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Front. Psychol. | doi: 10.3389/fpsyg.2018.02117

A Prospective Study of the Impact of Transcranial Alternating Current Stimulation on EEG Correlates of Somatosensory Perception

  • 1Department of Neuroscience, Brown University, United States
  • 2School of Engineering, Brown University, United States
  • 3Alpert Medical School, Brown University, United States
  • 4Harvard Medical School, United States
  • 5Department of Psychiatry and Human Behavior, Alpert Medical School of Brown University, United States
  • 6Providence VA Medical Center, Center for Neurorestoration and Neurotechnology (CfNN), United States
  • 7Butler Hospital, United States
  • 8Carney Institute for Brain Science, Brown University, United States

The (8-12 Hz) neocortical alpha rhythm is associated with shifts in attention across sensory systems, and is thought to represent a sensory gating mechanism for the inhibitory control of cortical processing. The present preliminary study sought to explore whether alpha frequency transcranial alternating current stimulation (tACS) could modulate alpha power in the somatosensory system, and whether such hypothesized modulation would causally impact perception of tactile stimuli at perceptual threshold. We combined electroencephalography (EEG) with simultaneous brief and intermittent tACS applied over primary somatosensory cortex at individuals’ endogenous alpha frequency (n=12 for EEG) during a tactile detection task (n=20 for behavior). EEG-measured pre-stimulus alpha power was higher on non-perceived than perceived trials, and analogous perceptual correlates emerged in early components of the tactile evoked response. Further, baseline normalized tactile detection performance was significantly lower during alpha tACS than sham, but the effect did not last into the post-tACS time period. Pre- to post-tACS changes in alpha power were linearly dependent upon baseline state, such that alpha power tended to increase when pre-tACS alpha power was low, and decrease when it was high. However, these observations were comparable in both groups, and not associated with evidence of tACS-induced alpha power modulation. Nevertheless, the tactile stimulus evoked response (ER) revealed a potentially lasting impact of alpha tACS on circuit dynamics. The post-tACS ER was marked by the emergence of a prominent peak ~70 ms post-stimulus, which was not discernible post-sham, or in either pre-stimulation condition. Computational neural modeling designed to simulate macro-scale EEG signals supported the hypothesis that the emergence of this peak could reflect synaptic plasticity mechanisms induced by tACS. The primary lesson learned in this study, which commanded a small sample size, was that while our experimental paradigm provided some evidence of an influence of tACS on behavior and circuit dynamics, it was not sufficient to induce observable causal effects of tACS on EEG-measured alpha oscillations. We discuss limitations and suggest improvements that may help further delineate a causal influence of tACS on cortical dynamics and perception in future studies.

Keywords: transcranial alternating current stimulation (tACS), somatosensory perception, tactile detection, alpha, Neuromodulation

Received: 13 Jul 2018; Accepted: 15 Oct 2018.

Edited by:

Gregor Thut, University of Glasgow, United Kingdom

Reviewed by:

Jérémie Lefebvre, University of Toronto, Canada
Michael S. Clayton, Jesus College, University of Oxford, United Kingdom  

Copyright: © 2018 Sliva, Black, Bowary, Agrawal, Santoyo, Philip, Greenberg, Moore and Jones. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Ms. Danielle D. Sliva, Department of Neuroscience, Brown University, Providence, 02912, Rhode Island, United States, danielle_sliva@brown.edu