Serial records of H-reflex of splnal motoneuron were obtained by the recording of action potential of soleus muscle, triggered by conditioning and testing electrical shocks on the posterior tibial nerve. The fascilitation and recovery process of the spinal motoneuron was studied by the serial records of the H-reflex. The clinical material was 30 cases including normal subjects, patients with pyramidal lesion, and patients in acute stage of cerebrel
intervantion. In commonly, the H-reflex triggered by test shock (H) was not observed by the test shock which was given within 3 millisecond (ms') following conditioning shock, but start to appeared at 4ms appeared in peak amplitude (maximal deflection) at 6ms., and disappeared by 9 to 13ms. Later than 9 to 13ms., H-reflex falled in a silent period. However, the detail of the abovementioned characteristics of the H-reflex appeared in some difference, i.e. on the patient with pyramidal lesion H-reflex continued to appear until 18ms. with maximal deflection of 150% of the H-reflex, on the normal subject those were 10ms. and on the patient in acute stadium of cerebral surgical intervention those were 9ms. and 50% . The author intended to describe the complate disappearance of H-reflex within 3ms. following conditioning shock as the first silent period, and presumed that the first silent
period would be the result of combination of refractory period of Group Ia fiber and inhibition of Group Ib fiber. The auther also would suppose the detailed characteristics of the H-reflex at the period of 4 to 10ms. following conditioning shock was caused by the afterhyperexcitability of the motoneuron by the conditioning shock as well as summation of the test shock, but the IPSP of Group Ib efferent impulses and influence of Renshow cell were other important mechanisms. The author intended to call abovementioned brocess the fascillitatry of human H-reflex.