Major depression (MD) is common during adolescence and associated with significant morbidity and mortality. One important factor for the development and maintenance of adolescent MD are disturbances in emotion regulation, including deficits in cognitive reappraisal (CR). CR is a particularly effective emotion regulation strategy that aims at reinterpreting emotional events to modify affective responses. Adolescents with MD apply this strategy less often than their healthy peers and show disturbances in brain activation patterns underlying CR.

In this study, MD adolescents will be randomly assigned to a group that receives a task-based training in CR or to a control training group. It will be examined whether the task-based CR training is superior to the control training with regard to improvements in negative affect, perceived stress in daily life and depressive symptoms. Moreover, during the four training sessions, the event-related potential "Late Positive Potential" (LPP) will be recorded to assess neurophysiological indices of CR processes and gaze fixations on emotional areas within negative pictures and affective responses to pictures will be collected to identify mechanisms underlying training effects.This study will provide first evidence for the efficacy of a short-time training that has previously shown to be effective in healthy individuals. Moreover, the study will identify neurobiological mechanisms that predict training effects. The results of this investigation will lay the ground for a clinical trial to investigate whether a CR training added to an established intervention improves treatment effects for adolescent MD.

Inclusion Criteria:

• Female and male participants
• age range: 12-18 years
• current diagnosis of MD (ICD-10 diagnoses F32.0; F32.1; F32.2, F33.0, F33.1, F.33.2)
• intelligence quotient (IQ) of ≥ 80

Exclusion Criteria:

• neurological disorders
• schizophrenic disorder
• pervasive developmental disorder
• bipolar disorder
• borderline personality disorder
• substance dependence disorder
• gender dysphoria.

Participants comorbid with psychiatric comorbidities other than those listed above are included if MD is the primary diagnosis.

Data in our study contains sensitive patient information, such as sociodemographic information and comorbidities. Since patients could possibly be identified by making our raw data publicly available, ethical principles of protecting patient confidentiality would be breached. Aggregated group data can be made available upon request.

Participant-blind clinical trial: the participants are blinded regarding the allocation to the respective training group (CR training or control training). Upon completion of the training (including questionnaire assessment), participants are unblinded regarding the allocation.