What Can Transcranial Alternating Current Stimulation Tell Us About Brain Oscillations?
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Purpose of the Review
Transcranial alternating current stimulation (tACS) allows to interfere with oscillatory brain activity. Here, we provide an overview of novel approaches for removing the tACS artefact to elucidate the mechanisms responsible for on-line tACS effects. Furthermore, we review recent findings on tACS after-effects and clinical applications.
tACS-induced entrainment of alpha oscillations was demonstrated in on-line electroencephalography (EEG) and magnetoencephalography (MEG) recordings. On-line effects have also been revealed by innovative tACS protocols utilizing amplitude modulation, cross-frequency coupling, non-sinusoidal waveforms, and non-electrical physiological measures. tACS after-effects on alpha power exceeding 1-h duration have been reported, and a behavioral relevance of these physiological changes was shown for the first time.
Our understanding of tACS on-line effects greatly benefited from new artefact removal approaches. After-effects of varying duration have been consistently reported but the underlying mechanism is still unclear. tACS as a neurotherapeutic is only emerging, but first evidence for successful tACS interventions in neuropsychiatric and neurological disorders is encouraging.
KeywordsElectroencephalogram Brain oscillations Transcranial electric stimulation Transcranial alternating current stimulation tACS artefact
This work was supported by a grant of the German Research Foundation (DFG, SPP1665 HE3353/8-1) awarded to Dr. Herrmann.
Compliance with Ethical Standards
Conflict of Interest
Dr. Herrmann has received honoraria as editor from Elsevier Publishers and has filed a patent application for transcranial electric stimulation.
Human and Animal Rights and Informed Consent
All reported studies/experiments with human or animal subjects performed by the authors have been previously published and complied with all applicable ethical standards (including the Helsinki declaration and its amendments, institutional/national research committee standards, and international/national/institutional guidelines).
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