The long-term goal of the proposed research is to understand the mechanisms which underlie the behavioral sparing and loss of functions that follow early damage of the cerebral cortex. In the proposed studies, the morphological changes associated with spared and impaired neural functions in cats, following removal of areas 17 and 18 at different stages of development, will be examined. Experiments will focus on survival and degeneration of neurons in the retina and in area PMLS of the cerebral cortex. For the retina, the spatial distribution of morphologically identified surviving ganglion cells will be determined, and the survival related to the pattern of their axon projections in the brain and to the cat's age at the time the damage is incurred. Corollary data on ganglion cell axon projections in the brain will also be obtained. For area PMLS, counts of surviving neurons will be made in each cortical layer, and related to the age of the cat at the time the lesion is incurred. In order to relate the degenerations to the pattern of axon projections, the origin of the pathway, in PMLS to areas 17 & 18, and termination of the reciprocal pathway, will be assessed at the same developmental stages areas 17 & 18 are removed. Additional studies will examine the organization of modified brain pathways from the thalamus and from cortical areas spared by the lesion to area PMLS. Conventional anterogradely and retrogradely transported axoplasmic tracer substances will be employed to identify neurons and brain pathways, and the distribution of surviving neurons and modified pathways will be related to spared functions. The data obtained form these studies may prove fundamental to understanding the neural and psychological disorders that follow damage of the immature cerebral cortex.