PROJECT SUMMARY Self-control refers to how we prevent inappropriate actions and thoughts. Poor self-control is manifest in symptoms of impulsivity, and is associated with numerous mental health problems. One proxy of real-world self-control is thought to involve rapid response inhibition. This metric, which is captured by the stop signal task, is embedded in the large-scale Adolescent Brain Cognitive Development study (ABCD). Indeed, the stop signal task is one of only three tasks for the fMRI part of ABCD. The researchers for ABCD will collect stop signal fMRI data in 12 000 adolescents repeatedly over 10 years. Stop signal metrics, especially the single subject aggregate measure of stop signal reaction time (SSRT) [how quickly people stop] will be correlated with fMRI activation and also with brain structure (gray and white matter). Individual differences in SSRT, and stop activation and structure, will then be correlated with a slew of personality and behavioral metrics. Meanwhile, recent developments in stop signal research, including by our group, suggest a potentially much richer dissection may be done of behavioral stopping than merely computing SSRT. The current proposal aims to test whether the dissected cognitive processes correspond to particular brain signatures (Aim 1 fMRI, Aim 2 EEG), and how well they account for variability in self-control for ‘real world’ self-report and other tests of impulsivity (Aim 3). We predict that these metrics will account for more variability in self-control than does SSRT itself, thus potentially putting the stop signal aspect of the ABCD endeavor, and others like it, on a firmer physiological footing