Mochizuki G, Ivanova T D, Garland S J
Graduate Program in Neuroscience, University of Western Ontario, London, ON N6G 1H1, Canada.
J Neurophysiol. 2007 Jun;97(6):3917-25. doi: 10.1152/jn.01025.2006. Epub 2007 Apr 4.
The purpose of this study was to determine the factors that influence the co-modulation of motor unit discharge rate in soleus muscles of both legs during upright standing. Single motor units were recorded from the left and right soleus muscles under three experimental conditions: standing quietly with the eyes open and closed, standing with the eyes closed while vibration was applied to one Achilles tendon, and swaying voluntarily or producing variable low-force isometric contractions at a frequency of 0.05 Hz. Correlations in motor unit discharge rate between left and right soleus motor units were assessed using common drive analysis. The results showed that common drive to motoneurons of the two muscles did not differ between standing with the eyes open or closed, but there was an order effect with the second task having significantly lower common drive than the first. Common drive was also significantly lower when vibration was applied to one leg compared with when no vibration was applied. Common drive was higher as subjects swayed anteriorly as compared with when they swayed posteriorly. There were no significant differences in common drive across phases of the variable isometric force contraction. Common drive was higher during voluntary sway than during variable force production; both of these values were significantly lower than those derived from the quiet standing task. These results suggest that proprioceptive and sub-cortical inputs contribute to the co-modulation of the firing rate of soleus motor unit pairs of the left and right leg during standing posture.
本研究的目的是确定在直立站立过程中影响双腿比目鱼肌运动单位放电率共同调制的因素。在三种实验条件下记录左右比目鱼肌的单个运动单位：睁眼和闭眼安静站立、闭眼站立同时对一侧跟腱施加振动，以及以0.05Hz的频率自主摆动或进行可变低力等长收缩。使用共同驱动分析评估左右比目鱼肌运动单位之间运动单位放电率的相关性。结果表明，睁眼或闭眼站立时，两块肌肉运动神经元的共同驱动没有差异，但存在顺序效应，第二项任务的共同驱动明显低于第一项。与不施加振动时相比，对一侧腿施加振动时共同驱动也显著降低。与向后摆动相比，受试者向前摆动时共同驱动更高。在可变等长力收缩的各阶段，共同驱动没有显著差异。自主摆动期间的共同驱动高于可变力产生期间；这两个值均显著低于安静站立任务中的值。这些结果表明，本体感觉和皮层下输入有助于站立姿势期间左右腿比目鱼肌运动单位对放电率的共同调制。
