Social anhedonia—a reduced tendency to enjoy interpersonal relationships and/or reduced interest in social interactions—poses a significant public health challenge. It is considered one of the most pervasive and debilitating features of severe mental illness, including psychosis. Social anhedonia substantially influences social functioning in psychosis, but currently there are no available treatments that target this debilitating hedonic deficit. Our limited understanding of the underlying mechanisms of social anhedonia presents a major obstacle for developing and evaluating interventions that target social anhedonia. This application aims to tackle this lack of knowledge by probing a process that is hypothesized to be central to social anhedonia: disrupted social reward learning. We developed our hypothesis from two complementary lines of work: a theoretical model of social anhedonia in psychosis and a growing body of work from affective neuroscience and behavioral neuroscience. To examine this hypothesized relationship between social reward learning and social anhedonia, this two-site study will recruit a sample enriched for social anhedonia (i.e., individuals who are within two years of their first psychotic episode) and employ a perturbation-based neuroimaging approach. The specificity of the relationship between reduced sensitivity to social reward and social anhedonia will be examined in two ways. First, we will employ two social reward learning tasks, each with both social and nonsocial reward conditions. Second, we will perturb social reward learning using Motivational Interviewing as a probe that is designed to increase sensitivity specifically to social reward. Participants will be randomized 1:1 to MI or a time- and format-matched control probe. At pre- and post-probe, participants will perform two social reward learning tasks in the scanner. We will examine the relationship between sensitivity to social reward and reduced subjective experience of social pleasure at both the behavioral and neural levels. The findings of this project will allow direct inferences about underlying mechanisms beyond demonstrating only the cross-sectional correlations between social reward sensitivity and social anhedonia. Thus, the findings of this project will provide valuable insights into the mechanistic pathways of social anhedonia and could provide novel neurobehavioral phenotypes that can serve as targets and biomarkers for developing novel treatments. Further, social anhedonia is not limited to severe mental illness, as some individuals with other mental disorders and also without mental illness report social anhedonia. The findings of this project will be valuable for our future efforts to determine whether the same underlying mechanism is related to social anhedonia across conditions and populations or not.