Lavoie B A, Cody F W, Capaday C
Centre de Recherche en Neurobiologie, Hôpital de l'Enfant-Jésus, Québec, Canada.
Exp Brain Res. 1995;103(1):97-107. doi: 10.1007/BF00241968.
The surface-recorded electromyographic (EMG) responses evoked in the ankle musculature by focal, transcranial, magnetic stimulation of the motor cortex were studied in healthy human subjects. Such soleus evoked motor responses (EMRs) were characterised over a wide range of background levels of motor activity and using different stimulus intensities. EMRs were recorded during predominantly (1) volitional and (2) postural tasks. In the former task subjects were seated and voluntarily produced prescribed levels of soleus activation by reference to a visual monitor of EMG. In the latter task subjects assumed standing postures without EMG feedback. Comparison of the EMRs of soleus, traditionally considered a slow anti-gravity extensor muscle, during these tasks was used to evaluate its cortical control in primarily volitional versus primarily postural activities. The form of soleus EMRs produced by single magnetic cortical stimuli comprised an initial (approx. 30 ms) increase and subsequent (approx. 50 ms) depression of EMG. Cortical stimulation could elicit substantial excitatory soleus EMG responses; for example, responses evoked by mild, magnetic stimuli (125% threshold for inducing a response in the relaxed muscle) as subjects exerted full voluntary plantarflexor effort averaged almost 20% of the maximum M-wave which could be elicited by an electrical stimulus to the posterior tibial nerve. Excitatory EMRs could be elicited in the voluntarily relaxed soleus muscle of the majority of subjects during sitting. The amplitude of soleus responses, induced by threshold stimuli for the relaxed state or approximately 125% threshold intensity, increased approximately linearly with background EMG over a wide range of volitional contraction levels. By contrast, there was no systematic change in the latency of excitatory soleus EMRs with increasing voluntary effort. The excitatory responses evoked in the voluntarily relaxed soleus of seated subjects by magnetic stimulation were regularly facilitated by incremental, voluntary contraction of the contralateral ankle extensors in a graded manner. However, such facilitation of responses was not observed when subjects voluntarily activated the muscle in which EMRs were elicited. The pattern of the responses elicited in soleus by magnetic stimulation during the postural task generally resembled that found during the volitional task. The amplitudes of excitatory soleus EMRs at a given stimulus intensity, obtained when subjects stood quietly, leaned forwards or stood on their toes to produce differing levels of ankle extensor contraction, increased with background EMG.(ABSTRACT TRUNCATED AT 400 WORDS)
在健康人体受试者中，研究了通过对运动皮层进行局灶性、经颅磁刺激在踝关节肌肉组织中诱发的表面记录肌电图（EMG）反应。在广泛的运动活动背景水平下，并使用不同的刺激强度，对这种比目鱼肌诱发运动反应（EMRs）进行了特征描述。EMRs记录于主要的（1）随意性任务和（2）姿势性任务期间。在前一项任务中，受试者坐着，通过参考EMG视觉监测器，自愿产生规定水平的比目鱼肌激活。在后一项任务中，受试者在没有EMG反馈的情况下采取站立姿势。在这些任务中，对传统上被认为是缓慢的抗重力伸肌的比目鱼肌的EMRs进行比较，以评估其在主要随意性活动与主要姿势性活动中的皮层控制。单次磁皮层刺激产生的比目鱼肌EMRs形式包括EMG最初（约30毫秒）增加和随后（约50毫秒）降低。皮层刺激可引发显著的兴奋性比目鱼肌EMG反应；例如，当受试者进行最大程度的随意跖屈用力时，轻度磁刺激（诱发放松肌肉反应的阈值的125%）引发的反应平均几乎达到由胫后神经电刺激诱发的最大M波的20%。在大多数受试者坐着时，可在其自愿放松的比目鱼肌中诱发兴奋性EMRs。在广泛的随意收缩水平范围内，由放松状态的阈值刺激或约125%阈值强度诱发的比目鱼肌反应幅度，随背景EMG大致呈线性增加。相比之下，随着随意用力增加，兴奋性比目鱼肌EMRs的潜伏期没有系统性变化。通过对侧踝关节伸肌的递增性随意收缩，以分级方式定期促进了磁刺激在坐着的受试者自愿放松的比目鱼肌中诱发的兴奋性反应。然而，当受试者自愿激活诱发EMRs的肌肉时，未观察到这种反应促进现象。姿势性任务期间磁刺激在比目鱼肌中诱发的反应模式通常类似于在随意性任务中发现的模式。当受试者安静站立、向前倾或踮脚尖以产生不同程度的踝关节伸肌收缩时，在给定刺激强度下获得的兴奋性比目鱼肌EMRs幅度随背景EMG增加。（摘要截断于400字）
