Research supported by this grant has examined the transformation within the superior colliculus of visual spatial information received from the retina and the visual cortex. A central question has been how collicular neurons, with their large receptive fields, might preserve spatial information available to them in the afferent input. A hypothesis has emerged from these studies which is based on the idea that the geometry of tectal oculomotor connections is a key to understanding the role of the large receptive fields in collicular function. Work to date has emphasized the sensory aspects of this hypothesis and the experiments described in this proposal are designed to investigate the output signals of the cat's superior colliculus with a view to refining the model further. Chronic recording and stimulation methods will be employed in alert, non-paralyzed cats to test the hypothesis that discharge occurs throughout a large volume of collicular tissue prior to any saccade; to test the hypothesis that a large zone of presaccadic discharge is necessary in normal collicular guidance of orienting saccades; to test the hypothesis that both colliculi are active simultaneously prior to saccades to paracentral visual targets; to assess quantitatively the degree to which saccades evoked electrically from the colliculus are models of normally occurring saccades; and to test the hypothesis that the caudal part of the cat's colliculus may emit oculomotor signals encoded in a head-centered coordinate system. The research will contribute to our understanding of how higher neural centers control the normal production of saccadic eye movements in the cat and will provide additional perspective on the usefulness of this non-primate animal model for the study of oculomotor control and its dysfunction.
