Changes in frequency representation in the auditory system of mice with age-related hearing impairment.

Aging C57BL/6 mice show a progressive decline in sensitivity to sound, beginning with high frequencies. In the inferior colliculus (IC), tonotopic organization--the orderly representation of frequency from low to high along the dorsoventral dimension--shows marked changes. No neurons respond to high frequencies, most respond best to a restricted range of frequencies, and ventral neurons become responsive to low frequencies. These age-related response alterations have implications for hearing problems of aging humans.