The Relationship Between Permanent Threshold Shift and the Loss of Hair Cells in Monkeys Exposed to Impulse Noise.

A compariosn of permanent threshold shift sustained by monkeys exposed to impulse noise with hair cell and nerve fiber loss in their inner ears demonstrated that impulse hoise damages the cochlea by destroying hair cells in a restricted area. Although this destruction was not disclosed by pure tone audiometry until there was a severe loss of outer hair cells extending over several millimeters of the basilar membrane, the overall correlation between the two measures of damage audiometric and histological was statistically significant. Individual deviations were hypothesized to be due to the redundancy among the population of sensory cells in the inner ear, spread of excitation as a function of intensity, release from inhibition or masking, and a possible change in the elasticity of the denuded basilar membrane which might have affected the traveling wave pattern. Author