BACKGROUND Transcranial alternating current stimulation (tACS) can entrain and enhance cortical oscillatory activity in a frequency-dependent manner. In our previous study (Nakazono et al., 2016), 20 Hz (β) tACS significantly increased excitability of primary motor cortex compared with 10 Hz (α) tACS. α oscillations are a prominent feature of the primary visual cortex (V1) in a resting electroencephalogram. Hence, we investigated whether α and β tACS can differentially influence multiple visual functions. METHODS Firstly, we evaluated the after-effects of α and β tACS on pattern-reversal (PR) and focal-flash (FF) visual evoked potentials (VEPs). Secondly, we determined the relationship between resting α oscillations and PR-VEPs modulated by tACS. Thirdly, the behavioral effects of tACS were assessed by contrast sensitivity. RESULTS α tACS modulated the amplitudes of PR-VEPs, compared with β tACS, but did not modulate the FF-VEPs. Time-frequency analysis revealed that α tACS facilitated event-related α phase synchronizations without increasing power, which consequently increased the PR-VEP amplitudes. There was a significant positive correlation between PR-VEP amplitudes and resting α oscillations. These findings suggested that α tACS modulated α oscillations, and affected visual functions of contrast and spatial frequency. Indeed, α tACS also improved subjects' contrast sensitivity at the behavioral level. Conversely, β tACS increased posterior α activity, but did not change VEP amplitudes. CONCLUSIONS α tACS can influence different neuronal populations from those influenced by β tACS. Thus, our results provide evidence that α tACS sharpens multiple visual functions by modulating α oscillations in V1.

中文翻译：

---

α 频率而非 β 频率的经颅交流电刺激可增强多种视觉功能

背景技术经颅交流电刺激(tACS)可以以频率依赖的方式夹带和增强皮质振荡活动。在我们之前的研究中（Nakazono 等，2016），与 10 Hz (α) tACS 相比，20 Hz (β) tACS 显着增加了初级运动皮层的兴奋性。α 振荡是静息脑电图中初级视觉皮层 (V1) 的一个突出特征。因此，我们研究了 α 和 β tACS 是否可以不同地影响多种视觉功能。方法 首先，我们评估了 α 和 β tACS 对模式反转 (PR) 和焦点闪光 (FF) 视觉诱发电位 (VEP) 的后效。其次，我们确定了静息 α 振荡与 tACS 调制的 PR-VEP 之间的关系。第三，通过对比敏感度评估 tACS 的行为影响。结果 与β tACS 相比，α tACS 调节了PR-VEPs 的振幅，但不调节FF-VEPs。时频分析表明，α tACS 在不增加功率的情况下促进了与事件相关的 α 相位同步，从而增加了 PR-VEP 幅度。PR-VEP 振幅与静息 α 振荡之间存在显着的正相关。这些发现表明 α tACS 调节了 α 振荡，并影响了对比度和空间频率的视觉功能。事实上，α tACS 还提高了受试者在行为水平上的对比敏感度。相反，β tACS 增加了后部 α 活性，但没有改变 VEP 幅度。结论 α tACS 可以影响受 β tACS 影响的不同神经元群。因此，