Non-invasive brain stimulation and the autonomic nervous system.

Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are non-invasive methods of brain stimulation (NIBS) that can induce significant effects on cortical and subcortical neural networks. Both methods are relatively safe if appropriate guidelines are followed, and both can exert neuromodulatory effects that may be applied to the investigation of the autonomic nervous system (ANS). In addition, ANS measures can shed important light onto the neurobiologic mechanisms of NIBS. Here we present a systematic review on studies testing NIBS and ANS simultaneously. We structure our findings into four broad (not mutually exclusive) categories: (i) studies in which ANS function was modified by NIBS versus those in which it was not; (ii) studies in which NIBS was used to understand ANS function, (iii) studies in which ANS was used to understand NIBS mechanisms and (iv) NIBS/ANS studies conducted in healthy subjects versus those in patients with neuropsychiatric diseases. Forty-four articles were identified and no conclusive evidence of the effects of NIBS on ANS was observed, mainly because of the heterogeneity of included studies. Based on a comprehensive summary of this literature we propose how NIBS might be further developed to enhance our understanding of the cortical mechanisms of autonomic regulation and perhaps to modulate autonomic activity for therapeutic purposes.