Highlights
- •First systematic investigation of intensity, frequency, and electrode montage, on the probability and intensity of elicited neurosensory side effects of tACS.
- •Detection of specific tuning curves for the various neurosensory side effects of tACS.
- •First report of pressure and dizziness as side effects of tACS.
- •First study on the effect of stimulation duration on the probability and the intensity of tACS-induced neurosensory sensations.
Abstract
Background
Electrical brain stimulation can elicit neurosensory side effects that are unrelated
to the intended stimulation effects. This presents a challenge when designing studies
with blinded control conditions.
Objective
The aim of this research was to investigate the role of different transcranial alternating
current stimulation (tACS) parameters, i.e. intensity, frequency, and electrode montage,
on the probability, duration and intensity of elicited neurosensory side effects.
Methods
In a first study, we examined the influence of tACS on sensations of phosphenes, dizziness,
pressure, and skin sensation in fifteen healthy subjects, during 8 s of stimulation
with different amplitudes (1500 μA, 1000 μA, 500 μA, 250 μA), frequencies (2 Hz, 4 Hz,
8 Hz, 16 Hz, 32 Hz, 64 Hz), and montages (F3/F4, F3/C4, F3/P4, P3/F4, P3/C4, P3/P4).
In a second study, ten healthy subjects were exposed to 60 s of tACS (1000 μA, 2 Hz
versus 16 Hz, F3/F4 versus P3/P4) and were asked to rate the intensity of sensations
every 12 s.
Results
The first study showed that all stimulation parameters had an influence on the probability
and intensity of sensations. Phosphenes were most likely and strongest for frontal
montages and higher frequencies. Dizziness was most likely and strongest for parietal
montages and at stimulation frequency of 4 Hz. Skin sensations and pressure was more
likely when stimulation was performed across central regions and at posterior montages,
respectively. The second study also revealed that the probability and the intensity
of sensations were neither modified during more extended periods of stimulation nor
affected by carry-over effects.
Conclusion
We demonstrated that the strength and the likelihood of sensations elicited by tACS
were specifically modulated by the stimulation parameters. The present work may therefore
be instrumental in establishing effective blinding conditions for studies with tACS.
Keywords
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Article info
Publication history
Published online: October 02, 2014
Accepted:
August 8,
2014
Received in revised form:
July 16,
2014
Received:
April 26,
2014
Footnotes
VR and RB are supported by the Graduate Training Centre of Neuroscience, International Max Planck Research School, Tuebingen, Germany. AG is supported by grants from the German Research Council [DFG GH 94/2-1, DFG EC 307], and from the Federal Ministry for Education and Research [BFNT 01GQ0761, BMBF 16SV3783, BMBF 03160064B, BMBF V4UKF014].
Financial disclosures: The authors report no conflict of interest.
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© 2014 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
