Nelson, Sarah E.Background: Social engagement differences are a core diagnostic feature of autism, though there is debate as to whether they reflect a decreased intrinsic motivation for social interaction due to neural differences in social reward processing. Much of the research in this area has methodological limitations, such as the lack of behavioral measurements of social motivation and non- ecologically relevant social reward stimuli. This is a particularly important topic to research in an adolescent age group, as peer bonds become integral to social and emotional development in this developmental stage. Objective: Assess how neural sensitivity to social reward is related to social motivation to engage with a peer in autistic and non-autistic adolescents. Method: 52 adolescents (11 autistic, 41 non-autistic, age 11-14) completed an fMRI task where they learned about commonalities and differences they had with an anonymous peer as well as randomized responses from a computer. Our primary measure of neural sensitivity to social reward is the differential activation in nucleus accumbens (NAc), a brain region that is often involved in reward processing, between positive peer responses and positive computer responses. Activation was also measured in Heschl's gyrus, an auditory processing area not closely related to reward, as a control comparison. Additionally, secondary exploratory analyses also included assessment of activation in the amygdala and orbitofrontal cortex (OFC), which are also involved in reward processing, to the peer versus the computer responses. Some time afterwards, the participants returned to have an in person interaction in a dyad with an age and gender matched peer in the study. After the interaction, the participants separately completed a behavioral measure of social reward, where they had the opportunity to choose between learning more about their peer partner or about non-social trivia. Each choice corresponded to different amounts of monetary reward (1-4 cents), meaning participants chose whether or not to forgo some monetary reward in order to learn more about their preferred topics. Social motivation was measured based on the proportion of responses where the participants chose to learn more about their partner compared to trivia. Results: The data was analyzed using mixed effects models that take into account neural activation, gender, age, and autism diagnosis status as fixed effects and dyad membership as a random intercept. We found a significant relationship between activation in the NAc (p=.019) and social motivation in the behavioral task. The secondary analyses did not reach significance after correcting for multiple comparisons, with amygdala (p=.033) and OFC (p=.5193) activation not significantly predicting social motivation. There was no significant relationship between activation in Heschl’s gyrus and social motivation (p=.635). Conclusions: The results of this study suggest that heterogeneity in autistic and non autistic adolescents' social motivation relates to their neural sensitivity to social reward in the NAc. The lack of a relationship between activation in Heschl’s gyrus and social motivation provides more support that this relationship is specifically related to differences in reward related regions. This finding can help us better understand and accommodate the social differences found in autism.en-USAutism,Social RewardSocial motivationAdolescentsThesis