Changes in amplitude and phase of distortion-product otoacoustic emission fine-structure and separated components during efferent activation

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The Journal of the Acoustical Society of America (Impact Factor: 1.5). 04/2011; 129(4):2068-79. DOI: 10.1121/1.3543945
Source: PubMed


Medial olivocochlear (MOC) efferent fibers synapse directly on the outer hair cells (OHCs). Efferent activation evoked by contralateral acoustic stimulation (CAS) will affect OHC amplification and subsequent measures of distortion-product otoacoustic emissions (DPOAEs). The aim of this study was to investigate measures of total and separated DPOAEs during efferent activation. Efferent activation produces both suppression and enhancement of the total DPOAE level. Level enhancements occurred near fine-structure minima and were associated with consistent MOC evoked upward shifts in DPOAE fine-structure frequency. Examination of the phase of the separated components revealed that frequency shifts stemmed from increasing phase leads of the reflection component during CAS, while the generator component phase was nearly invariant. Separation of the two DPOAE components responsible for the fine-structure revealed more consistent reduction of the levels of both components. Using vector subtraction (which takes into account both level and phase) to estimate the changes in the unseparated DPOAE provided consistent evidence of DPOAE suppression. Including phase information provided a more sensitive, valid and consistent estimate of CAS function even if one does not know the position of the DPOAE in the fine-structure.

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    • "The LSF minimization routine steps through the recording, creating a band-pass filter that changes center frequency as a function of DPOAE (see Long et al., 2008; for additional details). The composite DPOAE is estimated in a separate LSF analysis than the separated components, with the bandwidth of the filter used for the LSF analyses varied depending on the DPOAE component being estimated (cf, Long and Talmadge, 1997; Long et al., 2008; Henin et al., 2011b, 2014). Based on the sampling rate of 44,100 samples/s, estimates of composite DPOAE were obtained using a wideband analysis (n ¼ 2756, nstep ¼ 275, 16 Hz for 1 s/octave; n ¼ 5512, nstep ¼ 551, 8 Hz for 2 s/octave). "
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    ABSTRACT: Distortion product otoacoustic emissions (DPOAE) in newborns and adults were evoked by sweeping primaries up and down in frequency at 1 s/octave. Sweeping up and down in frequency resulted in changes in the amplitude vs. frequency functions of the composite DPOAE and its two major components. In addition, DPOAE component phases differed slightly between the up- and down-swept conditions. The changes in amplitude vs. frequency functions were quantified using a covariate correlation technique, yielding single-valued estimates of the magnitude of the frequency changes. Separate analyses were performed for the entire DPOAE frequency range and split into low and high frequency ranges. There were consistent changes in newborn and adult composite DPOAEs and reflection components, but not generator components. Adults had significant frequency changes in the composite DPOAE for all frequency ranges and in the reflection component for the entire frequency range. Newborns had significant frequency change in the reflection component for all frequency ranges. Differences in frequency change between adults and newborns may stem from developmental changes in cochlear processing. Alignment of the component phase differences between the up- and down-swept conditions resulted in elimination of frequency-change in reconstructed composite DPOAEs. Copyright © 2015 Elsevier B.V. All rights reserved.
    Hearing research 08/2015; 328. DOI:10.1016/j.heares.2015.08.012 · 2.97 Impact Factor
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    • "High-level primaries were used because fewer sweeps were necessary to obtain a good signal to noise ratio at these levels. Stimuli were calibrated using KEMAR head and torso simulator (see Henin et al. 2011). "

    Ear and Hearing 01/2015; Publication before Print. · 2.84 Impact Factor
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    • "About one-third, Contra units, respond to sound in the contralateral ear, and a small percentage of units, Either Ear units, respond to sound in either ear. A comparison of terminations of the types of neurons has not been made, an important issue since many studies have used contralateral sound to elicit MOC effects with the implicit assumption that they are similar to the effects elicited by ipsilateral or bilateral sound (Veuillet et al. 1991; Chery-Croze et al. 1993; Abdala et al. 2009; Henin et al. 2011). To address these issues, the present study constructs the cochlear frequency mapping for MOC axons and compares the terminations of Ipsi, Contra, and Either-Ear units. "
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    ABSTRACT: Medial olivocochlear (MOC) neurons are efferent neurons that project axons from the brain to the cochlea. Their action on outer hair cells reduces the gain of the "cochlear amplifier", which shifts the dynamic range of hearing and reduces the effects of noise masking. The MOC effects in one ear can be elicited by sound in that ipsilateral ear or by sound in the contralateral ear. In order to study how MOC neurons project onto the cochlea to mediate these effects, single-unit labeling in guinea pigs was used to study the mapping of MOC neurons for neurons responsive to ipsilateral sound vs. those responsive to contralateral sound. MOC neurons were sharply tuned to sound frequency with a well-defined characteristic frequency (CF). However, their labeled termination spans in the organ of Corti ranged from narrow to broad, innervating between 14 and 69 outer hair cells per axon in a "patchy" pattern. For units responsive to ipsilateral sound, the midpoint of innervation was mapped according to CF in a relationship generally similar to, but with more variability than, that of auditory-nerve fibers. Thus, based on CF mappings, most of the MOC terminations miss outer hair cells involved in the cochlear amplifier for their CF, which are located more basally. Compared to ipsilaterally responsive neurons, contralaterally responsive neurons had an apical offset in termination and a larger span of innervation (an average of 10.41% cochlear distance), suggesting that when contralateral sound activates the MOC reflex, the actions are different than those for ipsilateral sound.
    Journal of Neurophysiology 03/2014; 111(11). DOI:10.1152/jn.00045.2014 · 2.89 Impact Factor
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