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
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Article Info
Publication History
Accepted:
October 14,
2007
Received in revised form:
October 12,
2007
Received:
August 9,
2007
Footnotes
This study was funded by the Bernstein Center for Computational Neuroscience (01GQ0432) (A.A.) and the Rose Foundation (C.P.).
Identification
Copyright
© 2008 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
