Noninvasive brain stimulation: Repetitive transcranial magnetic stimulation and transcranial direct current stimulation

Abstract

Noninvasive brain stimulation provides an effective means of modulating the function of specific neural structures and shows potential for the rehabilitation of patients with brain disorders. Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are two of the most promising noninvasive brain stimulation methods. They can help to avoid surgical risks and provide theoretical advantages of neuromodulation of specific neural circuits. rTMS has been used in two ways: low-frequency stimulation to reduce cortical excitability or high-frequency stimulation to facilitate cortical excitability. Also, the anodal stimulation of tDCS increases the neuronal excitability of the brain area being stimulated and cathodal stimulation of tDCS decreases the neuronal excitability. These neuromodulative effects of rTMS and tDCS have been intensively studied in the field of neuromodulation and neurorehabilitation of patients with brain disorders during the last few decades. Most studies have shown beneficial effects of rTMS or tDCS on clinical symptoms in patients with brain disorders such as stroke and Parkinson's disease. How-ever, stimulation parameters have widely varied, and the small sample size of most studies reduces the strength of the evidence. Nevertheless, minimal side effects, positive evidence, and unveiling the mechanisms of neuromodulation using functional neuroimaging methods have made rTMS and tDCS attractive among the emerging neurorehabilitation tools. © Korean Medical Association.