Perez Monica A, Cohen Leonardo G
Human Cortical Physiology Section and Stroke Neurorehabilitation Clinic, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
Cortex. 2009 Oct;45(9):1065-71. doi: 10.1016/j.cortex.2008.12.006. Epub 2009 Jan 31.
During performance of a unimanual force generation task primary motor cortices (M1s) experience clear functional changes. Here, we evaluated the way in which M1s interact during parametric increases in right wrist flexion force in healthy volunteers. We measured the amplitude and the slope of motor evoked potentials (MEP) recruitment curves to transcranial magnetic stimulation (TMS) in the left and right flexor carpi radialis (FCR) muscles at rest and during 10%, 30% and 70% of maximal wrist flexion force. At rest, no differences were observed in the amplitude and slope of MEP recruitment curves in the left and right FCR muscles. With increasing right wrist flexion force, MEP amplitudes increased in both FCR muscles, with larger amplitudes in the right FCR. We found a significant correlation between the left and right MEP amplitudes across conditions. The slope of right and left FCR MEP recruitment curve was significantly steeper at 70% of force compared to rest and 10% of force. A significant correlation between the slope of left and right FCR MEP amplitudes was found at 70% of force only. Our results indicate a differential scaling of excitability in the corticospinal system controlling right and left FCR muscles at increasing levels of unimanual force generation. Specifically, these data highlights that at strong levels of unimanual force the increases in motor cortical excitability with increasing TMS stimulus intensities follow a similar pattern in both M1s, while at low levels of force they do not.
在执行单手力量生成任务期间，初级运动皮层（M1s）会经历明显的功能变化。在此，我们评估了健康志愿者在右手腕屈曲力量参数增加过程中M1s之间的相互作用方式。我们测量了在静息状态以及最大腕部屈曲力量的10%、30%和70%时，经颅磁刺激（TMS）诱发的左侧和右侧桡侧腕屈肌（FCR）运动诱发电位（MEP）募集曲线的幅度和斜率。静息时，左侧和右侧FCR肌肉的MEP募集曲线的幅度和斜率未观察到差异。随着右手腕屈曲力量增加，两侧FCR肌肉的MEP幅度均增加，右侧FCR的幅度更大。我们发现在不同条件下左右MEP幅度之间存在显著相关性。与静息状态和10%力量时相比，在70%力量时左右FCR肌肉MEP募集曲线的斜率显著更陡。仅在70%力量时发现左右FCR肌肉MEP幅度斜率之间存在显著相关性。我们的结果表明，在单手力量生成水平增加时，控制左右FCR肌肉的皮质脊髓系统兴奋性存在差异缩放。具体而言，这些数据突出表明，在单手力量较强时，随着TMS刺激强度增加，两个M1s中运动皮层兴奋性的增加遵循相似模式，而在力量较低时则不然。
