Influence of aging on medial olivocochlear system function

BACKGROUND There is still controversy regarding the influence of aging on medial olivocochlear (MOC) system function. The main objective of this study is to measure age-related changes of MOC system function in people with normal hearing thresholds. METHOD Bilateral assessment of the MOC effect for click-evoked otoacoustic emissions (CEOAEs; at 70±3 dB peak sound pressure level [pSPL], click at 50/second, 260 repeats, 2.5-20 millisecond window) and for distortion product otoacoustic emissions (DPOAEs; with [frequencies] f2/f1=1.22, [levels of primary tones] L1=65 dB SPL and L2=55 dB SPL; DP-grams for 2f1-f2 were collected for the f1 frequencies varying from 977 Hz to 5,164 kHz, with the resolution of four points per octave) was performed in a group of 146 (n=292 ears) healthy, right-handed subjects aged from 10-60 years with a bilateral hearing threshold from 0.25-4.0 kHz, not exceeding 20 dB hearing level; normal tympanograms; and a threshold of the contralateral stapedial reflex for broadband noise (BBN) of 75 dB SPL or higher. The MOC inhibition was assessed on the basis of changes in OAE level during BBN contralateral stimulation at 50 dB sensation level (mean, 65±3 dB SPL). RESULTS Comparative analysis of the MOC effect for CEOAE and DPOAE showed the weakest effect in the oldest age group (41-60 years) at almost all tested frequencies. Moreover, a weak, albeit significant, positive correlation between the level of OAE and the size of the MOC effect was documented. CONCLUSION On the basis of our study, we have found a decrease in the strength of the MOC system with increasing age in normally hearing subjects, as reflected by a decrease of the OAE suppression effects in older individuals and an increase of the number of CEOAE and DPOAE enhancements during contralateral acoustic stimulation in the elderly, especially in the high-frequency range.