The motor system displays strong changes in neural activity during action preparation. In the past decades, several techniques, including transcranial magnetic stimulation (TMS), electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), have allowed us to gain insights into the functional role of such preparatory activity in humans. More recently, new TMS tools have been proposed to study the mechanistic principles underlying the changes in corticospinal excitability during action preparation. The aim of the present review is to provide a comprehensive description of these advanced methods and to discuss the new knowledge they give access to, relative to other existing approaches. We start with a brief synthesis of the work that has been achieved so far using classic TMS protocols during action preparation, such as the so-called single-pulse and paired-pulse techniques. We then highlight three new approaches that recently arose in the field of action preparation, including (1) the exploitation of TMS current direction, known as directional TMS, which enables investigating different subsets of neurons in the primary motor cortex, (2) the use of paired-pulse TMS to study the suppressive influence of the cerebellum on corticospinal excitability and (3) the development of a double-coil TMS approach, which facilitates the study of bilateral changes in corticospinal excitability. The aim of the present article is twofold: we seek to provide a comprehensive description of these advanced TMS tools and to discuss their bearings for the field of action preparation with respect to more traditional TMS approaches, as well as to neuroimaging techniques such as EEG or fMRI. Finally, we point out perspectives for fundamental and clinical research that arise from the combination of these methods, widening the horizon of possibilities for the investigation of the human motor system, both in health and disease.

中文翻译：

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在动作准备过程中探测皮质脊髓兴奋性的先进 TMS 方法

在动作准备期间，运动系统显示出强烈的神经活动变化。在过去的几十年里，包括经颅磁刺激 (TMS)、脑电图 (EEG) 和功能磁共振成像 (fMRI) 在内的几种技术使我们能够深入了解这种准备活动在人类中的功能作用。最近，已经提出了新的 TMS 工具来研究动作准备过程中皮质脊髓兴奋性变化背后的机械原理。本综述的目的是提供对这些先进方法的全面描述，并讨论相对于其他现有方法，它们提供的新知识。我们首先简要综合迄今为止在行动准备期间使用经典 TMS 协议所取得的成果，例如所谓的单脉冲和成对脉冲技术。然后，我们重点介绍了最近在动作准备领域出现的三种新方法，包括（1）利用 TMS 电流方向，称为定向 TMS，它能够研究初级运动皮层中不同的神经元子集，（2）使用成对脉冲 TMS 研究小脑对皮质脊髓兴奋性的抑制影响和 (3) 双线圈 TMS 方法的发展，这有助于研究皮质脊髓兴奋性的双侧变化。本文的目的是双重的：我们试图全面描述这些先进的 TMS 工具，并讨论它们在行动准备领域相对于更传统的 TMS 方法的意义，以及神经成像技术，如 EEG 或 fMRI。最后，我们指出了这些方法结合所产生的基础和临床研究的前景，拓宽了研究人类运动系统（包括健康和疾病）的可能性。