Patterns of connections from the striate cortex to cortical visual areas in superior temporal sulcus of macaque and middle temporal gyrus of owl monkey.
Double label-emulsion autoradiography has been used in rhesus monkeys to study cortico-cortical connections, arising from two separate sites of the striate cortex, and going in the same hemisphere into the cortex in the medial part of the posterior (or ventral) bank of the superior temporal sulcus (area STS). The projections from a single cortical locus are segregated into several patches of labeled terminals in layers III-IV, which form bands in consecutive sections. Fields of distribution of these bands from two sites of area 17 may completely overlap, when they arise from neighboring regions, or may partially overlap, when they arise from more separated regions. The latter show a retinotopical order in these connections and, consequently, of area STS itself: central visual field is lateral and ventral in STS to peripheral visual field, and upper visual field is ventral and medial to lower visual field. Connections from area 17 to area MT in owl monkey were analyzed in a comparative study. Results show that these connections are also highly segregated into bands, and that those arising in separate, but neighboring regions of 17, may greatly overlap in MT. The retinotopy of these connections was not studied, however. The similar divergent distribution of area 17 connections to STS and MT, and the similarity of the topography of STS connections and of the known retinotopy of area MT, are considered as elements of homologies between these areas. Functional implications of these divergent patterns of connections to these motion-sensitive areas (Zeki, '74), are considered.