Centre for Interdisciplinary Research in Rehabilitation of Greater Montreal, CRIR, Montreal, Canada.
Department of Neuroscience, Université de Montréal, Montreal, Canada.
PLoS One. 2020 Jun 4;15(6):e0233843. doi: 10.1371/journal.pone.0233843. eCollection 2020.
The vestibular system is essential to produce adequate postural responses enabling voluntary movement. However, how the vestibular system influences corticospinal output during postural tasks is still unknown. Here, we examined the modulation exerted by the vestibular system on corticospinal output during standing. Healthy subjects (n = 25) maintained quiet standing, head facing forward with eyes closed. Galvanic vestibular stimulation (GVS) was applied bipolarly and binaurally at different delays prior to transcranial magnetic stimulation (TMS) which triggered motor evoked potentials (MEPs). With the cathode right/anode left configuration, MEPs in right Soleus (SOL) muscle were significantly suppressed when GVS was applied at ISI = 40 and 130ms before TMS. With the anode right/cathode left configuration, no significant changes were observed. Changes in the MEP amplitude were then compared to changes in the ongoing EMG when GVS was applied alone. Only the decrease in MEP amplitude at ISI = 40ms occurred without change in the ongoing EMG, suggesting that modulation occurred at a premotoneuronal level. We further investigated whether vestibular modulation could occur at the motor cortex level by assessing changes in the direct corticospinal pathways using the short-latency facilitation of the SOL Hoffmann reflex (H-reflex) by TMS. None of the observed modulation occurred at the level of motor cortex. Finally, using the long-latency facilitation of the SOL H-reflex, we were able to confirm that the suppression of MEP at ISI = 40ms occurred at a premotoneuronal level. The data indicate that vestibular signals modulate corticospinal output to SOL at both premotoneuronal and motoneuronal levels during standing.
前庭系统对于产生适当的姿势反应以进行自主运动至关重要。然而，前庭系统如何在姿势任务中影响皮质脊髓输出仍然未知。在这里，我们研究了前庭系统在站立时对皮质脊髓输出的调制作用。健康受试者（n = 25）保持安静站立，头朝前，眼睛闭着。在经颅磁刺激（TMS）之前，采用双极和双耳的电前庭刺激（GVS）以不同的延迟施加，该刺激触发运动诱发电位（MEPs）。在阴极右侧/阳极左侧配置下，当 GVS 在 TMS 之前的 ISI = 40 和 130ms 时施加时，右侧比目鱼肌（SOL）的 MEPs 明显受到抑制。在阳极右侧/阴极左侧配置下，未观察到明显变化。然后将 MEP 幅度的变化与 GVS 单独施加时的持续 EMG 变化进行比较。仅在 ISI = 40ms 时观察到 MEP 幅度的降低，而持续 EMG 没有变化，这表明调制发生在运动前神经元水平。我们进一步通过评估 TMS 对 SOL 霍夫曼反射（H-反射）的短潜伏期促进作用来研究前庭调制是否可以在运动皮层水平发生。未观察到任何观察到的调制发生在运动皮层水平。最后，使用 SOL H-反射的长潜伏期促进作用，我们能够证实 ISI = 40ms 时 MEP 的抑制发生在运动前神经元水平。数据表明，前庭信号在站立时通过两种方式调节 SOL 的皮质脊髓输出：运动前神经元和运动神经元水平。
