STUDIES IN THE PHYSIOLOGY OF THE NERVOUS SYSTEM. XII.: RHYTHMIC RESPONSES IN THE SIMPLE REFLEX —PROGRESSION—SCRATCH
Authors: Brown T. Graham 
Published: December 2014

1. In this paper are described certain rhythmic reflex movements which occur in response to “simple” stimuli—that is, to stimuli (rapid faradic) which are applied to a single peripheral nerve. In this case the nerves stimulated have been the ipsilateral and contralateral long saphenous nerves—nerves which are peculiar to the hind limbs themselves,2. The movements have been examined as they occur in two antagonistic muscles, tibialis anticus and gastrocnemius, which act upon the ankle joint; and in the decerebrate, high spinal (decapitate), and low spinal preparations of the cat; as well as in the normal and in the de‐afferented conditions of each of these preparations.3. In the low spinal preparation rhythmic reflex reactions have been evoked in response to contralateral stimuli when these were applied immediately after the division of the spinal cord which made the preparation low spinal. There was then in being the maintained extensor contraction which terminates the phenomena which are obtained upon rapid division of the spinal cord. This rhythmic reaction is one of some rarity in the low spinal preparation.4. Rhythmic responses which resemble the movements of progression and are obtained upon stimulation of the skin about the root of the hind limb are also figured.5. In the low spinal preparation simple stimuli may evoke rhythmic responses if applied immediately after the mechanical stimulation of the upper end of the caudal portion of the divided spinal cord. In the experiment here illustrated these occurred in response to a contralateral stimulus which evoked an abnormal crossed flexion‐reflex before the mechanical stimulation of the cord. The rhythmic response may open either with a flexor or with an extensor contraction. It resembles most closely the movements of progression, and the reciprocal relationships of the movements in the two antagonists are described in the text.6. In the high spinal preparation (decapitate) rhythmic movements of sartorius in response to contralateral stimulation of the great sciatic nerve are described. These in their rhythm closely corresponded to the movements of progression under narcosis which occurred in the same experiment.7. In the decerebrate preparation rhythmic responses are much more common than in the spinal preparations. They may occur in response either to ipsilateral or to contralateral stimuli. The rate of the rhythm in these movements may be comparatively fast, or it may be comparatively slow; while in many instances intermediate rates of rhythm occur.8. The slow rhythmic movements which occur in the decerebrate preparation upon the whole correspond to the rhythmic movements of progression. Various degrees of completeness of the rhythmic phenomenon occur.9. In the first place, an ipsilateral stimulus may evoke a flexion response which is at first arrhythmic, but is later broken by beats which occur as partial relaxations followed by complete restitutions of the maintained flexor contraction.10. A second degree of completeness is that in which the flexor response is from the commencement rhythmically interrupted, but in which the beats are either constituted by partial relaxations, or, if the relaxations be complete (that is, bring the length of the muscle to the level which obtained before stimulation), are not separated by pauses at the level of complete relaxation.11. The complete phenomenon is that in which the flexor beats are complete and are separated by well‐marked pauses at the level of complete relaxation.12. In the first and second of these three forms the extensor muscle shews little or no evidence of movement. In the second there may, however, be slight contractions synchronous with the flexor relaxations. In the third, or complete form, the extensor exhibits a maintained contraction—evidenced in the flexor pauses—which is broken by relaxations and reconstitutions which synchronise with the flexor contractions and relaxations.13. A contralateral stimulus may also evoke a rhythmic reaction in the decerebrate preparation. This may occur when the reaction is of the abnormal flexion type, or of the normal extension type. In the latter case the reaction opens with a maintained extensor contraction, which is later broken by the appearance of a rhythmic movement synchronous with a flexor rhythmic phenomenon. In the flexor this may be completely rhythmic or incompletely rhythmic—as in the case of ipsilateral responses.14. In the decerebrate preparation fast rhythmic movements which resemble the scratch‐reflex may also be obtained in response either to ipsilateral or to contralateral stimuli. Both the antagonists then simultaneously shew a certain amount of maintained contraction, and when the rhythmic phenomenon occurs, it does so as reciprocally ordered relaxations and contractions in the two muscles. The rhythmic series shews slowing towards the end, and pauses then occur between the beats. In the experiments examined, the flexor pauses seemed to occur at the level of maximum relaxation, while the extensor pauses occurred at the level of maximum contraction. In these pauses both the muscles exhibited a certain degree of maintained contraction—the flexor relaxations then being incomplete.15. In the de‐afferented condition of the various preparations rhythmic reflex responses may occur. One case here described (in which the extensor only was completely de‐afferented) is of interest in that there was a rhythmic rebound phenomenon as well as a rhythmic response during the application of the stimulus. Here during stimulation there seemed to be a foundation of maintained extensor contraction upon which the rhythmic phenomenon was superposed; for gastrocnemius gave indication of pauses at the level of maintained contraction, and remained in contraction after the cessation of the rhythmic responses during stimulation, while at the same time there appeared to be flexor pauses at the level of complete relaxation. In the rebound phenomenon, however, the reverse seemed to be the case; for the flexor exhibited pauses at the level of maximum contraction, while the extensor pauses were at the level of maximum relaxation.16. Although the stimuli used in these experiments were “simple,” it must not be assumed that the rhythmic phenomena here described may not be conditioned by a compounding of stimuli. In the decerebrate preparation there is a background of “extensor rigidity.” In the low spinal preparations the rhythmic phenomena occurred when there was also a similar state. So that the rhythmic phenomena described in this paper may have been conditioned by the interaction of two different states of the centres—the one conditioned by the peripheral stimulus used, and the other the background conditioned either by the decerebrate rigidity or by the mechanical stimulation of the spinal cord.