The problem of stimulation deafness. II. Histological changes in the cochlea as a function of tonal frequency.

Abstract

A group of 14 guinea-pig ears, previously exposed to pure tones at 1000 dynes/sq. cm., was examined for histologic damage. In 4 out of 4 ears subjected to a 300-cycle tone, damage involved virtually the entire apical half of the basilar membrane structures. In 3 of 4 ears subjected to 1000 cycles, damage was less extensive and centered about 2/3 of the way from round window to helicotrema. In 4 of 6 ears subjected to 5000 cycles, damage was sharply limited to a region about 1/2 way along the basilar membrane. All other ears were histologic -ally intact. No correlation between magnitude of lesion and magnitude of previously detd. loss in electrical sensitivity was evident; furthermore, each ear was known to have suffered a uniform electrical loss in the frequency-range of 100-10,000 cycles. The results suggest revision of current frequency-maps of the cochlea, the gross responsibility of changes in amplitude of vibration for graduations in magnitude of lesion, and the production of widespread invisible injury by acoustic over-exposure.