PROJECT SUMMARY/ABSTRACT Adolescents are more vulnerable than adults to substance use initiation and addiction due to neural restructuring during this developmental period. A complex circuitry connecting the cortex to striatum is both implicated in goal-directed action selection, and is dysregulated in addiction. Critically, developmental changes in connectivity of this broader corticostriatal circuitry, and how such changes relate to action selection and substance use across adolescence, have not been well characterized. Understanding developmental shifts in connectivity of corticostriatal circuitry across adolescence, both between cortex and striatum and within subregions of the striatum, may fill explanatory gaps in the adolescent risk-taking literature and provide insights into addiction mechanisms. The proposed work will use several advanced computational and neuroimaging techniques in an existing developmental dataset to characterize corticostriatal connectivity as it relates to goal- directed behavior and substance use during the transition from late childhood through early adulthood. Specific Aim 1 will use recently developed resting-state functional-connectivity analyses, in concert with diffusion- weighted structural connectivity measures, to understand dynamic shifts in connectivity strength between striatal regions and the cortex. Specific Aim 2 will employ dynamic causal modeling to understand age patterns in information transfer within the striatum, from ventral to dorsal regions, which can help to elucidate how circuitry involved in reward valuation drive choices across development. Finally, Specific Aim 3 will relate the strength of corticostriatal and intra-striatal structural and task-based functional connectivity to computational models of goal-directed task behavior across development, and will also explore how connectivity relates to self reports of drug use. This research can help to shape theories of adolescent risk taking by defining specific roles for various sub-circuits of corticostriatal circuitry in adolescents' risk taking. This work also has wider- reaching implications by elucidating how developmental shifts in corticostriatal circuitry may increase adolescents' vulnerability to drug use and addiction. During this fellowship, the applicant will learn to implement multiple advanced neuroimaging analyses and computational models of behavior in preparation for an academic career in developmental cognitive neuroscience.