Efferent modulation of hair cell function

Abstract

Purpose of review This review covers papers published between 2010 and early 2011 that presented new findings on inner ear-efferents and their ability to modulate hair cell function. Recent findings Studies published within the review period have increased our understanding of efferent mechanisms on hair cells in the cochlear and vestibular sensory epithelium and provide insights on efferent contributions to the plasticity of bilateral auditory processing. The central nervous system controls the sensitivity of hair cells to physiological stimuli by regulating the gain of hair cell electromechanical amplification and modulating the efficiency of hair cell-8th nerve transmission. A notable advance in the past year has been animal and human studies that have examined the contribution of the olivocochlear efferents to sound localization particularly in a noisy environment. Summary Acoustic activation of olivocochlear fibers provides a clinical test for the integrity of the peripheral auditory system and has provided new understanding about the function and limitations of the cochlear amplifier. While similar tests may be possible in the efferent vestibular system they have not yet been developed. The structural and functional similarities of the sensory epithelia in the inner ear offer hope that testing procedures may be developed that will allow reliable testing of the vestibular hair cell function.

New treatment options for hearing loss

“…Efferent neurons provide sound-evoked feedback to reduce cochlear amplification 190 . Afferent neuron synaptic loss that is caused by continuous moderate-level noise is increased in animals whose efferent neurons have been surgically lesioned 24 .…”

Evolution and Development of Hair Cell Polarity and Efferent Function in the Inner Ear

“…Salient parallels between the hearing organs in modern archosaurs and mammals suggest that the evolution of a hair cell population specializing in mechanical amplification -outer hair cells in mammals and short hair cells in archosaurs -was tied to the co-evolution of an efferent population specializing in modulating this amplifier [Köppl, 2011]. At least three functions of such gain modulation in a behavioral context are currently being discussed, with some evidence for each [Guinan, 2011;Rabbitt and Brownell, 2011]: first, adjustment of the dynamic range of hearing to varying noise backgrounds, enabling improved signal detection; second, down-regulation of auditory responses during selective attention to other modalities, and third and most controversial, protection from sound damage [Robertson, 2009]. The roles of other efferent subgroups, such as the mammalian lateral olivocochlear efferents, which synapse only on the afferent fibers beneath inner hair cells, are still unclear but under active investigation [Larsen and Liberman, 2010].…”

Rethinking Sound : Computer-assisted reading intervention with a phonics approach for deaf and hard of hearing children using cochlear implants or hearing aids

“…These have been found to play an important role in sensory integration (Rabbitt & Brownell, 2011).. These have been found to play an important role in sensory integration (Rabbitt & Brownell, 2011). Thus, efferent innervations modulate the inner ear's afferent inputs to meet the behavioral needs of the organism.…”

“…One interesting feature in the auditory system is that, besides its rich afferent pathways ascending the central nervous system (CNS), the sensitivity of hair cells to physiological stimuli is controlled by the CNS via descending efferent nerve fibers. These have been found to play an important role in sensory integration (Rabbitt & Brownell, 2011).. These have been found to play an important role in sensory integration (Rabbitt & Brownell, 2011).…”

“…Thus, efferent innervations modulate the inner ear's afferent inputs to meet the behavioral needs of the organism. For humans this is particularly important for sound localization in a noisy environment (Rabbitt & Brownell, 2011).…”