Cortical connections of the caudal subdivision of the dorsolateral area (V4) in monkeys

Abstract

Evidence suggests that all primates have rostral and caudal subdivisions in the region of visual cortex identified as the dorsolateral area (DL) or V4. However, the connections of DL/V4 have not been examined in terms of these subdivisions. To determine the cortical connections of the caudal subdivision of DL (DL_c) in squirrel monkeys, injections of the neuroanatomical tracers wheat germ agglutinin conjugated to horseradish peroxidase, Diamidino Yellow, and Fluoro‐Gold were made in cortex rostral to V II. To aid in delineating the borders of DL_C, cortex was also evaluated architectonically. Based on similar patterns of connections, DL_C extends from dorsolateral to ventrolateral cortex. DL_C receives strong, feedforward input from V II and projects in a feedforward fashion to the rostral subdivision of DL (DL_R) and caudal inferior temporal (IT) cortex, including a separate location in the inferior temporal sulcus. DL_C has weaker connections with V I, the middle temporal area (MT), cortex rostral to MT in the location of the fundal superior temporal area (FST), cortex dorsal to DL_C, ventral cortex‐rostral to V II, and cortex in the frontal lobe, lateral to the inferior arcuate sulcus. Only lateral DL_C has connections with V I, and only dorsolateral DL_C has connections with cortex dorsal to DL_C. The topographic organization of DL_C was inferred from its connections with V II. Thus, dorsolateral DL_C represents the lower field, lateral DL_C represents central vision, and ventrolateral DL_C represents the upper field. Limited observations were made on DL_R. Confirming earlier observations (Cusick and Kaas: Visual Neurosci. 1:211, 1988), DL_R is paler than DL_C myeloarchitectonically. DL_R receives only sparse feedforward input from V II, but stronger input from DL_C. DL_R has strong connections with cortex just rostral to dorsal V II, ventral posterior parietal cortex in the sylvian fissure, MT, the medial superior temporal area, FST, and the inferior temporal sulcus. DL_R also shares connections with IT cortex. Thus, while both DL_C and DL_R are involved in the pathway relaying visual information to IT cortex, an area specialized for object vision, DL_R also projects densely to areas such as MT involved in the pathway relaying to posterior parietal cortex, a region specialized for spatial localization and motion perception.