Speech-evoked envelope-following response (EFR) reflects brain encoding of speech periodicity that serves as a biomarker for pitch and speech perception and various auditory and language disorders. Although EFR is thought to originate from the subcortex, recent research illustrated a right-hemispheric cortical contribution to EFR. However, it is unclear whether this contribution is causal. This study aimed to establish this causality by combining transcranial direct current stimulation (tDCS) and measurement of EFR (pre- and post-tDCS) via scalp-recorded electroencephalography. We applied tDCS over the left and right auditory cortices in right-handed normal-hearing participants and examined whether altering cortical excitability via tDCS causes changes in EFR during monaural listening to speech syllables. We showed significant changes in EFR magnitude when tDCS was applied over the right auditory cortex compared with sham stimulation for the listening ear contralateral to the stimulation site. No such effect was found when tDCS was applied over the left auditory cortex. Crucially, we further observed a hemispheric laterality where aftereffect was significantly greater for tDCS applied over the right than the left auditory cortex in the contralateral ear condition. Our finding thus provides the first evidence that validates the causal relationship between the right auditory cortex and EFR.

中文翻译：

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右听觉皮层与语音诱发的包络跟随反应之间的因果关系：来自联合经颅刺激和脑电图的证据

语音诱发的包络跟随反应 (EFR) 反映了语音周期性的大脑编码，可作为音调和语音感知以及各种听觉和语言障碍的生物标志物。尽管 EFR 被认为起源于皮层下，但最近的研究表明右半球皮质对 EFR 的贡献。然而，尚不清楚这种贡献是否是因果关系。本研究旨在通过结合经颅直流电刺激 (tDCS) 和通过头皮记录的脑电图测量 EFR（tDCS 前后）来确定这种因果关系。我们将 tDCS 应用于右手听力正常参与者的左右听觉皮层，并检查通过 tDCS 改变皮质兴奋性是否会导致单耳听语音音节期间 EFR 的变化。与刺激部位对侧的听耳的假刺激相比，当 tDCS 应用于右听觉皮层时，我们显示出 EFR 幅度的显着变化。当 tDCS 应用于左听觉皮层时，没有发现这种效果。至关重要的是，我们进一步观察到半球侧向性，在对侧耳条件下，右侧应用 tD​​CS 的后效应明显大于左侧听觉皮层。因此，我们的发现提供了第一个证据来验证右听觉皮层和 EFR 之间的因果关系。我们进一步观察到半球偏侧性，在对侧耳条件下，右侧应用 tD​​CS 的后效应明显大于左侧听觉皮层。因此，我们的发现提供了第一个证据来验证右听觉皮层和 EFR 之间的因果关系。我们进一步观察到半球偏侧性，在对侧耳条件下，右侧应用 tD​​CS 的后效应明显大于左侧听觉皮层。因此，我们的发现提供了第一个证据来验证右听觉皮层和 EFR 之间的因果关系。