Papathanasiou I, Filipović S R, Whurr R, Rothwell J C, Jahanshahi M
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, UK.
Exp Brain Res. 2004 Jan;154(2):218-25. doi: 10.1007/s00221-003-1648-5. Epub 2003 Oct 8.
The excitability of the corticospinal motor pathways to transcranial magnetic stimulation (TMS) can be differentially modulated by a variety of motor tasks. However, there is emerging evidence that linguistic tasks may alter excitability of the corticospinal motor pathways also. In this study we evaluated the effect of several movement-free, low-level linguistic processes involved in reading and writing on the excitability of the bilateral corticospinal motor pathways in a group of right-handed subjects. The study included two series of tasks, visual searching/matching and imaginal writing/drawing. The tasks were designed to roughly correspond with elemental aspects of the reading and writing, grapheme recognition and grapheme generation, respectively. Each task series included separate blocks with different task targets: letters, digits, semantically easy-to-code (i.e. geometric) shapes, and semantically hard-to-code shapes, as well as control blocks with no task. During task performance, TMS was delivered randomly over the hand area of either the left or right motor cortex and the modulation of the excitability of the corticospinal motor pathways was measured bilaterally through changes of the size of the motor-evoked potential (MEP) induced in the relaxed right and left first dorsal interosseous (FDI) muscles. We found that the size of the MEP in hand muscles increased during visual searching/matching tasks, particularly when targets were letters or geometric shapes, and the increase was significant for the dominant hand (left hemisphere) only. No such consistent effects were seen across subjects during imaginal tasks. This study provides evidence that even the performance of certain low-level linguistic tasks can modulate the excitability of the corticospinal motor pathways, particularly those originating from the left (dominant) hemisphere, despite the absence of overt motor activity. Moreover, in the light of the recently increased awareness of the role of "mirror neurons" in perception, the results suggest that activation of motor circuits used in generation of the written output may be an essential part of the perception of the written material as well. Understanding the patterns of task-dependent changes in excitability of the corticospinal motor pathways will provide insights into the organisation of central nervous system functional networks involved in linguistic processes, and may also be useful for future development of novel approaches to rehabilitation therapy of linguistic and motor functions.
经颅磁刺激（TMS）作用下，皮质脊髓运动通路的兴奋性会受到多种运动任务的不同调节。然而，越来越多的证据表明，语言任务也可能改变皮质脊髓运动通路的兴奋性。在本研究中，我们评估了一组右利手受试者在阅读和书写过程中涉及的几种无运动、低水平语言加工过程对双侧皮质脊髓运动通路兴奋性的影响。该研究包括两个系列的任务，即视觉搜索/匹配和想象书写/绘图。这些任务分别被设计为大致对应于阅读和书写的基本方面，即字素识别和字素生成。每个任务系列都包括具有不同任务目标的单独模块：字母、数字、语义上易于编码（即几何）的形状、语义上难以编码的形状，以及无任务的对照模块。在任务执行过程中，TMS随机施加于左侧或右侧运动皮层的手部区域，并通过测量放松状态下左右第一背侧骨间肌（FDI）中诱发的运动诱发电位（MEP）大小的变化，双侧测量皮质脊髓运动通路兴奋性的调节情况。我们发现，在视觉搜索/匹配任务期间，手部肌肉的MEP大小增加，特别是当目标是字母或几何形状时，并且仅优势手（左半球）的增加具有显著性。在想象任务期间，未在受试者中观察到如此一致的效应。本研究提供了证据，表明即使是某些低水平语言任务的执行也能调节皮质脊髓运动通路的兴奋性，特别是那些起源于左（优势）半球的通路，尽管没有明显的运动活动。此外，鉴于最近对“镜像神经元”在感知中作用的认识不断增加，结果表明用于生成书面输出的运动回路的激活可能也是对书面材料感知的重要组成部分。了解皮质脊髓运动通路兴奋性的任务依赖性变化模式，将有助于深入了解参与语言加工过程的中枢神经系统功能网络的组织，并且可能对未来语言和运动功能康复治疗新方法的开发也有用。
