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 to 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 peri-stimulus 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.

中文翻译：

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视觉信息通过人类颈部中间神经元增加间接皮质脊髓兴奋

从视觉系统到颈部中间神经元 (IN) 用于手臂肌肉控制的输入的调节作用在人类中知之甚少。在本研究中，我们检查了视觉刺激是否调节介导皮质脊髓束 (CST) 输入到肱二头肌 (BB) 的颈椎 IN 系统的激发。28 名健康志愿者坐下，在六个实验中进行来自 BB 的肌电图记录，每个实验都有不同的目标。用于视觉刺激的闪光刺激器（持续时间为 50 微秒）放置在距离参与者眼睛 60 厘米处。CST 用经颅磁/电刺激（分别为 TMS/TES）刺激记录部位的对侧。在弱强直 BB 收缩期间随机传递 TMS/TES 视觉刺激。与对照条件相比，视觉刺激后 60-100 毫秒，单个 TMS/TES 诱导的运动诱发电位 (MEP) 显着增强。与使用 TMS 或 NERVE 获得的响应的代数总和相比，通过将腕部尺神经电刺激 [7.5-12 ms 的神经刺激 (NERVE)/TMS 间隔] 与视觉刺激相结合，MEP 显着增加. 有趣的是，与对照相比，视觉刺激后联合刺激诱导的 MEP 促进显着增加。单运动单元 (MU) 记录还揭示了在视觉刺激期间联合刺激对 MU 发射概率的进一步增强，这在刺激周围时间直方图的峰值中观察到，比开始潜伏期晚 1-2 毫秒。