PROJECT SUMMARY Suicidal ideation (SI) is a strong predictor of suicide–the second leading cause of death for adolescents and a national public health priority–and occurs in a significant proportion of adolescents. Adolescents who identify with a sexual- or gender-minority (SGM) group show even greater prevalence of SI, with approximately 74% of SGM youth having experienced SI. Considering these high rates of SI in SGM youth, it is critical to identify intervention targets as a first step in designing efficacious treatments to prevent death by suicide. One such intervention target may be low reward responsiveness, which is associated with SI above and beyond the influence of depression or anhedonia and tends to be blunted in SGM youth, particularly within social contexts. Despite this association, no research has evaluated low social reward responsiveness as a mechanism of SI in SGM youth. Further, no research has evaluated potential moderators, such as interpersonal stress, on the association among low social reward responsiveness and SI in SGM youth. This is critical, as SGM youth are at an increased risk of experiencing interpersonal stress due to experiences of stigma, prejudice, and discrimination. The proposed project will address these gaps by testing a novel mechanism linking SGM identity to increased SI risk and examining the moderating role of interpersonal stress, leveraging an innovative approach with a large high-risk sample of adolescents. The proposed study will test these pathways in a sample of 210 adolescents (aged 13-17) following discharge from acute psychiatric treatment for self-injurious thoughts and behaviors (SITBs). Based on prior research and our own work with adolescents in partial and inpatient treatment, we expect that ~50% of participants will hold an SGM identity. Participants will undergo an electroencephalogram (EEG), answer self-report measures, and complete semi-structured interviews to characterize SITB history. Acute interpersonal stressors, social support, and suicidal behavior will be assessed using a brief daily survey for 90 days following discharge, with self-report and interview measures obtained at 3-month follow-up. Through the longitudinal collection of these data, the present study aims to (1) Examine patterns of social reward responsiveness at the neural level in SGM youth compared to cisgender, heterosexual youth in acute psychiatric treatment for SITBs; (2) Evaluate low social reward responsiveness as a mechanism underlying increased SI severity in SGM youth after hospital discharge; and (3) Test interpersonal stress as a moderator in the relation between SGM status, low social reward responsiveness, and SI. Through support granted by this fellowship, the applicant will have the opportunity to develop advanced EEG skills, gain a deeper understanding of risk for psychopathology and SITBs in SGM youth, acquire proficiency in longitudinal data analysis, and receive individualized mentorship in grant...