Semmler J G, Nordstrom M A, Wallace C J
Department of Physiology, University of Adelaide, Australia.
Brain Res. 1997 Sep 5;767(2):314-20. doi: 10.1016/s0006-8993(97)00621-5.
We assessed the strength of motor unit (MU) short-term synchronization and common fluctuations in mean firing rate (common drive) in the same pairs of MUs in order to evaluate whether these features of voluntary MU discharge arise from a common mechanism. Shared, branched-axon inputs, with the most important being widely divergent monosynaptic projections to motoneurons from motor cortical cells, are regarded as the principal determinants of MU short-term synchronization. It is not known to what extent these synaptic inputs are responsible for common drive behaviour of MUs. MU spike trains from 77 pairs of concurrently active MUs in first dorsal interosseous muscle of 17 subjects were discriminated with the high reliability needed for common drive analysis. For each MU pair, the data used for comparison of the two analyses of correlated MU discharge came from a single trial (1-5 min duration) of isometric abduction of the index finger. Linear regression revealed a weak, significant positive correlation between the strength of MU short-term synchronization and the strength of common drive in the MU pairs (r2 = 0.06, P < 0.05, n = 77), which was slightly stronger when MU pairs with broad synchronous peaks (> 20 ms) were excluded (r2 = 0.09, P < 0.05, n = 63). These data suggest that less than 10% of the variation in the strength of common drive exhibited by pairs of MUs could be accounted for by differences in the strength of MU short-term synchronization. These two phenomena are therefore likely to arise predominantly from separate mechanisms. At least under these task conditions, the widely divergent, branched-axon inputs from single corticospinal neurons which are important in the generation of MU short-term synchronization play only a minor role in the production of common drive of MU discharge rates.
我们评估了运动单位（MU）短期同步性的强度以及同一对运动单位平均放电频率的共同波动（共同驱动），以评估这些自主运动单位放电特征是否源于共同机制。共享的、分支轴突输入，其中最重要的是运动皮层细胞向运动神经元广泛发散的单突触投射，被视为运动单位短期同步性的主要决定因素。目前尚不清楚这些突触输入在多大程度上导致运动单位的共同驱动行为。从17名受试者第一背侧骨间肌中77对同时活跃的运动单位的动作电位序列中进行辨别，以获得共同驱动分析所需的高可靠性。对于每对运动单位，用于比较相关运动单位放电的两种分析的数据来自食指等长外展的单次试验（持续1 - 5分钟）。线性回归显示，运动单位对中运动单位短期同步性强度与共同驱动强度之间存在微弱但显著的正相关（r2 = 0.06，P < 0.05，n = 77），当排除具有宽同步峰值（> 20毫秒）的运动单位对时，这种相关性略强（r2 = 0.09，P < 0.05，n = 63）。这些数据表明，运动单位对所表现出的共同驱动强度变化中，不到10%可由运动单位短期同步性强度的差异来解释。因此，这两种现象可能主要源于不同的机制。至少在这些任务条件下，来自单个皮质脊髓神经元的广泛发散的分支轴突输入在运动单位短期同步性产生中起重要作用，但在运动单位放电率共同驱动的产生中仅起次要作用。
