Levin M F, Lamarre Y, Feldman A G
Ecole de réadaptation, Centre de recherche en sciences neurologiques, Institut de réadaptation de Montréal, PQ, Canada.
Can J Physiol Pharmacol. 1995 Feb;73(2):316-30. doi: 10.1139/y95-042.
Sensorimotor mechanisms were studied on the basis of kinematic and electromyographic data as well as the static torque developed by the muscles as a function of joint angle. The latter relationship is known as the torque/angle characteristic. Fast single-joint movement may result from a shift in this characteristic and a change in its slope. Such movements were studied at the wrist in 9 normal and 1 deafferented subject. After training to flex the wrist to a target, subjects repeated the same movements but in random test trials movements were opposed by the load generated by linear position feedback to a torque motor. At the end of the loaded trials, the load was suddenly removed. In the second experiment, subjects made wrist movements to the target that were opposed by the load and, on random test trials, the movements were not loaded. In these test trials, the wrist arrived in a static position outside the target zone. In both experiments, subjects were instructed not to correct errors. The final torque/angle characteristics specified in the movements were reconstructed on the basis of the static wrist positions and torques before and after unloading. Normal subjects made movements by shifting the position of the torque/angle characteristic and by increasing its slope. If subjects indeed maintained the same pattern of control variables (descending commands), the same final position of the characteristic would be reproduced from trial to trial regardless of load perturbations. This assumption of equifinality was tested by comparing the final position of the wrist in nonloaded movements with that after removal of the load in loaded movements. Equifinality was observed in normal subjects. Movements in the deafferented subject were also associated with a shift of the torque/angle characteristic and a change in its slope. However, she was unable to consistently reproduce its final position. In spite of muscle coactivation, her maximal stiffness was lower than in normal subjects. In the absence of vision, the subject made movements with the load by increasing the slope of the characteristic instead of by shifting its position far enough. Load perturbation affected her final wrist position (inequifinality), which may reflect the presence of a significant hysteresis of the characteristic as a result of the absence of stretch reflexes. The deficits following deafferentation presumably result from the destruction of biomechanical and sensorimotor mechanisms including the ability of control variables to specify the positional frame of reference for afferent and descending systems.
基于运动学和肌电图数据以及肌肉产生的静态扭矩与关节角度的函数关系，对感觉运动机制进行了研究。后一种关系被称为扭矩/角度特性。快速单关节运动可能是由于这种特性的变化及其斜率的改变所致。在9名正常受试者和1名去传入神经受试者的手腕上对这种运动进行了研究。在训练将手腕弯曲到目标位置后，受试者重复相同的运动，但在随机测试试验中，运动会受到线性位置反馈到扭矩电机产生的负载的阻碍。在加载试验结束时，突然移除负载。在第二个实验中，受试者向目标进行手腕运动，运动受到负载的阻碍，并且在随机测试试验中，运动没有加载。在这些测试试验中，手腕到达目标区域之外的静态位置。在两个实验中，都指示受试者不要纠正错误。根据卸载前后手腕的静态位置和扭矩，重建运动中指定的最终扭矩/角度特性。正常受试者通过改变扭矩/角度特性的位置并增加其斜率来进行运动。如果受试者确实保持相同的控制变量模式（下行指令），那么无论负载扰动如何，每次试验都会再现相同的最终特性位置。通过比较无负载运动中手腕的最终位置与加载运动中移除负载后的最终位置，对这种等终性假设进行了测试。在正常受试者中观察到了等终性。去传入神经受试者的运动也与扭矩/角度特性的变化及其斜率的改变有关。然而，她无法始终如一地再现其最终位置。尽管存在肌肉共同激活，但其最大刚度低于正常受试者。在没有视觉的情况下，受试者通过增加特性的斜率而不是将其位置移动得足够远来进行有负载的运动。负载扰动影响了她手腕最终的位置（不等终性），这可能反映了由于缺乏牵张反射导致特性存在显著滞后。去传入神经后的缺陷可能是由于生物力学和感觉运动机制的破坏，包括控制变量为传入和下行系统指定位置参考框架的能力。
