Auditory efferent activation in CBA mice exceeds that of C57s for varying levels of noise.

The medial olivocochlear efferent (MOC) system enhances signals in noise and helps mediate auditory attention. Contralateral suppression (CS) of distortion product otoacoustic emissions (DPOAEs) has revealed age-related MOC declines. Here, differences in CS as a function of contralateral noise intensity (43-67 dB sound pressure level) were measured; 2f1-f2 DPOAE grams were recorded for young adult CBA and C57 mice. In CBAs, CS was a monotonic function of contralateral noise level. The C57s showed normal hearing, measured with DPOAE amplitudes and auditory brainstem response thresholds, but showed little CS, suggesting a loss of efferent dynamics preceding any deficiencies of the afferent auditory system.