Action preparation involves widespread modulation of motor system excitability, but the precise mechanisms are unknown. In this study, we investigated whether intracortical inhibition changes in task-irrelevant muscle representations during action preparation. We used transcranial magnetic stimulation (TMS) combined with electromyography in healthy human adults to measure motor evoked potentials (MEPs) and cortical silent periods (CSPs) in task-irrelevant muscles during the preparatory period of simple delayed response tasks. In Experiment 1, participants responded with the left-index finger in one task condition and the right-index finger in another task condition, while MEPs and CSPs were measured from the contralateral non-responding and tonically contracted index finger. During Experiment 2, participants responded with the right pinky finger while MEPs and CSPs were measured from the tonically contracted left-index finger. In both experiments, MEPs and CSPs were compared between the task preparatory period and a resting intertrial baseline. The CSP duration during response preparation decreased from baseline in every case. A laterality difference was also observed in Experiment 1, with a greater CSP reduction during the preparation of left finger responses compared to right finger responses. Despite reductions in CSP duration, consistent with a release of intracortical inhibition, MEP amplitudes were smaller during action preparation when accounting for background levels of muscle activity, consistent with earlier studies that reported decreased corticospinal excitability. These findings indicate intracortical inhibition associated with task-irrelevant muscles is transiently released during action preparation and implicate a novel mechanism for the controlled and coordinated release of motor cortex inhibition.

中文翻译：

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反应准备涉及释放与任务无关的肌肉中的皮质内抑制

动作准备涉及运动系统兴奋性的广泛调节，但确切的机制尚不清楚。在这项研究中，我们调查了在动作准备期间皮质内抑制是否会改变与任务无关的肌肉表现。我们在健康成人中使用经颅磁刺激 (TMS) 与肌电图相结合，在简单延迟反应任务的准备阶段测量与任务无关的肌肉的运动诱发电位 (MEP) 和皮质静默期 (CSP)。在实验 1 中，参与者在一种任务条件下用左食指做出反应，在另一种任务条件下用右手食指做出反应，而 MEP 和 CSP 从对侧无反应和紧张收缩的食指测量。在实验 2 中，参与者用右手小指回应，而 MEPs 和 CSPs 是从紧张收缩的左手食指测量的。在这两个实验中，MEP 和 CSP 在任务准备期和休息间试验基线之间进行了比较。在每种情况下，响应准备期间的 CSP 持续时间都从基线减少。在实验 1 中也观察到了侧向性差异，与右手手指反应相比，在左手指反应准备过程中 CSP 减少更大。尽管 CSP 持续时间减少，与皮质内抑制的释放一致，但考虑到肌肉活动的背景水平，在行动准备期间 MEP 振幅较小，这与报告皮质脊髓兴奋性降低的早期研究一致。