Gamma Activity Coupled to Alpha Phase as a Mechanism for Top-Down Controlled Gating

Coupling between neural oscillations in different frequency bands has been proposed to coordinate neural processing. In particular, gamma power coupled to alpha phase is proposed to reflect gating of information in the visual system but the existence of such a mechanism remains untested. Here, we recorded ongoing brain activity using magnetoencephalography in subjects who performed a modified Sternberg working memory task in which distractors were presented in the retention interval. During the anticipatory pre-distractor period, we show that the phase of alpha oscillations was coupled with the power of high (80-120Hz) gamma band activity, i.e. gamma power consistently was lower at the trough than at the peak of the alpha cycle (9-12Hz). We further show that high alpha power was associated with weaker gamma power at the trough of the alpha cycle. This result is in line with alpha activity in sensory region implementing a mechanism of pulsed inhibition silencing neuronal firing every ~100 ms.

不同频段神经振荡之间的耦合被认为可协调神经加工过程。具体而言，与阿尔法（alpha）相位耦合的伽马（gamma）功率被提出可反映视觉系统的信息门控机制，但该机制的存在尚未得到验证。本研究通过脑磁图（magnetoencephalography，MEG）记录了执行改良版斯滕伯格（Sternberg）工作记忆任务的受试者的连续脑活动，该任务在记忆保持间隔阶段呈现干扰刺激。在干扰刺激出现前的预期阶段，我们发现阿尔法（alpha，9-12Hz）振荡的相位与高频率（80-120Hz）伽马（gamma）频段活动的功率存在耦合：即在阿尔法周期的波谷处，伽马功率始终低于周期峰值处。我们进一步发现，较高的阿尔法功率与阿尔法周期波谷处较弱的伽马功率相关。该结果与感觉皮层中的阿尔法活动机制相符——该机制通过脉冲抑制每约100毫秒静默神经元放电。