Abstract
Olivocochlear efferents allow the central auditory system to adjust the functioning of the inner ear during active and passive listening. While many aspects of efferent anatomy, physiology and function are well established, others remain controversial. This article reviews the current knowledge on olivocochlear efferents, with emphasis on human medial efferents. The review covers (1) the anatomy and physiology of olivocochlear efferents in animals; (2) the methods used for investigating this auditory feedback system in humans, their limitations and best practices; (3) the characteristics of medial-olivocochlear efferents in humans, with a critical analysis of some discrepancies across human studies and between animal and human studies; (4) the possible roles of olivocochlear efferents in hearing, discussing the evidence in favor and against their role in facilitating the detection of signals in noise and in protecting the auditory system from excessive acoustic stimulation; and (5) the emerging association between abnormal olivocochlear efferent function and several health conditions. Finally, we summarize some open issues and introduce promising approaches for investigating the roles of efferents in human hearing using cochlear implants.
Highlights
The auditory nervous system is continuously sensing and interpreting the sounds around us
In Section “Roles of the Olivocochlear Efferent Reflexes in Human Hearing,” we review the possible roles of olivocochlear efferents in hearing, including their role in facilitating a normal development of the auditory system, in protecting the auditory system from acoustic overstimulation, and in facilitating the detection and recognition of signals embedded in noise
One should bear in mind, that [1] the suppressive effects of CAS depend on the CAS bandwidth [e.g., Fig. 3 in Ref. [98]]; [2] otoacoustic emissions (OAEs) suppression decreases with increasing age in listeners with normal audiometry [117, 118]; and [3] OAE suppression appears to be larger for OAE measured in the left than in the right ears [119], other studies have reported greater suppression in the right ear [120]
Summary
The auditory nervous system is continuously sensing and interpreting the sounds around us. The central nervous system can adjust their functioning, and the coding of sounds, via olivocochlear efferents. Olivocochlear efferents can be activated by selective attention and/or by sounds presented to either or both ears. In Section “Olivocochlear Efferent Effects in Humans,” we review the methods typically used for investigating the medial-olivocochlear efferents in humans. Section “Olivocochlear Efferent Effects in Humans” is devoted to reviewing the characteristics of medial-olivocochlear efferents in humans. In Section “Roles of the Olivocochlear Efferent Reflexes in Human Hearing,” we review the possible roles of olivocochlear efferents in hearing, including their role in facilitating a normal development of the auditory system, in protecting the auditory system from acoustic overstimulation, and in facilitating the detection and recognition of signals embedded in noise. The interested reader may broaden his/her scope by reading other excellent reviews on this topic [1,2,3,4,5,6,7,8]
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