The deafferented visual cortex: neuronal activity and visual evoked potentials.

The callosal transfer of information to the visual cortex following its unilateral deafferentation from its geniculate input was studied in both hemispheres. Deafferentation was performed in adult cats by sectioning the optic tract. Action potentials of single cortical cells and visual evoked potentials were recorded from area 17-18 boundary in acute and chronic operated cats. In the deafferented hemisphere, cortical cells were usually visually inactive. However, some recovery of function took place in this hemisphere in the chronic cats, as expressed by the increase in the proportion of S-cells. In the intact hemisphere diminution of responsiveness and reduction of selectivity to the stimulus orientation and direction were found. The responsiveness and selectivity level in the intact hemisphere increased with postoperative time. The ocular dominance distribution in this hemisphere was similar to that of our normal control cats. The characteristics of the visual evoked potentials were in keeping with the hemispheric dominance of the cortical cells found in the experimental cats. It was concluded that a plasticity related mechanism is involved in the recovery of callosal activation of visual cortical cells following deafferentation.