Comparison of auditory thresholds determined behaviorally and electrocochleographically in normal and kanamycin-treated gerbils

Abstract

The measurements of two electrical responses of the auditory periphery have been proposed for the objective assessment of the auditory sensitivity. The first is the classical method of measuring cochlear microphonic (CM) isopotential curves. The second is obtaining thresholds of whole-nerve action potentials (AP) by using shaped tone bursts. To determine the validity and shortcomings of both methods, measurements have been conducted on normal and kanamycin-treated gerbils and they are compared with behavioral audiometry. The study shows that between 500 and 24 000 Hz, AP threshold curves compare favorably with behavioral thresholds whereas CM isopotential curves generally do not. At very high frequencies, both responses fail to approximate the behavioral response pattern. Studies with kanamycin also support the idea that the whole-nerve action potentials can be objectively used for the measurement of audiometric patterns. Such a proposal is also consistent with the observations that AP generated by low-intensity tone bursts is produced by a relatively small number of primary auditory fibers whose characteristic frequencies correspond to the frequency of the stimulus. [Supported by Grants from the NINCDS.]