Rehabilitation Science, University of Alabama at Birmingham, Birmingham, AL, USA.
Department of Neurology, University of Alabama at Birmingham, Birmingham, AL, USA.
Gait Posture. 2020 Oct;82:68-74. doi: 10.1016/j.gaitpost.2020.08.132. Epub 2020 Aug 30.
Impaired dynamic balance control increases fall risk and contributes to immobility in individuals with Parkinson's disease (PD). It is unclear whether higher-level neural processes of the central nervous system contribute to impaired balance control.
Are dopamine-mediated neural processes of the higher-level central nervous system important for dynamic balance control in PD?
21 individuals with idiopathic PD performed step-threshold assessments before and after self-administered dopaminergic medication. Individuals withstood progressively larger postural perturbations, during which they were explicitly instructed to avoid stepping to recover balance. The perturbation magnitude which elicited stepping responses on four consecutive trials is referred to as the step-threshold. Dynamic balance control was quantified as the minimum margin of stability captured during the largest sub-threshold trial (i.e., the maximum amount of compensated postural instability during the task). We compared dynamic balance between off and on medication states and between individuals who exhibited motor adaptive behavior and those who did not.
Dopaminergic medications significantly improved step-thresholds and allowed individuals to withstand greater amounts of instability without stepping, indicating dopamine-mediated improvement in dynamic balance control. Individuals who displayed behavioral evidence for higher-level neural processes (motor adaptation across repeated perturbations) displayed superior dynamic balance control versus those who did not. Anteroposterior ground reaction forces captured during perturbations suggest that individuals alter force profiles to avoid stepping at ∼200 ms after perturbation onset-a latency consistent with a transcortical process.
Combined, our results indicate that higher-level, dopamine-mediated neural processes are responsible for dynamic balance control in PD. We hypothesize that this process incorporates sensorimotor integration, motor response initiation/inhibition, and goal- and reward-driven behaviors. Interventions targeting these processes may improve dynamic postural control in individuals with PD.
动态平衡控制受损会增加跌倒风险，并导致帕金森病（PD）患者行动不便。目前尚不清楚中枢神经系统的高级神经过程是否会对平衡控制受损产生影响。
多巴胺介导的中枢神经系统高级神经过程是否对 PD 患者的动态平衡控制很重要？
21 名特发性 PD 患者在自行服用多巴胺药物前后进行了阈上踏步测试。个体承受逐渐增大的姿势扰动，在此过程中，他们被明确要求避免踏步以恢复平衡。引起连续 4 次踏步反应的扰动幅度称为阈上踏步。动态平衡控制通过最大亚阈值试验期间捕获的最小稳定性余量来量化（即任务期间最大的补偿性姿势不稳定量）。我们比较了服药前后和是否表现出运动适应行为的个体之间的动态平衡。
多巴胺药物显著改善了阈上踏步，使个体能够承受更大的不稳定而无需踏步，表明多巴胺介导的动态平衡控制改善。表现出高级神经过程（重复扰动时的运动适应）行为证据的个体的动态平衡控制优于没有表现出该行为的个体。在扰动期间捕获的前后地面反作用力表明，个体改变力曲线以避免在扰动开始后约 200 毫秒踏步——这一时间与皮质间过程一致。
综合来看，我们的结果表明，高级的、多巴胺介导的神经过程负责 PD 中的动态平衡控制。我们假设这个过程包括感觉运动整合、运动反应的启动/抑制以及目标和奖励驱动的行为。针对这些过程的干预措施可能会改善 PD 患者的动态姿势控制。
