Ghafouri Mohammad, McIlroy William E, Maki Brian E
Centre for Studies in Aging, Sunnybrook and Women's College Health Sciences Centre, Toronto, Canada.
Exp Brain Res. 2004 Apr;155(4):532-6. doi: 10.1007/s00221-004-1855-8. Epub 2004 Feb 24.
In order to recover balance by grasping an object for support, the CNS must rapidly move the hand toward a specific target (handhold) in the environment. The early latency (80-140 ms) of these grasping reactions would seem to preclude a role for online visual feedback in the control of the initial limb movement; however, some studies have shown that vision can influence initiation of lower-limb postural reactions at similar latency. This study explored the role of vision in controlling the initial trajectory of grasping reactions triggered by sudden unpredictable medio-lateral platform translation. Healthy young adults were instructed to recover balance by grasping a marked section of a handrail, located to their right. To reinforce a dependence on arm reactions, movement of the feet was prevented by barriers. Liquid-crystal goggles were used to occlude vision during response initiation (200 ms interval starting at perturbation onset, PO). Results showed that the initial grasping trajectory (first 100 ms) and associated muscle activation were heavily modulated to take into account the direction and speed of the perturbation-induced body motion in relation to the handrail. This modulation was unaffected by occlusion of vision at PO, indicating that information about the rail location obtained prior to PO was incorporated into the control. These findings are consistent with the view that the CNS tunes the initial arm trajectory by combining an egocentric spatial map, formed prior to PO, with online feedback about the body motion from non-visual inputs (somatosensory and/or vestibular). This prevents potential delays associated with visual processing and ensures very rapid onset of arm movement that is directed appropriately even though the position of the body is perturbed unpredictably with respect to the target.
为了通过抓握物体来恢复平衡，中枢神经系统（CNS）必须迅速将手移向环境中的特定目标（抓手）。这些抓握反应的早期潜伏期（80 - 140毫秒）似乎排除了在线视觉反馈在控制初始肢体运动中的作用；然而，一些研究表明，视觉可以在类似潜伏期影响下肢姿势反应的起始。本研究探讨了视觉在控制由突然不可预测的平台向内外侧平移引发的抓握反应的初始轨迹中的作用。健康的年轻成年人被指示通过抓握位于其右侧的扶手的一个标记部分来恢复平衡。为了强化对手臂反应的依赖，脚部运动被障碍物阻止。在反应起始阶段（从扰动开始，即PO开始的200毫秒间隔）使用液晶护目镜遮挡视觉。结果表明，初始抓握轨迹（最初100毫秒）和相关的肌肉激活受到强烈调节，以考虑到与扶手相关的扰动引起的身体运动的方向和速度。这种调节不受PO时视觉遮挡的影响，表明在PO之前获得的关于扶手位置的信息被纳入了控制。这些发现与以下观点一致，即中枢神经系统通过将PO之前形成的以自我为中心的空间地图与来自非视觉输入（体感和/或前庭）的关于身体运动的在线反馈相结合，来调整手臂的初始轨迹。这防止了与视觉处理相关的潜在延迟，并确保即使身体相对于目标的位置被不可预测地扰动，手臂运动也能非常迅速地开始并得到适当引导。
