Resting neural activity patterns in auditory brain areas following conductive hearing loss

Introduction: A common cause of conductive hearing loss in young children is otitis media, which when chronic or recurrent can effect speech and language development. However, little is known about the effects of such conductive loss on resting activity levels in the auditory system. Hypothesis: Conductive hearing loss will change spontaneous activity levels at the inner hair cell synapse, and lead to auditory deprivation of central auditory pathways. Experiments: In a mouse model, a 50-60dB conductive loss was produced by blocking the ear canals. Resting neural activity patterns were quantified in cochlear nucleus and inferior colliculus using c-fos immuno-labelling. Conductive hearing loss subjects were compared to normal hearing controls and subjects with bilateral cochlear ablation. Results: Subjects with conductive hearing loss showed a trend in reduction in c-fos labelled cells in cochlear nucleus and a more significant reduction of labelled cells in the central nucleus of inferior colliculus compared to normal controls. Conclusions: There is a reduction in resting neural activity in auditory brainstem and midbrain as a result of conductive hearing loss. Such changes may influence the developing auditory brain during early postnatal years when the system is highly plastic.