A systematic review of accelerated transcranial magnetic stimulation induced neuroplasticity in patients with depression

Repetitive transcranial magnetic stimulation (rTMS) is an efficient non-pharmacological therapy for patients with depression, including those with treatment resistant depression (TRD). Accelerated treatment TMS-protocols (aTMS) are applied several times a day and hold the promise for rapid and efficient treatment responses superior to conventional rTMS. A better understanding of the neurobiological underpinnings of aTMS-related neuroplasticity is crucial to advance the field. To this aim, we conducted a systematic review of studies investigating neuroplasticity of aTMS-treatment. Two investigators screened the established research literature databases for publications following the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines and using Patient/Population, Intervention, Comparison and Outcome (PICO) acronyms. Among the selected 22 studies assessing 958 participants the following imaging methods were applied: functional MRI (fMRI) (n = 15), structural MRI (n = 1), diffusion tensor imaging (DTI) (n = 1), arterial spin labelling (ASL) (n = 2), 18 F-fluorodeoxyglucose positron emission tomography (18-FDG PET) (n = 1), and multimodal imaging (n = 2). The majority of reported aTMS-induced changes are confined to the anterior cingulate cortex (ACC), more specifically the subgenual ACC (sgACC). Associations between aTMS-induced neuroplasticity and clinical response were not consistent; however, the most frequently reported findings pertained to the sgACC. Future studies, investigating larger samples are required to consolidate the assumption that aTMS-induced plasticity of the sgACC may be associated with treatment response.