Project Summary A large body of empirical work has focused on risky behavior and mental disorders during adolescence, but our knowledge of the neurobehavioral developments in prosocial behavior is quite limited. The result is a portrait of adolescent brain development that focuses risk and psychopathology over more positive behavior. This focus is unfortunate because several prosocial behaviors that involve giving to others ? ranging from volunteering to providing instrumental or social assistance ? have been linked to healthy psychological, behavioral, and physical profiles. Giving resources and assistance to others is associated with lower mortality, fewer objective and subjective health problems, and lower depression. The health benefits of giving to others warrant an increased focus on the neurobehavioral developments that underlie this core aspect of prosocial behavior during adolescence, a key point of development that sets the stage for lifelong health and well-being. We aim to advance the field by utilizing a longitudinal design to pursue four specific aims: (1) clarify developmental changes in prosocial behavior during adolescence by longitudinally examining a specific, fundamental prosocial behavior (i.e., giving) and how it increasingly depends upon the situation (i.e., the potential recipient, the cost of giving); (2) examine how neurodevelopment in the reward, mentalizing, and cognitive control neural networks tracks with giving behavior; (3) assess how social relationships, perspective- taking, empathy, and values may relate to giving and neural development; (4) explore potential gender differences in average levels of giving and neural processes. Using a cohort-sequential longitudinal design, a total of 180 participants will be assessed at three times, every two-years, across a five-year period. The total sample will consist of three overlapping age cohorts of 60 participants each and will cover the age span from 9 to 17 yrs. (Cohort 1: 9-13 yrs., Cohort 2: 11-15 yrs., Cohort 3: 13-17 yrs.). At each time point, participants will participate in an established decision-making task optimized for the fMRI scanner in which they will be asked to make real financial contributions to their families, friends, and a stranger under varying conditions of cost to themselves. While making decisions, participants' brains will be scanned for activation and functional connectivity between regions and networks that have been implicated in mentalizing, cognitive control, and reward-related behaviors. Adolescents also will complete questionnaires and daily diary checklists that will assess aspects of social relationships, perspective-taking, empathy, and values thought to predict prosocial behavior.