The present study of the connections of the STG with medial paralimbic cortex showed that the caudal part of the STG (area Tpt and caudal area paAlt) and adjacent cortex of the upper bank of the superior temporal sulcus (caudal area TPO) have reciprocal connections with the caudal cingulate gyrus (areas 23a, b and c), retrosplenial cortex (area 30), and area 31. By contrast, cortex of the rostral-to-mid STG (areas Ts2, Ts3, and the rostral part of area paAlt) and adjacent upper bank of the STS (mid-area TPO) have few, if any, such interconnections. 
The fibers coursing through the extreme capsule originating in areas 10 and 9 continue as part of the white matter of the superior temporal gyrus (i.e., the middle longitudinal fasciculus) to target the midportion of the superior temporal gyrus (areas TAa, TS2, and TS3) and adjacent multisensory area TPO within the upper bank of the superior temporal sulcus.
Retrogradely labeled cells were found in the surrounding premotor cortex (areas 6V and 6D), primary motor cortex (area 4), primary somatosensory cortex (areas 3, 1 and 2), anterior and posterior secondary somatosensory cortex and the probable homologue of Broca's area (areas 44 and 45); furthermore, labeling was found in the supplementary motor area, anterior and posterior cingulate cortex (areas 24 and 23), prefrontal and orbital frontal cortex (areas 8A, 46V, 47/12L, 47/12O, 13), agranular, dysgranular and granular insula as well as in the cortex within the upper bank of the middle third of the superior temporal sulcus (area TPO).
area TPO in the upper bank of the superior temporal sulcus (STS) of macaque monkeys is thought to correspond to the superior temporal polysensory (STP) cortex, but has been shown to have neurochemical/connectional subdivisions. To examine directly the relationship between chemoarchitecture and cortical connections of area TPO, the upper bank of the STS was sectioned tangential to the cortical surface. Three subdivisions of area TPO (TPOr, TPOi, and TPOc) were examined with cytochrome oxidase (CO) histochemistry and neurofilament protein (NF) immunoreactivity and architectonic patterns were compared with connections on the same or adjacent sections. area TPOc, which may partly overlap with the location of the medial superior temporal area MST, exhibited regular patchy staining for CO in layers III/IV and a complementary pattern in the NF stain. area TPOr, but not TPOi, also had a patchy pattern of complementary staining in CO and neurofilament similar to TPOc, although not as distinct. The findings support the parcellation of area TPO into three subdivisions and extend findings of chemoarchitectonic modules within high-order association cortices..
In contrast, the input to area TH is from the rostral part of superior temporal gyrus, including the auditory association areas TS1-3, and from the middle sector of area TPO in the superior temporal sulcus.
Injections of anterograde and retrograde tracers confined to retrosplenial area 30 revealed that this area has reciprocal connections with adjacent areas 23, 19 and PGm, with the mid-dorsolateral part of the prefrontal cortex (areas 9, 9/46 and 46), with multimodal area TPO in the superior temporal sulcus, as well as the posterior parahippocampal cortex, the presubiculum and the entorhinal cortex.
The findings suggest that area TPO contains differently connected modules that may maintain at least initial segregation of visual versus auditory inputs. Other modules within area TPO receive directly converging input from the posterior parietal and the prefrontal cortices and may participate in a distributed cortical network concerned with visuospatial functions..
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. 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. 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.
Rostral superior temporal polysensory (STP) cortex (area TPO-1) receives input from the rostral superior temporal gyrus (STG), cortex of the circular sulcus, and parahippocampal gyrus (PHG) (areas 35, TF, and TL). Caudal STP cortex (area TPO-4) has afferent connections with the caudal STG, cortex of the caudal insula and caudal circular sulcus, caudal IPL, lower bank of the intraparietal sulcus (IPS), medial parietal lobe, cingulate gyrus, and mid- and caudal PHG (areas TF, TH, TL; prostriate area).
The results show that multimodal area TPO of the STS projects back to specific unimodal parasensory association areas of the parietal lobe (somatosensory), superior temporal gyrus (auditory), and posterior parahippocampal gyrus (visual). In addition, a substantial number of projections from area TPO are directed to distal parasensory association areas, area PG-Opt in the inferior parietal lobule, areas Ts1 and Ts2 in the rostral superior temporal gyrus, and areas TF and TL in the parahippocampal gyrus. It was also noted that the majority of the projections to these higher-order association areas originate from the middle divisions of area TPO (TPO-2 and TPO-3). Despite this overlap of the projection neurons, only an occasional double labeled neuron was observed in area TPO. These connections from area TPO to post-Rolandic association areas may have a modulating influence on the sensory association input leading to multimodal areas in the superior temporal sulcus..
Four rostral-to-caudal subdivisions of cortex (area TPO) in the upper bank of the STS have distinct projection patterns. area TPO-1 does not project to the parietal lobe; area TPO-2 projects to the inferior parietal lobule; area TPO-3 to the lower bank of the intraparietal sulcus (IPS) (area POa); and area TPO-4 to medial parietal cortex (area PGm).
The caudalmost area TPO projected in addition to the ventral and intrapeduncular pontine nuclei.
The mid-portion of multimodal area TPO of the upper bank, areas TPO2 and TPO3, projects preferentially to the central sector of the PM nucleus.
The polymodal region in the upper bank (area TPO) is divisible into four rostral-to-caudal architectonic sectors, exhibiting increasing degrees of laminar differentiation and cellularity as one proceeds caudally. Each rostrocaudal sector of area TPO also has reciprocal connections with the laterally adjacent area TAa, at the upper rim of the sulcus, and medially adjacent areas PGa and IPa, near the depth.
The frontal lobe projections of polymodal cortex (area TPO) in the upper bank of the STS are organized according to the rostral-to-caudal topography of the sulcus.
These included the following areas: frontal areas 9, 11, 12, 13, and 46; temporal polar area TG as well as LB and AB; superior temporal sulcus area TPO; agranular insular cortex; posterior parahippocampal cortex including areas TF, TL, and TH and the subiculum. Areas 23a and 23b received inputs mainly from frontal areas 46, 9, 11, and 14, parietal areas Opt and PGm, area TPO of superior temporal cortex, and areas TH, TL, and TF.
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