Departments of Neurology and Psychiatry, University of Colorado Denver, Mail Stop B185, 12631 East 17th Avenue, Aurora, CO 80045, USA.
Exp Brain Res. 2012 Feb;216(4):585-90. doi: 10.1007/s00221-011-2962-y. Epub 2011 Dec 1.
Prior reports have described a transient and focal decline in transcranial magnetic stimulation (TMS)-induced motor evoked potential (MEP) amplitude following fatiguing motor tasks. However, the neurophysiological causes of this change in MEP amplitude are unknown. The aim of this study was to determine whether post-task depression of MEPs is associated with repetitive central motor initiation. We hypothesized that MEP depression is related to repeated central initiation of motor commands in task-related cortex independent of motor fatigue. Twenty healthy adults had MEPs measured from the dominant first dorsal interosseous (FDI) muscle before and after six different tasks: rest (no activity), contralateral fatiguing hand-grip, ipsilateral fatiguing hand-grip, contralateral finger tapping, ipsilateral finger tapping, and imagined hand-grip (motor imagery). Changes in MEPs from baseline were assessed for each task immediately following the task and at 2-min intervals until MEPs returned to a stable baseline. Measures of subjective effort and FDI maximum voluntary contractions (MVC) were also recorded following each task. A statistically significant drop in MEP amplitude was noted only with contralateral finger tapping and imagined grip. Changes in MEP amplitude did not correlate with subjective fatigue or effort. There was no significant change in FDI MVCs following hand-grip or finger-tapping tasks. This study extends our knowledge of the observed decline in MEP amplitude following certain tasks. Our results suggest that central initiation of motor programs may induce a change in MEP amplitude, even in the absence of objective fatigue.
先前的报告描述了在疲劳性运动任务后，经颅磁刺激（TMS）诱发的运动诱发电位（MEP）幅度会出现短暂和局灶性下降。然而，这种 MEP 幅度变化的神经生理原因尚不清楚。本研究旨在确定任务后 MEP 抑制是否与重复的中枢运动起始有关。我们假设 MEP 抑制与任务相关皮层中运动指令的重复中枢发起有关，而与运动疲劳无关。20 名健康成年人在进行六项不同任务（休息、对侧手疲劳握力、同侧手疲劳握力、对侧手指敲击、同侧手指敲击和想象手握力）之前和之后，从优势第一背侧骨间肌（FDI）测量 MEP。在任务后立即和 2 分钟间隔评估每个任务的 MEP 与基线相比的变化，直到 MEP 恢复到稳定基线。在完成每项任务后，还记录了 MEPs 的主观努力和 FDI 最大自主收缩（MVC）的变化。仅在对侧手指敲击和想象握力时才观察到 MEP 幅度的明显下降。MEP 幅度的变化与主观疲劳或努力无关。在握力或手指敲击任务后，FDI MVC 没有明显变化。本研究扩展了我们对某些任务后 MEP 幅度下降的认识。我们的结果表明，运动程序的中枢发起即使在没有客观疲劳的情况下，也可能引起 MEP 幅度的变化。
