Noninvasive brain stimulation in psychiatric disorders: a primer

Abstract

Objective: Noninvasive brain stimulation (NIBS) techniques, such as transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS), are increasingly being used to treat mental disorders, particularly major depression. The aim of this comprehensive review is to summarize the main advances, limitations, and perspectives of the field.

Methods: We searched PubMed and other databases from inception to July 2017 for articles, particularly systematic reviews and meta-analyses, evaluating the use of NIBS in psychiatric disorders.

Results: We reviewed the mechanisms of action, safety, tolerability, efficacy, and relevant clinical parameters of NIBS. Repetitive TMS is already an established technique for the treatment of depression, and there is theoretically room for further methodological development towards a high-end therapeutic intervention. In contrast, tDCS is a technically easier method and therefore potentially suitable for wider clinical use. However the evidence of its antidepressant efficacy is less sound, and a recent study found tDCS to be inferior to antidepressant pharmacotherapy. Clinical trials using rTMS for other mental disorders produced mixed findings, whereas tDCS use has not been sufficiently appraised.

Conclusion: The most promising results of NIBS have been obtained for depression. These techniques excel in safety and tolerability, although their efficacy still warrants improvement.

Figure 1. Relative efficacy of rTMS compared to sham. The graph shows the results of a network meta-analysis that evaluated 4,233 depressed patients from 81 randomized clinical trials. The symbols (square, circle, triangle etc.) represent the ORs of the response rate observed for a given intervention compared to sham stimulation. Error bars represent 95%CI. 95%CI = 95% confidence interval; aTMS = accelerated transcranial magnetic stimulation; dTMS = deep (H1-coil) transcranial magnetic stimulation; HF-rTMS = high-frequency repetitive transcranial magnetic stimulation; LF-rTMS = low-frequency repetitive transcranial magnetic stimulation; OR = odds ratios; pTMS = priming transcranial magnetic stimulation; rTMS = repetitive transcranial magnetic stimulation; sTMS = synchronized transcranial magnetic stimulation; TBS = theta-burst stimulation.

Figure 2. Results from the Sertraline vs.Electric Current Therapy for Treating Depression Clinical Study (SELECT-TDCS) and Escitalopram vs.Electric Current Therapy to Treat Depression Clinical Study (ELECT-TDCS) trials.Error bars represent one standard deviation. HDRS = Hamilton Depression Rating Scale; SSRI = selective serotonin reuptake inhibitors; tDCS = transcranial direct current stimulation.