Perspectives on Auditory Neuropathy: Disorders of Inner Hair Cell, Auditory Nerve, and Their Synapse

The term auditory neuropathy (Starr, A. et al., 1996) was first used to describe a hearing disorder due to altered function of the auditory nerve in the presence of preserved functions of cochlear outer hair cells (OHCs; Starr, A. et al., 1991). The hearing loss has specific features reflecting impairment of auditory temporal processes that are typically unaffected with sensory outer hair disturbances (Zeng, F. G. et al., 1999). The disorder has also been referred to as type I afferent neuron dysfunction (Berlin, C. I. et al., 1993), auditory neuropathy/auditory dys-synchrony (Berlin, C. I.et al., 2003), and neural hearing loss (Rapin, I. and Gravel, J., 2003). We now know that dysfunction of the auditory nerve, having quite similar clinical features, accompanies a variety of disorders acting on the nerve, the inner hair cell, and/or their synapse. We will refer to the disorder as auditory neuropathy and emphasize whenever possible the site(s) of involvement in the auditory periphery. We will review how the varieties of auditory neuropathy are identified, the special psychoacoustic features of the hearing loss, candidate pathophysiological mechanisms, and cochlear and auditory nerve pathologies. We will introduce recent advances in knowledge of molecular organization of cochlear inner hair cell synapses and auditory nerve that suggest some mechanisms likely to be involved in auditory nerve dysfunction. © 2008 Elsevier Inc. All rights reserved