Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois, United States of America.
PLoS One. 2012;7(8):e43097. doi: 10.1371/journal.pone.0043097. Epub 2012 Aug 30.
Following stroke, reaching movements are slow, segmented, and variable. It is unclear if these deficits result from a poorly constructed movement plan or an inability to voluntarily execute an appropriate plan. The acoustic startle reflex provides a means to initiate a motor plan involuntarily. In the presence of a movement plan, startling acoustic stimulus triggers non-voluntary early execution of planned movement, a phenomenon known as the startReact response. In unimpaired individuals, the startReact response is identical to a voluntarily initiated movement, except that it is elicited 30-40 ms. As the startReact response is thought to be mediated by brainstem pathways, we hypothesized that the startReact response is intact in stroke subjects. If startReact is intact, it may be possible to elicit more task-appropriate patterns of muscle activation than can be elicited voluntarily. We found that startReact responses were intact following stroke. Responses were initiated as rapidly as those in unimpaired subjects, and with muscle coordination patterns resembling those seen during unimpaired volitional movements. Results were striking for elbow flexion movements, which demonstrated no significant differences between the startReact responses elicited in our stroke and unimpaired subject groups. The results during planned extension movements were less straightforward for stroke subjects, since the startReact response exhibited task inappropriate activity in the flexors. This inappropriate activity diminished over time. This adaptation suggests that the inappropriate activity was transient in nature and not related to the underlying movement plan. We hypothesize that the task-inappropriate flexor activity during extension results from an inability to suppress the classic startle reflex, which primarily influences flexor muscles and adapts rapidly with successive stimuli. These results indicate that stroke subjects are capable of planning ballistic elbow movements, and that when these planned movements are involuntarily executed they can be as rapid and appropriate as those in unimpaired individuals.
中风后，伸手动作缓慢、不连续且多变。目前尚不清楚这些缺陷是由于运动计划构建不当，还是由于无法自主执行适当的计划。声音惊跳反射为启动运动计划提供了一种无意识的方法。在存在运动计划的情况下，惊跳声刺激会引发非自愿的早期计划运动执行，这种现象称为 startReact 反应。在未受损的个体中，startReact 反应与自愿发起的运动相同，只是它会在 30-40 毫秒后被引出。由于 startReact 反应被认为是由脑干途径介导的，我们假设在中风患者中，startReact 反应是完整的。如果 startReact 反应完整，则有可能引出比自主引发更适合任务的肌肉激活模式。我们发现中风后 startReact 反应完整。反应发起速度与未受损受试者一样快，并且肌肉协调模式与未受损自愿运动中观察到的模式相似。对于肘部弯曲运动，结果令人瞩目，中风患者和未受损患者组引出的 startReact 反应之间没有显著差异。对于计划伸展运动，中风患者的结果则不那么直接，因为 startReact 反应在屈肌中表现出不适当的活动。随着时间的推移，这种不适当的活动逐渐减少。这种适应表明，这种不适当的活动是暂时的，与潜在的运动计划无关。我们假设，在伸展运动中，屈肌出现不适当的活动是由于无法抑制经典的惊跳反射，该反射主要影响屈肌，并且会随着连续刺激快速适应。这些结果表明，中风患者能够计划弹丸式肘部运动，并且当这些计划运动被无意识地执行时，它们可以像未受损个体那样迅速且适当。
