Data_Sheet_1_Transient Amplitude Modulation of Alpha-Band Oscillations by Short-Time Intermittent Closed-Loop tACS.PDF

Non-invasive brain stimulation (NIBS) techniques such as transcranial alternating current stimulation (tACS) have recently become extensively utilized due to their potential to modulate ongoing neuronal oscillatory activity and consequently to induce cortical plasticity relevant for various cognitive functions. However, the neurophysiological basis for stimulation effects as well as their inter-individual differences is not yet understood. In the present study, we used a closed-loop electroencephalography-tACS(EEG-tACS) protocol to examine the modulation of alpha oscillations generated in occipito-parietal areas. In particular, we investigated the effects of a repeated short-time intermittent stimulation protocol (1 s in every trial) applied over the visual cortex (Cz and Oz) and adjusted according to the phase and frequency of visual alpha oscillations on the amplitude of these oscillations. Based on previous findings, we expected higher increases in alpha amplitudes for tACS applied in-phase with ongoing oscillations as compared to an application in anti-phase and this modulation to be present in low-alpha amplitude states of the visual system (eyes opened, EO) but not high (eyes closed, EC). Contrary to our expectations, we found a transient suppression of alpha power in inter-individually derived spatially specific parieto-occipital components obtained via the estimation of spatial filters by using the common spatial patterns approach. The amplitude modulation was independent of the phase relationship between the tACS signal and alpha oscillations, and the state of the visual system manipulated via closed- and open-eye conditions. It was also absent in conventionally analyzed single-channel and multi-channel data from an average parieto-occipital region. The fact that the tACS modulation of oscillations was phase-independent suggests that mechanisms driving the effects of tACS may not be explained by entrainment alone, but rather require neuroplastic changes or transient disruption of neural oscillations. Our study also supports the notion that the response to tACS is subject-specific, where the modulatory effects are shaped by the interplay between the stimulation and different alpha generators. This favors stimulation protocols as well as analysis regimes exploiting inter-individual differences, such as spatial filters to reveal otherwise hidden stimulation effects and, thereby, comprehensively induce and study the effects and underlying mechanisms of tACS.

无创脑刺激（Non-invasive brain stimulation, NIBS）技术，例如经颅交流电刺激（transcranial alternating current stimulation, tACS），近年来因其能够调节进行中的神经元振荡活动，进而诱导与多种认知功能相关的皮质可塑性，已得到广泛应用。然而，刺激效应的神经生理学基础及其个体间差异仍未被阐明。本研究采用闭环脑电图-经颅交流电刺激（electroencephalography-tACS, EEG-tACS）范式，旨在探究枕顶区产生的α振荡的调制效应。具体而言，我们考察了重复短时间歇刺激范式（每一试次持续1秒）的效应：该刺激施加于视觉皮层（Cz与Oz位点），并根据视觉α振荡的相位与频率进行实时调整，以观察其对该类振荡振幅的影响。基于既往研究结果，我们曾提出两项假设：其一，与反相施加的tACS相比，与正在进行的振荡同相的tACS可使α振幅出现更显著的提升；其二，该调制效应仅存在于视觉系统的低α振幅状态（睁眼(eyes opened, EO)），而非高α振幅状态（闭眼(eyes closed, EC)）。但与预期相反，我们通过共同空间模式（common spatial patterns, CSP）方法估算空间滤波器，得到个体特异性的顶枕区空间成分后，发现α功率出现一过性抑制。此次观测到的振幅调制与tACS信号和α振荡之间的相位关系无关，也不受通过睁眼/闭眼条件操控的视觉系统状态影响。该结果在常规分析的平均顶枕区单通道与多通道数据中同样未被发现。tACS对振荡的调制不依赖相位这一现象表明，驱动tACS效应的机制或许不能仅用相位夹带（entrainment）来解释，而是需要神经可塑性变化或神经振荡的一过性干扰。本研究还支持这一观点：对tACS的响应存在个体特异性，其调制效应由刺激与不同α振荡发生器之间的相互作用所塑造。这提示我们，应采用利用个体间差异的刺激范式与分析方法——例如通过空间滤波器来揭示原本被掩盖的刺激效应，从而全面地诱导并研究tACS的效应及其潜在机制。