Department of Biomedical Engineering, The City College of New York, CUNY, 160 Convent Avenue, New York, NY, USA.
Department of Biomedical Engineering, The City College of New York, CUNY, 160 Convent Avenue, New York, NY, USA.
Brain Stimul. 2021 May-Jun;14(3):693-702. doi: 10.1016/j.brs.2021.04.008. Epub 2021 Apr 10.
Skin sensation is the primary factor limiting the intensity of transcranial electrical stimulation (tES). It is well established that different waveforms generate different sensations, yet transcranial stimulation has been limited to a relatively small number of prototypical waveforms.
We explore whether alternative stimulation waveforms could substantially reduce skin sensation and thus allow for stronger intensities in tES.
We systematically tested a range of waveforms in a series of 6 exploratory experiments stimulating human adults on the forearm and in one instance on the head. Subjects were asked to rate skin sensation level on a numerical scale from "none" to "extreme".
High frequency (>1 kHz) monophasic square wave stimulation was found to decrease in sensation with increasing duty cycle, baseline, and frequency, but the sensation was never lower than for constant current stimulation. For the purpose of injecting a net direct current (DC), a constant current is optimal. For stimulation with alternating current (AC), sensation decreased with increasing frequency, consistent with previous reports. Amplitude modulation did not reduce sensation below stimulation with constant AC amplitude, and biphasic square waveforms produced higher sensation levels than biphasic sinusoidal waveforms. Furthermore, for DC stimulation, sensation levels on the arm were similar to those reported on the head.
Our comparisons of various waveforms for monophasic and biphasic stimulation indicate that conventional DC and AC waveforms may provide the lowest skin sensations levels for transcutaneous electrical stimulation. These results are likely generalizable to tES applications.
皮肤感觉是限制经颅电刺激（tES）强度的主要因素。不同的波形产生不同的感觉已经得到很好的证实，但经颅刺激仅限于相对较少的典型波形。
我们探索替代刺激波形是否可以显著降低皮肤感觉，从而允许在 tES 中使用更强的强度。
我们在一系列 6 项探索性实验中系统地测试了一系列波形，这些实验刺激成年人的前臂，在一个实例中刺激头部。要求受试者在数字量表上对皮肤感觉水平进行评分，从“无”到“极度”。
发现高频（>1 kHz）单相方波刺激的占空比、基线和频率增加时，感觉会降低，但感觉从未低于恒定电流刺激。对于注入净直流电（DC）的目的，恒定电流是最佳的。对于交流电（AC）刺激，频率增加时感觉会降低，这与之前的报告一致。幅度调制不会使感觉低于恒定 AC 幅度的刺激，双相方波产生的感觉水平高于双相正弦波。此外，对于 DC 刺激，手臂上的感觉水平与头部报告的相似。
我们对单相和双相刺激的各种波形进行了比较，表明传统的 DC 和 AC 波形可能为经皮电刺激提供最低的皮肤感觉水平。这些结果可能适用于 tES 应用。
