The use of tACS on movement-related brain waves

Background. MEG and EEG are techniques used to study the electrical activity from different brain areas. The signal arises from synchronized postsynaptic potentials of neurons that generate electrophysiological oscillations in different frequency bands. During movement process, the EEG/MEG spectral power within the beta range (15–29 Hz) decreases in amplitude and this is termed as Event-Related Desynchronization (ERD) [1]. It has been revealed that ERD is related with increased excitability of neurons in sensorimotor areas [2], [3]. Moreover, ERD amplitudes at baseline and during movement vary between age groups of young and old [4]. Abnormal increases in beta EEG power at baseline ERD are also well documented in e.g. Parkinson’s diseases and stroke [5], [6].There is converging evidence suggesting an association of cortical oscillations in the motor cortex with neuroplasticity events underlying motor memory consolidation [7], [8]. Using EEG, positive effects of exercise on motor learning by quantifying the modulation of ERD has been studied [9]. It was revealed that improvements in motor learning was associated with a significant acute decrease in beta-band ERD in sensorimotor areas measured during a grip task. Based on previous research studies, non-invasive brain stimulation (NIBS) protocols can induce neuroplasticity changes[10]–[12]. For instance, tACS allows for inducing direct cortical alterations in the underlying intrinsic neural oscillations by modulating cortical excitability through electrodes placed on the surface of the scalp [11]. Therefore, NIBS is considered as promising therapy for patients with motor deficits caused by neurodegenerative diseases.Objective. Since NIBS could induce changes in neuroplasticity and ERD is closely related with motor performance, the objective of this study is to determine the effects of NIBS protocols (tDCS and tACS) on baseline ERD.Hypothesis. We will use of a novel HD-EEG cap which allows for simultaneous EEG recording and NIBS (tDCS or tACS); this will increase spatial accuracy of stimulation and eliminate the delay between stimulation and EEG recordings. We hypothesize that tDCS applied through a custom electrode configuration in the HD-EEG cap will decrease baseline ERD, whereas tACS could induce an increase in baseline ERD. Successful outcome will further help to design NIBS therapy for patients with motor deficits.

背景。脑磁图（Magnetoencephalography, MEG）与脑电图（Electroencephalography, EEG）是用于研究不同脑区电活动的技术。其信号源于神经元同步的突触后电位，该电位可产生不同频段的电生理振荡。在运动过程中，β频段（15~29 Hz）内的EEG/MEG谱功率振幅会出现下降，这一现象被称为事件相关去同步（Event-Related Desynchronization, ERD）[1]。已有研究证实，ERD与感觉运动区神经元的兴奋性升高存在关联[2,3]。此外，青年与老年群体在基线状态及运动过程中的ERD幅度存在差异[4]。基线ERD的β脑电功率异常升高在帕金森病、脑卒中这类病症中也有大量文献记载[5,6]。多项一致的证据表明，运动皮层的皮层振荡与运动记忆巩固相关的神经可塑性事件存在关联[7,8]。有研究通过EEG量化ERD的调制效应，探讨了运动对运动学习的积极作用[9]，结果显示运动学习能力的提升与握力任务中测得的感觉运动区β频段ERD的显著急性下降相关。过往研究表明，无创脑刺激（non-invasive brain stimulation, NIBS）方案可诱导神经可塑性变化[10]–[12]。例如，经颅交流电刺激（transcranial alternating current stimulation, tACS）可通过放置于头皮表面的电极调节皮层兴奋性，诱导内在神经振荡发生直接的皮层改变[11]。因此，NIBS被认为是治疗神经退行性疾病引发的运动功能缺损的极具前景的疗法。
研究目标。鉴于NIBS可诱导神经可塑性变化，且ERD与运动表现密切相关，本研究旨在探究NIBS方案（经颅直流电刺激transcranial direct current stimulation, tDCS与tACS）对基线ERD的影响。
研究假设。我们将采用一款新型高密度脑电图（high-density EEG, HD-EEG）帽，该设备可同时完成EEG记录与NIBS（tDCS或tACS）刺激，这将提升刺激的空间精度，并消除刺激与EEG记录之间的延迟。我们提出如下假设：通过HD-EEG帽上定制电极配置施加的tDCS将降低基线ERD，而tACS则可诱导基线ERD升高。若本研究取得成功，将进一步为运动功能缺损患者的NIBS治疗方案设计提供参考。