THE CAUSE OF REFLEX AFTERDISCHARGE IN THE FROG'S SPINAL CORD

Abstract

It is usually assumed that spinal reflex afterdischarge in the decerebrate or spinal animal is due to functional circuits of interneurons around which excitation can "chase its own tail" until fatigue brings the process to an end. This hypothesis has been tested in the frog. Reflex afterdischarge of motoneurons innervating the biceps femoris was produced by electrical stimulation of the ipsilateral foot. After the end of reflex stimulation, but during the afterdischarge, a direct single stimulus was applied to the animal's spinal cord. A strength of stimulus (of duration greater than five milliseconds) could always be found which would terminate the afterdischarge abruptly. This strong stimulus did not halt the afterdischarge by producing transient damage to the neurons of the cord, for when the stimulus was given during stimulation of the foot, there was no interruption of either reflex response or afterdischarge. Such experimental results are consistent with Forbes' hypothesis of reverberatory circuits.