Fehér Kristoffer D, Nakataki Masahito, Morishima Yosuke
Division of Systems Neuroscience of Psychopathology, Translational Research Centre, University Hospital of Psychiatry, University of Bern, Bern, Switzerland.
PRESTO, Japan Science and Technology Agency, Saitama, Japan.
Front Hum Neurosci. 2017 Sep 27;11:471. doi: 10.3389/fnhum.2017.00471. eCollection 2017.
Oscillatory neural activity is considered a basis of signal transmission in brain networks. However, the causal role of neural oscillations in regulating cortico-cortical signal transmission has so far not been directly demonstrated. To date, due to methodological limitations, studies on the online modulatory mechanisms of transcranial alternating current stimulation (tACS)-induced neural oscillations are confined to the primary motor cortex. To address the causal role of oscillatory activity in modulating cortico-cortical signal transmission, we have established a new method using concurrent tACS, transcranial magnetic stimulation (TMS) and electroencephalography (EEG). Through tACS, we introduced 6-Hz (theta) oscillatory activity in the human dorsolateral prefrontal cortex (DLPFC). During tACS, we applied single-pulse TMS over the DLPFC at different phases of tACS and assessed propagation of TMS-induced neural activity with EEG. We show that tACS-induced theta oscillations modulate the propagation of TMS-induced activity in a phase-dependent manner and that phase-dependent modulation is not simply explained by the instantaneous amplitude of tACS. The results demonstrate a phase-dependent modulatory mechanism of tACS at a cortical network level, which is consistent with a causal role of neural oscillations in regulating the efficacy of signal transmission in the brain.
振荡性神经活动被认为是脑网络中信号传递的基础。然而，神经振荡在调节皮质-皮质信号传递中的因果作用迄今尚未得到直接证实。迄今为止，由于方法学上的限制，关于经颅交流电刺激（tACS）诱发的神经振荡的在线调节机制的研究仅限于初级运动皮层。为了探究振荡活动在调节皮质-皮质信号传递中的因果作用，我们建立了一种结合tACS、经颅磁刺激（TMS）和脑电图（EEG）的新方法。通过tACS，我们在人类背外侧前额叶皮层（DLPFC）引入了6赫兹（θ）振荡活动。在tACS期间，我们在tACS的不同相位对DLPFC施加单脉冲TMS，并通过EEG评估TMS诱发的神经活动的传播。我们发现，tACS诱发的θ振荡以相位依赖的方式调节TMS诱发活动的传播，且相位依赖的调节不能简单地用tACS的瞬时幅度来解释。这些结果证明了tACS在皮质网络水平上的相位依赖调节机制，这与神经振荡在调节大脑中信号传递效率方面的因果作用相一致。
