This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This project seeks to understand the organization of auditory cortex in humans and the evolution of human-specific features of auditory cortex by comparing humans with chimpanzees (the animals most closely related to humans) and in macaque monkeys. The project will use neuroimaging and histological techniques to define higher-order auditory areas in humans, identify homologous areas in chimpanzees and macaques, and determine patterns of connectivity between auditory areas in the three species. In 2010, we developed experience with immunohistochemistry for vesicular glumate transporter 2 (VGLUT2), which has been posited to serve as a specific marker for cortical afferents arising from thalamic sensory nuclei. To confirm this, we examined VGLUT2 immunoreactivity in primary visual cortex from 3 species (humans, chimpanzees, and macaque monkeys) that are believed to differ in the laminar targets of geniculate projections. The results with VGLUT2 strongly support the idea that this transporter can serve as a marker for primary sensory thalamocortical afferents. We have now begun to label auditory cortex with anti-VGLUT to better understand the distribution of medial geniculate projections to this region. In addition, we have initiated a study of the distribution of medial geniculate fibers in the auditory cortex in chimpanzees using diffusion-tensor imaging.