PROJECT SUMMARY/ABSTRACT Apart from the emotional strain of losing a spouse, there are profound changes to bereaved individuals' daily routine; adults suddenly feel no reason to get up, go to bed, eat meals, or engage in activity at particular times of the day. Disruption of these key social timekeepers, or “zeitgebers”, disrupt the stability of circadian rhythms, placing these individuals at high risk for mood disorders like major depressive disorder (MDD) and other adverse health consequences related to poor self-care. Preventing MDD has public health importance due to its prevalence and associated physical disability, morbidity, and excess mortality. Preliminary data from the PI's K01 award (MH103467) show that a behavioral intervention that uses technology and motivational health coaching to target the stability of individuals' zeitgebers (sleep, meals, activity) is feasible and acceptable to older spousally-bereaved adults who are high risk for MDD because of subthreshold symptoms of depression. Feasibility analyses demonstrate a preliminary efficacy signal (with respect to reducing depression) and show that this intervention stabilizes circadian rhythms (the “target” or hypothesized mechanism of action). Results of this pilot study support moving forward with a full-scale efficacy trial. The primary aim of this R01 application is to test the efficacy of a technology-based behavioral intervention that targets the timing and regularity of sleep, meals, and physical activity for stabilizing circadian rhythms, to reduce symptoms of depression among older spousally-bereaved adults. Using an indicated prevention approach, we propose to enroll 150 spousally- bereaved adults aged 60 years and older in the first 6 months after spousal death who are at high risk for MDD because of subthreshold symptoms of depression. A confirmatory efficacy trial will be conducted in which participants will be randomly assigned to (a) self-monitor sleep, meals, and physical activity for 12 weeks using digital monitoring plus motivational health coaching (WELL; n=75); or (b) enhanced usual care (EUC, usual care plus study assessments, n=75). Objective actigraphic measures of the 24-hour pattern of day and nighttime activity – known as the rest-activity rhythm – will be measured to evaluate circadian rhythms as a mediator of treatment outcomes. Participants will be assessed at baseline, post-intervention, and 3-, 6-, and 12-months post- intervention. Results from this trial, whether positive or negative, will provide definitive decisions about future intervention development (i.e., effectiveness testing or dissemination of the intervention). The proposed trial aligns with Strategic Objective 3 (Strive for Prevention) and is responsive to research priority 3.2 by “developing context dependent interventions that target core mechanisms, including those that are common across mental illnesses, related to the prodromal, recent onset, and chronic stages of mental illness, in...