THE ACTION POTENTIALS OF THE AUDITORY NERVE

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Abstract
Action potentials of auditory nerve of the cat were led by coaxial electrodes through a resistance-capacity coupled amplifier and recorded with a cathode ray oscillograph. Continued stimulation, by clicks from a dynatron oscillator (60-12,000 c.p.s.) fed through a loud speaker, leads to a decrease in potential size as stimulation frequency increases. This "equilibration," involving decrease in the potential of each fiber and increase in the number of fibers responding alternately, shows a fast phase within 2 sec. and a slow one within 7 min. Above 1000 c.p.s. the unequilibrated response decreases by half, an octave higher it decreases again, and above 3000 c.p.s. asyn-chrony occurs. The lowest frequency indicating alter-nation of activity yields a measure of the "functional" refractory period of the sensori-neural mechanism, including the non-medullated peripheral terminations of the axons. This period is at most 1 ms. since alternation occurs at 1000 c.p.s. and the frequency of impulses in a fiber 1000/sec. Results support the "place resonance" theory of audition, since the ventral part of the nerve is more sensitive to lower tones and has a longer latency than does the dorsal part and since the cochlear response of the cat is similar to that of man. Response to clicks, recorded at the round window, shows the cochlear response to be followed by 1 to 3 groups of waves, differing in latency, maximal amplitude and threshold; the anatomical correlation ia unknown. The velocity of conduction in the auditory nerve is about 30 m/sec. Nerve impulses are initiated during the development of negative pressure at the tympanum. The stronger the stimulus, the less is the latency. Nerve response to 1 sound may be masked by simultaneous stimulation with another sound due to the refractory period, but the cochlear response shows an algebraic summation. The cochlear response is thought to be non-neural, the delay between cochlear response and nerve action potential being explained by chemical mediation of excitation between the sensory cells of the nerve fiber rather than solely by the conduction time. Pitch and loudness of audition are not functions of the nerve, but "masking" is due to the refractory period of the nerve.

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