College of Sports Sciences, Nihon University, Setagaya, Tokyo 154-8513, Japan; Neural Prosthetics Project, Department of Brain and Neuroscience, Tokyo Metropolitan Institute of Medical Science, Setagaya, Tokyo 156-8506, Japan; Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama 359-1192, Japan.
Neural Prosthetics Project, Department of Brain and Neuroscience, Tokyo Metropolitan Institute of Medical Science, Setagaya, Tokyo 156-8506, Japan.
Neurosci Res. 2024 Mar;200:20-27. doi: 10.1016/j.neures.2023.10.001. Epub 2023 Oct 2.
Noninvasive spinal stimulation has been increasingly used in research on motor control and neurorehabilitation. Despite advances in percutaneous electrical stimulation techniques, magnetic stimulation is not as commonly used as electrical stimulation. Therefore, it is still under discussion what neuronal elements are activated by magnetic stimulation of the human spinal cord. In this study, we demonstrated that transvertebral magnetic stimulation (TVMS) induced transsynaptic activation of spinal motoneuron pools in the lumbar cord. In healthy humans, paired-pulse TVMS was given over an intervertebral space between the L1-L2 vertebrae with an interpulse interval of 100 ms, and the stimulus-evoked electromyographic (EMG) responses were recorded in the lower limb muscles. The results show that the evoked EMG responses after the 2nd pulse were clearly suppressed compared with the widespread responses evoked after the 1st pulse in the muscles of the lower extremity, indicating that the transsynaptic activation of spinal motoneurons by the 2nd pulse was suppressed by the effects produced by the 1st pulse. The inconsistent modulation of response suppression to stimulus intensity across individuals suggests that the TVMS-evoked EMG responses are composed of the compound potentials mediated by the direct activation of motor axons and the transsynaptic activation of motoneuron pools through sensory afferents and that the recruitment order of those fibers by TVMS may be nonhomogeneous across individuals.
经皮电刺激技术虽已取得进步，但磁刺激的应用并不像电刺激那样普遍。因此，磁刺激能否激活人类脊髓的神经元仍存在争议。在这项研究中，我们证明了经椎间孔磁刺激（TVMS）可诱导脊髓运动神经元池的突触传递性激活。在健康人群中，采用 100 毫秒的双脉冲间隔，在 L1-L2 椎骨之间的椎间空间给予双脉冲 TVMS，在下肢体肌中记录刺激诱发的肌电图（EMG）反应。结果表明，与第 1 脉冲引起的广泛反应相比，第 2 脉冲后的诱发 EMG 反应明显受到抑制，表明第 2 脉冲对脊髓运动神经元的突触传递性激活受到第 1 脉冲产生的影响的抑制。个体之间对刺激强度的反应抑制的不一致调制表明，TVMS 诱发的 EMG 反应是由直接激活运动轴突介导的复合电位和通过感觉传入的脊髓运动神经元池的突触传递性激活组成的，并且这些纤维通过 TVMS 的募集顺序可能在个体之间是不均匀的。
