Department of Human Health and Nutritional Services, University of Guelph, Guelph, Canada.
Exp Brain Res. 2013 Jun;227(2):175-83. doi: 10.1007/s00221-013-3497-1. Epub 2013 Apr 4.
We previously showed that sinusoidal galvanic vestibular stimulation (GVS) does not modulate the firing of spontaneously active muscle spindles in relaxed human leg muscles. However, given that there is little, if any, fusimotor drive to relaxed human muscles, we tested the hypothesis that vestibular modulation of muscle spindles becomes apparent during volitional contractions at levels that engage the fusimotor system. Unitary recordings were made from 28 muscle spindle afferents via tungsten microelectrodes inserted percutaneously into the common peroneal nerve of seated awake human subjects. Twenty-one of the spindle afferents were spontaneously active at rest and each increased its firing rate during a weak static contraction; seven were silent at rest and were recruited during the contraction. Sinusoidal bipolar binaural galvanic vestibular stimulation (±2 mA, 100 cycles) was applied to the mastoid processes at 0.8 Hz. This continuous stimulation produced a sustained illusion of "rocking in a boat" or "swinging in a hammock" but no entrainment of EMG. Despite these robust vestibular illusions, none of the fusimotor-driven muscle spindles exhibited phase-locked modulation of firing during sinusoidal GVS. We conclude that this dynamic vestibular input was not sufficient to modulate the firing of fusimotor neurones recruited during a voluntary steady-state contraction, arguing against a significant role of the vestibular system in adjusting the sensitivity of muscle spindles via fusimotor neurones.
我们之前曾表明，正弦电流前庭刺激（GVS）不会调制松弛状态下人腿肌肉中自发活跃的肌梭的放电。然而，鉴于松弛状态下的肌肉几乎没有，如果有的话，梭内驱动，我们测试了这样一个假设，即前庭对肌梭的调制在参与梭内驱动系统的随意收缩水平下变得明显。通过经皮插入坐骨神经的钨微电极从 28 个肌梭传入纤维进行单元记录。在休息时，21 个梭内传入纤维自发活跃，每个纤维在弱静态收缩期间增加其放电率；7 个在休息时处于静息状态，在收缩期间被募集。正弦双极双耳电流前庭刺激（±2 mA，100 个周期）以 0.8 Hz 的频率施加于耳廓。这种连续刺激产生了持续的“乘船摇晃”或“吊床上摇摆”的幻觉，但没有肌电图的同步。尽管存在这些强烈的前庭错觉，但在正弦 GVS 期间，没有一个由梭内驱动的肌梭表现出放电的相位锁定调制。我们得出结论，这种动态前庭输入不足以调制在自愿稳态收缩期间募集的梭内神经元的放电，这表明前庭系统通过梭内神经元调节肌梭敏感性的作用不大。
