Monosynaptic Stochastic Stimulation of Spinal Motoneurones in the Cat

Abstract

THE artificial nature of a synchronous afferent volley was pointed out many years ago¹ and, although neurophysiological knowledge has been considerably advanced by use of the synchronous volley technique, it has definite limitations in providing a full understanding of reflex mechanisms in the intact animal. Each annulo-spinal ending in a muscle under tension discharges in a quasi-periodic manner, and the differing stretch thresholds in these receptors² cause the average discharge frequency of each ending to differ. The timing of the initiation of impulses in one ending will be statistically independent of the times of occurrence of impulses in other endings. The convergence of these asynchronous impulse patterns onto a particular motoneurone represents a situation very different from that of synchronous stimulation and introduces the effects of temporal summation. If the object of the experiment is to establish relationships between afferent and reflex impulse patterns, natural stimulation by stretching muscle has severe limitations, because the temporal impulse patterns arriving at a particular motoneurone cannot be obtained. In the experiments described here, an attempt has been made to overcome this problem while retaining a stimulus which is physiologically realistic.