Pleasant events as a Mechanism and Moderator of Outcomes in Cognitive-Behavioral Therapy vs. Light Therapy for Seasonal Depression

Behavioral theories of depression propose that low levels of response-contingent positive reinforcement (RCPR) lead to depressive symptoms, such as sadness and anhedonia (Lewinsohn & Gotlib, 1995). Research shows that increasing RCPR, i.e., the frequency with which one engages in pleasant activities, decreases depressed mood (Lewinsohn & Libet, 1972). Scheduling pleasant activities is the behavioral component in cognitive-behavioral therapy (CBT), an empirically-validated psychotherapy for depression (CBT; Beck et al., 1979). Here, we examined pleasant events, as measured by the Pleasant Events Schedule (PES), as a mechanism and moderator of outcomes in our completed randomized clinical trial comparing the efficacy of CBT, light therapy, and combination treatment in treating 84 adults with seasonal affective disorder (SAD).  First, we conducted repeated-measures ANOVAs to investigate change from pre- to post-treatment in PES scores.  PES cross-products scores, enjoyment derived from activities completed in the past month, significantly improved over the course of treatment, regardless of treatment modality.  Second, we used multiple regression analyses to examine whether change in PES scores over treatment is associated with depression severity at  followup the next winter and whether this association differs by treatment modality.  Change in PES enjoyment and cross-products scores over treatment was associated with next winter depression severity, regardless of treatment type. Third, we used multiple regression to examine whether baseline PES scores are associated with next winter depression severity, in general or depending on treatment type.  Baseline PES cross product scores were differentially associated with next winter depression severity in solo CBT vs. solo light therapy.