Jean-Charles Loyda, Nepveu Jean-Francois, Deffeyes Joan E, Elgbeili Guillaume, Dancause Numa, Barthélemy Dorothy
Département de Neurosciences, Faculté de Médecine, Université de Montréal, Montreal, Quebec, Canada.
Centre de recherche interdisciplinaire en réadaptation du Montréal métropolitain, site de l'Institut de réadaptation Gingras-Lindsay-de-Montréal, Montreal, Quebec, Canada.
J Neurophysiol. 2017 Sep 1;118(3):1488-1500. doi: 10.1152/jn.00778.2016. Epub 2017 Jun 14.
Unilateral arm movements require trunk stabilization through bilateral contraction of axial muscles. Interhemispheric interactions between primary motor cortices (M1) could enable such coordinated contractions, but these mechanisms are largely unknown. Using transcranial magnetic stimulation (TMS), we characterized interhemispheric interactions between M1 representations of the trunk-stabilizing muscles erector spinae at the first lumbar vertebra (ES L1) during a right isometric shoulder flexion. These interactions were compared with those of the anterior deltoid (AD), the main agonist in this task, and the first dorsal interosseous (FDI). TMS over the right M1 elicited ipsilateral silent periods (iSP) in all three muscles on the right side. In ES L1, but not in AD or FDI, ipsilateral motor evoked potential (iMEP) could precede the iSP or replace it. iMEP amplitude was not significantly different whether ES L1 was used to stabilize the trunk or was voluntarily contracted. TMS at the cervicomedullary junction showed that the size of cervicomedullary evoked potential was unchanged during the iSP but increased during iMEP, suggesting that the iSP, but not the iMEP, is due to intracortical mechanisms. Using a dual-coil paradigm with two coils over the left and right M1, interhemispheric inhibition could be evoked at interstimulus intervals of 6 ms in ES L1 and 8 ms in AD and FDI. Together, these results suggest that interhemispheric inhibition is dominant when axial muscles are involved in a stabilizing task. The ipsilateral facilitation could be evoked by ipsilateral or subcortical pathways and could be used depending on the role axial muscles play in the task. The mechanisms involved in the bilateral coordination of axial muscles during unilateral arm movement are poorly understood. We thus investigated the nature of interhemispheric interactions in axial muscles during arm motor tasks in healthy subjects. By combining different methodologies, we showed that trunk muscles receive both inhibitory and facilitatory cortical outputs during activation of arm muscles. We propose that inhibition may be conveyed mainly through interhemispheric mechanisms and facilitation by subcortical mechanisms or ipsilateral pathways.
单侧手臂运动需要通过轴性肌肉的双侧收缩来实现躯干稳定。初级运动皮层（M1）之间的半球间相互作用可能促成这种协同收缩，但这些机制在很大程度上尚不清楚。我们使用经颅磁刺激（TMS），对在右侧等长肩部屈曲过程中，第一腰椎竖脊肌（ES L1）这一躯干稳定肌肉的M1代表区之间的半球间相互作用进行了表征。将这些相互作用与三角肌前部（AD）（此任务中的主要主动肌）以及第一背侧骨间肌（FDI）的相互作用进行了比较。对右侧M1施加TMS会在右侧所有三块肌肉中引发同侧静息期（iSP）。在ES L1中，但在AD或FDI中并非如此，同侧运动诱发电位（iMEP）可能先于iSP出现或替代iSP。无论ES L1是用于稳定躯干还是自主收缩，iMEP幅度均无显著差异。在颈髓交界处施加TMS表明，颈髓诱发电位的大小在iSP期间保持不变，但在iMEP期间增大，这表明iSP而非iMEP是由皮质内机制引起的。使用双线圈范式，在左右M1上方各放置一个线圈，在ES L1中，当刺激间隔为6毫秒时可诱发半球间抑制，在AD和FDI中，当刺激间隔为8毫秒时可诱发半球间抑制。总之，这些结果表明，当轴性肌肉参与稳定任务时，半球间抑制占主导。同侧易化可由同侧或皮质下通路诱发，并可根据轴性肌肉在任务中所起的作用而被利用。在单侧手臂运动过程中，轴性肌肉双侧协调所涉及的机制尚不清楚。因此，我们研究了健康受试者在手臂运动任务期间轴性肌肉半球间相互作用的性质。通过结合不同方法，我们发现，在手臂肌肉激活期间，躯干肌肉会接收抑制性和易化性皮质输出。我们提出，抑制可能主要通过半球间机制传递，而易化则通过皮质下机制或同侧通路传递。
