Suprathreshold measures of auditory function in the aging chinchilla.

The purpose of this study was to examine the relationship between aging and suprathreshold auditory function in the chinchilla, a rodent with a relatively long life span and a range of hearing similar to that of humans. Subjects were six 11-12-year-old chinchillas and six young controls. Tests of auditory function utilized evoked potential (EVP) recordings from electrodes implanted in the inferior colliculus and measurements of 2f1-f2 distortion product otoacoustic emissions (DPOAEs). Tests of frequency resolution (EVP tuning curves for a 2 kHz probe tone), temporal resolution (EVP forward masking functions using a 2 kHz probe tone), cochlear non-linearity (remote masking), and a DPOAE 'tone challenge', in which DPOAEs at six frequencies were monitored before and after each of five 1-min exposures to a 2 kHz tone at 80 dB SPL, were performed. The results indicate that aged chinchillas can exhibit deficits in suprathreshold tests of auditory function even when the test stimulus is in a region of relatively normal-hearing sensitivity. The results support the notion that aging, independent of hearing loss, can influence suprathreshold auditory function.