Air conduction and bone conduction in aging mice

Abstract

Umbo velocity and Auditory Brainstem Response (ABR) measurements in aged mice suggest that there are functional changes in both the inner ear and middle ear for frequencies from 5 to 13 kHz (Doan et al., 1996). In this work, we use a combination of air conduction (AC) and bone conduction (BC) stimulation to better quantify the middle ear contribution to age-related hearing loss seen in mice. ABRs were recorded with AC and BC stimuli from BALB/c mice of four different age groups (1, 2, 8, and 12 months); mice of this strain are widely used as models for age-related hearing loss. Results show the threshold stimulus levels for both AC and BC increase as the mice get older, consistent with age-related hearing loss. At frequencies below 12 kHz, the age-related changes in thresholds for all age groups are similar for both stimuli: the AC-BC difference (the air-bone gap) is not statistically significant. This suggests in this frequency range, the hearing loss is primarily sensorineural. At 16 kHz, the air-bone gaps of the two oldest groups are statistically significant suggesting the middle ear contributes to the hearing loss. Thresholds at higher frequencies were not measurable in the two oldest groups.