PROJECT SUMMARY / ABSTRACT Our past research has demonstrated that feelings of social disconnectedness and conflictual relationships are factors that often undermine deterrents to suicide. Experiencing the death of a spouse or life partner is a profoundly distressing event that may cause abrupt changes in one’s daily routine, including decreased self- care and withdrawal from social activities. While most individuals adapt over time, a substantial number of older bereaved spouses (20-35%) experience depression, loneliness, suicidal thoughts, and early mortality, including death by suicide. Thus, late-life spousal bereavement provides a “natural experiment” in which to study the impact of a well-defined and common social stressor on suicide risk in late life. The objective of this R01 application is to examine the risk for and resilience to late-life suicide during the early spousal bereavement period by investigating the extent to which (1) social connectedness influences suicide risk and (2) whether circadian rhythm instability (inconsistent patterns of sleep, activity, meals, and socialization) helps explain this association. We will enroll 169 spousally-bereaved adults aged 65 years or older, who currently have at least subthreshold symptoms of depression or have a history of depression and/or suicide attempt. We will include participants early after spousal death: during the first six months post loss. All participants will complete repeated assessments over 12 months of multiple dimensions of social connectedness, clinical assessments (depression and suicide ideation), and objective assessments of circadian rhythmicity (actigraphy-derived 24-hour patterns of rest/activity, sleep onset and timing, and circadian phase advances or delays). Thus, we will be able to investigate whether circadian rhythmicity and delayed sleep onset and timing will be associated with higher suicide risk. Participants will also complete a behavioral probe, designed to promote self-care behaviors in older bereaved spouses (called “WELL” or Widowed Elders’ Lifestyle After Loss), a digital health intervention. WELL targets the timing and regularity of social activities, sleep, and meals to determine whether modifying social connectedness reduces suicide risk and whether circadian rhythm stability explains part of this association. Preliminary data indicate that WELL increases both (a) stability of circadian rhythms (i.e., regular sleep, activity, meals, and socialization) and (b) social connectedness. We will take full advantage of our longitudinal design and repeated assessments by using high-dimensional statistical models to examine how longitudinal change in multiple dimensions of social connectedness relates to change in circadian rhythm stability as a possible biobehavioral mechanism, and whether it directly and/or indirectly effects suicide risk in late-life. The proposed research aligns with RFA MH-22-135 by identifying (1) “mechanisms by which social disconnect...