Asymmetrical Interhemispheric Connections Develop in Cat Visual Cortex after Early Unilateral Convergent Strabismus: Anatomy, Physiology, and Mechanisms

Endogenous cytochrome oxidase activity within the mitochondria of neurons and neuropil was demonstrated histochemically under normal and experimental conditions. Since enzymatic changes were noted with chronic neuronal inactivity in the auditory system (Wong-Riley et al), the present study sought to examine functionally induced enzymatic changes in the visual system of kittens. Eight kittens were used experimentally: 5 had monocular lid suture for varying periods of time; one had binocular lid suture followed by monocular suture followed by binocular opening; two had monocular enucleation. All initial procedures were performed before eye opening. Materials from other normal kittens and cats were also used as controls. At the end of the experiments, the animals were perfused with aldehyde solutions and frozen sections of the brains were incubated for cytochrome oxidase activity (a detailed protocol was outlined). The results indicated that the deprivation caused by monocular suture produced a decrease in the cytochrome oxidase staining of the binocular segment of the deprived geniculate laminae. Enucleation yielded a greater decrease in the cytochrome oxidase activity in the affected geniculate laminae. However, the staining in the 'normal' lamina extended across the interlaminar border to include a row of surviving large cells in the 'denervated' lamina. The staining of the monocular segment appeared not to be affected by lid suture, but was decreased by enucleation. At the cortical level, lamina IV in area 17 of normal cats was stained darkly as a continuous band. Following lid suture, this pattern was replaced in part by alternating columns of light and dark staining, suggestive of ocular dominance columns. Thus, a decrease in neuronal activity due to reduced visual stimulation or destruction of the primary afferent nerves led to a significant decrease in the level of oxidative enzyme activity one to several synapses away.

The location and retinotopic organization of visual areas in the cat cortex were determined by systematically mapping visual cortex in over 100 cats. The positions of the receptive fields of single neurons or small clusters of neurons were related to the locations of the corresponding recording sites in the cortex to determine the representations of the visual field in these cortical areas. In this report, the first of a series, we describe the organization of area 17. A single representation of the cat's entire visual field corresponds closely to the cytoarchitectonically defined area 17. This area has the largest cortical surface area (380 mm2) and the highest cortical magnification factor (3.6 mm2/degree2 at area centralis) of all the cortical areas we have studied. There was perfect agreement between the borders of area 17 determined electrophysiologically and cytoarchitecturally. This area contains a first order transformation of the visual hemifield in which every adjacent point in the visual field is represented as an adjacent point in the cortex. Some variability exists among cats in the extent and retinotopic representation of the visual field in area 17.