Day B L, Rothwell J C, Thompson P D, Dick J P, Cowan J M, Berardelli A, Marsden C D
MRC Movement Disorders Research Group, University Department of Neurology, DeCrespigny Park, London.
Brain. 1987 Oct;110 ( Pt 5):1191-209. doi: 10.1093/brain/110.5.1191.
Using an isometric strain gauge, we measured the twitch force produced in the first dorsal interosseous (FDI) muscle by a single anodal shock to the contralateral scalp. At high intensities of stimulation this twitch can greatly exceed the force produced by supramaximal stimulation of peripheral nerve. This indicates that a single cortical shock can cause repetitive firing of some or all FDI motoneurons. Such repetitive firing was demonstrated using a collision technique in which a supramaximal ulnar nerve stimulus was given at the wrist shortly after a cortical shock. The antidromic volley from the peripheral nerve stimulation failed to obliterate completely the response to cortical stimulation. Additional EMG activity was visible in the normally silent period between ulnar M and F waves. This activity must have been due to the presence of repetitive volleys of activity set up in spinal motoneurons by the cortical shock. Such activity summates with the twitch produced by the ulnar M wave to produce a very large force twitch of the muscle. Multiple firing of some motoneurons can be observed in some individuals at cortical stimulation intensities below that necessary to evoke activity in all the motoneurons in the FDI pool. Multiple firing probably was caused by repetitive excitatory inputs impinging on spinal motoneurons. These could be demonstrated using poststimulus time histogram techniques on single motor units. Low intensities of cortical stimulation produced a single short duration (mean 1.8 ms) peak of increased motor unit firing 20 to 30 ms after the shock. At high intensities, this was followed by extra peaks some 4 to 5 ms later. H reflex testing showed that the threshold of the initial descending volley, produced by the cortical stimulus was uninfluenced by a voluntary contraction. These results are discussed with reference to the D and I waves recorded from pyramidal tract after anodal stimulation of the exposed cortex in animals.
我们使用等长应变计，通过对侧头皮单次阳极电刺激来测量第一背侧骨间肌（FDI）产生的抽搐力。在高强度刺激下，这种抽搐力可大大超过外周神经超强刺激所产生的力。这表明单次皮层电刺激可导致部分或所有FDI运动神经元重复放电。使用碰撞技术证实了这种重复放电，即在皮层电刺激后不久于腕部给予超强尺神经刺激。外周神经刺激产生的逆向冲动未能完全消除对皮层刺激的反应。在尺神经M波和F波之间通常的静息期可见额外的肌电图活动。这种活动必定是由于皮层电刺激在脊髓运动神经元中引发的重复冲动所致。这种活动与尺神经M波产生的抽搐相加，从而产生肌肉非常大的强力抽搐。在某些个体中，当皮层刺激强度低于引发FDI运动神经元池所有运动神经元活动所需强度时，可观察到一些运动神经元的多重放电。多重放电可能是由撞击脊髓运动神经元的重复兴奋性输入引起的。使用单运动单位的刺激后时间直方图技术可证实这些情况。低强度皮层刺激在刺激后20至30毫秒产生单个持续时间短（平均1.8毫秒）的运动单位放电增加峰值。在高强度时，随后约在4至-5毫秒出现额外的峰值。H反射测试表明，皮层刺激产生的初始下行冲动的阈值不受随意收缩的影响。结合动物暴露皮层阳极刺激后锥体束记录的D波和I波对这些结果进行了讨论。
