CONTROL OF LIMB DYNAMICS IN NORMAL SUBJECTS AND PATIENTS WITHOUT PROPRIOCEPTION
CONTROL OF LIMB DYNAMICS IN NORMAL SUBJECTS AND PATIENTS WITHOUT PROPRIOCEPTION
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DOI：
10.1152/jn.1995.73.2.820
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发表时间：
1995-02-01
影响因子：
2.5
通讯作者：
GHEZ, C
中科院分区：
文献类型：
--
作者：
SAINBURG, RL;GHILARDI, MF;GHEZ, C
1.我们最近的研究表明，缺乏肢体本体感觉输入的患者在进行多关节运动时尤其困难。在一个需要在手部路径方向上急剧反转的哑剧切割手势中，患者在运动反转时表现出很大的手部路径扭曲，这是因为未能协调肩部和肘关节单独反转的时间。我们假设，这些反转误差是由于肩关节加速度变化所产生的惯性相互作用的不可补偿的影响，这些惯性相互作用转移到肘部。我们现在搁置这一假设，并通过比较五名正常受试者和两名大纤维感觉神经病患者的运动表现来检验本体感觉输入的作用。受试者通过手和数字化平板电脑的前后直线重叠动作，追踪电脑屏幕上随机呈现的六条模板线中的每一条。这些线从一个共同的起点开始，但方向不同，长度也不同。方向和长度进行了调整，以便跟踪运动都需要相同的肘部偏移量，而肩部偏移量会有所不同。然后研究了不同相互作用力矩对肘部运动学的影响。受试者的优势手臂在水平面上由一个低惯性支架支撑，该支架在肘部和肩部下方装有滚珠关节和电位器。手的位置由连接在数字化平板上方1 cm的支架上的磁笔监控，并可显示为屏幕光标。受试者手臂的视觉被阻挡，屏幕光标在运动开始时被空白，以防止在运动过程中的视觉反馈。根据肘关节角度记录计算肘关节扭矩，并与肘关节肌电记录进行比较。在对照受试者中，无论方向如何，向外和向内的路径都是直的，并与模板线重叠。按照任务的规定，肘部运动学在运动方向上保持不变，而相互作用力矩变化很大。屈肘时二头肌活动开始的时间和三头肌活动的偏移量随相互作用力矩方向的变化而有系统地变化。控制根据需要利用或抑制这些相互作用力矩，以满足任务的运动学要求。相比之下，患者在运动反转时犯了特征性的错误，这种错误在运动方向上系统性地增加。这些反转错误是由于肘关节和肩关节反转的时机不当造成的。在整个反转阶段，患者没有使二头肌和三头肌的活动适应相互作用力矩方向相关的变化，而是共同收缩了拮抗剂。尽管这可能增加了关节的僵硬，但该策略在控制肘关节动力学方面并不有效：肘关节加速度与相互作用力矩的幅度直接相关。相互作用力通过上臂减速传递到肘部，使肘部过早地进入屈曲状态。这使得肩部和肘部正常同步的翻转动作脱钩，导致动作翻转时手部路径变形较大。我们的数据表明，相互作用力通常是通过前馈机制控制的，而这种控制在由于感觉神经病而被剥夺本体感觉的患者中严重受损。因此，我们得出结论，本体感觉信息在多关节运动中的关节间协调中起着重要作用。我们假设，运动过程中的信息用于更新肢体动力学的内部模型，然后使用该模型来编程运动命令。
1. We recently showed that patients lacking proprioceptive input from their limbs have particular difficulty performing multijoint movements. In a pantomimed slicing gesture requiring sharp reversals in hand path direction, patients showed large hand path distortions at movement reversals because of failure to coordinate the timing of the separate reversals at the shoulder and elbow joints. We hypothesized that these reversal errors resulted from uncompensated effects of inertial interactions produced by changes in shoulder joint acceleration that were transferred to the elbow. We now rest this hypothesis and examine the role of proprioceptive input by comparing the motor performance of five normal subjects with that of two patients with large-fiber sensory neuropathy.2. Subjects were to trace each of six template lines presented randomly on a computer screen by straight overlapping out-and-back movements of the hand an a digitizing tablet. The lines originated from a common starting position but were in different directions and had different lengths. Directions and lengths were adjusted so that tracing movements would all require the same elbow excursion, whereas shoulder excursion would vary. The effects of varying interaction torques on elbow kinematics were then studied. The subject's dominant arm was supported in the horizontal plane by a low-inertia brace equipped with ball bearing joints and potentiometers under the elbow and shoulder. Hand position was monitored by a magnetic pen attached to the brace 1 cm above a digitizing tablet and could be displayed as a screen cursor. Vision of the subject's arm was blocked and the screen cursor was blanked at movement onset to prevent visual feedback during movement. Elbow joint torques were calculated from joint angle recordings and compared with electromyographic recordings of elbow joint musculature.3. In control subjects, outward and inward paths were straight and overlapped the template lines regardless of their direction. As prescribed by the task, elbow kinematics remained the same across movement directions, whereas interaction torques varied substantially. The timing of the onsets of biceps activity and the offsets of triceps activity during elbow flexion varied systematically with direction-dependent changes in interaction torques. Controls exploited or dampened these interaction torques as needed to meet the kinematic demands of the task.4. In contrast, the patients made characteristic errors at movement reversals that increased systematically across movement directions. These reversal errors resulted from improper timing of elbow and shoulder joint reversals. Instead of adapting biceps and triceps activity to direction-dependent changes in interaction torques, the patients cocontracted antagonists throughout the reversal phase. Although this may have increased joint stiffness the strategy was nor effective in controlling elbow dynamics: elbow joint acceleration varied directly with the amplitude of the interaction torques. Interaction torques, transferred to the elbow by upper arm deceleration, drove the elbow into flexion prematurely. This decoupled the normally synchronous reversals at the shoulder and elbow and resulted in large hand path distortions at movement reversals.5. Our data indicate that interaction torques are normally controlled through feedforward mechanisms and that this control is severely impaired in patients deprived of proprioception because of sensory neuropathy. We therefore conclude that proprioceptive information plays an important role in interjoint coordination during multijoint movements. We hypothesize that information during movement serves to update an internal model of limb dynamics that is then used to program motor commands.