DISTRIBUTION OF RECURRENT FACILITATION AND INHIBITION IN CAT SPINAL CORD

Abstract

By means of experiments in which monosynaptic test reflexes are conditioned by antidromic stimulation of muscle nerves, an organized pattern is demonstrated in the distribution of recurrent facilitation and inhibition. Facilitation occurs most frequently where flexor nuclei are conditioned by stimulation of extensors. When extensors condition extensors, or flexors condition flexors, inhibition is usually seen. Little effect is obtained in attempts to condition extensors with flexors. Where there is pronounced conditioning between muscles of a myotatic unit, this conditioning is generally opposite in direction to direct inhibition or monosynaptic facilitation between the same muscles. The distribution of recurrent conditioning resembles that of group 1B actions. In the action of recurrent conditioning, there is an asymmetry which favors flexor nuclei. This appears to be part of a general asymmetry in the central interactions between extensors and flexors. Possible roles of recurrent action are discussed.