Exercise Neuroscience Research Group, School of Arts, Sciences and Humanities, University of São Paulo, SP, Brazil.
Laboratory of Strength Training, School of Physical Education and Sport, University of São Paulo, SP, Brazil.
J Physiol. 2020 Apr;598(8):1611-1624. doi: 10.1113/JP279068. Epub 2020 Mar 12.
Individuals with freezing of gait (FoG) due to Parkinson's disease (PD) have small and long anticipatory postural adjustments (APAs) associated with delayed step initiation. Individuals with FoG ('freezers') may require functional reorganization of spinal mechanisms to perform APAs due to supraspinal dysfunction. As presynaptic inhibition (PSI) is centrally modulated to allow execution of supraspinal motor commands, it may be deficient in freezers during APAs. We show that freezers presented PSI in quiet stance (control task), but they presented loss of PSI (i.e. higher ratio of the conditioned H-reflex relative to the test H-reflex) during APAs before step initiation (functional task), whereas non-freezers and healthy control individuals presented PSI in both the tasks. The loss of PSI in freezers was associated with both small APA amplitudes and FoG severity. We hypothesize that loss of PSI during APAs for step initiation in freezers may be due to FoG.
Freezing of gait (FoG) in Parkinson's disease involves deficient anticipatory postural adjustments (APAs), resulting in a cessation of step initiation due to supraspinal dysfunction. Individuals with FoG ('freezers') may require functional reorganization of spinal mechanisms to perform APAs. As presynaptic inhibition (PSI) is centrally modulated to allow execution of supraspinal motor commands, here we hypothesized a loss of PSI in freezers during APA for step initiation, which would be associated with FoG severity. Seventy individuals [27 freezers, 22 non-freezers, and 21 age-matched healthy controls (HC)] performed a 'GO'-commanded step initiation task on a force platform under three conditions: (1) without electrical stimulation, (2) test Hoffman reflex (H-reflex) and (3) conditioned H-reflex. They also performed a control task (quiet stance). In the step initiation task, the H-reflexes were evoked on the soleus muscle when the amplitude of the APA exceeded 10-20% of the mean baseline mediolateral force. PSI was quantified by the ratio of the conditioned H-reflex relative to the test H-reflex in both the tasks. Objective assessment of FoG severity (FoG-ratio) was performed. Freezers presented lower PSI levels during quiet stance than non-freezers and HC (P < 0.05). During step initiation, freezers presented loss of PSI and lower APA amplitudes than non-freezers and HC (P < 0.05). Significant correlations were only found for freezers between loss of PSI and FoG-ratio (r = 0.59, P = 0.0005) and loss of PSI and APA amplitude (r = -0.35, P < 0.036). Our findings suggest that loss of PSI for step initiation in freezers may be due to FoG.
患有帕金森病冻结步态（FOG）的个体，其与启动延迟相关的姿势预位调整（APA）较小且较长。FOG 患者（“冻结者”）可能需要脊柱机制的功能重组来执行 APA，因为上位神经系统功能障碍。由于突触前抑制（PSI）被中枢调节以允许执行上位神经系统运动指令，因此在 APA 期间，PSI 可能在冻结者中不足。我们表明，冻结者在安静姿势（对照任务）中表现出 PSI，但在启动前的 APA 期间（功能任务）表现出 PSI 丧失（即条件 H 反射相对于测试 H 反射的比率较高），而非冻结者和健康对照组在两项任务中均表现出 PSI。冻结者的 PSI 丧失与 APA 幅度小和 FOG 严重程度相关。我们假设，冻结者在启动步的 APA 期间 PSI 丧失可能是由于 FOG。
帕金森病中的冻结步态（FOG）涉及到姿势预位调整（APA）的不足，导致由于上位神经系统功能障碍而停止启动。FOG 患者（“冻结者”）可能需要对脊柱机制进行功能重组以执行 APA。由于突触前抑制（PSI）被中枢调节以允许执行上位神经系统运动指令，因此我们假设在 APA 期间冻结者的 PSI 丧失，这与 FOG 的严重程度有关。70 名参与者[27 名冻结者、22 名非冻结者和 21 名年龄匹配的健康对照组（HC）]在力平台上执行“GO”命令启动任务，共三种情况：（1）无电刺激，（2）测试霍夫曼反射（H-反射）和（3）条件化 H-反射。他们还执行了对照任务（安静站立）。在启动任务中，当 APA 幅度超过平均基线横向力的 10-20%时，在比目鱼肌上诱发 H-反射。在两个任务中，通过条件 H-反射与测试 H-反射的比值来量化 PSI。还对 FOG 严重程度（FOG-比值）进行了客观评估。冻结者在安静站立时的 PSI 水平低于非冻结者和 HC（P<0.05）。在启动时，冻结者的 PSI 丧失和 APA 幅度低于非冻结者和 HC（P<0.05）。仅在冻结者中发现 PSI 丧失与 FOG-比值（r=0.59，P=0.0005）和 PSI 丧失与 APA 幅度（r=-0.35，P<0.036）之间存在显著相关性。我们的研究结果表明，冻结者在启动时的 PSI 丧失可能是由于 FOG。
