Project Summary Acoustic communication is crucial for social interactions in many species, including humans. Understanding the neural underpinnings that govern the production and processing of communication sounds is paramount to advance the fields of auditory neuroscience and social behavior. Studies investigating speech and sound processing in humans have mostly implemented non-invasive methods, leaving a gap in knowledge about underlying neural mechanisms. My project bridges this gap by exploiting scientific advantages of echolocating bats, mammals that produce and process a rich repertoire of acoustic signals, to investigate the circuits that contribute to the discrimination of complex sounds that carry different meanings. Bats are social mammals with well-developed audio-vocal systems and produce ultrasonic vocalizations for navigation and social communication, providing a distinct opportunity to study the pathways, molecules and brain regions, which enable complex sound processing. Aim 1 combines behavior and neurophysiology to investigate the specific acoustic features of communication calls that are key to evoke behavioral responses and the neural systems involved in sound discrimination. Aim 2 combines psychophysical, neurophysiological, and pharmacological inactivation methods to study the midbrain-amygdala circuit's role in mediating discrimination of sounds that show overlap in spectro-temporal features but carry different semantic content. Aim 3 investigates circuit phenomena in a social context by combining neurophysiological recordings and targeted pharmacological inactivation in freely interacting bats. The overarching hypothesis of this research program is that social- emotional processing of auditory stimuli through a midbrain-amygdala circuit mediates the discrimination of sounds that carry different meaning. The significance of this project resides in the extraordinary scientific opportunities to bridge studies of auditory behaviors, single neuron recordings, circuit dissection and computational modeling in a mammalian model. This work will contribute key new knowledge of natural sound processing mechanisms in mammals that could inform a deeper understanding of human auditory communication disorders. Johns Hopkins University offers an outstanding environment to conduct this project, as it provides access to world class research facilities, seminars and workshops offered by the Center for Hearing and Balance, the Center for Language and Speech Processing; along with an extraordinary network of mentors and collaborators who will provide training and guidance to ensure the success of this project.