Applying experimental therapeutics to examine cognitive and chronological vulnerabilities as mediators of acute outcomes in cognitive-behavioral therapy and light therapy for winter depression.

Abstract

Objective: We applied the experimental therapeutics approach to test whether acute treatment outcomes for winter seasonal affective disorder (SAD) are mediated by a cognitive mechanism in cognitive–behavioral therapy (CBT-SAD) versus a chronobiologic mechanism in light therapy (LT). Method: Currently depressed adults with major depression, recurrent with seasonal pattern (N = 177; 83.6% female, 92.1% non-Hispanic White, M age = 45.6) were randomized to 6 weeks of LT or group CBT-SAD. SAD symptoms were assessed weekly on the Structured Clinical Interview for the Hamilton Rating Scale for Depression–SAD Version. At pre-, mid-, and posttreatment, participants completed measures of general depressogenic cognitions (Dysfunctional Attitudes Scale; DAS); SAD-specific negative cognitions (Seasonal Beliefs Questionnaire; SBQ); chronotype (Morningness–Eveningness Questionnaire; MEQ); and depressive symptoms (Beck Depression Inventory–Second Edition). Results: Parallel-process growth models showed evidence for hypothesized mechanisms. For SAD-specific negative cognitions (SBQ), both symptom measures showed (1) an effect of treatment group on the slope of the mediator, with CBT-SAD demonstrating greater decreases, and (2) an effect of the slope of the mediator on the slope of the outcome. These effects held for the SBQ but not the broader measure of depressogenic cognitions (DAS). For the chronotype measure (MEQ), treatment assignment affected change, whereby LT was associated with reduced “eveningness,” but this was unrelated to change in symptoms. Conclusions: CBT-SAD promoted decreases in SAD-specific negative cognitions, and these changes were related to decreases in symptoms. Consistent with the theory that LT corrects misaligned circadian rhythms, LT reduced eveningness, but this did not correspond to symptom improvement.

Temporal and specific pathways of change in cognitive behavioral therapy (CBT) and interpersonal psychotherapy (IPT) for depression

“…Third, future studies on cognitive change should explicitly measure different levels of cognitive change. When we compare our findings on dysfunctional thinking with recent other studies that investigated potential mediation of cognitive change in CBT for depression, the other study that found significant mediation of cognitive change specific to CBT (compared to light therapy) also used a measure of automatic negative thoughts (Rohan, Burt, Camuso, Perez, & Meyerhoff, 2020), while two other studies that did not find mediation or any temporal effects, but did show that dysfunctional attitudes decreased in all treatment conditions, did measure cognitive change with a measure of dysfunctional attitudes (Lemmens et al, 2017;Quigley et al, 2019). Future studies should take into account that different levels of cognitive change (automatic thoughts, dysfunctional attitudes, core beliefs or schemas) may play different roles within psychotherapy for depression.…”

Predictive validity of the Seasonal Beliefs Questionnaire for discriminating between seasonal and nonseasonal major depressive disorder.

“…As an advantage over symptom-based measures for distinguishing SAD versus nonseasonal MDD, seasonal beliefs, as measured by the SBQ, represent a malleable treatment target and potentially a cognitive vulnerability to SAD. A recent clinical trial comparing CBT-SAD to light therapy in 177 adults with SAD found evidence that seasonal beliefs mediate acute outcome in CBT-SAD (Rohan et al, 2020). Using parallel-process growth models, CBT-SAD promoted greater decreases in SBQ scores during treatment than light therapy, and these changes were related to decreases in symptoms only in CBT-SAD (Rohan et al, 2020).…”

“…A recent clinical trial comparing CBT-SAD to light therapy in 177 adults with SAD found evidence that seasonal beliefs mediate acute outcome in CBT-SAD (Rohan et al, 2020). Using parallel-process growth models, CBT-SAD promoted greater decreases in SBQ scores during treatment than light therapy, and these changes were related to decreases in symptoms only in CBT-SAD (Rohan et al, 2020). In contrast, depressogenic attitudes (DAS scores) improved comparably during CBT-SAD and light therapy, and the DAS did not mediate acute outcome in CBT-SAD.…”

Elucidating Treatment Targets and Mediators within a Confirmatory Efficacy Trial: Study Protocol for a Randomized Controlled Trial of Cognitive-Behavioral Therapy vs. Light Therapy for Winter Depression

“…Seasonal beliefs distinguish between individuals with SAD vs. non-seasonal unipolar depression (32,33). Seasonal beliefs change significantly more over the course of CBT-SAD than during LT, and greater change towards more flexible seasonal beliefs during treatment mediates both improvements in depression symptoms during active treatment (34) and lower depression scores one and two winters following treatment (35). This provides evidence that engagement of the seasonal beliefs target mediates CBT-SAD's acute antidepressant effects and its enduring benefits over LT.…”