目标:所有运动指令都流经运动神经元,控制它们神经支配的肌肉纤维,形成电机单元(MU)。由于MU内动作电位的高保真度,它们的放电曲线详细说明了对运动神经元的离子型兴奋/抑制以及代谢型神经调节命令的组织。神经调节输入(例如,去甲肾上腺素,血清素)增强运动神经元的兴奋性并促进持续的内向电流(PIC)。PIC通过在激活时增加去极化电流,在MU放电曲线中引入可量化的特性(即,PIC放大)并在低于招募所需的兴奋性输入水平下促进放电(即,PIC延长)。
方法:这里,我们引入了一种新的几何方法,通过在时变线性任务期间利用PIC放大引入的放电非线性来估计MU放电的神经调节和抑制贡献.具体而言,我们量化了与线性放电(“支撑高度”)的偏差和放电变化率(即,加速度斜率,衰减斜率,angle).我们在具有已知兴奋性的模拟运动神经元池上进一步表征了这些指标,抑制性,和神经调节输入和人MU(MU数量;胫骨前肌:1448,内侧腓肠肌:2100,比目鱼:1062,第一背侧骨间:2296)。
结果:在模拟电机池中,我们发现支撑高度和衰减斜率一致地表明神经调节和抑制模式(兴奋-抑制耦合)的变化,分别,而配对MU分析(ΔF)依赖于神经调节和抑制模式。此外,我们提供了人类MU中这些指标的估计值,并显示了在多个试验中匹配的MU的ΔF和支架高度测量的可比变异性。
结论:跨越两个数据集,我们发现支架高度量化为实现对单个MU的神经调节和抑制驱动的分级估计提供了一种直观的方法.这补充了常见的技术,并为神经调节水平和抑制性运动命令模式的解耦变化提供了途径。
Objective.All motor commands flow through motoneurons, which entrain control of their innervated muscle fibers, forming a motor unit (MU). Owing to the high fidelity of action potentials within MUs, their discharge profiles detail the organization of ionotropic excitatory/inhibitory as well as metabotropic neuromodulatory commands to motoneurons. Neuromodulatory inputs (e.g. norepinephrine, serotonin) enhance motoneuron excitability and facilitate persistent inward currents (PICs). PICs introduce quantifiable properties in MU discharge profiles by augmenting depolarizing currents upon activation (i.e. PIC amplification) and facilitating discharge at lower levels of excitatory input than required for recruitment (i.e. PIC prolongation).Approach. Here, we introduce a novel geometric approach to estimate neuromodulatory and inhibitory contributions to MU discharge by exploiting discharge non-linearities introduced by PIC amplification during time-varying linear tasks. In specific, we quantify the deviation from linear discharge (\'brace height\') and the rate of change in discharge (i.e. acceleration slope, attenuation slope, angle). We further characterize these metrics on a simulated motoneuron pool with known excitatory, inhibitory, and neuromodulatory inputs and on human MUs (number of MUs; Tibialis Anterior: 1448, Medial Gastrocnemius: 2100, Soleus: 1062, First Dorsal Interosseus: 2296).Main results. In the simulated motor pool, we found brace height and attenuation slope to consistently indicate changes in neuromodulation and the pattern of inhibition (excitation-inhibition coupling), respectively, whereas the paired MU analysis (ΔF) was dependent on both neuromodulation and inhibition pattern. Furthermore, we provide estimates of these metrics in human MUs and show comparable variability in ΔFand brace height measures for MUs matched across multiple trials.Significance. Spanning both datasets, we found brace height quantification to provide an intuitive method for achieving graded estimates of neuromodulatory and inhibitory drive to individual MUs. This complements common techniques and provides an avenue for decoupling changes in the level of neuromodulatory and pattern of inhibitory motor commands.