The tolerability of transcranial electrical stimulation used across extended periods in a naturalistic context by healthy individuals
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Abstract
Transcranial electrical stimulation (tES) is one of the most widely implemented forms of non-invasive neuromodulation in basic and clinical neuroscience. Further, the use of tES by healthy populations for various purposes is growing widespread daily. The effects of tES protocols on the skin and other tissues has remained uncharacterized when used across extended periods of time by healthy individuals. Therefore, we examined the basic safety and tolerability profile of two distinct tES protocols used repeatedly across an extended period of time by healthy subjects and report our findings here for the first time. The safety and tolerability profile previously accumulated regarding extended use of tES in clinical populations is compelling and supports a low-risk or non-significant risk designation. In the present study, we tested the tolerability (safety) and compliance, compared to sham, of two common tES approaches having a current density < 2 mA/cm2; transcranial Direct Current Stimulation (tDCS) or transcranial Pulsed Current Stimulation (tPCS) used by healthy subjects three to five days (17 - 20 minutes per day) per week for up to six weeks in a naturalistic environment. In this study 100 healthy subjects were randomized to one of three treatment groups: tDCS (n = 33), tPCS (n = 30), or sham (n = 37) and blinded to the treatment condition. The tES and sham waveforms were delivered through self-adhering electrodes on the right lateral forehead and back of the neck. We conducted 1905 treatment sessions (636 sham, 623 tDCS, and 646 tPCS sessions) on study volunteers over a six-week period. There were no serious adverse events in any treatment condition. Common side effects were primarily restricted to influences upon the skin and included skin tingling, itching, and mild burning sensations. The incidence of these events in active tES treatment arms (tPCS, tDCS) was equivalent or significantly lower than their incidence in the sham treatment arm. Other adverse events had a rarity (< 5% incidence) that could not be statistically distinguished across the treatment groups. Some subjects withdrew early from the study for atypical headache (sham n = 2, tDCS n = 2, and tPCS n = 3), atypical discomfort (sham n = 0, tDCS n = 1, and tPCS n = 1), or atypical skin irritation (sham n = 2, tDCS n = 8, and tPCS n = 1). The compliance (elected sessions completed) for tPCS was significantly greater when compared to sham (p = 0.007). The present study represents the most comprehensive analysis of tES tolerability and safety in healthy subjects to date. Limited to the hardware, electrodes, and protocols tested here, we conclude that repeated use of limited output tES across extended periods, is well tolerated and poses no significant risks to healthy subjects, as previously observed in clinical studies.
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2015. The tolerability of transcranial electrical stimulation used across extended periods in a naturalistic context by healthy individuals. PeerJ PrePrints 3:e1097v2 https://doi.org/10.7287/peerj.preprints.1097v2Author comment
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Competing Interests
WJT is a co-founder and equity holding employee of Thync, Inc. WJT is an inventor on pending and issued patents related to methods, systems, and devices for non-invasive neuromodulation. MB holds equity in Soterix Medical, Inc. The City College of New York holds patents on tES with MB and LP as inventors.
Author Contributions
Bhaskar Paneri conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Niranjan Khadka performed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Vaishali Patel performed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Chris Thomas performed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
William Tyler conceived and designed the experiments, contributed reagents/materials/analysis tools, wrote the paper, reviewed drafts of the paper.
Lucas C Parra conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Marom Bikson conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Human Ethics
The following information was supplied relating to ethical approvals (i.e., approving body and any reference numbers):
The study was conducted in accordance to protocols and procedures approved by the Institutional Review Board of the City College of New York. All volunteer participants provided written informed consent to participate in the study. The CCNY IRB Approval number is 592792-10
Funding
Partial funding for this study was provided by a grant to the City College of New York from Thync, Inc., Los Gatos, California, USA. WJT is a co-founder of Thync, Inc., which partially funded this study and is a co-author on the manuscript. WJT assisted in the design of the studies and assisted in the writing of the manuscript, but had no role in collecting or analyzing the data.
