Project Summary. Intravenous ketamine, which displays rapid antidepressant and anti-suicidality properties, is posited to reverse symptoms by rapidly enhancing neuroplasticity; but surprisingly little is known regarding its feasibility, safety, and effectiveness for reducing suicidal outcomes among real-world, heterogenous samples at imminent risk. Furthermore, a significant barrier to clinical adoption is the lack of evidence for durability of ketamine's effects, raising concerns about illusory recovery and subsequent rebound of suicide risk. We posit that ketamine will rapidly decrease suicidal ideation and rapidly increase cognitive flexibility in a real-world sample, allowing for rigid, negative biases in cognition to be rapidly reversed. We further expect these neurocognitive changes will provide a clinical window of opportunity in which to introduce 1) standard crisis-oriented psychiatric care; and 2) automated cognitive training (CT) techniques, which will consolidate adaptive forms of cognitive processing (specifically, positive and life-oriented implicit representations of self) while neuroplasticity remains high. Instantiating adaptive forms of processing (through standard care and/or automated CT) after first 'priming' the brain with ketamine represents a potentially synergistic treatment approach that could extend the acute effects of a single ketamine infusion beyond its typical 3-7 day window, efficiently fostering protective anti- suicidal effects that are both rapid and enduring. In this study, 200 Medical Unit inpatients (age 18-65) will be enrolled by referral from the psychiatric consultation/liaison service in a large Level 1 trauma hospital, following consult for a medically serious suicide attempt (SA). Leveraging medical unit physicians who are well-accustomed to utilizing ketamine infusion routinely in their inpatient medical settings, inpatients will be randomized in a parallel arm design to receive a single infusion of ketamine “pre-treatment”—shortly prior to subsequent psychiatric inpatient stay—or no- infusion. Patients will complete acute measures of explicit SI and cognitive target engagement (implicit suicide-self associations; Aim 1). In a fully crossed (2 x 2 factorial), parallel arm design, patients will then be randomized to receive a brief web-app-based cognitive training protocol during the post-infusion "window of opportunity," designed to implicitly reverse negative self-representations, instilling beneficial self-representations in their place, or a sham variant of the same training. Patients, investigators, and outcome raters will be blinded to treatment condition. Comprehensive feasibility/safety data will be captured for both intervention components. Remote assessments and the medical record will then be used to capture SI and SAs over a 12-month naturalistic follow-up to assess whether: ketamine followed by standard psychiatric inpatient care has a beneficial impact over no-infusion standard-of-care (A...