Introduction
MDD, depressed, depressive symptoms
SECONDARY
With a lifetime prevalence of up to 20 % (Up to date, there are several treatment options for MDD with relatively high response rates (On a neural level, enhanced activations in areas of the Cognitive Control Network (CCN) and the Default Mode Network (DMN) were found in depressed patients during guided rumination-induction paradigms (Understanding rumination as a result of maladaptive ER (Following these first promising results, we developed an eight-session psychotherapeutic training, combining mindfulness-based as well as cognitive behavioral ER therapy: Mindfulness-based Emotion Regulation Training (MBERT). This approach was fNIRS-adapted, allowing in situ measurements of neural processes. To the best of our knowledge, this study is the first to investigate the efficacy and the in situ neural correlates of such a mindfulness-based ER approach in the treatment of MDD. In the study at hand, we compared MBERT in a RCT with treatment as usual (TAU; no additional interventions with unrestricted continuation of existing treatments) in 42 patients suffering from MDD using a cross-over design. Our treatment consisted of a psychoeducative explanation of rumination, its link to negative emotions and impairments in ER, followed by eight psychotherapeutic training sessions practicing cognitive behavioral and mindfulness-based ER strategies under instruction and support by a clinical psychologist/psychotherapist. Each of the eight training sessions consisted of 20 training trials, in which the ER strategies were practiced, and rest trials without any specific (cognitive) task as control condition. To evaluate the efficacy of this treatment approach, we used psychometric (primary outcomes) and subjective (secondary outcomes) rating endpoints. Further, in situ fNIRS measurements were conducted to measure hemodynamic responses in the course of each session (secondary outcome). In general, we hypothesized a reduction in depressive symptoms as well as increases in self-compassion and self-efficacy due to the MBERT compared to TAU (primary outcomes). These hypotheses are derived from the knowledge about the general factors and mechanisms of psychotherapy and of “third wave CBT” in particular, namely enhanced self-compassion (