Influence of Stimulus Pattern on Reflex Deglutition

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Abstract
Deglutition evoked in the dog by superior laryngeal nerve stimulation is relatively indefatigable. 1500 swallows in an hr. of continuous stimulation are possible. An optimal stimulus frequency, at which deglutition is elicited with the shortest latency, the lowest threshold, and the most rapid continuing rate, is a species characteristic (dog, 20-30/sec; rabbit, 60-80; cat, 30-50). A limiting frequency (dog, 50-100), above which the reflex is unobtainable with moderate stimuli, is precise to within 3/sec. for any given condition, but varies, as does the latent period (0.5-60 sec), but not the optimal frequency, with the time since the preceding swallow, the intensity of stimulation, the rapidity of respiration, and the depth of anesthesia, and under strychnine or myanesin. The latent period for a 2d ipsilateral excitation is roughly proportional to the time (up to 3 min.) since the cessation of the first, whereas contralateral facilitation disappears in about 10 sec. Concurrent stimulation of one superior laryngeal above the limiting frequency does not affect the response to optimal stimulation of the other or of a glossopharyngeal; but central summation results on stimulation of both superior laryngeals at subliminal frequency or intensity. Block with rapid stimulation is thus upstream to the crossed summation. The optimal response is remarkably independent of the temporal patterning of trains of stimuli; the CMS seemingly counts and adds pulses irrespective of when delivered, within spans of hundreds of milliseconds.
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