Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan.
Department of Physical Therapy, School of Rehabilitation Sciences, Health Sciences University of Hokkaido, Tobetsu-cho, Hokkaido, Japan.
J Neurophysiol. 2021 Mar 1;125(3):828-842. doi: 10.1152/jn.00425.2020. Epub 2021 Jan 27.
Modulatory actions of inputs from the visual system to cervical interneurons (IN) for arm muscle control are poorly understood in humans. In the present study, we examined whether visual stimulation modulates the excitation of cervical IN systems mediating corticospinal tract (CST) inputs to biceps brachii (BB). Twenty-eight healthy volunteers were seated, and electromyogram recordings from the BB were performed across six experiments, each with discrete objectives. A flash stimulator for visual stimulation (50-μs duration) was placed 60 cm from the participant's eye. The CST was stimulated with transcranial magnetic/electrical stimulation (TMS/TES, respectively) contralateral to the recording site. Visual stimulation with TMS/TES was randomly delivered during weak tonic BB contractions. Single TMS/TES-induced motor-evoked potentials (MEPs) were markedly enhanced from 60-100 ms after visual stimulation compared with the control condition. The MEPs were significantly increased by combining the electrical stimulation of the ulnar nerve at the wrist [7.5-12 ms of nerve stimulation (NERVE)/TMS interval] with and without visual stimulation compared with the algebraic summation of responses obtained with either TMS or NERVE. Interestingly, the combined stimulation-induced MEP facilitation was significantly increased after visual stimulation compared with the control. Single motor unit (MU) recording also revealed the further enhancement of combined stimulation effects on the firing probabilities of MU during visual stimulation, which was observed in the peaks of the peristimulus time histogram, 1-2 ms later than the onset latency. The present findings suggest that visual stimulation facilitates the oligosynaptic CST excitation of arm motoneurons mediated by the cervical IN system. To date, little is known about how visual information modulates the human cervical motor systems, including the presumed interneuron (IN) circuitry. This study demonstrates that photic visual stimulation influences presumed oligosynaptic corticospinal transmission to arm motoneurons, which are mediated by cervical INs. In animals, these systems are known to be crucial for visually guided switching movements, and similar visual input systems to INs may exist in humans.
视觉系统输入对控制手臂肌肉的颈神经元（IN）的调节作用在人类中知之甚少。在本研究中，我们研究了视觉刺激是否会调节介导皮质脊髓束（CST）传入二头肌（BB）的颈 IN 系统的兴奋。28 名健康志愿者就座，在六个实验中进行了 BB 的肌电图记录，每个实验都有不同的目的。视觉刺激的闪光刺激器（50-μs 持续时间）放置在离参与者眼睛 60cm 的位置。CST 用经颅磁/电刺激（TMS/TES，分别）刺激对侧记录部位。在弱强直性 BB 收缩期间，视觉刺激随机进行 TMS/TES 刺激。与对照条件相比，视觉刺激后 TMS/TES 诱导的单运动诱发电位（MEP）在 60-100ms 时明显增强。与单独 TMS 或 NERVE 相比，在腕部电刺激尺神经[神经刺激（NERVE）/TMS 间隔 7.5-12ms]与视觉刺激相结合时，MEP 显著增加。有趣的是，与对照相比，联合刺激诱导的 MEP 促进作用在视觉刺激后显著增加。单运动单位（MU）记录还显示，在视觉刺激期间，联合刺激对 MU 放电概率的增强作用进一步增强，这在刺激时程直方图的峰中观察到，比起始潜伏期晚 1-2ms。本研究结果表明，视觉刺激促进了由颈 IN 系统介导的手臂运动神经元的少突触 CST 兴奋。到目前为止，人们对视觉信息如何调节包括假定的中间神经元（IN）回路在内的人类颈运动系统知之甚少。本研究表明，光视觉刺激会影响假定的少突触皮质脊髓传入到由颈 IN 介导的臂运动神经元，在动物中，这些系统被认为对视觉引导的切换运动至关重要，并且在人类中可能存在类似的视觉输入系统到 IN。
