Cochlear efferent innervation and function

Abstract

Purpose of review: This review covers topics relevant to olivocochlear-efferent anatomy and function for which there are new findings in papers from 2009 to early 2010.

Recent findings: Work within the review period has increased our understanding of medial olivocochlear (MOC) mechanisms in outer hair cells, MOC-reflex tuning, MOC effects on distortion product otoacoustic emissions, the time course of MOC effects, MOC effects in psychophysical tests and on understanding speech, MOC effects in attention and learning, and lateral efferent function in binaural hearing. In addition, there are new insights into efferent molecular mechanisms and their effect on cochlear development.

Summary: Techniques for measuring efferent effects using otoacoustic emissions are now well developed and have promise in clinical applications ranging from predicting which patients are susceptible to acoustic trauma to characterizing relationships between efferent activation and learning disabilities. To realize this promise, studies are needed in which these techniques are applied with high standards.

Figure 1

Medial olivocochlear (MOC) inhibition increases as the bandwidth of a constant-level elicitor increases, showing that sound excitations over almost the whole range of hearing are integrated in activating the efferents that affect one cochlear frequency region. For narrow-band elicitors (0.5 octaves), ipsilateral noise was approximately twice as effective as contralateral noise, but for wide-band elicitors (>6 octaves), ipsilateral and contralateral elicitors were equally effective. Patterned after the data Lilaonitkul and Guinan [14] for probe frequencies near 1 kHz, and 60 dB SPL elicitors centered on the probe frequency.