Cognitive and Chronobiological Vulnerabilities as Mediators of Acute Outcomes in CBT-SAD and Light Therapy for Winter Depression
Conference Year
January 2019
Abstract
Both light therapy (LT) and cognitive-behavioral therapy (CBT-SAD) are efficacious first-line acute treatments for winter seasonal affective disorder (SAD), but little research has tested mechanisms underlying their anti-depressant effects. The present study examined whether acute treatment outcomes are mediated by a chronobiologic mechanism in LT versus a cognitive mechanism in CBT-SAD.
177 individuals with current seasonal affective disorder participated in a 6-week randomized clinical trial comparing CBT-SAD and LT. At baseline, mid-treatment, and post-treatment, participants completed measures of general depressogenic cognitions (Dysfunctional Attitudes Scale; DAS); season-specific negative cognitions surrounding the seasons, light availability, and weather (Seasonal Beliefs Questionnaire; SBQ); chronotype (Morningness-Eveningness Questionnaire; MEQ), and depressive symptoms (Beck Depression Inventory-Second Edition; BDI-II). Interview-rated SAD symptoms were obtained weekly (Structured Clinical Interview for the Hamilton Rating Scale for Depression-SAD Version; SIGH-SAD). Parallel-process growth curve modeling (Cheong et al., 2003) was used to simultaneously examine the effect of treatment group assignment on change in putative mechanism as well as change in depressive symptoms.
Initial models tested change in symptoms and mechanisms separately. These single-construct growth curve models showed that for both treatments, depression symptoms assessed via BDI-II showed a linear decrease over the treatment period while depression symptoms assessed via SIGH-SAD showed an accelerating decrease. DAS and SBQ scores showed linear decrease over treatment, while MEQ showed linear increase (less “eveningness”). Parallel-process growth models showed evidence for hypothesized mechanisms: for SAD-specific negative cognitions (SBQ), both symptom measures showed evidence for (1) an effect of treatment group on the slope of the cognitive 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 such that LT was associated with reduced “eveningness”. This change was unrelated to change in SAD symptoms.
This study provides evidence that CBT-SAD promotes decreases in SAD-specific negative cognitions, and that these changes in turn are related to decreases in SAD symptoms. In addition, LT indeed reduced eveningness, indicating that LT corrects misaligned circadian rhythms. However, this did not correspond to improvement in depressive symptoms, suggesting that another process is creating the therapeutic effects of LT.
Primary Faculty Mentor Name
Kelly Rohan
Status
Graduate
Student College
College of Arts and Sciences
Program/Major
Psychological Science
Primary Research Category
Social Sciences
Cognitive and Chronobiological Vulnerabilities as Mediators of Acute Outcomes in CBT-SAD and Light Therapy for Winter Depression
Both light therapy (LT) and cognitive-behavioral therapy (CBT-SAD) are efficacious first-line acute treatments for winter seasonal affective disorder (SAD), but little research has tested mechanisms underlying their anti-depressant effects. The present study examined whether acute treatment outcomes are mediated by a chronobiologic mechanism in LT versus a cognitive mechanism in CBT-SAD.
177 individuals with current seasonal affective disorder participated in a 6-week randomized clinical trial comparing CBT-SAD and LT. At baseline, mid-treatment, and post-treatment, participants completed measures of general depressogenic cognitions (Dysfunctional Attitudes Scale; DAS); season-specific negative cognitions surrounding the seasons, light availability, and weather (Seasonal Beliefs Questionnaire; SBQ); chronotype (Morningness-Eveningness Questionnaire; MEQ), and depressive symptoms (Beck Depression Inventory-Second Edition; BDI-II). Interview-rated SAD symptoms were obtained weekly (Structured Clinical Interview for the Hamilton Rating Scale for Depression-SAD Version; SIGH-SAD). Parallel-process growth curve modeling (Cheong et al., 2003) was used to simultaneously examine the effect of treatment group assignment on change in putative mechanism as well as change in depressive symptoms.
Initial models tested change in symptoms and mechanisms separately. These single-construct growth curve models showed that for both treatments, depression symptoms assessed via BDI-II showed a linear decrease over the treatment period while depression symptoms assessed via SIGH-SAD showed an accelerating decrease. DAS and SBQ scores showed linear decrease over treatment, while MEQ showed linear increase (less “eveningness”). Parallel-process growth models showed evidence for hypothesized mechanisms: for SAD-specific negative cognitions (SBQ), both symptom measures showed evidence for (1) an effect of treatment group on the slope of the cognitive 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 such that LT was associated with reduced “eveningness”. This change was unrelated to change in SAD symptoms.
This study provides evidence that CBT-SAD promotes decreases in SAD-specific negative cognitions, and that these changes in turn are related to decreases in SAD symptoms. In addition, LT indeed reduced eveningness, indicating that LT corrects misaligned circadian rhythms. However, this did not correspond to improvement in depressive symptoms, suggesting that another process is creating the therapeutic effects of LT.