scholarly journals Reflex Control of the Human Inner Ear: A Half-Octave Offset in Medial Efferent Feedback That Is Consistent With an Efferent Role in the Control of Masking

2009 ◽  
Vol 101 (3) ◽  
pp. 1394-1406 ◽  
Author(s):  
Watjana Lilaonitkul ◽  
John J. Guinan
Keyword(s):  
Otoacoustic Emissions ◽  
High Sensitivity ◽  
Outer Hair Cells ◽  
Tuning Curves ◽  
Cochlear Amplification ◽  
Inhibitory Feedback ◽  
Probe Frequency ◽  
Medial Olivocochlear ◽  
Human Inner Ear

The high sensitivity and frequency selectivity of the mammalian cochlea is due to amplification produced by outer hair cells (OHCs) and controlled by medial olivocochlear (MOC) efferents. Data from animals led to the view that MOC fibers provide frequency-specific inhibitory feedback; however, these studies did not measure intact MOC reflexes. To test whether MOC inhibition is primarily at the frequency that elicits the MOC activity, acoustically elicited MOC effects were quantified in humans by the change in otoacoustic emissions produced by 60-dB SPL tone and half-octave-band noise elicitors at different frequencies relative to a 40-dB SPL, 1-kHz probe tone. On average, all elicitors produced MOC effects that were skewed (elicitor frequencies -1 octave below the probe produced larger effects than those -1 octave above). The largest MOC effects were from elicitors below the probe frequency for contra- and bilateral elicitors but were from elicitors centered at the probe frequency for ipsilateral elicitors. Typically, ipsilateral elicitors produced larger effects than contralateral elicitors and bilateral elicitors produced effects near the ipsi+contra sum. Elicitors at levels down to 30-dB SPL produced similar patterns. Tuning curves (TCs) interpolated from these data were V-shaped with Q10s ∼2. These are sharper than MOC-fiber TCs found near 1 kHz in cats and guinea pigs. Because cochlear amplification is skewed (more below the best frequency of a cochlear region), these data are consistent with an anti-masking role of MOC efferents that reduces masking by reducing the cochlear amplification seen at 1 kHz.

scholarly journals Vibration of the organ of Corti within the cochlear apex in mice

2014 ◽  
Vol 112 (5) ◽  
pp. 1192-1204 ◽  
Author(s):  
Simon S. Gao ◽  
Rosalie Wang ◽  
Patrick D. Raphael ◽  
Yalda Moayedi ◽  
Andrew K. Groves ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Phase Difference ◽  
Basilar Membrane ◽  
Organ Of Corti ◽  
Lateral Compartment ◽  
Outer Hair Cells ◽  
Supporting Cells ◽  
Tuning Curves ◽  
Cochlear Amplification

The tonotopic map of the mammalian cochlea is commonly thought to be determined by the passive mechanical properties of the basilar membrane. The other tissues and cells that make up the organ of Corti also have passive mechanical properties; however, their roles are less well understood. In addition, active forces produced by outer hair cells (OHCs) enhance the vibration of the basilar membrane, termed cochlear amplification. Here, we studied how these biomechanical components interact using optical coherence tomography, which permits vibratory measurements within tissue. We measured not only classical basilar membrane tuning curves, but also vibratory responses from the rest of the organ of Corti within the mouse cochlear apex in vivo. As expected, basilar membrane tuning was sharp in live mice and broad in dead mice. Interestingly, the vibratory response of the region lateral to the OHCs, the “lateral compartment,” demonstrated frequency-dependent phase differences relative to the basilar membrane. This was sharply tuned in both live and dead mice. We then measured basilar membrane and lateral compartment vibration in transgenic mice with targeted alterations in cochlear mechanics. Prestin499/499, Prestin−/−, and TectaC1509G/C1509G mice demonstrated no cochlear amplification but maintained the lateral compartment phase difference. In contrast, SfswapTg/Tg mice maintained cochlear amplification but did not demonstrate the lateral compartment phase difference. These data indicate that the organ of Corti has complex micromechanical vibratory characteristics, with passive, yet sharply tuned, vibratory characteristics associated with the supporting cells. These characteristics may tune OHC force generation to produce the sharp frequency selectivity of mammalian hearing.

Otoacoustic Emissions as a Promising Diagnostic Tool for the Early Detection of Mild Hearing Impairment - Technical Advances in Acquisition, Analysis and Modeling

2016 ◽  
Vol 879 ◽  
pp. 2355-2360
Author(s):  
Arturo Moleti ◽  
Renata Sisto ◽  
Filippo Sanjust ◽  
Teresa Botti ◽  
Sandro Gentili
Keyword(s):  
Diagnostic Tool ◽  
Otoacoustic Emissions ◽  
Basilar Membrane ◽  
Hearing Threshold ◽  
High Sensitivity ◽  
Outer Hair Cells ◽  
Frequency Resolution ◽  
Phase Gradient ◽  
Time Frequency ◽  
Generation Mechanisms

Otoacoustic emissions are a by-product of the active nonlinear amplification mechanism located in the cochlear outer hair cells, which provides high sensitivity and frequency resolution to human hearing. Being intrinsically sensitive to hearing loss at a cochlear level, they represent a promising non-invasive, fast, and objective diagnostic tool. On the other hand, the complexity of their linear and nonlinear generation mechanisms and other confounding physical phenomena (e.g., interference between different otoacoustic components, acoustical resonances in the ear canal, transmission of the middle ear) introduce a large inter-subject variability in their measured levels, which makes it difficult using them as a direct measure of the hearing threshold using commercially available devices. Nonlinear cochlear modeling has been successfully used to understand the complexity of the otoacoustic generation mechanisms, and to design new acquisition and analysis techniques that help disentangling the different components of the otoacoustic response, therefore improving the correlation between measured otoacoustic levels and audiometric thresholds. In particular, nonlinear cochlear modeling was able to effectively describe the complex (amplitude and phase) response of the basilar membrane, and the generation of otoacoustic emissions by two mechanisms, nonlinear distortion and linear reflection by cochlear roughness. Different phase-frequency relations are predicted for the otoacoustic components generated by the two mechanisms, so they can be effectively separated according to their different phase-gradient delay, using an innovative time-frequency domain filtering technique based on the wavelet transform. A brief introduction to these topics and some new theoretical and experimental results are presented and discussed in this study.

scholarly journals The Role of Prestin in the Generation of Electrically Evoked Otoacoustic Emissions in Mice

2008 ◽  
Vol 99 (4) ◽  
pp. 1607-1615 ◽  
Author(s):  
Markus Drexl ◽  
Marcia M. Mellado Lagarde ◽  
Jian Zuo ◽  
Andrei N. Lukashkin ◽  
Ian J. Russell
Keyword(s):  
Hair Cells ◽  
Otoacoustic Emissions ◽  
Temporal Structure ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Wild Type ◽  
Short Delay ◽  
Delay Component

Electrically evoked otoacoustic emissions are sounds emitted from the inner ear when alternating current is injected into the cochlea. Their temporal structure consists of short- and long-delay components and they have been attributed to the motile responses of the sensory-motor outer hair cells of the cochlea. The nature of these motile responses is unresolved and may depend on either somatic motility, hair bundle motility, or both. The short-delay component persists after almost complete elimination of outer hair cells. Outer hair cells are thus not the sole generators of electrically evoked otoacoustic emissions. We used prestin knockout mice, in which the motor protein prestin is absent from the lateral walls of outer hair cells, and Tecta ΔENT/ΔENT mice, in which the tectorial membrane, a structure with which the hair bundles of outer hair cells normally interact, is vestigial and completely detached from the organ of Corti. The amplitudes and delay spectra of electrically evoked otoacoustic emissions from Tecta ΔENT/ΔENT and Tecta +/+ mice are very similar. In comparison with prestin +/+ mice, however, the short-delay component of the emission in prestin −/− mice is dramatically reduced and the long-delay component is completely absent. Emissions are completely suppressed in wild-type and Tecta ΔENT/ΔENT mice at low stimulus levels, when prestin-based motility is blocked by salicylate. We conclude that near threshold, the emissions are generated by prestin-based somatic motility.

The Role of the Medial Olivocochlear Reflex in Psychophysical Masking and Intensity Resolution in Humans: A Review

2021 ◽  
Author(s):  
Skyler G. Jennings
Keyword(s):  
Otoacoustic Emissions ◽  
Acoustic Stimulation ◽  
Forward Masking ◽  
Frequency Resolution ◽  
Vestibular Neurectomy ◽  
Contralateral Acoustic Stimulation ◽  
Cochlear Gain ◽  
Medial Olivocochlear ◽  
Intensity Resolution

This review addresses the putative role of the medial olivocochlear (MOC) reflex on psychophysical masking and intensity resolution in humans. A framework for interpreting psychophysical results in terms of the expected influenced of the MOC reflex is introduced. This framework is used to review the effects of a precursor or contralateral acoustic stimulation on 1) simultaneous masking of brief tones, 2) behavioral estimates of cochlear gain and frequency resolution in forward masking, 3) the build-up and decay of forward masking, and 4) measures of intensity resolution. Support, or lack thereof, for a role of the MOC reflex in psychophysical perception is discussed in terms of studies on estimates of MOC strength from otoacoustic emissions and the effects of resection of the olivocochlear bundle in patients with vestibular neurectomy. Novel, innovative approaches are needed to resolve the dissatisfying conclusion that current results are unable to definitively confirm or refute the role of the MOC reflex in masking and intensity resolution.

scholarly journals Frequency tuning of the contralateral medial olivocochlear reflex in humans

2012 ◽  
Vol 108 (1) ◽  
pp. 25-30 ◽  
Author(s):  
Wei Zhao ◽  
Sumitrajit Dhar
Keyword(s):  
Otoacoustic Emissions ◽  
Frequency Tuning ◽  
Acoustic Trauma ◽  
Fixed Frequency ◽  
Sound Perception ◽  
Spontaneous Otoacoustic Emissions ◽  
Functional Roles ◽  
Cochlear Gain ◽  
Medial Olivocochlear

Activation of the medial olivocochlear (MOC) efferents attenuates cochlear gain and reduces the amplitudes of mechanical, electrical, and neural cochlear outputs. The functional roles of the MOC efferents are not fully understood, especially in humans, despite postulations that they are involved in protection against acoustic trauma, facilitation of transient-sound perception, etc. Delineating the frequency tuning properties of the MOC efferents would provide critical evidence to support or refute these postulated functional roles. By utilizing spontaneous otoacoustic emissions (SOAEs), a cochlear measure sensitive to MOC modulation, we systematically demonstrate in humans that the contralateral MOC reflex is tuned to a fixed frequency band between 500 and 1,000 Hz independent of SOAE frequency. Our results question the role of the MOC reflex in protection against acoustic trauma or facilitation of transient-sound perception.

Physiologically silent sodium channels in mammalian outer hair cells

1994 ◽  
Vol 72 (2) ◽  
pp. 1037-1040 ◽  
Author(s):  
C. M. Witt ◽  
H. Y. Hu ◽  
W. E. Brownell ◽  
D. Bertrand
Keyword(s):  
Sodium Channels ◽  
Hair Cells ◽  
Sodium Current ◽  
High Sensitivity ◽  
Outer Hair Cells ◽  
Inward Current ◽  
Cell Recording ◽  
Voltage Dependent

1. Voltage-dependent properties of isolated guinea pig outer hair cells (OHCs) were investigated using whole-cell recording. An inward current was detected in approximately 10% of the cells. This inward current was identified as belonging to the voltage-activated sodium current family on the basis of its high sensitivity to tetrodotoxin and the effect of substitution of impermeant ions. Although this is the first report of a sodium current in the mammalian cochlea, it differs from the classical neuronal sodium current by having a variable magnitude from cell to cell and an inactivation that is shifted to hyperpolarized potentials. The sensory processing role of hair cells in general and outer hair cells in particular could be disrupted by the presence of a regenerative voltage-dependent current. The functional role of the OHC sodium channels is puzzling, particularly as they may be silent in vivo.

scholarly journals Otoacoustic emissions and contralateral suppression in tinnitus sufferers with normal hearing

2020 ◽  
Vol 36 (1) ◽  
Author(s):  
Doaa Elmoazen ◽  
Hesham Kozou ◽  
Basma Elabassiery
Keyword(s):  
Otoacoustic Emissions ◽  
Pure Tone Audiometry ◽  
Normal Hearing ◽  
Outer Hair Cells ◽  
Control Group ◽  
Efferent System ◽  
Distortion Product ◽  
Contralateral Suppression ◽  
Significant Difference

Abstract Background The general consensus on the role of hearing loss in generating tinnitus is not relevant in tinnitus patients with normal hearing thresholds. One source of tinnitus may be related to damage to outer hair cells (OHC) of the cochlea. If the OHC of the human cochlea are to be involved in the generation of tinnitus, testing of Otoacoustic emissions (OAE) could provide a reliable means of recording OHC dysfunction. We investigated the role of OHC and cochlear efferent system in tinnitus development in normal hearing ears through studying of Distortion Product Otoacoustic Emissions (DPOAE) and Transient Evoked Otoacoustic Emissions (TEOAE) amplitudes, contralateral suppression amplitudes and suppression value in 15 normal hearing tinnitus patients and 15 control subjects. Results Mean f2 DPOAE amplitudes and contralateral suppression were significantly lower in tinnitus group compared to controls for all frequencies from 1001 to 6348 Hz. Suppression values of DPOAEs revealed lower but not significant difference between tinnitus and control groups for all frequencies except 1587 and 6348 Hz. TEOAE amplitudes and contralateral suppression were significantly lower in tinnitus groups for all frequencies from 1000 to 4000 Hz compared to the control group. Suppression value of TEOAEs revealed no significant difference between the two groups for all frequencies except 3000 and 4000 Hz were significantly lower in the tinnitus group compared to the control group. Conclusions Normal hearing manifested by pure tone audiometry in non-vascular tinnitus sufferers does not exclude OHC and/or cochlear efferent pathology.

scholarly journals All Three Rows of Outer Hair Cells Are Required for Cochlear Amplification

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Michio Murakoshi ◽  
Sho Suzuki ◽  
Hiroshi Wada
Keyword(s):  
Hair Cells ◽  
Noise Exposure ◽  
Dynamic Range ◽  
Basilar Membrane ◽  
Organ Of Corti ◽  
High Sensitivity ◽  
Element Model ◽  
Outer Hair Cells ◽  
Displacement Amplitude ◽  
Cochlear Amplification

In the mammalian auditory system, the three rows of outer hair cells (OHCs) located in the cochlea are thought to increase the displacement amplitude of the organ of Corti. This cochlear amplification is thought to contribute to the high sensitivity, wide dynamic range, and sharp frequency selectivity of the hearing system. Recent studies have shown that traumatic stimuli, such as noise exposure and ototoxic acid, cause functional loss of OHCs in one, two, or all three rows. However, the degree of decrease in cochlear amplification caused by such functional losses remains unclear. In the present study, a finite element model of a cross section of the gerbil cochlea was constructed. Then, to determine effects of the functional losses of OHCs on the cochlear amplification, changes in the displacement amplitude of the basilar membrane (BM) due to the functional losses of OHCs were calculated. Results showed that the displacement amplitude of the BM decreases significantly when a single row of OHCs lost its function, suggesting that all three rows of OHCs are required for cochlear amplification.

scholarly journals Distinct roles of stereociliary links in the nonlinear sound processing and noise resistance of cochlear outer hair cells

2020 ◽  
Vol 117 (20) ◽  
pp. 11109-11117
Author(s):  
Woongsu Han ◽  
Jeong-Oh Shin ◽  
Ji-Hyun Ma ◽  
Hyehyun Min ◽  
Jinsei Jung ◽  
...  
Keyword(s):  
Hair Cells ◽  
Otoacoustic Emissions ◽  
Essential Role ◽  
High Sensitivity ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Sound Processing ◽  
Mechanoelectrical Transduction ◽  
Distortion Product ◽  
Membrane Attachment

Outer hair cells (OHCs) play an essential role in hearing by acting as a nonlinear amplifier which helps the cochlea detect sounds with high sensitivity and accuracy. This nonlinear sound processing generates distortion products, which can be measured as distortion-product otoacoustic emissions (DPOAEs). The OHC stereocilia that respond to sound vibrations are connected by three kinds of extracellular links: tip links that connect the taller stereocilia to shorter ones and convey force to the mechanoelectrical transduction channels, tectorial membrane-attachment crowns (TM-ACs) that connect the tallest stereocilia to one another and to the overlying TM, and horizontal top connectors (HTCs) that link adjacent stereocilia. While the tip links have been extensively studied, the roles that the other two types of links play in hearing are much less clear, largely because of a lack of suitable animal models. Here, while analyzing genetic combinations of tubby mice, we encountered models missing both HTCs and TM-ACs or HTCs alone. We found that the tubby mutation causes loss of both HTCs and TM-ACs due to a mislocalization of stereocilin, which results in OHC dysfunction leading to severe hearing loss. Intriguingly, the addition of the modifier allele modifier of tubby hearing 1 in tubby mice selectively rescues the TM-ACs but not the HTCs. Hearing is significantly rescued in these mice with robust DPOAE production, indicating an essential role of the TM-ACs but not the HTCs in normal OHC function. In contrast, the HTCs are required for the resistance of hearing to damage caused by noise stress.

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