Unilateral interruption of geniculate and callosal inputs to the visual cortex of cats: ocular dominance and responsiveness of cells in the deafferented and in the intact hemispheres.

In order to study the ocular dominance and responsiveness of cells in the deafferented visual cortex, the geniculate and the callosal inputs were interrupted in adult cats by either simultaneous (OTCCX) or separate surgical transection of the optic tract (OTX) and the posterior corpus callosum (CCX). Unit recording was chronically carried out mainly in the boundary of areas 17-18, the callosal projection zone. A small proportion of visually responsive cells was encountered in the deafferented hemisphere of the OTCCX (8.3%) and the OTX (6.3%) cats. In the intact hemisphere, 59.7% of the cells were visually responsive in the OTCCX cats and 57.0% in the OTX cats; they were 61.6% of the cells in the CCX cats and 85.6% in the normal controls (both hemispheres). The majority of the cells in the deafferented hemisphere of the OTCCX (88.9%) and the OTX (82.4%) cats were binocularly driven. In the intact hemisphere of the OTCCX cats, 85.1% of the cells were binocularly driven, in comparison to 77.6% in the OTX cats, 48.8% in the CCX cats, and 81.5% in the normal controls. We therefore concluded that following unilateral elimination of the geniculate input as well as the callosal transection, binocularity in the intact hemisphere was preserved despite the remarkable diminution in the responsiveness level there. Furthermore, the supply of visual input to the deafferented hemisphere was not affected after callosotomy, suggesting an alternative transfer, albeit minor, via an anterior callosal or another commissural pathway.