Purpose In our previous studies, we showed that the brain modulates the auditory system, and the modulation starts during speech planning. However, it remained unknown whether the brain uses similar mechanisms to modulate the orofacial somatosensory system. Here, we developed a novel behavioral paradigm to (a) examine whether the somatosensory system is modulated during speech planning and (b) determine the somatosensory modulation's time course during planning and production. Method Participants ( N = 20) completed two experiments in which we applied electrical current stimulation to the lower lip to induce somatosensory sensation. In the first experiment, we used a staircase method (one-up, four-down) to determine each participant's perceptual threshold at rest (i.e., the stimulus that the participant detected on 85% of trials). In the second experiment, we estimated each participant's detection ratio of electrical stimuli (with a magnitude equivalent of their perceptual threshold) delivered at various time points before speaking and during a control condition (silent reading). Results We found that the overall detection ratio in the silent reading condition remained unchanged relative to the detection ratio at rest. Approximately 536 ms before speech onset, the detection ratio in the speaking condition was similar to that in the silent reading condition; however, the detection ratio in the speaking condition gradually started to decrease and reached its lowest level at 58 ms before speech onset. Conclusions Overall, we provided compelling behavioral evidence that, as the speech motor system prepares speech movements, it also modulates the orofacial somatosensory system in a temporally specific manner.

中文翻译：

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口面部体感系统在言语规划和产生过程中受到调节

目的在我们之前的研究中，我们表明大脑会调节听觉系统，并且调节是在言语计划期间开始的。然而，大脑是否使用类似的机制来调节口面部体感系统仍不清楚。在这里，我们开发了一种新颖的行为范式，以（a）检查体感系统在语音规划期间是否受到调制，以及（b）确定在规划和制作期间体感调制的时间进程。 方法参加者（氮= 20）完成了两项实验，其中我们对下唇施加电流刺激以诱发体感。在第一个实验中，我们使用阶梯法（一个向上，四个向下）来确定每个参与者在休息时的感知阈值（即参与者在 85% 的试验中检测到的刺激）。在第二个实验中，我们估计了每个参与者在说话前和控制条件（默读）期间的不同时间点发出的电刺激（其幅度相当于其感知阈值）的检测率。 结果我们发现，安静阅读条件下的总体检测率相对于静止时的检测率保持不变。言语开始前约536 ms，说话条件下的检测率与默读条件下的检测率相似；然而，说话条件下的检测率逐渐开始下降，并在说话开始前 58 毫秒达到最低水平。 结论总体而言，我们提供了令人信服的行为证据，表明当言语运动系统准备言语运动时，它还会以时间特定的方式调节口面部体感系统。