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Neuroimage. 2016 Oct 15;140:99-109. doi: 10.1016/j.neuroimage.2016.03.065. Epub 2016 Apr 1.

Physiological processes non-linearly affect electrophysiological recordings during transcranial electric stimulation.

Author information

1
Centre for Integrative Neuroscience & MEG Center, University of Tübingen, Germany; IMPRS for Cognitive and Systems Neuroscience, Tübingen, Germany. Electronic address: nima.noury@cin.uni-tuebingen.de.
2
Centre for Integrative Neuroscience & MEG Center, University of Tübingen, Germany; F. Hoffmann-La Roche, Pharma Research and Early Development, Basel, Switzerland.
3
Centre for Integrative Neuroscience & MEG Center, University of Tübingen, Germany. Electronic address: markus.siegel@uni-tuebingen.de.

Abstract

Transcranial electric stimulation (tES) is a promising tool to non-invasively manipulate neuronal activity in the human brain. Several studies have shown behavioral effects of tES, but stimulation artifacts complicate the simultaneous investigation of neural activity with EEG or MEG. Here, we first show for EEG and MEG, that contrary to previous assumptions, artifacts do not simply reflect stimulation currents, but that heartbeat and respiration non-linearly modulate stimulation artifacts. These modulations occur irrespective of the stimulation frequency, i.e. during both transcranial alternating and direct current stimulations (tACS and tDCS). Second, we show that, although at first sight previously employed artifact rejection methods may seem to remove artifacts, data are still contaminated by non-linear stimulation artifacts. Because of their complex nature and dependence on the subjects' physiological state, these artifacts are prone to be mistaken as neural entrainment. In sum, our results uncover non-linear tES artifacts, show that current techniques fail to fully remove them, and pave the way for new artifact rejection methods.

KEYWORDS:

EEG; MEG; Neural entrainment; Stimulation artifacts; Transcranial alternating current stimulation (tACS); Transcranial direct current stimulation (tDCS); Transcranial electric stimulation (tES)

[Indexed for MEDLINE]

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