Gage William H, Zabjek Karl F, Hill Stephen W, McIlroy William E
Toronto Rehabilitation Institute, 550 University Avenue, Toronto, ON Canada, M5G 2A2.
Exp Brain Res. 2007 Aug;181(4):627-37. doi: 10.1007/s00221-007-0959-3. Epub 2007 May 9.
To determine the potential differences in control underlying compensatory and voluntary reach-to-grasp movements the current study compared the kinematic and electromyographic profiles associated with upper limb movement. Postural perturbations were delivered to evoke compensatory reach-to-grasp in ten healthy young adult volunteers while seated on a chair that tilted as an inverted pendulum in the frontal plane. Participants reached to grasp a laterally positioned stable handhold and pulled (or pushed) to return the chair to vertical. The distinguishing characteristic between the two behaviors was the onset latency and speed of movement. Consistent with compensatory balance reactions, the perturbation-evoked reach response was initiated very rapidly (137 vs. 239 ms for voluntary). As well the movement time was shorter, and peak velocity was greater for PERT movements. In spite of the profound differences in timing, the sequence of muscle activity onsets and the order of specific kinematic events were not different between maximum velocity voluntary (VOL) and perturbation-evoked (PERT) reach-to-grasp movements. Peak velocity and grasp aperture occurred prior to hand contact with the target for PERT and VOL movements, and wrist trajectory was influenced by the direction of perturbation relative to the target. To achieve such target specific control for responses initiated within 100 ms of the perturbation, and when characteristics of body movement were unpredictable, the perturbation-evoked movements would need to incorporate sensory cues associated with body movement relative to the target into the earliest aspects of the movement. This suggests reliance on an internal spatial map constructed prior to the onset of perturbation. Parallels in electromyographic and kinematic profiles between compensatory and voluntary reach-to-grasp movements, in spite of temporal differences, lead to the view they are controlled by common neural mechanisms.
为了确定代偿性和自主性抓握动作控制的潜在差异，本研究比较了与上肢运动相关的运动学和肌电图特征。对10名健康年轻成年志愿者进行姿势扰动，以诱发代偿性抓握动作，他们坐在一把在额平面内像倒立摆一样倾斜的椅子上。参与者伸手去抓侧面放置的稳定把手，然后拉（或推）以使椅子恢复垂直。这两种行为的区别特征在于运动的起始潜伏期和速度。与代偿性平衡反应一致，扰动诱发的伸手反应启动非常迅速（自主性反应为239毫秒，而扰动诱发反应为137毫秒）。此外，扰动诱发动作的运动时间更短，峰值速度更大。尽管在时间上存在显著差异，但最大速度自主性（VOL）和扰动诱发（PERT）抓握动作之间的肌肉活动起始顺序和特定运动学事件的顺序并无不同。对于PERT和VOL动作，峰值速度和抓握孔径在手部接触目标之前出现，并且手腕轨迹受相对于目标的扰动方向影响。为了在扰动后100毫秒内启动的反应实现这种目标特异性控制，并且当身体运动特征不可预测时，扰动诱发的动作需要将与相对于目标的身体运动相关的感觉线索纳入运动的最早阶段。这表明依赖于在扰动开始之前构建的内部空间地图。尽管存在时间差异，但代偿性和自主性抓握动作在肌电图和运动学特征上的相似性导致这样一种观点，即它们由共同的神经机制控制。
