Rowland Rebecca S, Jenkinson Ned, Chiou Shin-Yi
School of Sport, Exercise, and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom.
Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom.
Front Aging Neurosci. 2021 Aug 17;13:718784. doi: 10.3389/fnagi.2021.718784. eCollection 2021.
Anticipatory postural adjustments (APAs) are a feedforward mechanism for the maintenance of postural stability and are delayed in old adults. We previously showed in young adults that APAs of the trunk induced by a fast shoulder movement were mediated, at least in part, by a cortical mechanism. However, it remains unclear the relationship between delayed APAs and motor cortical excitability in ageing. Using transcranial magnetic stimulation we examined motor evoked potentials (MEPs) of the erector spinae (ES) muscles in healthy young and old adults prior to a fast shoulder flexion task. A recognition reaction time (RRT) paradigm was used where participants responded to a visual stimulus by flexing their shoulders bilaterally as fast as possible. The activity of bilateral anterior deltoid (AD) and ES muscles was recorded using electromyography (EMG). The onset of AD and ES EMG was measured to represent RRT and APAs, respectively. We found increases in amplitudes of ES MEPs at 40 ms than 50 ms prior to the EMG onset of the AD in both groups. The amplitude of ES MEPs at 40 ms prior to the onset of AD EMG correlated with the onset of ES activity counterbalancing the perturbation induced by the shoulder task in the elderly participants only. Our findings suggest that timing of increasing corticospinal excitability prior to a self-paced perturbation becomes more relevant with ageing in modulating postural control of the trunk.
预期姿势调整（APAs）是一种用于维持姿势稳定性的前馈机制，在老年人中会延迟。我们之前在年轻人中发现，快速肩部运动诱发的躯干APAs至少部分是由皮质机制介导的。然而，衰老过程中延迟的APAs与运动皮质兴奋性之间的关系仍不清楚。我们使用经颅磁刺激，在健康的年轻人和老年人进行快速肩部屈曲任务之前，检测竖脊肌（ES）的运动诱发电位（MEPs）。采用识别反应时（RRT）范式，参与者对视觉刺激做出尽可能快的双侧肩部屈曲反应。使用肌电图（EMG）记录双侧三角肌前部（AD）和ES肌肉的活动。分别测量AD和ES肌电图的起始时间来代表RRT和APAs。我们发现，两组中，在AD肌电图起始前40毫秒时ES MEPs的振幅比50毫秒时更高。仅在老年参与者中，AD肌电图起始前40毫秒时ES MEPs的振幅与ES活动的起始时间相关，ES活动可抵消肩部任务诱发的扰动。我们的研究结果表明，在自我调节的扰动之前增加皮质脊髓兴奋性的时间，在调节躯干姿势控制方面，随着年龄增长变得更加重要。
