Project Summary/Abstract The goal of this F32 fellowship project and training plan is to prepare the candidate to independently conduct innovative research aimed at improving our understanding of suicide risk and preventing suicidal behaviors (SB) in high-risk populations. Despite decades of suicide risk research, our ability to predict and prevent suicide is inadequate,24 and suicide rates continue to rise.37 Among young adults ages 18-35, suicide is the 2nd leading cause of death.37 The proposed research is critical to understanding and reducing suicide during the high-risk developmental period of young adulthood. Social pain and social exclusion are theoretically and empirically associated with suicide ideation and SB, but the mechanisms by which social pain leads to SB are largely untested. The central hypothesis is that a maladaptive response to social pain (elicited by perceived chronic social exclusion) leads to impaired decision-making (deficits in value comparisons) and blunted physiological reactivity (blunted sympathetic arousal and blunted parasympathetic withdrawal), which is associated with SB. To test this hypothesis, virtual reality (VR) simulation, a valid and safe laboratory proxy for SB, 39,50 will be used in combination with highly sensitive objective measures of cognition and physiological arousal. These mechanisms will be examined in a transdiagnostic sample of 125 young adults (ages 18-35) with recent suicide ideation and/or SB. This multi-method study is a within-person crossover design, in which the sequence of the social exclusion manipulation (exclusion vs. neutral control) is randomized across participants. Participants complete decision-making tasks and VR suicide scenarios with physiological assessment, as well as interview and self-report measures of suicide risk and social exclusion at pre-, post-, and 4-month follow-up. This study has two specific aims: 1) Identify cognitive and physiological mechanisms linking social pain and engagement in VR SB scenarios; 2) Determine the predictive value of laboratory-derived cognitive and physiological mechanisms for future real-world SB and the potential moderators (e.g., rejection sensitivity, perceptions of rejection) of these associations. My study will provide causal evidence for 2 modifiable mechanisms for SB: impaired decision-making and physiological arousal. This is critical to improving our assessment, prediction, and treatment of SB. This is the fundamental step towards my long-term goal of isolating key mechanisms in the real-world and developing effective interventions (e.g., attentional or cognitive bias modification,84,85 real-time biofeedback86) targeting mechanisms at critical time points to reduce SB. With the proposed training and research plan, the candidate will develop expertise in physiological, cognitive, and VR methodology, as well as the practical, clinical, and statistical skills necessary to conduct cutting-edge research on suicide risk with high-ri...