Cortical visual input to the orbito-insular cortex in the cat

The anatomical pathways supplying the visual signal to the cat orbito-insular cortex (OIC) from primary visual areas were studied by an anterograde axonal transport technique. L-[5-3H]proline was injected, in different animals, in each of areas 17, 18, 19 and the lateral suprasylvian visual area (LS). Serial histological sections were processed by autoradiographic technique after long (8-16 days) or short (30 h) survival times. The axonal flow labelled direct pathways from LS to the ipsilateral orbital gyrus and the ventral bank of the anterior ectosylvian sulcus; this region seems to correspond to that from which many authors recorded photically evoked potentials. Long survival animals injected in LS showed labels also in the contralateral OIC. No axonal flow could be demonstrated from areas 17, 18 and 19 to OIC, either at short of long survival times. The results suggest that, apart from possible sub cortical afferences, a critical visual input may reach OIC from the extrageniculostriate visual system through LS. The functional relevance of extrastriate input to OIC is discussed.