Auditory deprivation during development alters efferent neural feedback and perception

Auditory experience plays a critical role in hearing development. Developmental auditory deprivation due to otitis media, a common childhood disease, produces long-standing changes in the central auditory nervous system, even after the middle ear pathology is resolved. The effects of sound deprivation due to otitis media have been mostly studied in the ascending neural system but remain to be examined in the descending pathway that runs from the auditory cortex to the cochlea via the brainstem. Alterations in the efferent neural system could be important because the descending olivocochlear pathway influences the neural representation of transient sounds in noise in the afferent auditory system and is thought to be involved in auditory relearning following injury. The main objectives of the present study were to (1) investigate whether degraded auditory input due to otitis media during childhood is associated with weakened medial olivocochlear efferent neural responses, even after the resolution of the middle ear pathology, and (2) to examine the involvement of the efferent neural feedback in perceptual masking deficits associated with auditory deprivation due to otitis media. We measured contralateral inhibition of otoacoustic emissions--a biomarker for medial efferent activity--and speech-in-noise recognition in children with a medical history of otitis media (N=76) and age-matched controls (N=99). All children had normal auditory function at the time of experimentation. We found that the inhibitory strength of the medial olivocochlear efferents is weaker in children with a documented history of otitis media relative to controls. In addition, children with otitis media history required a more advantageous signal-to-noise ratio than controls to achieve the same criterion performance level. Importantly, the deficits in perceptual masking were related to efferent inhibition, and these effects could not be attributed to the middle ear or cochlear mechanics. These findings raise the possibility that perceptual masking deficits--a hallmark of impaired (central) auditory processing--resulting from otitis media can arise from the altered brainstem efferent feedback. To date, it was known that degraded auditory experience reorganizes the ascending neural pathways; here, we show that the lack of optimal auditory input to the afferent system during development could have a long-standing impact on the functioning of the descending neural pathways.