Physiology of transcranial direct and alternating current stimulation

Abstract

Non-invasive brain stimulation with direct (transcranial direct current stimulation, tDCS) or alternating currents (transcranial alternating current stimulation, tACS) has been developed in neuroscience research in the last decades and since then has become an effective tool to induce neuroplasticity and modulate cognition and behaviour in humans. The primary effect of tDCS is a subthreshold modulation of resting membrane potentials, which results in alterations of cortical excitability and spontaneous cortical activity. Sufficiently long stimulation results in long-lasting neuroplastic after effects. Beyond these local effects, tDCS induces modifications of functional cortical and subcortical networks. On the other hand, tACS is presumed to primarily entrain oscillatory cortical activity, dependent on the frequency of stimulation, and has been widely applied to investigate motor and cognitive functions. Here we provide an overview about physiological mechanisms of tDCS and tACS, and review their potential application in studies of brain function and cognition.