Abstract
Age-related hearing loss (presbycusis) is the leading cause of hearing loss worldwide, but current human studies do not separate this pathology from lifetime noise exposure. Laboratory macaques live in environments with minimal noise-induced hearing trauma and have long lifespans, making them optimal presbycusis models. We describe age-related auditory changes using two clinical, non-invasive physiological measures in aging macaques: distortion product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs). ABRs and DPOAEs were measured in anesthetized young (6–9 years old, n = 36 ears) and aging (26–35 years old, n = 20 ears) Macaca mulatta. ABR and DPOAE thresholds were elevated in aging subjects compared to young macaques at all tested frequencies. ABR thresholds were significantly correlated with age for frequencies >8 kHz, but DPOAE thresholds were not, a pattern likely attributable to a high-frequency ceiling effect for DPOAE measures. For frequencies <8 kHz, DPOAE thresholds showed significant correlation with age. However, this was not observed with ABR thresholds, suggesting differential sensitivity to age-related changes for auditory nerve and brainstem function compared to cochlear outer hair cell function. Ongoing analysis on temporal processing/adaptation metrics will further elucidate age-related changes. Future work will correlate these findings with histological analysis. [Work Supported by NIH R01-DC-015988.]
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