The development of binocular connectivity in striate cortex in cats will be investigated in terms of the role of the corpus callosum (CC) in that process. Preliminary data indicate that CC section within postnatal weeks 2-3 can limit the formation of a significant number of binocular connections, as many as can be disrupted by abnormal visual experience later in development. The earlier the CC section the greater the reduction in binocularity; this is independent of visual experience. It is theorized that a CC section during week 1 will lead to greater deficits in binocularity indicating that the initial formation of binocular connections in striate cortex is totally dependent on the presence of active CC inputs to cortex. It is hypothesized that the CC helps to soft-wire those connections; subsequent normal visual experience will hardwire, or make permanent, the binocular connections. This proposal will accomplish several goals: 1) test this theory, 2) replicate the critical period for a callosal role in visual development, 3) determine whether the strabismus resulting from CC section causes any of the visual deficits, and 4) determine whether various deficits resulting from CC section are all related to the failure to develop binocular connections in striate cortex. Three major experiments will be used to achieve these goals. Cats will be given a CC section at weekly intervals during postnatal month 1 (the proposed callosal critical period), and at monthly intervals during months 2-6 (the experiential critical period). Sham-operated cats produced at the same times will serve as controls. Cats will: A) be tested behaviorally for threshold of visual acuity through 6 months old; optical factors will be ruled out, B) examine eye alignment photographically through this period, and C) undergo single unit recording in striate cortex at 8 months old to determine the ocular dominance distribution within striate regions representing central-peripheral visual field, plus the visual acuity of individual cells correlated with their cortical lamina and visual field location; also, CC sectioned cats will be dark-reared to see if their strabismus affects cortical physiology. These studies are significant because we will gain critical knowledge about mechanisms of formation of major connections, we will gain new information on the development of binocularity, a major feature of mammalian vision, we will learn about the nature and mechanisms of the corpus callosum's recently revealed major role in development. Secondarily, we will learn about the potential interrelationships of visual deficits.
