BCBL, Basque Center on Cognition, Brain and Language, Paseo Mikeletegi, 69, 2°, 20009, Donostia/San Sebastian, Spain.
Ikerbasque, Basque Foundation for Science, Bilbao, Spain.
Eur J Neurosci. 2018 Oct;48(7):2642-2650. doi: 10.1111/ejn.13811. Epub 2018 Jan 18.
Cortical oscillations phase-align to the quasi-rhythmic structure of the speech envelope. This speech-brain entrainment has been reported in two frequency bands, that is both in the theta band (4-8 Hz) and in the delta band (<4 Hz). However, it is not clear if these two phenomena reflect passive synchronization of the auditory cortex to the acoustics of the speech input, or if they reflect higher processes involved in actively parsing speech information. Here, we report two magnetoencephalography experiments in which we contrasted cortical entrainment to natural speech compared to qualitative different control conditions (Experiment 1: amplitude-modulated white-noise; Experiment 2: spectrally rotated speech). We computed the coherence between the oscillatory brain activity and the envelope of the auditory stimuli. At the sensor-level, we observed increased coherence for the delta and the theta band for all conditions in bilateral brain regions. However, only in the delta band (but not theta), speech entrainment was stronger than either of the control auditory inputs. Source reconstruction in the delta band showed that speech, compared to the control conditions, elicited larger coherence in the right superior temporal and left inferior frontal regions. In the theta band, no differential effects were observed for the speech compared to the control conditions. These results suggest that whereas theta entrainment mainly reflects perceptual processing of the auditory signal, delta entrainment involves additional higher-order computations in the service of language processing.
皮层振荡与语音包络的准节律结构相位对齐。这种语音-大脑的同步已在两个频带中被报道，即在 theta 频带（4-8 Hz）和 delta 频带（<4 Hz）中。然而，目前尚不清楚这两种现象是反映听觉皮层对语音输入的声学的被动同步，还是反映主动解析语音信息所涉及的更高过程。在这里，我们报告了两个脑磁图实验，其中我们对比了自然语音引起的皮层同步与定性不同的对照条件（实验 1：调幅白噪声；实验 2：频谱旋转语音）。我们计算了脑振荡活动与听觉刺激包络之间的相干性。在传感器水平上，我们观察到在双侧大脑区域中，所有条件的 delta 和 theta 频段的相干性都增加了。然而，只有在 delta 频段（而不是 theta 频段），语音同步比任何对照听觉输入都要强。在 delta 频段的源重建显示，与对照条件相比，语音在右侧颞上区和左侧额下回区引起更大的相干性。在 theta 频段，与对照条件相比，没有观察到语音的差异效应。这些结果表明，虽然 theta 同步主要反映了听觉信号的感知处理，但 delta 同步涉及语言处理服务的额外的高级计算。
