Monzée Joël, Lamarre Yves, Smith Allan M
Centre de Recherche en Sciences Neurologiques, Département de Physiologie, Université de Montréal, Montreal, Quebec H3C 3T8, Canada.
J Neurophysiol. 2003 Feb;89(2):672-83. doi: 10.1152/jn.00434.2001.
A total of 20 right-handed subjects were asked to perform a grasp-lift-and-hold task using a precision grip. The grasped object was a one-degree-of-freedom manipuladum consisting of a vertically mounted linear motor capable of generating resistive forces to simulate a range of object weights. In the initial study, seven subjects (6 women, 1 man; ages 24-56 yr) were first asked to lift and hold the object stationary for 4 s. The object presented a metal tab with two different surface textures and offered one of four resistive forces (0.5, 1.0, 1.5, and 2.0 N). The lifts were performed both with and without visual feedback. Next, the subjects were asked to perform the same grasping sequence again after ring block anesthesia of the thumb and index finger with mepivacaine. The objective was to determine the degree to which an internal model obtained through prior familiarity might compensate for the loss of cutaneous sensation. In agreement with previous studies, it was found that all subjects applied significantly greater grip force after digital anesthesia, and the coordination between grip and load forces was disrupted. It appears from these data, that the internal model alone is insufficient to completely compensate for the loss of cutaneous sensation. Moreover, the results suggest that the internal model must have either continuous tonic excitation from cutaneous receptors or at least frequent intermittent reiteration to function optimally. A subsequent study performed with 10 additional subjects (9 women, 1 man; ages 24-49 yr) indicated that with unimpaired cutaneous feedback, the grasping and lifting forces were applied together with negligible forces and torques in other directions. In contrast, after digital anesthesia, significant additional linear and torsional forces appeared, particularly in the horizontal and frontal planes. These torques were thought to arise partially from the application of excessive grip force and partially from a misalignment of the two grasping fingers. These torques were further increased by an imbalance in the pressure exerted by the two opposing fingers. Vision of the grasping hand did not significantly correct the finger misalignment after digital anesthesia. Taken together, these results suggest that mechanoreceptors in the fingertips signal the source and direction of pressure applied to the skin. The nervous system uses this information to adjust the fingers and direct the pinch forces optimally for grasping and object manipulation.
共有20名右利手受试者被要求使用精确抓握方式执行抓握-提起-保持任务。所抓握的物体是一个单自由度操作器，由一个垂直安装的线性电机组成，该电机能够产生阻力以模拟一系列物体重量。在初始研究中，首先要求7名受试者（6名女性，1名男性；年龄24 - 56岁）提起并保持物体静止4秒。该物体有一个带有两种不同表面纹理的金属片，并提供四种阻力（0.5、1.0、1.5和2.0牛）中的一种。提起操作在有视觉反馈和无视觉反馈两种情况下进行。接下来，在使用甲哌卡因对拇指和食指进行环形阻滞麻醉后，要求受试者再次执行相同的抓握序列。目的是确定通过先前熟悉获得的内部模型在多大程度上可以补偿皮肤感觉的丧失。与先前的研究一致，发现所有受试者在手指麻醉后施加的抓握力显著增大，并且抓握力与负载力之间的协调性受到破坏。从这些数据来看，似乎仅靠内部模型不足以完全补偿皮肤感觉的丧失。此外，结果表明内部模型必须要么有来自皮肤感受器的持续强直性兴奋，要么至少有频繁的间歇性重复才能最佳地发挥作用。随后对另外10名受试者（9名女性，1名男性；年龄24 - 49岁）进行的研究表明，在皮肤反馈未受损的情况下，抓握和提起力与其他方向上可忽略不计的力和扭矩一起施加。相比之下，在手指麻醉后，出现了显著的额外线性和扭转力，特别是在水平和额平面。这些扭矩被认为部分源于过度抓握力的施加，部分源于两个抓握手指的不对齐。两个相对手指施加的压力不平衡进一步增加了这些扭矩。在手指麻醉后，看到抓握的手并不能显著纠正手指的不对齐。综上所述，这些结果表明指尖的机械感受器会发出施加在皮肤上的压力的来源和方向的信号。神经系统利用这些信息来调整手指并最佳地引导捏力以进行抓握和物体操作。
