Physiological Mechanisms of Onset Adaptation and Contralateral Suppression of DPOAEs in the Rat

Abstract

An investigation was undertaken to measure medial olivocochlear (MOC) reflexes in anesthetized rats before and after sectioning of the middle-ear muscles. Distortion product otoacoustic emission (DPOAE) magnitude and phase temporal responses were measured ipsilaterally to study MOC-mediated BDPOAE onset adaptation^and in the presence of a contralateral noise to study MOC-mediated contralateral Bsuppression^(terms as used by previous researchers). Distortion product otoacoustic emission onset adaptation and contralateral suppression had predictable changes in direction of magnitude and phase that were dependent on the inputYoutput function. After sectioning of the middle-ear muscles (MEMs), DPOAE onset adaptation and contralateral suppression were greatly reduced, and there were little, if any, changes in phase. These Bresidualĉ hanges were interpreted as a result of the MOC reflex. The results suggest that what appears to be DPOAE onset adaptation and contralateral suppression can be mediated primarily by MEM reflexes. When studying MOC effects on otoacoustic emissions (OAEs) using acoustic stimulation, it is necessary to make recordings over a span of stimulus levels. In addition, looking at both magnitude and phase of the OAE may help separate what is due to the MOC reflex from MEM reflex.

Separating medial olivocochlear from acoustic reflex effects on transient evoked otoacoustic emissions in unanesthetized mice

“…In fact, a Student's t-test showed that there was no statistically significant difference between MEM and MOC thresholds in this group of mice (n=14). This conclusion is similar to that of prior studies in rats [14,16].…”

“…Nevertheless, the method used in this study serves as a sensitive indicator of contralateral MEM suppression that may contaminate MOC 090026-4 efferent effects on TEOAEs. Because of the similarity of MEM and MOC thresholds, in this study as well as previous reports in rats [14,16], both should be evaluated in studies of the efferent innervation to OHCs.…”

Simultaneous Measurement of Noise-Activated Middle-Ear Muscle Reflex and Stimulus Frequency Otoacoustic Emissions

“…An MEM reflex-induced change in ear canal sound pressure may easily be mistaken for a MOC reflex, which can have a similar temporal pattern (Guinan et al, 1983. This problem was highlighted in experiments with rats by Relkin et al (2005). They showed that what appeared to be MOC effects were greatly reduced after sectioning of the MEMs.…”

The Effect of Contralateral Acoustic Stimulation on Spontaneous Otoacoustic Emissions

“…The magnitude of DPOAEs gradually reduces after stimulus onset even in the absence of CAS (Liberman et al 1996;Kim et al 2001;Kujawa and Liberman 2001;Relkin et al 2005). In contrast, the term adaptation is used in this paper to signify a release from MOC-induced changes in SOAEs.…”

“…In cats, post-onset adaptation and contralateral suppression of distortion product otoacoustic emissions (DPOAEs) were preserved when middle-ear muscles were severed, but were greatly reduced after olivocochlear bundle sectioning (Liberman et al 1996). However in rats, the MEM reflex is the main contributor to post-onset adaptation and contralateral suppression of DPOAEs, which virtually disappear after middle-ear muscle sectioning (Relkin et al 2005). These differences highlight the necessity for speciesspecific knowledge about the physiology of the MOC efferent system and its modulatory effect on the cochlea.…”