Institute of Movement Sciences, Aix-Marseille University, CNRS, ISM UMR 7287, 163 avenue de Luminy, Marseille Cedex 09, 13288, France.
Eur J Neurosci. 2014 Jan;39(1):132-40. doi: 10.1111/ejn.12392. Epub 2013 Oct 25.
The corticospinal (CS) system plays an important role in fine motor control, especially in precision grip tasks. Although the primary motor cortex (M1) is the main source of the CS projections, other projections have been found, especially from the supplementary motor area proper (SMAp). To study the characteristics of these CS projections from SMAp, we compared muscle responses of an intrinsic hand muscle (FDI) evoked by stimulation of human M1 and SMAp during an isometric static low-force control task. Subjects were instructed to maintain a small cursor on a target force curve by applying a pressure with their right precision grip on a force sensor. Neuronavigated transcranial magnetic stimulation was used to stimulate either left M1 or left SMAp with equal induced electric field values at the defined cortical targets. The results show that the SMAp stimulation evokes reproducible muscle responses with similar latencies and amplitudes as M1 stimulation, and with a clear and significant shorter silent period. These results suggest that (i) CS projections from human SMAp are as rapid and efficient as those from M1, (ii) CS projections from SMAp are directly involved in control of the excitability of spinal motoneurons and (iii) SMAp has a different intracortical inhibitory circuitry. We conclude that human SMAp and M1 both have direct influence on force production during fine manual motor tasks.
皮质脊髓（CS）系统在精细运动控制中起着重要作用，特别是在精细抓握任务中。虽然初级运动皮层（M1）是 CS 投射的主要来源，但也发现了其他投射，特别是来自补充运动区（SMAp）的投射。为了研究 SMAp 中这些 CS 投射的特征，我们比较了在等长静态低力控制任务中，刺激人类 M1 和 SMAp 时引起的固有手部肌肉（FDI）的肌肉反应。要求受试者通过用右手的精确抓握在力传感器上施加压力，将小光标保持在目标力曲线上。使用神经导航经颅磁刺激以相等的感应电场值在定义的皮质靶标刺激左侧 M1 或左侧 SMAp。结果表明，SMAp 刺激可引起潜伏期和幅度与 M1 刺激相似的可重复肌肉反应，并且具有明显且明显缩短的静息期。这些结果表明，（i）来自人类 SMAp 的 CS 投射与 M1 一样迅速有效，（ii）SMAp 的 CS 投射直接参与控制脊髓运动神经元的兴奋性，以及（iii）SMAp 具有不同的皮质内抑制回路。我们得出结论，人类 SMAp 和 M1 都对精细手动运动任务中的力产生有直接影响。
