Recent innovations in non-invasive brain stimulation (NIBS) for the treatment of unipolar and bipolar depression: a narrative review

Depression, either bipolar or unipolar, is a highly prevalent and disabling condition. Even though several treatment options exist for depressed patients, a significant portion of individuals receiving conventional pharmacotherapy fails to achieve and sustain remission. For this reason, there is a strong need for effective alternatives to pharmacotherapy. In this respect, non-invasive brain stimulation (NIBS), including transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), have been increasingly investigated in the last two decade as promising treatment strategies for major depression and treatment-resistant depression (TRD). Indeed, due to their safety and tolerability and to the growing evidence on their efficacy, NIBS has been included in international treatment guidelines, having become part of the standard clinical practice. Even though several clinical trials involving NIBS in patients with major depression and TRD have been conducted, literature in specific areas is still marked by some inconsistencies, due to small sample-sizes, lack of multicentre-studies and to the difficulty in comparing different treatment modalities and stimulation protocols. In light of the above, we sought to provide a brief, updated compendium of the latest innovative acquisition for the use of NIBS in the treatment of depression, either unipolar or bipolar, as well as TRD with a specific focus on innovative set-up, devices, target areas, and parameters that may affect the outcome.