Overview of mechanical damage to the inner ear: noise as a tool to probe cochlear function.

The majority of experiments causing mechanical damage to the cochlea involve the use of sound pressure waves to cause overstimulation. This presentation is an overview of the research during the past years on the structural damage produced by noise. The effect of noise on the cochlea depends on the type of noise exposure-impulse or continuous. Experiments have been conducted to determine the effect of increasing intensity, the effect of increasing duration, and the effect of equal energy presented over varying periods of time. The initial mechanism of damage, the progression of damage over time, and the ability of hair cells to recover are discussed. Noise has been used as a tool to probe cochlear function by selectively damaging regions along the length of the sensory epithelium and by selectively damaging one of the two types of hair cells. Results obtained from these types of experiments have given us information on cochlear mechanics, as well as of stereocilia micromechanics and transduction. Information on susceptibility of hair cells to noise confirms previous results, suggesting the presence of structural and metabolic gradients both longitudinally and radially within the sensory epithelium. Moreover, noise lesions have been used to map the afferent innervation pattern to the cochlear nucleus, and noise studies show correlation of hair cell damage with efferent innervation pattern.