Function of the corpus callosum in the representation of the visual field in cat visual cortex

Interposed between areas 17 and 18 of cat cerebral cortex is an architectonically distinct zone that represents a substantial portion of the ipsilateral visual field. The extent of this representation was assessed following severance of the corpus callosum by recording the activities of neurons and plotting their receptive fields. The results show that, even after the hemispheres are disconnected, the transition zone still contains a representation of part of the ipsilateral visual hemifield, albeit a reduced one. The extent of this representation is contracted towards the midline so that just one-half to one-third of the azimuths mapped in intact cats can be plotted. As in the intact cat, the width of the region represented is not equal at all elevations, for it extends to only -1.4 deg near the visual axis whereas it extends to -6.6 deg at an elevation of -20 deg. The retention of this representation after the transition zone neurons have been disconnected from the opposite hemisphere indicates that other pathways make a functional contribution to the representation of the ipsilateral field in this region of cortex.