the preferred directions of these cells showed a significant preference for movement with an upper-nasal component. With a statistical criterion, 60.6% of these cells were considered to show a significant asymmetry in responding to movement in opposing directions. Directional selectivity was tested for 92 cells following acute, unilateral lesions of the visual cortex. For the 80 cells recorded, homolateral to the ablated cortex, 27.5% were judged as directionally selective using the statistical criterion, while 12.5% were selective with the null criterion. Of the 12 cells isolated in the colliculus, contralateral to the lesions, 7 were judged as directionally selectve with the statistical, and 3 with the null criterion. The effects of visual cortical lesions upon directional selectivity appeared confined to cells in the superficial layers of the colliculus. Directional selectivity of many cells in the superficial layers of the tectum of the hamster may be organized cortically. A clear spatial correspondence was observed for the receptive-fields of visual, somatosensory and auditory neurons. As suggested for other species, the hamster''s superior colliculus appears to play an important role in orienting the animal toward visual, somatosensory and auditory stimuli.