Behavioral, compound action potential, and single unit thresholds: relationship in normal and abnormal ears.

Comparisons were made for two species (chinchilla and mongolian gerbil) among mean behavioral audiogram, mean just detectable action potential (AP) responses to tone bursts, and single-fiber response thresholds at the characteristic frequency, averaged in one-octave bands. In normal animals and in a group of Kayamycin-treated chinchillas, these mean measures appear to have a well-ordered relationship. Unit and AP thresholds are within 10 dB from one another throughout the frequency range. Behavioral thresholds are usually 15--20 dB more sensitive, but the three curves are roughly parallel except at the highest frequencies, where the behavioral threshold begins to increase approximately one-half octave above the physiological ones. Individual examples for four gerbils and four chinchillas having hair cell losses due to Kanamycin intoxication reinforce the notion based on mean data that in most cases AP thresholds can serve to predict the behavioral threshold configuration.