No (financial) means left to continue inclusion to achieve predetermined sample size. Instead of continuation (high probability of unanalyzed data) it was decided to stop inclusion and analyze data, so the scientific community can benefit from it.

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).

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.

Inclusion Criteria:

• age ≥ 18
• diagnosis of chronic or recurrent MDD according to DSM-V criteria, both current or remitted
• able to give informed consent and perform experimental tasks

Exclusion Criteria:

• in remission of first (not chronic) episode or having a first (not chronic) current episode
• insufficient comprehension of the Dutch language
• physical, cognitive, or intellectual impairments interfering with participation such as deafness, blindness, or sensorimotor handicaps
• formerly involved in MBCT or MBSR or other 8-week Mindfulness-Based Intervention (MBI)
• meets criteria for bipolar disorder, schizophrenia, schizophreniform disorder, schizoaffective illness or anorexia nervosa
• current psychosis
• high level of suicidality
• drug or alcohol addiction in the past 6 months.

Patients with chronic or recurrent MDD who are referred for MBCT at the RadboudUMC Centre for Mindfulness or at different locations of a local mental health institute (Pro Persona) will be recruited for the current study. Those patients will follow regular medical intake-procedures in accordance to procedures at the respective institutes and are screened for chronic or recurrent depression and other in- and exclusion criteria. Depression will be considered chronic if patients meet the DSM-V criteria of a 'persistent depressive disorder', which is combination of the 'chronic depressive disorder' and 'dysthymic disorder' as defined in the DSM-IV.

The authors intend to make the data available to other researchers after completion of the study and will comply with open access procedures, including open access publishing, as much as possible.

The final report of the primary endpoint (assesment of whether MBCT-induced change in depressive symptoms is mediated by change in RNT) is expected December 2023.

Restricted access. Meaning that interested researchers are welcome to contact us (authors) or the data-manager of the radboud data repository with requests for data. A team consisting of a data-manager and researchers will review the quality of the request and grant permission of the request is in accordance with the terms of use drafted by the Radboudumc and Radboud University.