Project Summary/Abstract Juveniles acquire crucial skills by imitating skilled adults, as when infants imitate their parents' speech sounds. Evidence suggests that cortico-basal ganglia (CBG) circuitry critically supports this process both in general and specifically when juvenile zebra finches learn to imitate an adult tutor, an experimentally tractable phenomenon. A cortical pathway in juvenile zebra finches can generate stereotyped song that becomes more similar to tutor song over the course of learning. A song-dedicated CBG circuit influences activity in this pathway, acutely increasing the variability of song acoustics from rendition to rendition. My preliminary data suggest that the CBG circuit also acutely induces a directional shift in song acoustics, compared to song generated by the cortical pathway without CBG influence. The proposed experiments test the idea that the CBG drives rapid acoustic shifts, directed at the imitation target, that slowly consolidate in downstream motor cortical structures. To test this hypothesis, I have developed a (1) novel song analysis and (2) a novel longitudinal experimental design that uses (3) innovative optogentic techniques in this model system. These experiments have the potential to significantly advance our understanding of CBG support for zebra finch song learning, and to test CBG reinforcement learning models in a learning domain that does not require external reinforcement.