The long-term objectives of the proposed research are to increase our understanding of the functions of extrastriate visual pathways in normal animals and to learn more about the mechanisms of compensatory changes that occur in these pathways following damage to visual cortical areas 17, 18 and 19 early in life. To accomplish these goals, a series of anatomical, electrophysiological, and behavioral studies will be carried out in cats. The studies will concentrate on the posteromedial lateral suprasylvian (PMLS) visual cortical area and its afferent pathways.
The specific aims of the proposed experiments are: (1) Determine the properties of lateral geniculate neurons that provide enhanced projections to PMLS cortex following early visual cortex (areas 17, 18, and 19) damage and examine whether the information they provide to PMLS cortex differs from normal. (2) Carry out a quantitative analysis of the spatial receptive-field properties of PMLS neurons, determine the role of areas 17, 18, and 19 in the elaboration of those properties in normally reared cats, and determine if the residual properties differ in cats with early or adult visual cortex damage. (3) Study the behavioral psychophysical capacities of cats with early or adult visual cortex damage and directly assess whether PMLS cortex is involved in these capacities. (4) Determine whether the enhanced projections to PMLS cortex following early visual cortex damage require normal patterned visual experience to develop. (5) Determine whether functional vs. physical removal of inputs from visual cortex is necessary for physiological compensation in PMLS cortex and whether normal experience with stimulus movement is necessary for the compensation. (6) Determine whether callosal inputs are required for the development of physiological compensation In PMLS cortex following early visual cortex damage. (7) Investigate whether physiological compensation involves neural reorganization or a persistence of pre-existing properties and evaluate suggestions that the mechanisms differ for different properties. (8) Investigate the possibility that PMLS cortex normally is involved in the control of eye movements. (9) Carry out preliminary experiments to determine the neuropharmacological mechanisms of physiological compensation and investigate whether compensation can be made to occur following visual cortex damage in adult cats. Together, the proposed experiments will provide information about normal visual system organization and development and about the mechanisms of recovery from brain damage in neonates and adults.
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