THE SUPERNORMAL PERIOD IN THE RECOVERY CYCLE OF MOTONEURONS

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Abstract
A study of the phenomenon of spontaneous "doubling" in the rhythmic discharge of soleus and triceps motoneurones of the decerebrate cat was made in 25 animals. An analogy between the phenomenon of spontaneous "doubling" in the rhythmic discharge of soleus and triceps motoneurones and bigeminus rhythm in the heart leads to the suggestion that a supernormal period exists in the recovery cycle of these neurones. Procedures known to enhance supernor-mality in peripheral tissue, namely, acidity, and adm. of veratrine, increase the frequency with which spontaneous doubling appears, make possible the establishment of "double" rhythms, and permit "tripling" and even perhaps "quadrupling." With veratrine as many as 6 discharges in rapid series have been counted. Cooling increases doubling. The apparently paradoxical effect of this agent is noted also in isolated nerve fibers. The various phenomena observed may be explained best by the assumption that the neurones studied recover from a propagated discharge via supernormality. The immediate usefulness of supernormality may be to permit the rapid development of muscular tension at the start of reflex activity. The possibility is opened for the existence in the CNS of a type of temporal summation based on threshold lowering following a subliminal stimulus (the 2d phase of summation).

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