Interventions combining mindfulness training with non-invasive brain stimulation and their impact on mental health outcomes: Protocol for a systematic review and meta-analysis of randomized controlled trials

Background: Mindfulness training programs and non-invasive brain stimulation are both evidence-based interventions that have applications in mental health disorders. While both have showed promising results on a range of symptoms related to mental health, their combination has more recently grabbed the attention of researchers. There is a theoretical framework for their synergistic effects, and these effects can be tested through a variety of neurophysiological and clinical outcomes. This emerging field of research, which is regularly extended with new trials, has not yet been systematically reviewed. This systematic review protocol aims to present a rationale for combining these two interventions and to document the methodical approach to our systematic review before data extraction. Methods and analysis: Four electronic databases (Medline, EMBASE, CENTRAL, PsycINFO) and three clinical trial registries (Clinical Trials, EU Trials, WHO ICTRP) were searched. All randomized controlled trials testing the combination of mindfulness-based interventions and non-invasive brain stimulation in humans will be included. As primary outcome, data on change in anxiety and depression symptoms from baseline, and, as secondary outcomes, other mental health outcomes data will be gathered. Data will be extracted independently by two authors using a predefined extraction form. Depending on the clinical heterogeneity of the included studies, the research team will decide whether a quantitative synthesis is appropriate for each of the predefined outcomes. If there is considerable statistical heterogeneity, subgroup analyses and meta-regression will be performed. Bias will be assessed using a revised Cochrane risk-of-bias tool for randomized trials and the strength of evidence in our review will be assessed using the GRADE form in GRADEPro. Ethics and dissemination: Ethics approval and consent to participate were not applicable to our systematic review. Our dissemination plan includes the publication of our systematic review and meta-analysis in an international peer-reviewed journal as well as international communication of our results. Trial registration: PROSPERO registration number CRD42022353971.