Target Engagement with Transcranial Current Stimulation

Transcranial electric stimulation (tES) applies a weak electric current to the scalp, which causes an electric field that changes brain activity and behavior. Despite the rapidly growing number of studies that report successful modulation of behavior in both healthy participants and patients, little is known about how tES modulates brain activity. In this chapter, we discuss what we know and what we do not know about the targeting of brain networks with tES. We provide an in-depth review of studies that use computational models, in vitro and in vivo animal models, and human participants to elucidate the mechanism of action of tES. The main emerging themes are (1) that the stimulation interacts with endogenous network dynamics, (2) functional connectivity represents an attractive and underexplored target for tES, and (3) that low-frequency cortical oscillations during sleep and anesthesia have become the flagship network target to elucidate the mechanisms of tES.