Thalamo‐cortical organization of the visual system in the cat

Abstract

Thalamo‐cortical relationships in the visual system of the cat were studied by the method of retrograde degeneration. Localized lesions limited to area 17 result in degeneration only in the dorsolateral geniculate body; cell changes are marked in 3 laminae (A, A₁, B), mild in nucleus interlaminaris centralis and minimal in nucleus interlaminaris medialis. Lesions limited to areas 18 and 19 are followed by marked degeneration in the medial interlaminar nucleus, mild in the other laminae; in addition, the lateral part of the posterior thalamic nucleus (ventral or inferior pulvinar) is also atrophied. Following large striate lesions which marginally involved areas 18 and 19, there is also mild, localozed degeneration in the anteroventral and reticular thalamic nuclei. Whin cortical lesions are limited to the convexity of the suprasylvian gyri, degeneration is present in the lateral aspect of laminae A, A₁, B and nucleus interlaminaris centralis and in the medial part of the posterior nucleus, in addition to lateral dorsal, lateral posterior and pulvinar nuclei. Lesions in the ectosylvian gyri result in slight but definite degeneration in the lateral part of lamina A of the dorsal lateral geniculate, but nothing in the posterior nucleus. The geniculate projections to areas 17, 18 and 19, to the suprasylvian and ectosylvian gyri all show a rostrocaudal organization. The geniculostriate projection is also topographically organized in a mediolateral manner.Thus, the geniculocortical projection in the cat is not striate specific but spreads over the occipito‐temporal cortex at least as far as the acoustic areas of the ectosylvian gyri. In this species the dorsal lateral geniculate body is not a unitary structure but is a complex of nuclei, all of which receive retinal fibers, and the cortical projections of which overlap those of the posterior, lateral dorsal, lateral posterior, pulvinar, medial geniculate, reticular and anterior thalamic nuclei.