Department of Kinesiology, Brock University , St. Catharines, Ontario , Canada.
Movement and Sport Sciences, Department of Neurosciences and Movement Sciences, University of Fribourg , Fribourg , Switzerland.
J Neurophysiol. 2018 Sep 1;120(3):1010-1016. doi: 10.1152/jn.00709.2017. Epub 2018 May 23.
Cortical excitability increases during the performance of more difficult postural tasks. However, it is possible that changes in postural threat associated with more difficult tasks may in themselves lead to alterations in the neural strategies underlying postural control. Therefore, the purpose of this study was to examine whether changes in postural threat are responsible for the alterations in corticospinal excitability and short-interval intracortical inhibition (SICI) that occur with increasing postural task difficulty. Fourteen adults completed three postural tasks (supported standing, free standing, or standing on an unstable board) at two surface heights (ground level or 3 m above ground). Single- and paired-pulse magnetic stimuli were applied to the motor cortex to compare soleus (SOL) and tibialis anterior (TA) test motor-evoked potentials (MEPs) and SICI between conditions. SOL and TA test MEPs increased from 0.35 ± 0.29 to 0.82 ± 0.41 mV (SOL) and from 0.64 ± 0.51 to 1.96 ± 1.45 mV (TA), respectively, whereas SICI decreased from 52.4 ± 17.2% to 39.6 ± 15.4% (SOL) and from 71.3 ± 17.7% to 50.3 ± 19.9% (TA) with increasing task difficulty. In contrast to the effects of task difficulty, only SOL test MEPs were smaller when participants stood at high (0.49 ± 0.29 mV) compared with low height (0.61 ± 0.40 mV). Because the presence of postural threat did not lead to any additional changes in the excitability of the motor corticospinal pathway and intracortical inhibition with increasing task difficulty, it seems unlikely that alterations in perceived threat are primarily responsible for the neurophysiological changes that are observed with increasing postural task difficulty. NEW & NOTEWORTHY We examined how task difficulty and postural threat influence the cortical control of posture. Results indicated that the motor corticospinal pathway and intracortical inhibition were modulated more by task difficulty than postural threat. Furthermore, because the presence of postural threat during the performance of various postural tasks did not lead to summative changes in motor-evoked potentials, alterations in perceived threat are not responsible for the neurophysiological changes that occur with increasing postural task difficulty.
在进行更困难的姿势任务时，皮质兴奋性会增加。然而，与更困难任务相关的姿势威胁的变化本身可能导致姿势控制的神经策略发生改变。因此，本研究的目的是检验姿势威胁的变化是否是导致随着姿势任务难度增加而出现皮质脊髓兴奋性和短潜伏期皮质内抑制（SICI）变化的原因。14 名成年人在两种表面高度（地面或离地面 3 米）下完成三种姿势任务（支撑站立、自由站立或站在不稳定的板上）。应用单脉冲和双脉冲磁刺激来比较腓肠肌（SOL）和胫骨前肌（TA）测试运动诱发电位（MEP）和 SICI 之间的条件。SOL 和 TA 测试 MEP 分别从 0.35±0.29 增加到 0.82±0.41 mV（SOL）和从 0.64±0.51 增加到 1.96±1.45 mV（TA），而 SICI 从 52.4±17.2%降低到 39.6±15.4%（SOL）和从 71.3±17.7%降低到 50.3±19.9%（TA），随着任务难度的增加而降低。与任务难度的影响相反，只有当参与者站在高处（0.49±0.29 mV）时，SOL 测试 MEP 才小于低处（0.61±0.40 mV）。由于随着任务难度的增加，姿势威胁的存在并没有导致运动皮质脊髓通路和皮质内抑制的兴奋性发生任何额外的变化，因此，感觉威胁的改变不太可能是导致随着姿势任务难度增加而观察到的神经生理变化的主要原因。新内容和值得注意的内容：我们研究了任务难度和姿势威胁如何影响姿势的皮质控制。结果表明，运动皮质脊髓通路和皮质内抑制更多地受到任务难度的调节，而不是姿势威胁。此外，由于在执行各种姿势任务时存在姿势威胁并没有导致运动诱发电位的累积变化，因此，感知威胁的改变并不是导致随着姿势任务难度增加而发生的神经生理变化的原因。
