Joshua Downer - US grants

Project summary How is auditory cortex functionally organized, and how does this organization support the perception of behaviorally relevant signals like conspecific vocalizations or speech? Non-human primate models of the auditory cortex can help us to answer these questions, yet our understanding of their correspondence to humans is incomplete. Extensive anatomical findings across primate species, including humans, point to three hierarchical processing stages in auditory cortex: the core, the belt and the parabelt. Across sensory systems, it is believed that the representations of sensory stimuli become less general and more tied to the behavioral relevance of the organism as you ascend the sensory hierarchy. For instance, higher order visual cortex contains neurons that selectively respond to face stimuli, whereas primary visual cortex is more selective for low level features across all categories of stimuli. It stands to reason that selective representations of human speech would be found in higher order human auditory cortex, and there is evidence to support this. However, we know very little about the functional organization of human auditory cortex, nor the basic sensory transformations along the auditory cortical hierarchy from which such selective representations would arise. The non-human primate model is particularly attractive for tackling these outstanding issues, since it is evolutionarily close to humans and invasive techniques can readily be applied to understand neural function. However, we have yet to extensively investigate non-human primate auditory cortex beyond the core fields. In particular, parabelt fields are very rarely probed. The purpose of the proposed research is to extensively map non-human primate auditory cortex, from core to belt to parabelt, using both mesoscopic and microscopic recording methods, then to compare monkey and human core-belt-parabelt organization using identical methods and stimuli. In doing so, we believe we will provide a large step toward understanding the sensory processes that give rise to complex auditory perception and support vocal communication. Moreover, we hope to uncover those aspects of auditory cortex that are either unique to a given species, or conserved across species. The findings from the proposed work carry the potential to not only inform our basic understanding of sensory processing, but may also provide key foundations to understanding the etiology of communication disorders with strong auditory components.