Transcranial direct current stimulation as a therapeutic tool for the treatment of major depression: insights from past and recent clinical studies

Abstract

Transcranial direct current stimulation (tDCS) is a noninvasive method of brain stimulation that has been increasingly tested for the treatment of neuropsychiatric disorders. It has useful characteristics, such as low cost, ease of use, reliable sham methodology, and relatively powerful effects on cortical excitability. Because of its potential to modulate cortical excitability noninvasively, tDCS has been tested for the treatment of depression for several decades. Therefore, we reviewed evidence on the use of tDCS for major depression examining evidence from past and recent tDCS studies. We also briefly compared tDCS with other techniques of neuromodulation, namely deep brain stimulation, vagal nerve stimulation, and transcranial magnetic stimulation; and suggest future directions for the use of tDCS in major depression. Results from past clinical trials testing direct current stimulation as a therapeutic tool had mixed methodology and showed heterogeneous results. Recent studies on tDCS and depression using novel approaches, such as different parameters of stimulation, have improved its neuromodulatory effect thus resulting in larger clinical effects. In fact, two recent small trials have shown that tDCS is associated with significant clinical gains. On the basis of these findings there is still not enough evidence to support tDCS as a therapeutic modality for depression. However, findings to date encourage further studies in this area that should explore novel parameters of stimulation. In fact, it appears that current methods of tDCS might not be fully optimized and, in fact, (1) individualized parameters of stimulation, (2) longer stimulation sessions, and (3) methods to focalize tDCS might be useful strategies to provide greater clinical benefits.