Tazoe Toshiki, Perez Monica A
Department of Physical Medicine and Rehabilitation, Center for the Neural Basis of Cognition, Systems Neuroscience Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
Department of Physical Medicine and Rehabilitation, Center for the Neural Basis of Cognition, Systems Neuroscience Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
J Neurosci. 2014 Oct 15;34(42):13924-34. doi: 10.1523/JNEUROSCI.1648-14.2014.
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.
有人提出，同侧运动通路在损伤后同侧运动的控制和功能恢复中发挥作用。然而，在完整人体中，同侧运动通路参与自主活动的程度在很大程度上仍不清楚。我们通过对初级运动皮层的手臂代表区进行经颅磁刺激，在坐位下逐渐增加单侧和双侧等长力的过程中，检测近端手臂肌肉中的同侧运动诱发电位（iMEP）。我们证明，与单侧收缩相比，同名（肘屈肌）肌肉双侧收缩时iMEP面积和波幅减小，而异名（肘屈肌和伸肌）肌肉双侧收缩时iMEP面积和波幅增加，无论测试的力水平如何。为了进一步了解双侧效应所涉及的神经元输入，我们研究了投射到同侧运动通路上的颈部传入神经的作用。头部向内侧（远离测试肌肉）和外侧（朝向测试肌肉）旋转分别增强了同名和异名肌肉的双侧iMEP效应。相比之下，头部屈伸对iMEP产生非特异性双侧效应。iMEP起源的运动皮层内的皮质抑制表现出与iMEP变化相匹配的调制。我们得出结论，对近端手臂肌肉的同侧投射可通过对侧手臂肌肉的自主收缩进行选择性调节，这可能涉及介导不对称紧张性颈反射的回路，至少部分作用于皮层水平。双侧作用模式可能代表了一种在运动行为中激活同侧运动通路的策略。
