Olivocochlear efferent function: issues regarding methods and the interpretation of results

Abstract

As studies of the olivocochlear (OC) efferent system have matured, issues have been identified that need to be taken into account in the design of new studies and in the interpretation of existing work. The need for high signal-to-noise ratios (SNRs), multiple alternations of conditions, and avoiding middle-ear-muscle activation have been previously highlighted. Less well-known issues include: Contralateral medial OC (MOC) effects may not be good proxies for ipsilateral (ipsi) MOC effects; MOC-induced changes in otoacoustic emissions (OAEs) may not accurately show MOC-induced changes in auditory-nerve (AN) responses; measuring OAE differences from before to after psychophysical trials yields the transient OAE change but not tonic MOC activation; tonic MOC activation may be measurable by several techniques including by OAE differences in trials in which the subject’s judgment was correct vs. trials that were incorrect; SNRs can be preserved by Bootstrap statistical tests; differences in task difficulty may outweigh differences in subject attention; lateral efferent effects are little understood and may be tied to MOC effects; to assess whether MOC strength predicts protection from acoustic trauma, prospective tests in humans are needed.

Concurrent measures of contralateral suppression of transient-evoked otoacoustic emissions and of auditory steady-state responses

“…When associating MOC activity with auditory perception, the most relevant effect is on the neural output (Guinan, 2014). The finding of larger contralateral suppression of ASSRs than of TEOAEs appears consistent with previous reports showing that the MOC can exhibit larger effects on neural responses than on OAEs (Puria et al, 1996;Chabert et al, 2002;Lichtenhan et al, 2016).…”

The middle ear muscle reflex in the diagnosis of cochlear neuropathy

“…Modulation of ipsilateral responses by contralateral sound has long been used as an assay for either the MEMR or the MOCR in awake humans and in awake or anesthetized animals (Guinan, 2015). The extent to which each of the two reflexes contribute to this binaural effect depends on species, stimulus level and the type and level of anesthesia.…”

Efferent modulation of pre-neural and neural distortion products

“…It is important to consider that even at the pre-neural cochlear level, MOC effects imparted at the base of OHCs are unlikely to proceed “unfiltered” by the many complex drives which activate IHCs (Guinan, 2012, 2014). While it has been demonstrated that the MOC reflex modulates basilar membrane motion (Cooper & Guinan, 2006), IHCs (and consequently auditory nerve fibers) are driven by motion at the top of the organ of Corti , not the basilar membrane.…”