Rodriguez-Falces Javier, Negro Francesco, Farina Dario
Department of Electrical and Electronic Engineering, Public University of Navarra, Pamplona, Spain;
Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy; and.
J Neurophysiol. 2017 Apr 1;117(4):1749-1760. doi: 10.1152/jn.00497.2016. Epub 2017 Jan 18.
We investigated whether correlation measures derived from pairs of motor unit (MU) spike trains are reliable indicators of the degree of common synaptic input to motor neurons. Several 50-s isometric contractions of the biceps brachii muscle were performed at different target forces ranging from 10 to 30% of the maximal voluntary contraction relying on force feedback. Forty-eight pairs of MUs were examined at various force levels. Motor unit synchrony was assessed by cross-correlation analysis using three indexes: the output correlation as the peak of the cross-histogram (ρ) and the number of synchronous spikes per second (CIS) and per trigger (E). Individual analysis of MU pairs revealed that ρ, CIS, and E were most often positively associated with discharge rate (87, 85, and 76% of the MU pairs, respectively) and negatively with interspike interval variability (69, 65, and 62% of the MU pairs, respectively). Moreover, the behavior of synchronization indexes with discharge rate (and interspike interval variability) varied greatly among the MU pairs. These results were consistent with theoretical predictions, which showed that the output correlation between pairs of spike trains depends on the statistics of the input current and motor neuron intrinsic properties that differ for different motor neuron pairs. In conclusion, the synchronization between MU firing trains is necessarily caused by the (functional) common input to motor neurons, but it is not possible to infer the degree of shared common input to a pair of motor neurons on the basis of correlation measures of their output spike trains. The strength of correlation between output spike trains is only poorly associated with the degree of common input to the population of motor neurons. The synchronization between motor unit firing trains is necessarily caused by the (functional) common input to motor neurons, but it is not possible to infer the degree of shared common input to a pair of motor neurons on the basis of correlation measures of their output spike trains.
我们研究了源自运动单位（MU）动作电位序列对的相关性测量指标是否是运动神经元共同突触输入程度的可靠指标。依靠力反馈，在肱二头肌上进行了几次持续50秒的等长收缩，收缩目标力范围为最大自主收缩的10%至30%。在不同力水平下检查了48对运动单位。使用三个指标通过互相关分析评估运动单位同步性：作为交叉直方图峰值的输出相关性（ρ）、每秒同步动作电位的数量（CIS）和每次触发的同步动作电位数量（E）。对运动单位对的个体分析表明，ρ、CIS和E最常与放电率呈正相关（分别为87%、85%和76%的运动单位对），与动作电位间隔变异性呈负相关（分别为69%、65%和62%的运动单位对）。此外，同步指标与放电率（以及动作电位间隔变异性）之间的关系在不同运动单位对之间差异很大。这些结果与理论预测一致，理论预测表明动作电位序列对之间的输出相关性取决于输入电流的统计特性以及不同运动神经元对不同的运动神经元内在特性。总之，运动单位放电序列之间的同步必然是由运动神经元的（功能性）共同输入引起的，但不可能根据其输出动作电位序列的相关性测量来推断一对运动神经元共享的共同输入程度。输出动作电位序列之间的相关强度与运动神经元群体的共同输入程度仅存在较弱的关联。运动单位放电序列之间的同步必然是由运动神经元的（功能性）共同输入引起的，但不可能根据其输出动作电位序列的相关性测量来推断一对运动神经元共享的共同输入程度。
