Suicide is the second leading cause of death among 10-34 year-olds. Aligning with the NIMH's Prioritized Agenda for Suicide Prevention Research, this K23 career development award seeks to advance what is known about the brain/behavior mechanisms underlying self-critical rumination ─ defined as persistent negative-self- evaluation ─ and self-reassurance ─ providing compassion to self. This K23's central hypothesis is that circuit alterations in the dorsolateral and dorsomedial prefrontal cortex, dorsal anterior cingulate, and insula underlying self-critical rumination and self-reassurance is associated with increased suicidal thoughts and behavior (STB) in adolescents. Our central methodology is to examine self-critical rumination and self- reassurance using task-dependent and task-independent functional magnetic resonance imaging (fMRI) and ecological momentary assessment (EMA) in 90 12-15 year-old girls recruited on the range of STB. This age group represents a critical developmental period for these self-referential processes and youth in this age- group experienced a sharp increase in suicide rates over the last decade. Our focus on only girls is due to greater prevalence of self-criticism among females compared to males, but we plan to examine potential sex- differences in future studies. This K23's research goals are to: (i) test the associations between in vivo self- critical rumination, self-reassurance, and STB; (ii) identify neural mechanisms underlying self-critical rumination and self-reassurance; (iii) integrate the findings from the scanner with STB assessed in adolescents' real world environment. This K23's career development goals are to gain hands-on mentorship with (i) task-dependent and task-independent fMRI to assess circuit function; (ii) EMA for better real-world assessment of self-critical rumination and self-reassurance; (iii) statistical approaches for imaging and EMA data; (iv) professional development and collaboration skills. This K23 is significant, because identifying specific neural mechanisms underlying the interplay between self-critical rumination, self-reassurance, and STB can help ascertain which teens are at a greater risk for STB and contribute to development of novel, mechanistically-informed interventions. This study, combined with the completion of proposed training goals, will effectively propel the candidate towards establishing an independent program of research focused on identifying bio-behavioral mechanisms and developing preventative interventions for youth suicide risk. This K23 is innovative because this will be the first project to identify specific neural mechanisms of self-critical rumination and self- reassurance in adolescents focusing on: (i) identifying construct-specific neural mechanisms; (ii) a trans- diagnostic sample of teenagers selected on the range of STB; (iii) integration of imaging and EMA techniques. The proposed mentors (Drs. Dickstein, Armey, Jones, and Brick) and consultants (...