Architectonic analysis of the auditory-related areas of the superior temporal region in human brain.

Architecture of auditory areas of the superior temporal region (STR) in the human was analyzed in Nissl-stained material to see whether auditory cortex is organized according to principles that have been described in the rhesus monkey. Based on shared architectonic features, the auditory cortex in human and monkey is organized into three lines: areas in the cortex of the circular sulcus (root), areas on the supratemporal plane (core), and areas on the superior temporal gyrus (belt). The cytoarchitecture of the auditory area changes in a stepwise manner toward the koniocortical area, both from the direction of the temporal polar proisocortex as well as from the caudal temporal cortex. This architectonic dichotomy is consistent with differences in cortical and subcortical connections of STR and may be related to different functions of the rostral and caudal temporal cortices. There are some differences between rhesus monkey and human auditory anatomy. For instance, the koniocortex, root area PaI, and belt area PaA show further differentiation into subareas in the human brain. The relative volume of the core area is larger than that of the belt area in the human, but the reverse is true in the monkey. The functional significance of these differences across species is not known but may relate to speech and language functions.