Selective Activation of a Transient Reflex by Restricting Stimulation to Certain Frequencies

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Abstract
Summary.: Experiments have been carried out on decerebrate cats with a view to studying the effect of frequency of stimulation upon reflex activity.With frequencies between 50–100 per sec. stimulation of the sciatic nerve activated a late secondary extensor reflex after a latent period of 3–5 sec. This reflex was transient in the sense that it lasted only about 15–30 sec. The optimal frequency, for which this transient reflex was maximal, was 90—100 per sec.The transient extensor contraction was found to be part of a complex general defensor pattern involving extension of all limbs, ventroflexion of the trunk and the tail, wihdrawal of the head, and a number of vegetative components such as micturition, raise of blood pressure (cf. Aschkenaz 1939), and pupil dilatation. The vegetative effects were also observed in animals which had received dial and therefore did not show the motor reactions. The whole defensor reflex pattern was optimally evoked by the frequency optimal for the extensor contraction.The transient extensor reflex turned up bilaterally. When evoked by an ipsilateral stimulus in the midst of a crossed extensor it showed itself as a transitory contraction in the trough of the ipsilateral inhibitory effect. However, it turned up equally well without a background of crossed extension. When elicited by crossed stimulation the transient effect had the shape of a hump on the ordinary crossed extensor reflex, provided that the frequency of the stimulus was sufficiently high.No proprioceptive background was necessary for the transient extensor contraction, as shown by deafferentation.Section of the spinal cord in the lower thoracic region did not abolish the reflex.The transient reflex could be elicited from n. popliteus but not from nn. peroneus, saphenus and glut. sup.

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