View looking down on the dorsal surface of the STG. Rostral is at bottom, caudal at top, medial to the left, and lateral to the right. HG, Heschls' Gyrus; PT, Planum Temporale.
The goal of the present study was to determine whether the architectonic criteria used to identify the core, lateral belt and parabelt auditory cortices in macaque monkeys (Macaca fascicularis) could be used to identify homologous regions in humans (Homo sapiens). Current evidence indicates that auditory cortex in humans, as in monkeys, is located on the superior temporal gyrus (STG), and is functionally and structurally altered in illnesses such as schizophrenia and Alzheimer disease. In this study, we used serial sets of adjacent sections processed for Nissl substance, acetylcholinesterase, and parvalbumin to identify the distinguishing cyto- and chemoarchitectonic features of the core, lateral belt and parabelt in monkey. These criteria were evaluated in postmortem tissue from a human subject, leading to the identification of additional criteria specific to human. The criteria were validated in an additional set of 8 human subjects. Regions were delineated and their volumes estimated using the Cavalieri method in these subjects, and the sources of methodologic contribution to variability of the estimates was assessed. Serial reconstructions of the auditory cortex in humans were made showing the location of the lateral belt and parabelt with respect to gross anatomical landmarks. The summary diagram shown at left depicts the borders of the left auditory core, lateral belt, internal parabelt, and external parabelt, and the location of area Tpt, in human brain. Architectonic criteria for the core, lateral belt, and parabelt were readily adapted from monkey to human. Additionally, we found evidence for an architectonic subdivision within the parabelt, present in both species. Variability of regional volume estimates was readily constrained using a multifaceted approach to reduce potential sources of variability in regional delineation. These findings provide the foundation for unbiased quantitative studies of alterations in the circuitry of the STG in schizophrenia.