Over the past decade several studies have shown that transcranial alternating current stimulation (tACS) delivered at the beta (15-25 Hz) frequency range can increase corticospinal excitability of the primary motor cortex (M1). The aim of this study was to systematically quantify the effect size of beta-tACS on corticospinal excitability in healthy volunteers, as well as to identify significant outcome predictors. A meta-analysis was performed on the results of 47 experiments reported in 21 studies. Random effects modelling of the effect sizes showed that beta-tACS significantly increases M1 excitability (Ē = 0.287, 95% CI = 0.133-0.440). Further analysis showed that tACS intensities above 1 mA peak-to-peak yield a robust increase in M1 excitability, whereas intensities of 1 mA peak-to-peak and below do not induce a reliable change. Additionally, results showed an impact of tACS montages on these effects. No difference in effect size for online compared to offline application of tACS was found. In conclusion, these findings indicate that beta-tACS can increase cortical excitability if stimulation intensity is above 1 mA, yet more research is needed to titrate the stimulation parameters that yield optimal results.

中文翻译：

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β-tACS 对皮质脊髓兴奋性的影响：荟萃分析

在过去十年中，几项研究表明，在 beta (15-25 Hz) 频率范围内传递的经颅交流电刺激 (tACS) 可以增加初级运动皮层 (M1) 的皮质脊髓兴奋性。本研究的目的是系统地量化 β-tACS 对健康志愿者皮质脊髓兴奋性的影响大小，并确定重要的结果预测因子。对 21 项研究中报告的 47 项实验的结果进行了荟萃分析。效应大小的随机效应模型显示，β-tACS 显着增加 M1 兴奋性（Ē = 0.287，95% CI = 0.133-0.440）。进一步分析表明，高于 1 mA 峰峰值的 tACS 强度使 M1 兴奋性显着增加，而 1 mA 峰峰值及以下的强度不会引起可靠的变化。此外，结果显示 tACS 蒙太奇对这些效果的影响。未发现在线与离线应用 tACS 的效果大小存在差异。总之，这些发现表明，如果刺激强度高于 1 mA，β-tACS 可以增加皮层兴奋性，但还需要更多的研究来调整产生最佳结果的刺激参数。