Improved implicit self-esteem is associated with extended antidepressant effects following a novel synergistic intervention.

INTRODUCTION: In a previously published randomized controlled trial, automated self-association training (ASAT), a novel digital intervention, was found to extend the rapid antidepressant effect of a single infusion of ketamine for at least 30 days. In this secondary analysis, we aimed to understand the potential role of implicit self-esteem in the combined antidepressant effect of ketamine and ASAT training, by investigating the novel synergistic treatment's effects on implicit self-associations and their relation to symptom improvement. METHODS: A total of 154 adults (ages 18-60) with treatment-resistant unipolar depression and lower-than-normative explicit self-esteem were randomized in a double-blind, parallel-arm design to receive one of three treatment allocations: an active/active treatment combination consisting of one infusion of ketamine (0.5 mg/kg) followed by four days of ASAT ( ~ 30-40 min/day), or one of two control arms that lacked either the active drug or the active behavioral component. The Implicit Association Test (IAT) was used to behaviorally assess the strength of association between self-related stimuli and negative concepts. Linear regression models were used to test the relationship between group assignment, IAT scores acquired immediately post-treatment, and both acute and extended clinical outcomes (% change in Montgomery-Asberg Depression Rating Scale scores, relative to pre-treatment baseline) in the trial. RESULTS: The group assigned to ketamine + ASAT intervention, compared to the other groups, had a pattern of IAT scores indicating more positive self-associations immediately after treatment relative to the control arms (F(1, 131) = 3.979; p = 0.048). In regression models, IAT scores tracked with concurrent (acute post-treatment) % change in MADRS scores across all treatment arms (p = 0.001), and mediated more extended (Day 30) depression improvements specifically for the ketamine+ASAT arm (group * IAT interaction term: ß = -0.201; p = 0.049). DISCUSSION: Our findings suggest that changing implicit self-worth during a post-ketamine 'plasticity window' is one key mechanism whereby the novel ketamine+ASAT treatment combination exerts its antidepressant benefit, confirming the intended treatment target at the level of implicit cognition. Future studies should seek to further enhance the reliability of the biobehavioral intervention's impact on implicit cognition, as this mechanism appears linked to the intervention's enduring clinical benefits.

Rapid neuroplasticity changes and response to intravenous ketamine: a randomized controlled trial in treatment-resistant depression.

Intravenous ketamine is posited to rapidly reverse depression by rapidly enhancing neuroplasticity. In human patients, we quantified gray matter microstructural changes on a rapid (24-h) timescale within key regions where neuroplasticity enhancements post-ketamine have been implicated in animal models. In this study, 98 unipolar depressed adults who failed at least one antidepressant medication were randomized 2:1 to a single infusion of intravenous ketamine (0.5 mg/kg) or vehicle (saline) and completed diffusion tensor imaging (DTI) assessments at pre-infusion baseline and 24-h post-infusion. DTI mean diffusivity (DTI-MD), a putative marker of microstructural neuroplasticity in gray matter, was calculated for 7 regions of interest (left and right BA10, amygdala, and hippocampus; and ventral Anterior Cingulate Cortex) and compared to clinical response measured with the Montgomery-Asberg Depression Rating Scale (MADRS) and the Quick Inventory of Depressive Symptoms-Self-Report (QIDS-SR). Individual differences in DTI-MD change (greater decrease from baseline to 24-h post-infusion, indicative of more neuroplasticity enhancement) were associated with larger improvements in depression scores across several regions. In the left BA10 and left amygdala, these relationships were driven primarily by the ketamine group (group * DTI-MD interaction effects: p = 0.016-0.082). In the right BA10, these associations generalized to both infusion arms (p = 0.007). In the left and right hippocampus, on the MADRS only, interaction effects were observed in the opposite direction, such that DTI-MD change was inversely associated with depression change in the ketamine arm specifically (group * DTI-MD interaction effects: p = 0.032-0.06). The acute effects of ketamine on depression may be mediated, in part, by acute changes in neuroplasticity quantifiable with DTI.

A Novel, Brief, Fully Automated Intervention to Extend the Antidepressant Effect of a Single Ketamine Infusion: A Randomized Clinical Trial.

OBJECTIVE: Intravenous ketamine, which displays rapid antidepressant properties, is posited to reverse depression by rapidly enhancing neuroplasticity. The authors tested whether an automated, computer-based approach could efficiently leverage enhanced neuroplasticity to extend the durability of rapid clinical response. METHODS: A total of 154 adults (ages 18-60) with treatment-resistant unipolar depression were randomized in a double-blind, parallel-arm design to receive an active/active treatment combination (ketamine plus active "automated self-association training" [ASAT]; N=53) or one of two control arms that lacked either the active drug component (saline plus active ASAT; N=51) or the active behavioral component (ketamine plus sham ASAT; N=50). One day after a single infusion of intravenous ketamine (0.5 mg/kg over 40 minutes) or inert placebo (saline), active ASAT-targeting self-worth through automated "evaluative conditioning" training delivered by computer-or sham ASAT (consisting of identical computer tasks that included no positive or self-referential stimuli) was given, delivered twice daily over 4 consecutive days (eight sessions, ≤20 minutes per session). The prespecified primary outcome measure throughout the main (30-day) study period was score on the Montgomery-Åsberg Depression Rating Scale (MADRS). RESULTS: Ketamine rapidly and significantly reduced depression scores at 24 hours postinfusion (group-by-time interaction: standardized beta [ß]=-1.30, 95% CI=-1.89, -0.70; t=-4.29, df=150). In intent-to-treat linear mixed models, depression scores in the ketamine+ASAT group remained significantly and stably low over the 30-day study period relative to those of the saline+ASAT group (ß=-0.61, 95% CI=-0.95, -0.28; t=-3.62, df=148). By contrast, depression scores following ketamine+sham treatment followed a significant, increasing linear trajectory from 24 hours to 30 days, approaching the levels observed in the saline+ASAT group (group-by-time interaction relative to the saline+ASAT group: ß=0.015, 95% CI=0.003, 0.03; t=2.35, df=568). CONCLUSIONS: After priming the brain with ketamine, training positive self-associations could provide an efficient, low-cost, portable, noninvasive, and highly dissemination-ready strategy for leveraging and extending ketamine's rapid antidepressant effects.