Introduction~Depression is highly prevalent and is ranked by the world health organization (WHO) as the number one contributor to disability worldwide. The highly recurrent nature of the disorder contributes greatly to the burden of Major Depressive Disorder (MDD) and with every new depressive episode, outcome prospective worsen. Mindfulness Based Cognitive Therapy (MBCT) is an effective treatment to reduce relapse rates and (residual) symptoms that contribute to recurrence in MDD. However, the mechanisms underlying this MBCT-induced effect are far from clear.~Elucidating these mechanisms will provide insight in the existing individual differences in effectiveness of MBCT. Consequently, this insight will help to improve effectiveness of treatment and even personalize treatment regimes. One likely candidate that could play a major role in the positive effects of MBCT on depressive symptoms, is repetitive negative thinking (RNT). Depressive rumination is the most well-studied form in the context of depression and has been described as the process of thinking perseveratively about one's feelings and problems (such as symptoms of depression) and their possible causes and consequences. It is believed that during MBCT participants develop the ability to become aware of automatic maladaptive cognitive processes such as depressive rumination, and learn to decenter and disengage from them. Because of this core skill to be learned during MBCT patients may be prevented to enter a vicious cycle of ruminative thinking that could otherwise aggravate symptoms of depression or have resulted in a new depressive episode.~Objectives~Our main objectives are (i) to replicate the beneficial effects of MBCT on depressive symptoms and RNT in patients with chronic or recurrent depression (crMDD), and (ii) to investigate whether individual levels of RNT (iia) mediate and/or (iib) moderate the MBCT-induced reduction in depressive symptoms.~To this end self-report questionnaires of depressive symptoms, content-independent RNT and depressive rumination will be administered before, half-way and after MBCT (intervention group) or before, half-way and after a waiting-period (waitlist group).~Secondary objectives~To triangulate research findings an experimental task (breathing focus task) that measures intrusive thoughts during task performance will be administered.~Moreover, research will focus on cognitive control and affective biases therein, because this process is related to RNT. Two major constituents of cognitive control will be measured, i.e. working memory processing and motivational biases of cognitive control (with respectively a working-memory update/ignore emotion task and Pavlovian-to-instrumental transfer task) before and after MBCT/waitlist. This behavioural data will be used to assess whether working memory and motivational biases are indeed (i) related to RNT and MDD, (ii) are changed by MBCT and (iii) whether these changes are related to clinical effects of MBCT.~Additionally, the timing of change will be investigated by administering weekly self-report questionnaires.~Design:~A multicenter, wait-list controlled-trial, with assignment to an intervention group (MBCT + treatment as usual (TAU)) or waitlist-control group (TAU) based on date of intake and start date of MBCT. Thus, assignment is not randomized and the study does not interfere with regular clinical practice (e.g. planning MBCT). If patients have to wait > 7 weeks for the next MBCT, they are invited to participate in the wait-list group while patients that have to wait < 7 weeks will be assigned to the intervention group. Note that although a full MBCT-training training lasts 8 weeks, for feasibility a cut-off of 7 weeks instead of 8 was deliberately chosen because this allows us to assign more patients to the wait-list group. This was done to prevent (as much as possible) an anticipated skewed allocation in favour of the intervention group.~Healthy controls will be invited to one measurement as a benchmark for the innovative cognitive tasks and do not follow MBCT.~Statistical analysis:~A detailed description of the planned analyses can be found within the attached Statistical Analysis Plan.
Mindfulness-Based Cognitive Therapy (MBCT) is effective in reducing relapse rates and (residual) symptoms in major depressive disorder (MDD). However, the mechanisms underlying those MBCT-induced effects are far from clear. The goal of this study is to get more insight into the working mechanisms of MBCT. The main question to be answered is whether MBCT-induced reduction in depressive symptoms is mediated and/or moderated by repetitive negative thinking (RNT), or other factors hypothesized to be involved in the working mechanism of MBCT (e.g. mindfulness skills and self-compassion).