Castronovo Anna Margherita, Mrachacz-Kersting Natalie, Stevenson Andrew James Thomas, Holobar Ales, Enoka Roger Maro, Farina Dario
Department of Bioengineering, Imperial College London , London , United Kingdom.
Department of Health Science and Technology, Aalborg University , Aalborg , Denmark.
J Neurophysiol. 2018 Oct 1;120(4):1616-1624. doi: 10.1152/jn.00093.2018. Epub 2018 Jul 5.
Declines in motor function with advancing age have been attributed to changes occurring at all levels of the neuromuscular system. However, the impact of aging on the control of muscle force by spinal motor neurons is not yet understood. In this study on 20 individuals aged between 24 and 75 yr (13 men, 7 women), we investigated the common synaptic input to motor neurons of the tibialis anterior muscle and its impact on force control. Motor unit discharge times were identified from high-density surface EMG recordings during isometric contractions at forces of 20% of maximal voluntary effort. Coherence analysis between motor unit spike trains was used to characterize the input to motor neurons. The decrease in force steadiness with age ( R = 0.6, P < 0.01) was associated with an increase in the amplitude of low-frequency oscillations of functional common synaptic input to motor neurons ( R = 0.59; P < 0.01). The relative proportion of common input to independent noise at low frequencies increased with variability (power) in common synaptic input. Moreover, variability in interspike interval did not change and strength of the common input in the gamma band decreased with age ( R = 0.22; P < 0.01). The findings indicate that age-related reduction in the accuracy of force control is associated with increased common fluctuations to motor neurons at low frequencies and not with an increase in independent synaptic input. NEW & NOTEWORTHY The influence of aging on the role of spinal motor neurons in accurate force control is not yet understood. We demonstrate that aging is associated with increased oscillations in common input to motor neurons at low frequencies and with a decrease in the relative strength of gamma oscillations. These results demonstrate that the synaptic inputs to motor neurons change across the life span and contribute to a decline in force control.
随着年龄增长，运动功能下降被认为是神经肌肉系统各级发生变化所致。然而，衰老对脊髓运动神经元控制肌肉力量的影响尚不清楚。在这项针对20名年龄在24至75岁之间的个体（13名男性，7名女性）的研究中，我们调查了胫前肌运动神经元的共同突触输入及其对力量控制的影响。在等长收缩过程中，以最大自主努力的20%的力量，从高密度表面肌电图记录中识别运动单位放电时间。运动单位放电序列之间的相干分析用于表征运动神经元的输入。随着年龄增长，力量稳定性下降（R = 0.6，P < 0.01）与运动神经元功能性共同突触输入的低频振荡幅度增加有关（R = 0.59；P < 0.01）。低频下共同输入相对于独立噪声的相对比例随共同突触输入的变异性（功率）增加而增加。此外，峰间期的变异性没有变化，γ波段共同输入的强度随年龄下降（R = 0.22；P < 0.01）。研究结果表明，与年龄相关的力量控制准确性降低与运动神经元低频下共同波动增加有关，而与独立突触输入增加无关。新发现与值得注意之处衰老对脊髓运动神经元在精确力量控制中作用的影响尚不清楚。我们证明，衰老与运动神经元共同输入的低频振荡增加以及γ振荡相对强度降低有关。这些结果表明，运动神经元的突触输入在整个生命周期中发生变化，并导致力量控制下降。
