Evidence That the Cortical Motor Command for the Initiation of Dynamic Plantarflexion Consists of Excitation followed by Inhibition
Evidence That the Cortical Motor Command for the Initiation of Dynamic Plantarflexion Consists of Excitation followed by Inhibition
复制标题
证据表明，用于启动动态跖屈的皮质运动命令包括兴奋和随后的抑制
作者：
W. Taube;J. Lundbye;M. Schubert;A. Gollhofer;Christian Leukel
在动态运动开始时，运动皮质(M1)的兴奋在空间上仅限于代表受累肌肉的区域，而邻近区域则受到抑制。目前的研究阐明了动态收缩的皮质运动指令是否也局限于负责快速皮质脊髓投射的特定皮质神经元群体。因此，在磁刺激M1和脑干后的动态收缩期间，以高时间分辨率评估皮质脊髓的传递。通过颈髓刺激(CMS)和经颅磁刺激M1(M1条件)，以不同的刺激间隔对比目鱼肌H反射进行调节，可获得较高的时间分辨率。这项技术提供了促进和抑制的精确时间进程。CMS-和M1-条件反射产生了H-反射的“早期促进”，在CMS-条件化的情况下，H-反射发生的时间早了约3ms。早期的易化被认为是由直接单突触投射到脊髓运动神经元的激活引起的。CMS条件反射导致了随后的“晚期促进”，这被认为反映了慢传导和/或间接皮质脊髓通路的活动。相比之下，M1-条件反射产生了一种“迟缓障碍”，甚至“迟缓抑制”。由于晚期的障碍仅见于M1-而不是CMS-条件反射，有人认为，动态任务中的皮质激活仅限于快速、直接的皮质脊髓投射，而负责慢速和/或间接投射皮质脊髓通路的皮质运动神经元受到抑制。将下降的皮质驱动限制在快速的皮质脊髓通路的功能意义可能是确保在动态运动执行期间有一个暂时聚焦的运动指令。
At the onset of dynamic movements excitation of the motor cortex (M1) is spatially restricted to areas representing the involved muscles whereas adjacent areas are inhibited. The current study elucidates whether the cortical motor command for dynamic contractions is also restricted to a certain population of cortical neurons responsible for the fast corticospinal projections. Therefore, corticospinal transmission was assessed with high temporal resolution during dynamic contractions after both, magnetic stimulation over M1 and the brainstem. The high temporal resolution could be obtained by conditioning the soleus H-reflex with different interstimulus intervals by cervicomedullary stimulation (CMS-conditioning) and transcranial magnetic stimulation (TMS) of M1 (M1-conditioning). This technique provides a precise time course of facilitation and inhibition. CMS- and M1-conditioning produced an ‘early facilitation’ of the H-reflex, which occurred around 3 ms earlier with CMS-conditioning. The early facilitation is believed to be caused by activation of direct monosynaptic projections to the spinal motoneurons. CMS-conditioning resulted in a subsequent ‘late facilitation’, which is considered to reflect activity of slow-conducting and/or indirect corticospinal pathways. In contrast, M1-conditioning produced a ‘late dis-facilitation’ or even ‘late inhibition’. As the late dis-facilitation was only seen following M1- but not CMS-conditioning, it is argued that cortical activation during dynamic tasks is restricted to fast, direct corticospinal projections whereas corticomotoneurons responsible for slow and/or indirectly projecting corticospinal pathways are inhibited. The functional significance of restricting the descending cortical drive to fast corticospinal pathways may be to ensure a temporally focused motor command during the execution of dynamic movements.