Predicting vulnerability to acoustic injury with a noninvasive assay of olivocochlear reflex strength

Permanent noise-induced damage to the inner ear is a major cause of hearing impairment, arising from exposures occurring during both work- and pleasur e-related activities. Vulnerability to noise-induced hearing loss is highly variable: some have tough, whereas others have tender ears. This report do cuments, in an animal model, the efficacy of a simple nontraumatic assay of normal ear function in predicting vulnerability to acoustic injury. The as say measures the strength of a sound-evoked neuronal feedback pathway to th e inner ear, the olivocochlear efferents, by examining otoacoustic emission s created by the normal ear, which can be measured with a microphone in the external ear. Reflex strength was inversely correlated with the degree of hearing loss after subsequent noise exposure. These data suggest that one f unction of the olivocochlear efferent system is to protect the ear from aco ustic injury. This assay, or a simple modification of it, could be applied to human populations to screen for individuals most at risk in noisy enviro nments.