Interactions between neural and muscle systems during the early stage of motor learning

本研究探讨了视觉引导力跟踪性能短期改善的可能神经肌肉机制。18名健康志愿者在视觉引导的力跟踪条件下用食指外展（5%MVC，1%MVC/秒）进行缓慢斜坡收缩。第一骨间肌（FDI）的肌电图（EMG）活动量随着试验次数的增加而逐渐减少。相反，经颅磁刺激（TMS）引起的运动诱发电位（MEP）的幅度没有显示出显着的变化。用一对肌内电极记录的单个运动单位（MU）活动的调查表明，在30个MU中有51个MU单位的阈值力（F-th）随着试验次数的增加而逐渐增加。在2 MU中检测到单个MU的F-th显著降低。有没有系统的变化，在射击频率的MU，这表明在F-th在电机task. To确定可能的变化在肌肉力量生产机制的增加，在抽搐力的变化进行了评估，由尖峰触发的平均技术。在11个MU中，有26个在运动任务后比对照条件下增加了20%以上的抽搐力。无论是H反射的大小，也没有皮肤反射后的运动任务相比，以前的显着变化。这些结果表明，减少的数量recuited MU和增强的肌纤维可能在性能的改善中发挥至关重要的作用。这可能是因为大脑有效地检索有关运动任务中涉及的肌肉的并发变化的信息，然后重新组织运动程序，以便优化关于肌肉特性的下降运动输出。

The present study investigated possible neuromuscular mechanisms underlying short-term improvement of visually-guided force tracking performance. Eighteen healthy volunteers performed slow ramp contractions with index finger abduction (5 % MVC,1 % MVC/sec) under a visually-guided force tracking condition. The amount of electromyographic(EMG) activity in the first interosseus muscle(FDI) showed a gradual decrease with the increasing trial number. In contrast, the magnitude of the motor evoked potential(MEP) elicited by trascranial magnetic stimulation(TMS) did not show a significant change. Investigation of single motor unit(MU) activity recorded with a pair of intramuscular electrodes demonstrated that in 51 of 30 MUs threshold force (F-th) of the MU unit progressively increased with the increasing trial number. A significant decrease in F-th of single MU was detected in 2 MU. There were no systematic changes in the firing rate of MUs which showed an increase in the F-th during the motor task was found. To determine possible changes in muscular force producing mechanisms, changes in the twitch force of single MU was assessed by a spike-triggered averaging technique. In twenty-six of eleven MUs, the twitch force increased more than 20 % after the motor task compared to that under the control condition. Neither the magnitude of H-reflex nor cutaneous reflexes showed a significant change after the motor task compared to those before. These findings suggest that a decrease in number of recuited MUs and potentiation of muscle fibers could play a crucial role in improvement of the performance. It may be that the brain effectively retrieves information concerning concurrent changes in the muscle involved in the motor task, then re-organize the motor program in order to optimize the descending motor output regarding the properties of the muscles.