Corticospinal input in human gait: Modulation of magnetically evoked motor responses
Corticospinal input in human gait: Modulation of magnetically evoked motor responses
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DOI：
10.1007/pl00005693
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发表时间：
1997-06-01
影响因子：
2
通讯作者：
Dietz, V
中科院分区：
文献类型：
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作者：
Schubert, M;Curt, A;Dietz, V
在运动时对运动皮质进行经颅磁刺激(TMS)，以研究皮质脊髓输入对步态模式的意义。研究了健康成人在跑步机上行走时，施加阈值以下磁刺激对胫前肌(TA)、腓肠肌(GM)和小指展肌(AD)肌电的诱发运动反应(EMR)。分析了在步幅周期的16个阶段中每个阶段随机引入的15个刺激的平均值。在TA和GM中，EMR的相位相关幅度调制并不总是平行于步态相关的EMG活动的调制。EMR的起搏潜伏期无明显变化。通过比较步态中的EMR幅度和紧张性随意肌肉收缩时获得的EMR幅度(相应的背景EMC活动时)，计算净调制反应。在运动模式中，两个肌肉中的大净反应发生在肌电活动的相变之前或期间。这种EMR的易化作用在小腿屈肌显著高于伸肌，最大值在摆动前和摆动后期出现在TA。在摆动阶段和主动足背屈阶段之前，对TA EMR的这种促进作用的比较显示，在步态条件下，早期促进作用的数量增加了，但开始时间相似。EMR在运动过程中的调制易化部分可以用动态和静态运动条件下不同的脊髓效应来解释。然而，我们认为，在步态过程中皮质脊髓兴奋性的变化也反映在这种易化中。这一建议是基于：(1)在步态周期的摆动阶段之前和在自主动态激活期间，TA EMR的易化效应的开始相似但大小不同，(2)EMR和EMG幅度在这一阶段的反向变化，以及(3)这种倒置的发生在：刺激强度低于运动阈值(运动阈值在WEL期间确定；紧张性收缩和EMR在步态期间被促进)。假设促进是相关联的，以确保姿势稳定，并且在腿部肌肉有节奏地激活之前和期间的阶段最有效，从而导致运动模式的预期调整。
Transcranial magnetic stimulation (TMS) of the motor cortex was applied during locomotion to investigate the significance of corticospinal input upon the gait pattern. Evoked motor responses (EMR) were studied in the electromyogram (EMG) of tibialis anterior (TA), gastrocnemius (GM) and, for reference, abductor digiti minimi (AD) muscles by applying below-threshold magnetic stimuli during treadmill walking in healthy adults. Averages of 15 stimuli introduced randomly at each of 16 phases of the stride cycle were analysed. Phase-dependent amplitude modulation of EMR was present in TA and GM which did not always parallel the gait-associated modulation of the EMG activity. No variation of onset latency of the EMR was observed. The net modulatory response was calculated by comparing EMR amplitudes during gait with EMR amplitudes obtained (at corresponding background EMC activities) during tonic voluntary muscle contraction. Large net responses in both muscles occurred prior lo or during phasic changes of EMG activity in the locomotor pattern. This facilitation of EMR was significantly higher in leg flexor than extensor muscles, with maxima in TA prior to and during late swing phase. A comparison of this facilitation of TA EMR prior to swing phase and prior to a phasic voluntary foot dorsiflexion revealed a similar onset but an increased amount of early facilitation in the gait condition. The modulated facilitation of EMR during locomotion could in part be explained by spinal effects which are different under dynamic and static motor conditions. However, we suggest that changes in corticospinal excitability during gait are also reflected in this facilitation. This suggestion is based on: (I) the similar onset yet dissimilar size of facilitatory effects in TA EMR prior to the swing phase of the stride cycle and during a voluntary dynamic activation, (2) the inverse variation of EMR and EMG amplitudes during this phase, and (3) the occurrence of this inversion at: stimulation strengths below motor threshold (motor threshold was determined during weal; tonic contraction and EMR were facilitated during gait). It is hypothesized that the facilitation is phase Linked to ensure postural stability and is most effective during the phases prior to and during rhythmical activation of the leg muscles resulting in anticipatory adjustment of the locomotor pattern.