Selective Activation of Ipsilateral Motor Pathways in Intact Humans
Selective Activation of Ipsilateral Motor Pathways in Intact Humans
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DOI：
10.1523/jneurosci.1648-14.2014
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发表时间：
2014-10-15
影响因子：
5.3
通讯作者：
Perez, Monica A.
中科院分区：
文献类型：
--
作者：
Tazoe, Toshiki;Perez, Monica A.
有研究认为，同侧运动通路在控制同侧运动和损伤后功能恢复中发挥作用。然而，同侧运动通路在多大程度上参与了完好无损的人类的自愿活动在很大程度上仍不清楚。利用经颅磁刺激对手臂初级运动皮质的表征，我们检测了坐位单侧和双侧等长力增加时，同侧手臂近端肌肉的运动诱发电位(IMEPs)。我们发现，与单侧收缩相比，同名(肘屈肌)双侧收缩时IMEP的面积和幅度减小，而异名(肘屈肌和伸肌)的双侧收缩时IMEP的面积和幅度增加，与测试的力量大小无关。为了进一步了解参与双侧效应的神经元输入，我们研究了颈部传入投射到同侧运动通路的贡献。头部内侧(远离受试者肌肉)和外侧(朝向受试者肌肉)旋转分别增强了同名和异名肌肉的双侧IMEP效应。相反，头部屈曲和伸展对iMEP产生非特异性的双侧效应。在iMEPs起源的运动皮质中，皮质内抑制显示出与iMEPs变化相容的调制。我们的结论是，对侧臂肌肉的自主收缩可以选择性地调节同侧臂近端肌肉的投射，这可能涉及到至少部分作用于皮质水平的非对称紧张性颈部反射的回路。双边动作的模式可能代表了一种使同侧运动通路参与运动行为的策略。
It has been proposed that ipsilateral motor pathways play a role in the control of ipsilateral movements and recovery of function after injury. However, the extent to which ipsilateral motor pathways are engaged in voluntary activity in intact humans remains largely unknown. Using transcranial magnetic stimulation over the arm representation of the primary motor cortex, we examined ipsilateral motor-evoked potentials (iMEPs) in a proximal arm muscle during increasing levels of unilateral and bilateral isometric force in a sitting position. We demonstrate that iMEP area and amplitude decreased during bilateral contraction of homonymous (elbow flexor) muscles and increased during bilateral contraction of heteronymous (elbow flexor and extensor) muscles compared with a unilateral contraction, regardless of the level of force tested. To further understand the neuronal inputs involved in the bilateral effects, we examined the contribution from neck afferents projecting onto ipsilateral motor pathways. Medial (away from the muscle tested) and lateral (toward the muscle tested) rotation of the head enhanced bilateral iMEP effects from homonymous and heteronymous muscles, respectively. In contrast, head flexion and extension exerted nonspecific bilateral effects on iMEPs. Intracortical inhibition, in the motor cortex where iMEPs originated, showed modulation compatible with the changes in iMEPs. We conclude that ipsilateral projections to proximal arm muscles can be selectively modulated by voluntary contraction of contralateral arm muscles, likely involving circuits mediating asymmetric tonic neck reflexes acting, at least in part, at the cortical level. The pattern of bilateral actions may represent a strategy to engage ipsilateral motor pathways in a motor behavior.