PROJECT SUMMARY Anxiety disorders are near the top of the list of the most troublesome public health concerns we face, costing billions of dollars annually. Equally important are the many individual lives devastated by debilitating distress and chronic avoidance, leading to diminished quality of life, lost potential and emergent comorbid conditions (e.g. depression). Chronic, abnormally heightened threat processing is a linchpin in the pathophysiology and maintenance of anxiety disorders. Research to date on threat processing in anxiety has used passive viewing of static threat stimuli. However, real-life threats are not static—the nature of threats changes over time. We propose to remedy this important limitation of the extant research with a dynamic threat processing game (the Boom). The Boom is designed to assess a profile of neural responses to dynamically evolving threats among youth with and without elevated anxiety. The Boom is developmentally sensitive, engaging for youth, and calibrated for the detection of individual differences in threat processing. Employing child-friendly cartoon-like images, the game assesses youths’ processing of successive, naturally-evolving threat contexts: vigilance for potential threats, followed by detection of direct or indirect acute threats, and an opportunity to reappraise indirect threats that do not require an immediate response. We propose a multi-method (EEG, behavior, and multi- informant phenotyping) study to evaluate the validity and reliability of the Boom for assessing 10- to 14- year-olds’ neural responses to dynamically evolving threat contexts, to begin to unpack successive stages in a threat processing cascade among community and clinically-referred youth with varying anxiety severity. The Boom provides a unique lens into dynamic threat processing disruptions in anxiety that are not measured by existing assessments. However, establishing the reliability and validity of the Boom is a critical first step. Following psychometric validation, we expect the Boom will yield important insights into mechanisms contributing to the development and maintenance of anxiety disorders. This work may inform the design of novel or personalized interventions for anxiety disorders targeting dynamic threat processing disruptions. This study will deliver quantitative, developmentally informed brain-based biomarkers, for two key Research Domain Criteria (RDoC) negative valence constructs, Potential Threat and Acute Threat. Moreover, this project is well-aligned with the NIMH Strategic Plan Strategy 1.1, which includes identification and validation of novel assays to quantify changes in the activity of brain circuits.