Cortical projections of the dorsolateral visual area in owl monkeys: the prestriate relay to inferior temporal cortex.

The dorsolateral visual area (DL) is one of a number of visual areas that have been defined by electrophysiological mapping procedures and cortical architecture in the extrastriate cortex of owl monkeys. The projections of DL were determined by the intra-axonal transport of 3H-proline, 3H-acetyl-wheat germ agglutinin, and horseradish peroxidase after cortical injections. The major ipsilateral projection of DL defined a new subdivision of the visual cortex in owl monkeys, the caudal inferior temporal cortex. Single injections in DL sometimes produced label in two separate regions in the caudal inferior temporal cortex, suggesting that functional subdivisions exist in this projection zone. Other targets of DL included the region of the frontal eye fields, the dorsomedial visual area, the dorsointermediate visual area (DI), a region of the cortex rostral to DI which we call the temporoparietal cortex, and possibly the ventral (V) and posterior parietal areas. A major feedback projection of DL was to V-II. Projections from DL to V-II and the dorsomedial visual area were roughly retinotopic. Projections from DL to the contralateral cerebral hemisphere were to DL and the inferior temporal cortex. Overall, the results support the concept that a major relay of visual information proceeds from V-I to V-II to DL and then to the inferior temporal cortex. In addition, similarities in connection patterns of DL in owl monkeys and V4 in macaque monkeys suggest that DL and much or all of V4 are homologous.