Motor Control Laboratory, Department of Kinesiology, Arizona State University, Box 870404, Tempe, AZ 85287-0404, USA.
Exp Brain Res. 2010 Mar;201(3):509-25. doi: 10.1007/s00221-009-2064-2. Epub 2009 Nov 10.
The present project was aimed at investigating how two distinct and important difficulties (coordination difficulty and pronounced dependency on visual feedback) in Parkinson's disease (PD) affect each other for the coordination between hand transport toward an object and the initiation of finger closure during reach-to-grasp movement. Subjects with PD and age-matched healthy subjects made reach-to-grasp movements to a dowel under conditions in which the target object and/or the hand were either visible or not visible. The involvement of the trunk in task performance was manipulated by positioning the target object within or beyond the participant's outstretched arm to evaluate the effects of increasing the complexity of intersegmental coordination under different conditions related to the availability of visual feedback in subjects with PD. General kinematic characteristics of the reach-to-grasp movements of the subjects with PD were altered substantially by the removal of target object visibility. Compared with the controls, the subjects with PD considerably lengthened transport time, especially during the aperture closure period, and decreased peak velocity of wrist and trunk movement without target object visibility. Most of these differences were accentuated when the trunk was involved. In contrast, these kinematic parameters did not change depending on the visibility of the hand for both groups. The transport-aperture coordination was assessed in terms of the control law according to which the initiation of aperture closure during the reach occurred when the hand distance-to-target crossed a hand-target distance threshold for grasp initiation that is a function of peak aperture, hand velocity and acceleration, trunk velocity and acceleration, and trunk-target distance at the time of aperture closure initiation. When the hand or the target object was not visible, both groups increased the hand-target distance threshold for grasp initiation compared to its value under full visibility, implying an increase in the hand-target distance-related safety margin for grasping. The increase in the safety margin due to the absence of target object vision or the absence of hand vision was accentuated in the subjects with PD compared to that in the controls. The pronounced increase in the safety margin due to absence of target object vision for the subjects with PD was further accentuated when the trunk was involved compared to when it was not involved. The results imply that individuals with PD have significant limitations regarding neural computations required for efficient utilization of internal representations of target object location and hand motion as well as proprioceptive information about the hand to compensate for the lack of visual information during the performance of complex multisegment movements.
本研究旨在探讨帕金森病（PD）中两种显著且重要的困难（协调困难和对手动反馈的强烈依赖）如何相互影响，即手在向目标物体运输过程中的协调与抓握运动中手指的起始闭合。PD 患者和年龄匹配的健康受试者在手和/或目标物体可见或不可见的情况下进行抓握运动。通过将目标物体放置在受试者伸展的手臂内外，来改变躯干在任务执行中的参与程度，以评估在 PD 患者中，与视觉反馈可用性相关的不同条件下，增加节段间协调复杂性的效果。PD 患者的抓握运动的总体运动学特征因目标物体可见性的消除而发生显著改变。与对照组相比，PD 患者的运输时间明显延长，尤其是在开口闭合期间，并且在没有目标物体可见性的情况下，手腕和躯干运动的峰值速度降低。当涉及躯干时，这些差异大部分被放大。相比之下，这两组的运动学参数都不随手的可见性而变化。通过根据控制律评估运输-开口协调，即当手距离目标的距离超过用于抓握起始的手-目标距离阈值时，开口开始闭合，该阈值是峰值开口、手速度和加速度、躯干速度和加速度以及开口起始时的躯干-目标距离的函数。当手或目标物体不可见时，两组都增加了用于抓握起始的手-目标距离阈值，与完全可见时的阈值相比，这意味着手-目标距离相关的安全裕度增加了。与对照组相比，PD 患者由于目标物体视觉缺失或手视觉缺失而导致安全裕度增加的幅度更大。与不涉及躯干时相比，当涉及躯干时，PD 患者由于目标物体视觉缺失而导致安全裕度的显著增加进一步放大。结果表明，PD 患者在利用目标物体位置和手部运动的内部表示以及手部的本体感觉信息来补偿复杂多节段运动执行过程中视觉信息缺失方面存在显著的神经计算局限性。
