Cortical connections of areas V3 and VP of macaque monkey extrastriate visual cortex.

The cortical connections of visual area 3 (V3) and the ventral posterior area (VP) in the macaque monkey were studied by using combinations of retrograde and anterograde tracers. Tracer injections were made into V3 or VP following electrophysiological recording in and near the target area. The pattern of ipsilateral cortical connections was analyzed in relation to the pattern of interhemispheric connections identified after transection of the corpus callosum. Both V3 and VP have major connections with areas V2, V3A, posterior intraparietal area (PIP), V4, middle temporal area (MT), medial superior temporal area (dorsal) (MSTd), and ventral intraparietal area (VIP). Their connections differ in several respects. Specifically, V3 has connections with areas V1 and V4 transitional area (V4t) that are absent for VP; VP has connections with areas ventral occipitotemporal area (VOT), dorsal prelunate area (DP), and visually responsive portion of temporal visual area F (VTF) that are absent or occur only rarely for V3. The laminar pattern of labelled terminals and retrogradely labeled cell bodies allowed assessment of the hierarchical relationships between areas V3 and VP and their various targets. Areas V1 and V2 are at a lower level than V3 and VP; all of the remaining areas are at a higher level. V3 receives major inputs from layer 4B of V1, suggesting an association with the magnocellular-dominated processing stream and a role in routing magnocellular-dominated information along pathways leading to both parietal and temporal lobes. The convergence and divergence of pathways involving V3 and VP underscores the distributed nature of hierarchical processing in the visual system.