PROJECT SUMMARY To decrease the worldwide burden of mental illness, it is essential to understand how precise mechanisms underlying treatments influence transdiagnostic symptoms of psychopathology. The goal of this R15 AREA award is to specifically target distress intolerance, a transdiagnostic vulnerability factor for psychopathology that tends to improve with psychotherapy. A critical barrier to understanding how psychotherapy improves distress tolerance (and subsequent symptoms of psychopathology) is the lack of knowledge of how specific treatment elements influence thoughts, feelings and emotion regulation behaviors used during distressing states. The objective of this R15 AREA grant is to evaluate and intervene on self-efficacy for withstanding distress and willingness to experience distress, which are the components theoretically proposed as core to distress tolerance, to see how they influence emotion regulation behaviors used in daily life, and how they ultimately reduce symptoms of psychopathology. To accomplish this, we will (Aim 1) use ecological momentary assessment (EMA) to evaluate associations between willingness, self-efficacy, use of engagement-based emotion regulation (i.e., labeling, processing, curiously exploring, sharing emotions) and use of disengagement-based emotion regulation (i.e., distraction, avoidance, procrastination, denial, thought suppression, expressive suppression) in daily life. We will then randomly assign participants to one of four single session in-person interventions: (1) willingness, where participants will link their core values to experiencing emotion; (2) self-efficacy, where participants will engage in an emotional exposure using self- compassionate self-talk, (3) a combined condition, or (4) a psychoeducational control. The effects of the intervention will be assessed on (Aim 2a) a second week of EMA in which participants will be reminded to use their new skill when they report distress, (Aim 2b) a third week of EMA when reminders are removed, and on (Aim 3) transdiagnostic symptoms of psychopathology assessed between each week of EMA and after a one month followup. The central hypothesis is that greater momentary willingness and self-efficacy influence greater use of engagement and lower use of disengagement behaviors, and together changes in these components of distress tolerance underlie transdiagnostic symptom improvement. The proposed research is significant because it explores how specific treatment elements influence daily functioning, thus revealing how psychotherapy enacts symptom change. The proposed research is innovative because it combines several established but underused methods (EMA, single session interventions, just-in-time intervention) in an experimental therapeutics framework to examine how distress tolerance contributes to improved mental health. This grant will form the foundation of a series of future directions in exploring the importance of treating distress tolerance and ...