Jo Hang Jin, Ambike Satyajit, Lewis Mechelle M, Huang Xuemei, Latash Mark L
Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
Department of Neurology, Pennsylvania State University - Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Pharmacology, Pennsylvania State University - Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
Clin Neurophysiol. 2016 Jan;127(1):684-692. doi: 10.1016/j.clinph.2015.05.023. Epub 2015 Jun 3.
We investigated the unintentional drift in total force and in sharing of the force between fingers in two-finger accurate force production tasks performed without visual feedback by patients with Parkinson's disease (PD) and healthy controls. In particular, we were testing a hypothesis that adaptation to the documented loss of action stability could lead to faster force drop in PD.
PD patients and healthy controls performed accurate constant force production tasks without visual feedback by different finger pairs, starting with different force levels and different sharing patterns of force between the two fingers.
Both groups showed an exponential force drop with time and a drift of the sharing pattern towards 50:50. The PD group showed a significantly faster force drop without a change in speed of the sharing drift. These results were consistent across initial force levels, sharing patterns, and finger pairs. A pilot test of four subjects, two PD and two controls, showed no consistent effects of memory on the force drop.
We interpret the force drop as a consequence of back-coupling between the actual and referent finger coordinates that draws the referent coordinate towards the actual one. The faster force drop in the PD group is interpreted as adaptive to the loss of action stability in PD. The lack of group differences in the sharing drift suggests two potentially independent physiological mechanisms contributing to the force and sharing drifts.
The hypothesis on adaptive changes in PD with the purpose to ensure stability of steady states may have important implications for treatment of PD. The speed of force drop may turn into a useful tool to quantify such adaptive changes.
我们研究了帕金森病（PD）患者和健康对照者在无视觉反馈的双指精确力产生任务中，总力以及手指间力分配的无意漂移情况。具体而言，我们在检验一个假设，即适应已记录的动作稳定性丧失可能导致PD患者力下降更快。
PD患者和健康对照者通过不同手指对执行无视觉反馈的精确恒力产生任务，从不同的力水平和两指间不同的力分配模式开始。
两组均显示力随时间呈指数下降，且分配模式向50:50漂移。PD组力下降明显更快，而分配漂移速度无变化。这些结果在初始力水平、分配模式和手指对之间是一致的。对四名受试者（两名PD患者和两名对照者）的初步测试显示，记忆对力下降没有一致的影响。
我们将力下降解释为实际手指坐标与参考手指坐标之间反向耦合的结果，这种耦合将参考坐标拉向实际坐标。PD组力下降更快被解释为对PD患者动作稳定性丧失的适应性反应。分配漂移方面缺乏组间差异表明，有两种潜在独立的生理机制导致了力和分配漂移。
关于PD适应性变化以确保稳态稳定性的假设可能对PD治疗具有重要意义。力下降速度可能成为量化此类适应性变化的有用工具。
