Outer Hair Cell Somatic Electromotility In Vivo and Power Transfer to the Organ of Corti

AbstractThe active amplification of sound-induced vibrations in the cochlea, known to be crucial for auditory sensitivity and frequency selectivity, is not well understood. The outer hair cell (OHC) somatic electromotility is a potential mechanism for such amplification. Its effectiveness in vivo is putatively limited by the electrical low-pass filtering of the cell's transmembrane potential. However, the transmembrane potential is an incomplete metric. We propose and estimate two metrics to evaluate the effectiveness of OHC electromotility in vivo. One metric is the OHC electromechanical ratio defined as the amplitude of the ratio of OHC displacement to the change in its transmembrane potential. The in vivo electromechanical ratio is derived from the recently measured in vivo displacements of the reticular lamina and the basilar membrane at the 19 kHz characteristic place in guinea pigs and using a model. The ratio, after accounting for the differences in OHC vibration in situ due to the impedances from the adjacent structures, is in agreement with the literature values of the in vitro electromechanical ratio measured by others. The second and more insightful metric is the OHC somatic power. Our analysis demonstrates that the organ of Corti is nearly optimized to receive maximum somatic power in vivo and that the estimated somatic power could account for the active amplification

Розробка модуля Ethernet контролю для дистанційного керування електроживильною установкою

Sound processing in the inner ear involves separation of the constituent frequencies along the length of the cochlea. Frequencies relevant to human speech (100 to 500 Hz) are processed in the apex region. Among mammals, the guinea pig cochlear apex processes similar frequencies and is thus relevant for the study of speech processing in the cochlea. However, the requirement for extensive surgery has challenged the optical accessibility of this area to investigate cochlear processing of signals without significant intrusion. A simple method is developed to provide optical access to the guinea pig cochlear apex in two directions with minimal surgery. Furthermore, all prior vibration measurements in the guinea pig apex involved opening an observation hole in the otic capsule, which has been questioned on the basis of the resulting changes to cochlear hydrodynamics. Here, this limitation is overcome by measuring the vibrations through the unopened otic capsule using phase-sensitive Fourier domain optical coherence tomography. The optically and surgically advanced method described here lays the foundation to perform minimally invasive investigation of speech-related signal processing in the cochlea. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.Funding Agencies|NIH NIDCD [R01DC000141]; NIH [R01DC004554, R01DC010201, R01DC011796]; Swedish Research Council [K2014-63X-14061-14-5]; Torsten Soderberg Foundation</p

A mechanoelectrical mechanism for detection of sound envelopes in the hearing organ

To understand speech, the slowly varying outline, or envelope, of the acoustic stimulus is used to distinguish words. A small amount of information about the envelope is sufficient for speech recognition, but the mechanism used by the auditory system to extract the envelope is not known. Several different theories have been proposed, including envelope detection by auditory nerve dendrites as well as various mechanisms involving the sensory hair cells. We used recordings from human and animal inner ears to show that the dominant mechanism for envelope detection is distortion introduced by mechanoelectrical transduction channels. This electrical distortion, which is not apparent in the sound-evoked vibrations of the basilar membrane, tracks the envelope, excites the auditory nerve, and transmits information about the shape of the envelope to the brain.Funding Agencies|Swedish Research Council [K2014-63X-14061-14-5, 2017-06092]; Torsten Soderberg foundation; Strategic research area for systems neurobiology (Region Ostergotland); Linkoping University; NIH-NIDCD [R01 DC-004554, R01 DC 000141]</p

In Vivo Outer Hair Cell Length Changes Expose the Active Process in the Cochlea

BACKGROUND: Mammalian hearing is refined by amplification of the sound-evoked vibration of the cochlear partition. This amplification is at least partly due to forces produced by protein motors residing in the cylindrical body of the outer hair cell. To transmit power to the cochlear partition, it is required that the outer hair cells dynamically change their length, in addition to generating force. These length changes, which have not previously been measured in vivo, must be correctly timed with the acoustic stimulus to produce amplification. METHODOLOGY/PRINCIPAL FINDINGS: Using in vivo optical coherence tomography, we demonstrate that outer hair cells in living guinea pigs have length changes with unexpected timing and magnitudes that depend on the stimulus level in the sensitive cochlea. CONCLUSIONS/SIGNIFICANCE: The level-dependent length change is a necessary condition for directly validating that power is expended by the active process presumed to underlie normal hearing

Passive and active structural acoustic filtering in cochlear mechanics: Analysis and applications.

A linear physiologically-based finite element model is developed for analyzing the global mechanical-electrical-acoustic (active) filtering in the mammalian cochlea. The model consists of a two-duct fluid-filled rectangular geometry, the micro-mechanical structural network interacting with the fluid, electrical circuit equivalent of cells and fluid in every cross-section connected by longitudinal cables representing the conductivity of the cochlear fluids and includes the mechano-electrical and electro-mechanical transduction at the outer hair cells. The acoustic pressures, structural displacements, and electrical potentials are determined numerically and compared with experiments. For the first time, the response of the cochlea to both acoustic and electrical excitation are predicted using the same physiological model and compared with experiments. Reducing the amount of activity present in the model reduces the gain and lowers the frequency of peak BM velocity response compared to a fully active model, in accordance with experimental data. This model also possesses near invariance to click induced noise at different gain levels. Using the same model parameters, the predictions of the local BM velocity response to electrical stimulation match available experimental data, providing an independent test of the model capability. Predictions of electrically evoked otoacoustic emissions are found to match experimental results as well. Roughness introduced into BM stiffness is found to result in fine structures in a fully-active model and have little effect on a model with reduced activity. A new kind of passive hydraulic and pneumatic silencer called the structural acoustic silencer for broadband passive noise control is designed based on analogy with passive mechanics of the cochlea and compared with physical tests from experiments. The design of the silencer is done numerically using three dimensional finite element method. The structural acoustic silencers indeed result in broadband transmission loss. The relation between transmission loss and plate dispersion in the silencer is shown for the first time.Ph.D.Applied SciencesAudiologyHealth and Environmental SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124539/2/3150070.pd

Half-octave shift in mammalian hearing is an epiphenomenon of the cochlear amplifier.

The cochlear amplifier is a hypothesized positive feedback process responsible for our exquisite hearing sensitivity. Experimental evidence for or against the positive feedback hypothesis is still lacking. Here we apply linear control theory to determine the open-loop gain and the closed-loop sensitivity of the cochlear amplifier from available measurements of basilar membrane vibration in sensitive mammalian cochleae. We show that the frequency of peak closed-loop sensitivity is independent of the stimulus level and close to the characteristic frequency. This implies that the half-octave shift in mammalian hearing is an epiphenomenon of the cochlear amplifier. The open-loop gain is consistent with positive feedback and suggests that the high-frequency cut-off of the outer hair cell transmembrane potential in vivo may be necessary for cochlear amplification

System block diagram for the linear local feedback model of the cochlear amplifier; G_AS is the transfer function from actuator to sensor, K_FB is the feedback gain, and G_IS corresponds to the passive transfer function from input to sensor.

<p>For other details, see text.</p

BM tuning curves for varying sound stimulus levels (left) and the corresponding closed-loop sensitivity derived from those measurements (right) in the basal turn mammalian cochlea.

<p>The left panel (<b>A</b>) is BM displacement relative to stapes from Nuttall and Dolan <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045640#pone.0045640-Nuttall1" target="_blank">[4]</a> in guinea pigs; (<b>C</b>) is BM displacement relative to pressure at ear canal in chinchilla from Rugerro et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045640#pone.0045640-Ruggero1" target="_blank">[5]</a>; (<b>E</b>) is BM displacement re pressure from Cooper and Rhode <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045640#pone.0045640-Cooper1" target="_blank">[23]</a> also in chinchilla; and (<b>G</b>) is BM re stapes from the model predictions in Ramamoorthy et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045640#pone.0045640-Ramamoorthy1" target="_blank">[8]</a>. The right panels (<b>B</b>), (<b>D</b>), (<b>F</b>), and (<b>H</b>) show the corresponding closed-loop sensitivities. In (<b>A</b>)–(<b>F</b>), the numbers on the plot indicate the stimulus level in dBSPL; in (<b>G</b>) and (<b>H</b>), the numbers represent percentage of maximum MET conductance slope vs. HB displacement used in the model. From all four datasets, the BM tuning curves demonstrate shift in peak frequency (half-octave shift) with changes in stimulus level, whereas the closed-loop sensitivities do not.</p

Phase of closed-loop sensitivity at 18 kHz CF vs. stimulus level for guinea pig 2381-2SE from [4].

<p>Phase of closed-loop sensitivity at 18 kHz CF vs. stimulus level for guinea pig 2381-2SE from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045640#pone.0045640-Nuttall1" target="_blank">[4]</a>.</p