The effects of noninvasive brain stimulation on heart rate and heart rate variability: A systematic review and meta‐analysis

Noninvasive brain stimulation (NIBS) techniques such as transcranial magnetic stimu-lation and transcranial direct current stimulation are widely used to test the involve-ment of specific cortical regions in various domains such as cognition and emotion. Despite the capability of stimulation techniques to test causal directions, this ap-proach has been only sparsely used to examine the cortical regulation of autonomic nervous system (ANS) functions such as heart rate (HR) and heart rate variability (HRV) and to test current models in this regard. In this preregistered (PROSPERO) sys-tematic review and meta-analysis, we aimed to investigate, based on meta- regression, whether NIBS represents an effective method for modulating HR and HRV meas-ures, and to evaluate whether the ANS is modulated by cortical mechanisms affected by NIBS. Here we have adhered to the PRISMA guidelines. In a series of four meta- analyses, a total of 131 effect sizes from 35 sham-controlled trials were analyzed using robust variance estimation random-effects meta- regression technique. NIBS was found to effectively modulate HR and HRV with small to medium effect sizes. Moderator analyses yielded significant differences in effects between stimulation of distinct cortical areas. Our results show that NIBS is a promising tool to investigate the cortical regulation of ANS, which may add to the existing brain imaging and animal study literature. Future research is needed to identify further factors modulating the size of effects. As many of the studies reviewed were found to be at high risk of bias, we recommend that methods to reduce potential risk of bias be used in the design and conduct of future studies.