Schubert M, Curt A, Jensen L, Dietz V
Department of Clinical Neurology and Neurophysiology, University of Freiburg, Germany.
Exp Brain Res. 1997 Jun;115(2):234-46. doi: 10.1007/pl00005693.
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 EMG activities) during tonic voluntary muscle contraction. Large net responses in both muscles occurred prior to 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: (1) 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 weak 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.
在运动过程中对运动皮层进行经颅磁刺激（TMS），以研究皮质脊髓输入对步态模式的意义。在健康成年人在跑步机上行走时，通过施加阈下磁刺激，在胫前肌（TA）、腓肠肌（GM）以及作为参考的小指展肌（AD）的肌电图（EMG）中研究诱发运动反应（EMR）。分析了在步幅周期的16个阶段中的每个阶段随机引入的15次刺激的平均值。TA和GM中存在EMR的相位依赖性幅度调制，但其并不总是与EMG活动的步态相关调制平行。未观察到EMR起始潜伏期的变化。通过比较步态期间的EMR幅度与在强直性随意肌肉收缩期间获得的（在相应背景EMG活动下）EMR幅度来计算净调制反应。在运动模式中，EMG活动的相位变化之前或期间，两块肌肉均出现了较大的净反应。腿部屈肌的EMR促进作用明显高于伸肌，在摆动后期之前和期间，TA中的促进作用最大。比较摆动期之前和阶段性随意足背屈之前TA的EMR促进作用，发现起始相似，但在步态条件下早期促进作用的量增加。运动过程中EMR的调制促进作用部分可以由脊髓效应来解释，脊髓效应在动态和静态运动条件下有所不同。然而，我们认为步态期间皮质脊髓兴奋性的变化也反映在这种促进作用中。这一观点基于：（1）在步幅周期的摆动期之前和随意动态激活期间，TA的EMR促进作用起始相似但大小不同；（2）在此阶段EMR和EMG幅度的反向变化；（3）在低于运动阈值的刺激强度下出现这种反转（运动阈值在弱强直性收缩期间确定，而EMR在步态期间得到促进）。据推测，这种促进作用与相位相关，以确保姿势稳定性，并且在腿部肌肉有节奏激活之前和期间的阶段最为有效，从而导致运动模式预先调整。
