Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada;
Department of Biomedical Sciences, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, New York;
J Neurophysiol. 2015 Jan 1;113(1):192-202. doi: 10.1152/jn.00339.2014. Epub 2014 Oct 1.
A number of studies have highlighted the sophistication of corrective responses in lengthened muscles during the long-latency epoch. However, in various contexts, unloading can occur, which requires corrective actions from a shortened muscle. Here, we investigate the sophistication of inhibitory responses in shortened muscles due to unloading. Our first experiment quantified the inhibitory responses following an unloading torque that displaced the hand either into or away from a peripheral target. We observed larger long-latency inhibitory responses when perturbed into the peripheral target compared with away from the target. In our second experiment, we characterized the degree of inhibition following unloading with respect to different levels of preperturbation muscle activity. We initially observed that the inhibitory activity during the short-latency epoch scaled with increased levels of preperturbation muscle activity. However, this scaling peaked early in the R2 epoch (∼ 50 ms) but then quickly diminished through the rest of the long-latency epoch. Finally, in experiment 3, we investigated whether inhibitory perturbation responses consider intersegmental dynamics of the limb. We quantified unloading responses for either pure shoulder or pure elbow torques that evoked similar motion at the shoulder but different elbow motion. The long-latency inhibitory response in the shoulder, unlike the short-latency, was greater for the shoulder torque compared with the response following an elbow torque, as previously observed for a loading response. Taken together, these results illustrate that the long-latency unloading response is capable of a similar level of complexity as observed when loads are applied to the limb.
许多研究都强调了在长潜伏期时期，延长肌肉中的矫正反应的复杂性。然而，在各种情况下，可能会发生卸载，这需要缩短的肌肉做出矫正动作。在这里，我们研究了由于卸载而导致缩短的肌肉中的抑制反应的复杂性。我们的第一个实验量化了在手被外力推向或拉离外周目标时，卸载扭矩引起的抑制反应。我们发现，与远离目标相比，当手被推向外周目标时，长潜伏期的抑制反应更大。在第二个实验中，我们根据不同的预扰动肌肉活动水平来描述卸载后的抑制程度。我们最初观察到，在短潜伏期期间，抑制活动与预扰动肌肉活动的水平成正比。然而，这种比例在 R2 时期（约 50 毫秒）早期达到峰值，然后在长潜伏期的其余部分迅速下降。最后，在实验 3 中，我们研究了抑制性扰动反应是否考虑了肢体的节段间动力学。我们对仅引起肩部或仅引起肘部运动的纯肩部或纯肘部扭矩的卸载反应进行了量化，这两种运动在肩部引起相似的运动，但肘部运动不同。与加载反应一样，与肘部扭矩后的反应相比，肩部扭矩的长潜伏期抑制反应（不同于短潜伏期）在肩部更大。总之，这些结果表明，与施加到肢体上的负荷相比，长潜伏期的卸载反应具有相似的复杂程度。
