Département de Physiologie, Université de Montréal; Centre for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital,Laval, PQ, Canada.
Département de Physiologie, Université de Montréal; Centre for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital,Laval, PQ, Canada.
Behav Brain Res. 2013 Jan 1;236(1):350-358. doi: 10.1016/j.bbr.2012.09.008. Epub 2012 Sep 13.
The difference between voluntary and involuntary motor actions has been recognized since ancient times, but the nature of this difference remains unclear. We compared corticospinal influences at wrist positions established before and after voluntary motion with those established before and after involuntary motion elicited by sudden removal of a load (the unloading reflex). To minimize the effect of motoneuronal excitability on the evaluation of corticospinal influences, motor potentials from transcranial magnetic stimulation of the wrist motor cortex area were evoked during an EMG silent period produced by brief muscle shortening. The motoneuronal excitability was thus equalized at different wrist positions. Results showed that the unloading reflex was generated in the presence of a corticospinal drive, rather than autonomously by the spinal cord. Although the tonic EMG levels were substantially different, the corticospinal influences remained the same at the pre- and post-unloading wrist positions. These influences however changed when subjects voluntarily moved the wrist to another position. Previous studies showed that the corticospinal system sets the referent position (R) at which neuromuscular posture-stabilizing mechanisms begin to act. In self-initiated actions, the corticospinal system shifts the R to relay these mechanisms to a new posture, thus converting them from mechanisms resisting to those assisting motion. This solves the classical posture-movement problem. In contrast, by maintaining the R value constant, the corticospinal system relies on these posture-stabilizing mechanisms to allow involuntary responses to occur after unloading. Thus, central control strategies underlying the two types of motor actions are fundamentally different.
自愿运动和非自愿运动之间的区别自古以来就被人们所认识，但这种区别的本质仍不清楚。我们比较了在自愿运动前后以及在突然卸去负荷（卸荷反射）引起的非自愿运动前后建立的手腕位置的皮质脊髓影响。为了尽量减少运动神经元兴奋性对皮质脊髓影响评估的影响，在短暂肌肉缩短产生的肌电静默期期间，通过经颅磁刺激手腕运动皮质区域来诱发运动电位。因此，在不同的手腕位置上使运动神经元兴奋性均等。结果表明，卸荷反射是在皮质脊髓驱动存在的情况下产生的，而不是由脊髓自主产生的。尽管紧张性肌电图水平有很大差异，但在卸荷前后的手腕位置上，皮质脊髓的影响保持不变。然而，当受试者自愿将手腕移动到另一个位置时，这些影响发生了变化。先前的研究表明，皮质脊髓系统设定了参考位置（R），神经肌肉姿势稳定机制开始在此处发挥作用。在自我发起的动作中，皮质脊髓系统将 R 转移，将这些机制转移到新的姿势，从而将它们从抵抗运动的机制转换为辅助运动的机制。这解决了经典的姿势-运动问题。相比之下，通过保持 R 值不变，皮质脊髓系统依赖于这些姿势稳定机制，以便在卸荷后允许发生非自愿反应。因此，两种运动动作的中枢控制策略在根本上是不同的。
