Project Summary/Abstract This project aims to investigate the circuit mechanisms enabling an ethologically relevant sensorimotor transformation. Specifically, we characterize the neural basis for rapid vocal exchanges in the singing mouse (Scotinomys teguina), a highly vocal neotropical rodent species capable of producing an audible, stereotyped song. Pairs of S. teguina often precisely coordinate the timing of their vocalizations in a process known as countersinging. In preliminary work, we revealed a short-latency pathway from an orofacial region of motor cortex to the muscles involved in vocal production. In this proposal, we will test the hypothesis that neural dynamics in motor cortex, guided by selective acoustic cues, can modify downstream song production circuits to enable rapid vocal communication across individuals. From these studies, we will perform the first characterization of the circuit mechanisms underlying rapid vocal exchanges in a mammalian model system. In Aim 1, we will characterize the acoustic aspects of song that elicit countersinging behavior. We will examine responses to the playback of a range of natural and synthetic sensory stimuli to test perceptual boundaries and factors leading to vocal responsiveness. In Aim 2, we will use several complementary perturbations to address the role of motor cortex on vocal production and countersinging coordination. In Aim 3, we will use population recordings to examine the responses of cortical neural populations during vocal perception and production. We will then characterize the broader neural circuitry leading to countersinging by uncovering both upstream and downstream synaptic partners.