Transcranial alternating current stimulation with speech envelopes modulates speech comprehension
Transcranial alternating current stimulation with speech envelopes modulates speech comprehension
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DOI：
10.1016/j.neuroimage.2018.01.038
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发表时间：
2018-05-15
期刊：
影响因子：
5.7
通讯作者：
Herrmann, Christoph S.
中科院分区：
文献类型：
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作者：
Wilsch, Anna;Neuling, Toralf;Herrmann, Christoph S.
听觉皮层对语音信号的宽带时间包络的皮层夹带对于语音理解是至关重要的。夹带导致高和低神经兴奋性的阶段，其结构和解码输入的语音信号。语音的夹带在theta频率范围（4- 8Hz）中最强，theta频率范围是语音包络的平均频率。如果语音信号降级，则语音包络的夹带较弱并且语音可懂度下降。除了感知诱发的皮质夹带，经颅交流电刺激（tACS）通过向大脑施加电信号来夹带神经振荡。因此，已显示听觉皮层中tACS诱导的夹带改善听觉感知。当前研究的目的是通过tACS在外部调制语音清晰度，使得电流对应于所呈现的语音流的包络（即，EQUE-tACS）。参与者进行了Oldenburg句子测试，其中句子在噪音中呈现，并结合了噪音-tACS。至关重要的是，tACS是在相对于句子开始的0-250 ms的时间滞后（以50 ms为一步）下诱导的（听觉刺激与tACS同时或先于tACS）。我们进行了单一主题的正弦曲线，线性和二次拟合的句子理解性能跨越时间滞后。我们可以证明，正弦拟合描述调制的句子理解最好。重要的是，正弦拟合的平均频率为5.12 Hz，对应于刺激包络的振幅谱的峰值。这一发现得到了支持的一个显着的5赫兹峰值的平均功率谱的个人性能的时间序列。总之，包络tACS调制噪声中的语音清晰度，大概是通过增强和破坏（分别与同相或异相刺激的时间滞后）皮质夹带到听觉皮层中的语音包络。
Cortical entrainment of the auditory cortex to the broadband temporal envelope of a speech signal is crucial for speech comprehension. Entrainment results in phases of high and low neural excitability, which structure and decode the incoming speech signal. Entrainment to speech is strongest in the theta frequency range (4-8 Hz), the average frequency of the speech envelope. If a speech signal is degraded, entrainment to the speech envelope is weaker and speech intelligibility declines. Besides perceptually evoked cortical entrainment, transcranial alternating current stimulation (tACS) entrains neural oscillations by applying an electric signal to the brain. Accordingly, tACS-induced entrainment in auditory cortex has been shown to improve auditory perception. The aim of the current study was to modulate speech intelligibility externally by means of tACS such that the electric current corresponds to the envelope of the presented speech stream (i.e., envelope-tACS). Participants performed the Oldenburg sentence test with sentences presented in noise in combination with envelope-tACS. Critically, tACS was induced at time lags of 0-250 ms in 50-ms steps relative to sentence onset (auditory stimuli were simultaneous to or preceded tACS). We performed single-subject sinusoidal, linear, and quadratic fits to the sentence comprehension performance across the time lags. We could show that the sinusoidal fit described the modulation of sentence comprehension best. Importantly, the average frequency of the sinusoidal fit was 5.12 Hz, corresponding to the peaks of the amplitude spectrum of the stimulated envelopes. This finding was supported by a significant 5-Hz peak in the average power spectrum of individual performance time series. Altogether, envelope- tACS modulates intelligibility of speech in noise, presumably by enhancing and disrupting (time lag with in-or out-of-phase stimulation, respectively) cortical entrainment to the speech envelope in auditory cortex.