ER-6 UPMC: Physiologie et physiopathologie de la motricité chez l'Homme-Médecine Physique et Réadaptation, Hôpital Pitié Salpêtrière, 75013 Paris, France.
J Physiol. 2011 Jul 15;589(Pt 14):3545-58. doi: 10.1113/jphysiol.2011.206268. Epub 2011 May 23.
Motor skill acquisition in the lower limb may induce modifications of spinal network excitability. We hypothesized that short-term motor adaptation in precision grip tasks would also induce modifications of cervical spinal network excitability. In a first series of experiments, we studied the impact of two different precision grip force control tasks (a visuomotor force-tracking task and a control force task without visual feedback) on cervical spinal network excitability in healthy subjects. We separately tested the efficacy of two key components of the spinal circuitry: (i) presynaptic inhibition on flexor carpi radialis (FCR) Ia terminals, and (ii) disynaptic inhibition directed from extensor carpi radialis (ECR) to FCR. We found that disynaptic inhibition decreased temporarily after both force control tasks, independently of the presence of visual feedback. In contrast, the amount of presynaptic inhibition on FCR Ia terminals decreased only after the visuomotor force tracking task. This temporary decrease was correlated with improved tracking accuracy during the task (i.e. short-term motor adaptation). A second series of experiments confirmed these results and showed that the visuomotor force-tracking task resulted also in an increase of the Hmax/Mmax ratio and the slope of the ascending part of the H-reflex recruitment curve. In order to address the role of presynaptic inhibition in the motor adaptation process, we conducted a third series of experiments during which presynaptic inhibition was recorded before and after two consecutive sessions of visuomotor force tracking. The results showed that (i) improved tracking accuracy occurred during both sessions, and (ii) presynaptic inhibition decreased only after the first session of visuomotor force tracking. Taken together, these results suggest thus that the nature of the motor task performed has a specific impact on the excitability of these cervical spinal circuits. These findings also suggest that early motor adaptation is associated with a modulation of presynaptic Ia inhibition in the upper limb.
下肢运动技能的获得可能会引起脊髓网络兴奋性的改变。我们假设，在精确抓握任务中的短期运动适应也会引起颈椎网络兴奋性的改变。在一系列的实验中，我们研究了两种不同的精确抓握力控制任务（视觉运动力跟踪任务和没有视觉反馈的控制力任务）对健康受试者颈椎网络兴奋性的影响。我们分别测试了脊髓回路的两个关键组成部分的效果：（i）对桡侧腕屈肌（FCR）Ia 终末的突触前抑制，以及（ii）从桡侧腕长伸肌（ECR）到 FCR 的双突触抑制。我们发现，在两种力控制任务后，双突触抑制暂时降低，而与视觉反馈的存在无关。相反，FCR Ia 终末的突触前抑制量仅在视觉运动力跟踪任务后降低。这种暂时的减少与任务期间跟踪精度的提高（即短期运动适应）有关。第二个系列的实验证实了这些结果，并表明视觉运动力跟踪任务也导致 Hmax/Mmax 比值和 H 反射募集曲线上升部分的斜率增加。为了研究突触前抑制在运动适应过程中的作用，我们在两次连续的视觉运动力跟踪后进行了第三个系列的实验，记录了突触前抑制。结果表明，（i）在两次会话期间都提高了跟踪精度，（ii）只有在第一次视觉运动力跟踪后，突触前抑制才降低。总之，这些结果表明，所执行的运动任务的性质对这些颈椎脊髓回路的兴奋性有特定的影响。这些发现还表明，早期运动适应与上肢 Ia 抑制的调制有关。
