Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA.
Shirley Ryan AbilityLab, Chicago, IL, USA.
Exp Brain Res. 2019 Sep;237(9):2353-2365. doi: 10.1007/s00221-019-05592-1. Epub 2019 Jul 10.
The timing and magnitude of muscle responses to perturbations are critical for acting in uncertain environments. A planned movement can strongly influence average muscle responses to perturbations, but certainty in when a perturbation will arrive changes this effect. The objective of this study was to investigate how uncertainty in perturbation timing influences the preparation and release of involuntary, perturbation-triggered responses. We hypothesized that uncertainty would influence the average magnitude of triggered responses and how they develop in time. We investigated three levels of uncertainty in when a proprioceptive cue to move would arrive by changing the duration and variability of the time between a preparation and movement cue. Participants performed ballistic elbow extension movements in response to the movement cue. Unexpected, large perturbations that flexed the elbow were delivered at various times between the preparation and movement cues to evaluate how cue uncertainty influenced the development of triggered responses. We found that this uncertainty strongly influences how a motor response is prepared, and the efficacy of triggering that response by a postural perturbation. When timing was certain, the motor plan was prepared within 150 ms of the expected disturbance, and consistently released earlier by a perturbation than could be done voluntarily. Less predictable stimuli led to much earlier planning and a lower probability of releasing the plan early. These results clarify how uncertainty in when to move influences the planning and early release of perturbation-triggered responses, demonstrating an effect similar to previous reports on the planning of volitional movements.
肌肉对扰动的反应时间和幅度对于在不确定环境中行动至关重要。计划好的运动可以强烈影响肌肉对扰动的平均反应，但扰动何时发生的确定性会改变这种影响。本研究的目的是调查扰动时间的不确定性如何影响无意识、由扰动触发的反应的准备和释放。我们假设不确定性将影响触发反应的平均幅度以及它们随时间的发展方式。我们通过改变准备和运动线索之间的时间间隔的持续时间和可变性来研究三种不同的扰动时间不确定性水平。参与者根据运动线索进行弹式肘部伸展运动。在准备和运动线索之间的不同时间点意外地施加了较大的弯曲肘部的扰动，以评估线索不确定性如何影响触发反应的发展。我们发现，这种不确定性强烈影响了运动反应的准备方式，以及通过姿势扰动触发该反应的效果。当时间确定时，运动计划在预期干扰前 150 毫秒内准备好，并始终比自愿更快地通过扰动释放。更不可预测的刺激导致更早的计划和更早释放计划的可能性降低。这些结果阐明了何时移动的不确定性如何影响由扰动触发的反应的计划和早期释放，展示了与先前关于自愿运动计划的报告相似的效果。
