Objectives: Mindfulness-Based Cognitive Therapy for Depression (MBCT-D) has been shown to be effective at repairing positive affect deficits in depressed individuals, but the mechanism of action underpinning these changes has not been empirically examined. To address this issue, secondary analyses of two randomised controlled trials in individuals with residual depression were conducted. Method: Study 1 was a cross-sectional mediation analysis of a trial reporting superior effects of MBCT-D to a waitlist control in bolstering momentary positive affect in individuals with residual depression symptoms (n = 130). Study 2 replicated this analysis in the subset of individuals with residual depression symptoms (n = 117) from a second, larger trial comparing MBCT-D to maintenance antidepressants (M-ADM) to prevent depressive relapse that also included a positive affect outcome. Results: In Study 1, an increase in external sensory observing uniquely mediated the superiority of MBCT-D over the control in repairing momentary positive affect. Replicating these findings, in Study 2, MBCT-D was superior to M-ADM at repairing positive affect and this was cross-sectionally mediated by changes in external sensory observing. Conclusions: These findings suggest that one way in which MBCT-D enhances positive affect in individuals with residual depression may be by training the capacity to attend to external sensory experience.
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