Maertens de Noordhout A, Rothwell J C, Day B L, Thompson P D, Delwaide P J, Marsden C D
Département Universitaire de Neurologie, Hôpital de la Citadelle, Liège, Belgique.
Rev Neurol (Paris). 1989;145(1):1-15.
The new techniques of percutaneous electric and magnetic stimulation of the motor cortex in conscious man provide a unique opportunity of functional testing of the central motor pathways. These techniques seem to be safe and no immediate or delayed adverse reactions have been reported. The physiological studies so far performed suggest that the structures which are preferentially excited by these methods are the fast conducting pyramidal neurones. It has been shown that a single cortical stimulus is able to activate spinal motoneurones repeatedly. This phenomenon can easily be explained if the cortical stimulus generates multiple descending volleys in the central motor pathways. By comparison with experiments of stimulation of the exposed motor cortex in animals, it is likely that electric brain stimulation directly activates the axons of the pyramidal neurons at their origin and to a lesser extent also recruits these neurons transsynaptically, via some cortical interneurones. Magnetic stimulation of the brain at the vertex seems to act mostly by the latter mechanism. These different modes of action of the two methods of cortical stimulation explain the latency differences of the EMG responses obtained with either technique. Increased excitability of the spinal motoneurones and the existence of multiple descending volleys in response to a single cortical stimulus result in shortening of the latencies and greater amplitude of the responses recorded during voluntary contraction of the target muscle. Stimulation of the motor cortex has been used in pilot studies conducted on patients suffering from various disorders of the central motor pathways, such as multiple sclerosis, cervical spondylosis, motor neurone disease or stroke. The sensitivity of the technique looks promising. In M.S., the EMG responses usually show an increased central conduction latency, a reduced amplitude and a prolonged duration. The severity of the electrophysiological abnormalities is not very well correlated with clinical weakness, but the correlations seems to be better with hyperreflexia and the presence of brisk finger flexor jerks. The same abnormalities are observed in cervical spondylosis, although to a lesser extent. In motor neurone disease, the responses have a moderately increased latency and their size and duration are markedly reduced. Patients with acute hemispheric stroke usually show absent responses on the contralateral side. Finally, electric cortical stimulation can be very useful in monitoring the functional integrity of descending motor tracts during surgical operations performed on the spinal cord.
在清醒人体中经皮电刺激和磁刺激运动皮层的新技术，为中枢运动通路的功能测试提供了独特的机会。这些技术似乎是安全的，且尚未有即时或延迟不良反应的报道。迄今为止所进行的生理学研究表明，这些方法优先兴奋的结构是传导速度快的锥体神经元。已经表明，单次皮层刺激能够反复激活脊髓运动神经元。如果皮层刺激在中枢运动通路中产生多个下行冲动群，那么这种现象就很容易解释。与刺激动物暴露的运动皮层的实验相比，脑电刺激很可能直接激活锥体神经元的轴突起始部位，并且在较小程度上也通过一些皮层中间神经元经突触募集这些神经元。在头顶进行脑磁刺激似乎主要通过后一种机制起作用。皮层刺激这两种方法的这些不同作用方式，解释了用这两种技术获得的肌电图反应的潜伏期差异。脊髓运动神经元兴奋性增加以及对单次皮层刺激存在多个下行冲动群，导致在目标肌肉自主收缩期间记录到的反应潜伏期缩短且幅度增大。运动皮层刺激已用于对患有各种中枢运动通路疾病的患者进行的初步研究，如多发性硬化症、颈椎病、运动神经元病或中风。该技术的敏感性看起来很有前景。在多发性硬化症中，肌电图反应通常显示中枢传导潜伏期延长、幅度降低和持续时间延长。电生理异常的严重程度与临床肌无力的相关性不是很好，但与反射亢进和快速的手指屈肌抽搐的存在相关性似乎更好。在颈椎病中也观察到同样的异常，尽管程度较轻。在运动神经元病中，反应潜伏期适度延长，其大小和持续时间明显缩短。急性半球性中风患者通常在对侧无反应。最后，在对脊髓进行手术操作期间，皮层电刺激对于监测下行运动束的功能完整性可能非常有用。
