Comparatively weak after-effects of transcranial alternating current stimulation (tACS) on cortical excitability in humans

Antal, Andrea; Boros, Klára; Poreisz, Csaba; Chaieb, Leila; Terney, Daniella; Paulus, Walter

doi:10.1016/j.brs.2007.10.001

« Previous Next »BRAIN STIMULATION: Basic, Translational, and Clinical Research in Neuromodulation
Volume 1, Issue 2 , Pages 97-105, April 2008

Comparatively weak after-effects of transcranial alternating current stimulation (tACS) on cortical excitability in humans

Andrea Antal, PhD
- Department of Clinical Neurophysiology, Georg-August University, Göttingen, Germany
- Address reprint requests to: Dr Andrea Antal, Department of Clinical Neurophysiology, Georg-August University, Robert Koch Straße 40, 37075 Göttingen, Germany.
Klára Boros, MD
- Department of Clinical Neurophysiology, Georg-August University, Göttingen, Germany
Csaba Poreisz, MD
- Department of Clinical Neurophysiology, Georg-August University, Göttingen, Germany
Leila Chaieb, MS
- Department of Clinical Neurophysiology, Georg-August University, Göttingen, Germany
Daniella Terney, MD
- Department of Clinical Neurophysiology, Georg-August University, Göttingen, Germany
- Department of Neurology, University of Szeged, Szeged, Hungary
Walter Paulus, MD
- Department of Clinical Neurophysiology, Georg-August University, Göttingen, Germany

Received 9 August 2007; received in revised form 12 October 2007; accepted 14 October 2007.

Objective

Interference with brain rhythms by noninvasive transcranial stimulation that uses weak transcranial alternating current may reveal itself to be a new tool for investigating cortical mechanisms currently unresolved. Here, we aim to extend transcranial direct current stimulation (tDCS) techniques to transcranial alternating current stimulation (tACS).

Background

Parameters such as electrode size and position were taken from those used in previous tDCS studies.

Methods

Motor evoked potentials (MEPs) revealed by transcranial magnetic stimulation (TMS), electroencephalogram (EEG)-power, and reaction times measured in a motor implicit learning task, were analyzed to detect changes in cortical excitability after 2-10 minutes of AC stimulation and sinusoidal DC stimulation (tSDCS) by using 1, 10, 15, 30, and 45 Hz and sham stimulation over the primary motor cortex in 50 healthy subjects (eight-16 subjects in each study).

Results

A significantly improved implicit motor learning was observed after 10 Hz AC stimulation only. No significant changes were observed in any of the analyzed frequency bands of EEG and with regard to the MEP amplitudes after AC or tSDCS stimulation. Similarly, if the anodal or cathodal DC stimulation was superimposed on 5, 10, and 15 Hz AC stimulation, the MEP amplitudes did not change significantly.

Conclusions

Transcranial application of weak AC current may appear to be a tool for basic and clinical research in diseases with altered EEG activity. However, its effect seems to be weaker than tDCS stimulation, at least in the present context of stimulus intensity and duration. Further studies are required to extend cautiously the safety range and uncover its influence on neuronal circuitries.

Keywords: transcranial alternating current stimulation, transcranial magnetic stimulation, electroencephalogram, motor cortex, serial reaction time task