SUPRATHRESHOLD MEASURES OF AUDITORY FUNCTION IN THE AGING CHINCHILLA

The purpose of this study was to examine the relationship between agin g and suprathreshold auditory function in the chinchilla, a rodent wit h a relatively long life span and a range of hearing similar to that o f humans. Subjects were six 11-12-year-old chinchillas and six young c ontrols. Tests of auditory function utilized evoked potential (EVP) re cordings from electrodes implanted in the inferior colliculus and meas urements of 2f(1)-f(2) distortion product otoacoustic emissions (DPOAE s). Tests of frequency resolution (EVP tuning curves for a 2 kHz probe tone), temporal resolution (EVP forward masking functions using a 2 k Hz probe tone), cochlear non-linearity (remote masking), and a DPOAE ' tone challenge', in which DPOAEs at six frequencies were monitored bef ore and after each of five 1-min exposures to a 2 kHz tone at 80 dB SP L, were performed. The results indicate that aged chinchillas can exhi bit deficits in suprathreshold tests of auditory function even when th e test stimulus is in a region of relatively normal-hearing sensitivit y. The results support the notion that aging, independent of hearing l oss, can influence suprathreshold auditory function.