ABSTRACT The goal of this project is to evaluate the temporal and predictive association of emotion reactivity (ER) and cognitive reappraisal (CR) (a well-studied emotion regulation strategy) with intensity and duration of suicidal ideation (SI) in middle-aged and older adults following their discharge from a suicide-related hospitalization, a period of high suicide risk. Our preliminary Event Related Potential (ERP) and self-reported affect data on middle-aged : a) increased ER and reduced CR at Discharge were independently associated with increased intensity and longer duration of suicidal ideation at Week 6; and b) patients with combined high ER and low CR at Discharge had higher intensity and longer duration of suicidal ideation at Week 6 than the rest of the patients. and older adults (N=36) who were hospitalized for suicidality demonstrated that We will recruit 162 middle-aged and older adults (40-90 years old) who have been hospitalized for suicidal ideation or suicidal behavior [Columbia Suicide Severity Rating Scale (C-SSRS) at Admission > 1, i.e., 1=Wishes to be Dead]. We will follow the participants for 6 months after discharge. Suicidal ideation and behavior will be measured weekly through an interviewer-administered instrument (C-SSRS). ER and CR will be assessed with: 1) electrocortical measures (Late Positive Potential) and self-reported affect during an emotion reactivity and regulation EEG task (primary measures), and 2) the Emotion Regulation Questionnaire and the Perth Emotional Reactivity Scale (secondary measures). Assessments will be conducted at Admission (without EEG), Discharge, and at Weeks 6, 12, 18, and 24. 1. Examine the Independent Effects of ER and CR on Intensity and Duration of SI. 2. Examine the Combined Effects of ER and CR on Intensity and Duration of SI. Exploratory Analyses: 1. Examine whether demographic variables, discharge clinical characteristics, rehospitalization, medical comorbidities, and other suicide risk factors moderate the relationship of ER and CR with suicidal ideation. 2. Examine association of the longitudinal profile of ER and CR with the longitudinal profile of intensity and duration of suicidal ideation. Primary Aims: This is the first study to examine the predictive relationship of ER and CR with suicidal ideation in middle-aged and older adults at high suicide risk. Understanding this relationship will help identify: a) mechanisms which increase suicidal ideation, and b) subgroups of patients at increased suicide risk. Consistent with the concept of “Precision Medicine”, the findings may contribute to the development of personalized psychosocial interventions for this population.