Cortico-cortical projections from the prefrontal cortex to the superior temporal sulcal area (STs) in the monkey studied by means of HRP method.

Cortico-cortical connections from the prefrontal cortex to the superior temporal sulcal cortex (STs area) were studied in the monkey by means of retrograde axonal transport of horseradish peroxidase (HRP). After injections of 0.15-0.6 microliter of 50% HRP into the STs area, labeled cells were found in various cortical regions. In the prefrontal-STs projections, main features of topographic correlation were revealed; the posterior part of the STs area receives fibers from the superior frontal convexity (areas dorsal to the principal sulcus) and areas 8 and 6, whereas the anterior part of the STs area receives fibers from the inferior frontal convexity (areas ventral to the principal sulcus) and the frontal pole (area FD). The principal sulcus sends fibers to the entire STs area except for its ventral wall of the posterior part. A small cortical area adjacent to the inferior ramus of the arcuate sulcus (area 45 of ref. 41) sends fibers to the entire STs area. In addition, the orbitofrontal cortex projects mainly to the rostral part of the STs area, and the parahippocampal gyrus (areas TF and TH) projects to the deeper part of the entire STs area.