Age-Related Central Gain Compensation for Reduced Auditory Nerve Output in Non-Tinnitus Patients with Normal Hearing

Abstract

Tinnitus in audiometrically normal listeners has been associated with reduced wave I amplitudes of the evoked auditory brainstem response but normal wave V amplitudes, a characteristic thought to be indicative of increased central gain compensation for reduced auditory nerve output. It remains uncertain, however, if central gain compensation is specific to tinnitus or can also occur for other conditions that reduce the auditory nerve output, such as aging. Here, we investigate if central gain increases with increasing age for people with normal hearing or very mild hearing losses. For 94 such people (aged 12-68 years, 64 women), we found that the amplitude of wave I decreased with increasing age but the amplitude of wave V was not correlated with the amplitude of wave I after accounting for age-related subclinical hearing loss and cochlear mechanical damage. Furthermore, the wave I/V amplitude ratio (the inverse of central gain) decreased with increasing age. Those findings are consistent with the presence of central gain compensation in aging. An analysis of the correlation between age and wave I/III or III/V amplitude ratios suggests that central gain compensation in aging likely occurs in the cochlear nuclei. For each of seven participants with tinnitus, the amplitude of wave I, wave V, and the wave I/V amplitude ratio were not significantly different from those of the non-tinnitus group. We conclude that increased central gain occurs with aging and is not specific to tinnitus.