Deroche Mickael L D, Nguyen Don L, Gracco Vincent L
Centre for Research on Brain, Language and Music, McGill University, Montreal, QC, Canada.
Haskins Laboratories, New Haven, CT, United States.
Front Integr Neurosci. 2017 Dec 15;11:35. doi: 10.3389/fnint.2017.00035. eCollection 2017.
The inferior parietal lobe (IPL) is a region of the cortex believed to participate in speech motor learning. In this study, we investigated whether transcranial direct current stimulation (tDCS) of the IPL could influence the extent to which healthy adults (1) adapted to a sensory alteration of their own auditory feedback, and (2) changed their perceptual representation. Seventy subjects completed three tasks: a baseline perceptual task that located the phonetic boundary between the vowels /e/ and /a/; a sensorimotor adaptation task in which subjects produced the word "head" under conditions of altered or unaltered feedback; and a post-adaptation perceptual task identical to the first. Subjects were allocated to four groups which differed in current polarity and feedback manipulation. Subjects who received anodal tDCS to their IPL (i.e., presumably increasing cortical excitability) lowered their first formant frequency (F1) by 10% in opposition to the upward shift in F1 in their auditory feedback. Subjects who received the same stimulation with unaltered feedback did not change their production. Subjects who received cathodal tDCS to their IPL (i.e., presumably decreasing cortical excitability) showed a 5% adaptation to the F1 alteration similar to subjects who received sham tDCS. A subset of subjects returned a few days later to reiterate the same protocol but without tDCS, enabling assessment of any facilitatory effects of the previous tDCS. All subjects exhibited a 5% adaptation effect. In addition, across all subjects and for the two recording sessions, the phonetic boundary was shifted toward the vowel /e/ being repeated, consistently with the selective adaptation effect, but a correlation between perception and production suggested that anodal tDCS had enhanced this perceptual shift. In conclusion, we successfully demonstrated that anodal tDCS could (1) enhance the motor adaptation to a sensory alteration, and (2) potentially affect the perceptual representation of those sounds, but we failed to demonstrate the reverse effect with the cathodal configuration. Overall, tDCS of the left IPL can be used to enhance speech performance but only under conditions in which new or adaptive learning is required.
顶下小叶（IPL）是大脑皮层的一个区域，据信参与言语运动学习。在本研究中，我们调查了对IPL进行经颅直流电刺激（tDCS）是否会影响健康成年人：（1）适应自身听觉反馈感觉改变的程度，以及（2）改变其知觉表征。70名受试者完成了三项任务：一项基线知觉任务，确定元音/e/和/a/之间的语音边界；一项感觉运动适应任务，受试者在反馈改变或未改变的条件下说出单词“head”；以及一项与第一项相同的适应后知觉任务。受试者被分为四组，每组在电流极性和反馈操作上有所不同。接受IPL阳极tDCS（即可能增加皮层兴奋性）的受试者，其第一共振峰频率（F1）相对于听觉反馈中F1的向上偏移降低了10%。接受相同刺激但反馈未改变的受试者，其发音没有变化。接受IPL阴极tDCS（即可能降低皮层兴奋性）的受试者，对F1改变的适应程度与接受伪tDCS的受试者相似，为5%。一部分受试者几天后返回，重复相同的实验方案，但不进行tDCS，以便评估先前tDCS的任何促进作用。所有受试者均表现出5%的适应效果。此外，在所有受试者和两次记录过程中，语音边界都向重复的元音/e/方向移动，这与选择性适应效应一致，但知觉与发音之间的相关性表明，阳极tDCS增强了这种知觉偏移。总之，我们成功证明阳极tDCS可以：（1）增强对感觉改变的运动适应，以及（2）潜在地影响这些声音的知觉表征，但我们未能证明阴极配置具有相反的效果。总体而言，左侧IPL的tDCS可用于增强言语表现，但仅在需要新的或适应性学习的条件下。
