Reappraisal of DL/V4 boundaries based on connectivity patterns of dorsolateral visual cortex in macaques.

We placed injections of 3-5 distinguishable tracers in different dorsolateral locations in the visual cortex of four macaque monkeys to help define the extent of the dorsolateral visual complex (DL) commonly known as area V4. Injections well within DL/V4 region labeled neurons in V2, V3, MT, IT, and sometimes V1. In contrast, injections in caudal area 7a dorsal to current descriptions of DL/V4 produced a different pattern of labeled neurons largely involving posterior parietal and adjoining occipital cortex, as well as cortex of the medial wall. Injections placed in the dorsal prelunate cortex (DP), near the expected location of the dorsal border of DL/V4, labeled neurons in a third pattern, including regions of the posterior parietal and occipital cortex, inferior temporal (IT) cortex, and sometimes parts of dorsal area V2, DL/V4 complex and MT. Injections placed near or ventral to previous estimates of the ventral border of the rostral divisions of DL (DLr) and near the expected rostroventral border of V4 with TEO labeled cells in a pattern distinctively different from either central DL/V4 injections or those dorsal to DL/V4. Injections placed rostroventral to DL/V4 labeled neurons over a large extent of the IT cortex, while failing to label neurons in V1, V2 and MT. Injections that partially involved the rostroventral border of DL/V4 produced a similar pattern of labeled neurons, but also labeled a few cells in ventral V1 and V2, as well as many in DL/V4. Dorsal and rostroventral injections also labeled different regions of the prefrontal cortex, but only DL/V4 injections that included area DP labeled neurons in the prefrontal cortex. The results revealed contrasting and transitional connection patterns for four regions of the dorsolateral visual cortex, and they provided evidence for the locations of dorsal and rostroventral borders of the DL/V4 complex.