Chemoarchitectonics and corticocortical terminations within the superior temporal sulcus of the rhesus monkey: evidence for subdivisions of superior temporal polysensory cortex.

Cortex of the upper bank of the superior temporal sulcus (STS) in macaque monkeys, termed the superior temporal polysensory (STP) region, corresponds largely to architectonic area TPO and is connectionally distinct from adjacent visual areas. To investigate whether or not the STP region contains separate subdivisions, immunostaining for parvalbumin and neurofilament protein (using the SMI-32 antibody) was compared with patterns of corticocortical terminations in the STS. Chemoarchitectonic results provided evidence for three caudal-to-rostral subdivisions: TPOc, TPOi, and TPOr. Area TPOc was characterized by patchy staining for parvalbumin and SMI-32 in cortical layers IV/III and III, respectively. Area TPOi had more uniform chemoarchitectonic staining, whereas area TPOr had a thicker layer IV than TPOi. The connectional results showed prefrontal cortex in the location of the frontal eye fields (area 8) and dorsal area 46 projected in a columnar pattern to all cortical layers of area TPOc, to layer IV of TPOi, and in a columnar fashion, with a moderate increase in density in layer IV, to TPOr. In TPOc, columns of frontal connections showed a periodicity similar to that of the SMI-32 staining. The caudal inferior parietal lobule (area 7a) and superior temporal gyrus projected to each subdivision of area TPO, displaying either panlaminar or fourth-layer terminations. In addition to STP cortex, parvalbumin and SMI-32 immunostaining allowed identification of caudal visual areas of the STS, including MT, MST, FST, and V4t. These areas received first- and sixth-layer projections from prefrontal cortex and area 7a.