Perirhinal and parahippocampal cortices of the macaque monkey: cytoarchitectonic and chemoarchitectonic organization.

Findings from recent tract-tracing studies examining the cortical and subcortical connectivity of the medial temporal lobe showed that the pattern of connections of areas TH and TF of the parahippocampal cortex were consistent with previous boundary demarcations of this region. In contrast, the connections of the perirhinal cortex (areas 35 and 36) indicated that the border of area 36 should be placed several millimeters more lateral than in earlier descriptions in the literature. The connections of this region also suggested that the perirhinal cortex extends rostrodorsally to include the medial portion of what is typically referred to as the temporal pole (areas TG, 38, or Pro). To determine if cyto- and chemoarchitectonic characteristics are consistent with the boundary scheme suggested by our tract-tracing studies, we carried out a detailed analysis of Nissl- and SMI-32-stained material throughout the perirhinal and parahippocampal cortices of the macaque monkey. The staining patterns seen in both these preparations are in excellent agreement with the boundaries defined by earlier connectional studies. Based on these studies, we recognize areas 35 and area 36 of the perirhinal cortex and area 36 contains five subdivisions. The parahippocampal cortex is composed of areas TH and TF and area TF contains two subdivisions. For both the perirhinal and parahippocampal cortices, we provide descriptions of the cytoarchitectonic and chemoarchitectonic features that are most useful for defining each cortical subdivision, as well as the features most useful for defining the boundaries with adjacent cortical regions. We discuss these findings in the context of the results of previous tract-tracing studies.