Fuchs Katharina, Krauskopf Thomas, Lauck Torben B, Klein Lukas, Mueller Marc, Herget Georg W, Von Tscharner Vinzenz, Stutzig Norman, Stieglitz Thomas, Pasluosta Cristian
Department of Microsystems Engineering, Laboratory for Biomedical Microtechnology, University of Freiburg, Freiburg im Breisgau, Germany.
BrainLinks-BrainTools, University of Freiburg, Freiburg im Breisgau, Germany.
Front Neurosci. 2021 Sep 13;15:727527. doi: 10.3389/fnins.2021.727527. eCollection 2021.
Patients with a lower limb amputation rely more on visual feedback to maintain balance than able-bodied individuals. Altering this sensory modality in amputees thus results in a disrupted postural control. However, little is known about how lower limb amputees cope with augmented visual information during balance tasks. In this study, we investigated how unilateral transfemoral amputees incorporate visual feedback of their center of pressure (CoP) position during quiet standing. Ten transfemoral amputees and ten age-matched able-bodied participants were provided with real-time visual feedback of the position of their CoP while standing on a pressure platform. Their task was to keep their CoP within a small circle in the center of a computer screen placed at eye level, which could be achieved by minimizing their postural sway. The visual feedback was then delayed by 250 and 500 ms and was combined with a two- and five-fold amplification of the CoP displacements. Trials with eyes open without augmented visual feedback as well as with eyes closed were further performed. The overall performance was measured by computing the sway area. We further quantified the dynamics of the CoP adjustments using the entropic half-life (EnHL) to study possible physiological mechanisms behind postural control. Amputees showed an increased sway area compared to the control group. The EnHL values of the amputated leg were significantly higher than those of the intact leg and the dominant and non-dominant leg of controls. This indicates lower dynamics in the CoP adjustments of the amputated leg, which was compensated by increasing the dynamics of the CoP adjustments of the intact leg. Receiving real-time visual feedback of the CoP position did not significantly reduce the sway area neither in amputees nor in controls when comparing with the eyes open condition without visual feedback of the CoP position. Further, with increasing delay and amplification, both groups were able to compensate for small visual perturbations, yet their dynamics were significantly lower when additional information was not received in a physiologically relevant time frame. These findings may be used for future design of neurorehabilitation programs to restore sensory feedback in lower limb amputees.
与身体健全的个体相比，下肢截肢患者在维持平衡时更多地依赖视觉反馈。因此，改变截肢者的这种感觉模式会导致姿势控制紊乱。然而，对于下肢截肢者在平衡任务中如何应对增强的视觉信息知之甚少。在本研究中，我们调查了单侧经股骨截肢者在安静站立时如何整合其压力中心（CoP）位置的视觉反馈。十名经股骨截肢者和十名年龄匹配的身体健全参与者在站在压力平台上时，获得了其CoP位置的实时视觉反馈。他们的任务是将CoP保持在与眼睛水平齐平的电脑屏幕中心的一个小圆圈内，这可以通过最小化姿势摆动来实现。然后将视觉反馈延迟250和500毫秒，并与CoP位移的两倍和五倍放大相结合。进一步进行了睁眼无增强视觉反馈以及闭眼的试验。通过计算摆动面积来测量整体性能。我们还使用熵半衰期（EnHL）对CoP调整的动态进行了量化，以研究姿势控制背后可能的生理机制。与对照组相比，截肢者的摆动面积增加。截肢腿的EnHL值显著高于完整腿以及对照组的优势腿和非优势腿。这表明截肢腿的CoP调整动态较低，这通过增加完整腿的CoP调整动态得到了补偿。与没有CoP位置视觉反馈的睁眼条件相比，接收CoP位置的实时视觉反馈在截肢者和对照组中均未显著减小摆动面积。此外，随着延迟和放大的增加，两组都能够补偿小的视觉干扰，然而当在生理相关的时间框架内没有接收到额外信息时，它们的动态显著降低。这些发现可用于未来神经康复计划的设计，以恢复下肢截肢者的感觉反馈。
