Moraczewski, DustinThe motivation to interact with others and the feeling of reward following a social interaction is integral to the development and maintenance of successful so- cial relationships. For those with autism spectrum disorder (ASD) successful social interaction is often more challenging relative to those who are neurotypical (NT) and atypical social reward processing may contribute to such deficits. However, our understanding of the relationship between brain systems associated with re- ward and higher-order social-cognitive processing during both typical and atypical development is limited. Middle childhood is an important time to examine the de- velopment of the functional relationship between these brain systems as this is a time when children’s social worlds expand in size and complexity and those with ASD often fall behind. The goal of the current dissertation is to characterize the development of the functional relationship between the ventral striatum (VS)—a hub of reward processing—and other brain regions implicated in reward and social-cognitive processing during an interactive social context in middle childhood. Using novel Bayesian multilevel modeling, Aim 1 examines VS functional connectivity within the NT group while Aim 2 examines group differences between the ASD and NT groups. Finally, given that heterogeneity is ubiquitous in both NT and ASD populations, Aim 3 takes a dimensional perspective through examining VS connectivity as a function of individual differences in autistic traits and subjective reports of social reward within the entire sample. Results suggest that participant age may be particularly important for the development of the relationship between reward and social-cognitive brain systems, such that older children of both groups exhibit greater sensitivity the absence of a social reward and to the contingency of a non-social reward. This dissertation underscores the importance of examining multidimensional heterogeneity in both NT and ASD populations.enDissertationNeurosciences