Cortical connections of the dorsomedial visual area in new world owl monkeys (Aotus trivirgatus) and squirrel monkeys (Saimiri sciureus).

The dorsomedial visual area (DM) is an extrastriate area that was originally described in owl monkeys as a complete representation of the visual hemifield in a heavily myelinated wedge of cortex just rostral to dorsomedial visual area V2. More recently, connections of DM in owl monkeys have been described (Krubitzer and Kaas [1993] J. Comp. Neurol 334:497-528). As part of an effort to determine whether DM exists in other primates, we compared the architecture, connections, and visual topography of DM in owl monkeys and the presumptive DM in squirrel monkeys. In both species of New World monkeys, the DM region was more heavily myelinated than adjacent cortex, and this region was connected with the first and second visual areas, the middle temporal area (MT), the medial area, the ventral posterior parietal area, the dorsointermediate area, the dorsolateral area, the ventral posterior and ventral anterior areas, the medial superior temporal area, the fundal area of the superior temporal sulcus, the inferior temporal cortex, and frontal cortex in or near the frontal eye field. In squirrel monkeys, both blob and interblob regions of V1 contributed equally to DM, whereas the blob regions provided most of the projections to V1 in owl monkeys. In squirrel monkeys, connections were also found with cortex on the ventral surface in the ventral occipital temporal sulcus. In owl monkeys and squirrel monkeys, connections were with both the upper and lower visual field representations in V1, V2, and MT, demonstrating that DM contains a complete representation of the visual field. These similarities in architecture, connections, and retinotopy argue that DM is a visual area of both owl and squirrel monkeys.