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The mammalian ear embeds a cellular amplifier that boosts sound-induced hydromechanical waves as they propagate along the cochlea. The operation of this amplifier is not fully understood and is difficult to disentangle experimentally. In the prevailing view, cochlear waves are amplified by the piezo-electric action of the outer hair cells (OHCs), whose cycle-by-cycle elongations and contractions inject power into the local motion of the basilar membrane (BM). Concomitant deformations of the opposing (or “top”) side of the organ of Corti are assumed to play a minor role and are generally neglected. However, analysis of intracochlear motions obtained using optical coherence tomography calls this prevailing view into question. In particular, the analysis suggests that (i) the net local power transfer from the OHCs to the BM is either negative or highly inefficient; and (ii) vibration of the top side of the organ of Corti plays a primary role in traveling-wave amplification. A phenomenological model derived from these observations manifests realistic cochlear responses and suggests that amplification arises almost entirely from OHC-induced deformations of the top side of the organ of Corti. In effect, the model turns classic assumptions about spatial impedance relations and power-flow direction within the sensory epithelium upside down.

To detect the expression of Epac1 and Epac2 in the inner ear of guinea pigs and its association with microcirculation in the inner ear.The temporal bones of 30 healthy red-eye guinea pigs (60 ears) weighing 200-350 g were collected, then the surrounding bone wall of the cochlea was removed under a dissection microscope. Real-time quantitative PCR (RT-qPCR) and Western blot were used to detect mRNA and protein expression, respectively, of Epac1 and Epac2 in the inner ear and to compare their expression in heart, liver, kidney, intestine, and lung tissues. The specimens of the cochlea included the stria vascularis, basilar membrane, saccule, and utricles isolated under a microscope to detect the localization of Epac1 and Epac2 proteins in various parts of the inner ear through immunofluorescence staining.The RT-qPCR and Western blot results showed that Epac1 mRNA was universally expressed in the inner ear, heart, liver, kidneys, intestines, and lungs, and was highly expressed in the liver, kidneys, and intestines (p 0.05 vs heart, liver, kidney, intestine; p 0.05 vs lung). Epac2 mRNA was expressed in the inner ear and heart, but not in the liver, kidneys, intestines, or lungs (p 0.05 vs Heart). Epac1 and Epac2 proteins were both expressed in the inner ear, heart, liver, kidneys, intestines, and lungs. The relative expression of Epac1 proteins in the inner ear was significantly different from the liver, kidneys, intestines, and lungs (p 0.05). The relative expression of Epac2 proteins in the inner ear was significantly different from the liver, kidneys, and lungs (p 0.05), but not from the heart (p = 0.127) or intestines (p = 0.274). Immunofluorescence staining observed under confocal microscopy indicated that Epac1 and Epac2 proteins were expressed in the stria vascularis, basilar membrane, saccule, and utricles of the inner ear. They were expressed in maginal cells, intermediate cells, and basal cells of the stria vascularis, and highly expressed in capillary endothelial cells.Epac1 and Epac2 mRNA and proteins were both expressed in the inner ear of guinea pigs and evenly expressed in the spiral ganglion, basilar membrane, saccule, and utricles. However, their expression in capillary endothelial cells of the stria vascularis was more obvious, suggesting that cyclic adenosine monophosphate-Epac1 signaling may play an important role in maintaining the function of the blood-labyrinth barrier and regulating the stability of microcirculation in the inner ear.

Since it has been difficult to directly observe the morphology of the living cochlea, our ability to infer the mechanical functioning of the living ear has been limited. Nearly all our knowledge about cochlear morphology comes from postmortem tissue that was fixed and processed using procedures that possibly distort the structures and fluid spaces of the organ of Corti. In this study, optical coherence tomography was employed to obtain volumetric images of the high-frequency hook region of the gerbil cochlea, as viewed through the round window, with far better resolution capability than had been possible before. The anatomical structures and fluid spaces of the organ of Corti were segmented and quantified in vivo and over a 90-min postmortem period. We find that the arcuate-zone and pectinate-zone widths change very little postmortem. The volume of the scala tympani between the round-window membrane and basilar membrane and the volume of the inner spiral sulcus decrease in the first 60-min postmortem. While textbook drawings of the mammalian organ of Corti and cortilymph prominently depict the tunnel of Corti, the outer tunnel is typically missing. This is likely because textbook drawings are typically made from images obtained by histological methods. Here, we show that the outer tunnel is nearly twice as big as the tunnel of Corti or the space of Nuel. This larger outer tunnel fluid space could have a substantial, little-appreciated effect on cochlear micromechanics. We speculate that the outer tunnel forms a resonant structure that may affect reticular-lamina motion. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10162-022-00836-4.

We investigated the effect of a biasing tone close to 5, 15, or 30 Hz on the response to higher-frequency probe tones, behaviorally, and by measuring distortion-product otoacoustic emissions (DPOAEs). The amplitude of the biasing tone was adjusted for criterion suppression of cubic DPOAE elicited by probe tones presented between 0.7 and 8 kHz, or criterion loudness suppression of a train of tone-pip probes in the range 0.125–8 kHz. For DPOAEs, the biasing-tone level for criterion suppression increased with probe-tone frequency by 8–9 dB/octave, consistent with an apex-to-base gradient of biasing-tone-induced basilar membrane displacement, as we verified by computational simulation. In contrast, the biasing-tone level for criterion loudness suppression increased with probe frequency by only 1–3 dB/octave, reminiscent of previously published data on low-side suppression of auditory nerve responses to characteristic frequency tones. These slopes were independent of biasing-tone frequency, but the biasing-tone sensation level required for criterion suppression was ~ 10 dB lower for the two infrasound biasing tones than for the 30-Hz biasing tone. On average, biasing-tone sensation levels as low as 5 dB were sufficient to modulate the perception of higher frequency sounds. Our results are relevant for recent debates on perceptual effects of environmental noise with very low-frequency content and might offer insight into the mechanism underlying low-side suppression.

Lesions causing changes in the microstructure of the organ of Corti may lead to hearing impairment.The aim of this study was to investigate the effect of various structural lesions on the organ of Corti and the auditory function.A finite element method of the cochlea and the organ of Corti were established based on computed tomography scanning and anatomical data. We evaluated the accuracy of the model by comparing the simulation results to reported experimental data. We simulated and analyzed the impact of the lesions on the sound-sensing function of the cochlea by adjusting the biomaterial parameters of each component of the cochlea.In the explored frequency range, the stereocilia and outer hair cells and basilar membrane sclerosis resulted in 23.4%, 47.2%, and 57.8% reduction of basilar membrane displacement, respectively. Lesions of the basilar membrane and stereocilia and outer hair cells in the Corti caused a hearing response curve shift to higher frequencies and a decrease of the amplitude of the basilar membrane.Lesions of the internal structure of the Corti cause diminished movement of basement membrane and decreased sensorial function, which ultimately lead to hearing loss.

Optical coherence tomography (OCT) has become a powerful tool for measuring vibrations within the organ of Corti complex (OCC) in cochlear mechanics experiments. However, the one-dimensional nature of OCT measurements, combined with experimental and anatomical constraints, make these data ambiguous: Both the relative positions of measured structures and their orientation relative to the direction of measured vibrations are not known a priori. We present a method by which these measurement features can be determined via the use of a volumetric OCT scan to determine the relationship between the imaging/measurement axes and the canonical anatomical axes. We provide evidence that the method is functional by replicating previously measured radial vibration patterns of the basilar membrane (BM). We used the method to compare outer hair cell and BM vibration phase in the same anatomical cross section (but different optical cross sections), and found that outer hair cell region vibrations lead those of the BM across the entire measured frequency range. In contrast, a phase lead is only present at low frequencies in measurements taken within a single optical cross section. Relative phase is critical to the workings of the cochlea, and these results emphasize the importance of anatomically oriented measurement and analysis.

This paper discusses the role of two-dimensional (2-D)/three-dimensional (3-D) cochlear fluid hydrodynamics in the generation of the large nonlinear dynamical range of the basilar membrane (BM) and pressure response, in the decoupling between cochlear gain and tuning, and in the dynamic stabilization of the high-gain BM response in the peak region. The large and closely correlated dependence on stimulus level of the BM velocity and fluid pressure gain [Dong, W., and Olson, E. S. (2013). Biophys. J. 105(4), 1067-1078] is consistent with a physiologically oriented schematization of the outer hair cell (OHC) mechanism if two hydrodynamic effects are accounted for: amplification of the differential pressure associated with a focusing phenomenon, and viscous damping at the BM-fluid interface. The predictions of the analytical 2-D Wentzel-Kramers-Brillouin (WKB) approach are compared to solutions of a 3-D finite element model, showing that these hydrodynamic phenomena yield stable high-gain response in the peak region and a smooth transition among models with different effectiveness of the active mechanism, mimicking the cochlear nonlinear response over a wide stimulus level range. This study explains how an effectively anti-damping nonlinear outer hair cells (OHC) force may yield large BM and pressure dynamical ranges along with an almost level-independent admittance.

The mammalian cochlea relies on the active forcing of sensory outer hair cells (OHCs) to amplify traveling wave responses along the basilar membrane. These forces are the result of electromotility, wherein current through the OHCs leads to conformational changes in the cells that provide stresses on surrounding structures. OHC transducer current can be detected via the voltage in the scala tympani (the cochlear microphonic, CM), and the CM can be used as an indicator of healthy cochlear operation. The CM represents a summation of OHC currents (the inner hair cell contribution is known to be small) and to use CM to probe the properties of OHC transduction requires a model that simulates that summation. We developed a finite element model for that purpose. The pattern of current generators (the model input) was initially based on basilar membrane displacement, with the current size based on in vitro data. The model was able to reproduce the amplitude of experimental CM results reasonably well when the input tuning was enhanced slightly (peak increased by ∼6 dB), which can be regarded as additional hair bundle tuning, and with a current/input value of 200–260 pA/nm, which is ∼4 times greater than the largest in vitro measures.

The prevailing theory of cochlear function states that outer hair cells amplify sound-induced vibration to improve hearing sensitivity and frequency specificity. Recent micromechanical measurements in the basal turn of gerbil cochleae through the round window have demonstrated that the reticular lamina vibration lags the basilar membrane vibration, and it is physiologically vulnerable not only at the best frequency but also at the low frequencies. These results suggest that outer hair cells from a broad cochlear region enhance hearing sensitivity through a global hydromechanical mechanism. However, the time difference between the reticular lamina and basilar membrane vibration has been thought to result from a systematic measurement error caused by the optical axis non-perpendicular to the cochlear partition. To address this concern, we measured the reticular lamina and basilar membrane vibrations in the transverse direction through an opening in the cochlear lateral wall in this study. Present results show that the phase difference between the reticular lamina and basilar membrane vibration decreases with frequency by ~ 180 degrees from low frequencies to the best frequency, consistent with those measured through the round window. Together with the round-window measurement, the low-coherence interferometry through the cochlear lateral wall demonstrates that the time difference between the reticular lamina and basilar membrane vibration results from the cochlear active processing rather than a measurement error.

In cochlear implant surgery, insertion of perimodiolar electrode arrays into the scala tympani can be complicated by trauma or even accidental translocation of the electrode array within the cochlea. In patients with partial hearing loss, cochlear trauma can not only negatively affect implant performance, but also reduce residual hearing function. These events have been related to suboptimal positioning of the cochlear implant electrode array with respect to critical cochlear walls of the scala tympani (modiolar wall, osseous spiral lamina and basilar membrane). Currently, the position of the electrode array in relation to these walls cannot be assessed during the insertion and the surgeon depends on tactile feedback, which is unreliable and often comes too late. This study presents an image-guided cochlear implant device with an integrated, fiber-optic imaging probe that provides real-time feedback using optical coherence tomography during insertion into the human cochlea. This novel device enables the surgeon to accurately detect and identify the cochlear walls ahead and to adjust the insertion trajectory, avoiding collision and trauma. The functionality of this prototype has been demonstrated in a series of insertion experiments, conducted by experienced cochlear implant surgeons on fresh-frozen human cadaveric cochleae. ispartof: SCIENTIFIC REPORTS vol:12 issue:1 ispartof: location:England status: published

The basilar membrane in the cochlea can be modeled as an array of fluid coupled segments driven by stapes vibration and by the undamping nonlinear force simulating cochlear amplification. If stimulated with two tones, the model generates additional tones due to nonlinear distortion. These distortion products (DPs) can be transmitted into the ear canal and produce distortion-product otoacoustic emissions (DPOAEs) known to be generated in the healthy ear of various vertebrates. This study presents a solution for DPs in a two-dimensional nonlinear cochlear model with cochlear roughness—small irregularities in the impedance along the basilar membrane, which may produce additional DPs due to coherent reflection. The solution allows for decomposition of various sources of DPs in the model. In addition to the already described nonlinear-distortion and coherent-reflection mechanisms of DP generation, this study identifies a long-latency DPOAE component due to perturbation of nonlinear force. DP wavelets that are coherently reflected due to impedance irregularities travel toward the stapes across the primary generation region of DPs and there evoke perturbation of the nonlinear undamping force. The ensuing DP wavelets have opposite phase to the wavelets arising from coherent reflection, which results in partial cancellation of the coherent-reflection DP wavelets.

Within the cochlea, the basilar membrane (BM) is coupled to the reticular lamina (RL) through three rows of piezo-like outer hair cells (OHCs) and supporting cells that endow mammals with sensitive hearing. Anatomical differences across OHC rows suggest differences in their motion. Using optical coherence tomography, we measured in vivo and postmortem displacements through the gerbil round-window membrane from approximately the 40–47 kHz best-frequency (BF) regions. Our high spatial resolution allowed measurements across the RL surface at the tops of the three rows of individual OHCs and their bottoms, and across the BM. RL motion varied radially; the third-row gain was more than 3 times greater than that of the first row near BF, whereas the OHC-bottom motions remained similar. This implies that the RL mosaic, comprised of OHC and phalangeal-process tops joined together by adhesion molecules, is much more flexible than the Deiters’ cells connected to the OHCs at their bottom surfaces. Postmortem, the measured points moved together approximately in phase. These imply that in vivo, the RL does not move as a stiff plate hinging around the pillar-cell heads near the first row as has been assumed, but that its mosaic-like structure may instead bend and/or stretch.

Sound evokes sub-nanoscale vibration within the sensory epithelium. The epithelium contains not only immotile cells but also contractile outer hair cells (OHCs) that actively shrink and elongate synchronously with the sound. However, the in vivo motion of OHCs has remained undetermined. The aim of this work is to perform high-resolution and -accuracy vibrometry in live guinea pigs with an SC-introduced spectral-domain optical coherence tomography system (SD-OCT). In this study, to reveal the effective contribution of SC source in the recording of the low reflective materials with the short total acquisition time, we compare the performances of the SC-introduced SD-OCT (SCSD-OCT) to that of the conventional SD-OCT. As inanimate comparison objects, we record a mirror, a piezo actuator, and glass windows. For the measurements in biological materials, we use in/ex vivo guinea pig cochleae. Our study achieved the optimization of a SD-OCT system for high-resolution in vivo vibrometry in the cochlear sensory epithelium, termed the organ of Corti, in mammalian cochlea. By introducing a supercontinuum (SC) light source and reducing the total acquisition time, we improve the axial resolution and overcome the difficulty in recording the low reflective material in the presence of biological noise. The high power of the SC source enables the system to achieve a spatial resolution of 1.72 ± 0.00 μm on a mirror and reducing the total acquisition time contributes to the high spatial accuracy of sub-nanoscale vibrometry. Our findings reveal the vibrations at the apical/basal region of OHCs and the extracellular matrix, basilar membrane.

Hypothesis Measuring the length of the basilar membrane (BM) in the cochlear hook region will result in improved accuracy of cochlear duct length (CDL) measurements. Background Cochlear implant pitch mapping is generally performed in a patient independent approach, which has been shown to result in place-pitch mismatches. In order to customize cochlear implant pitch maps, accurate CDL measurements must be obtained. CDL measurements generally begin at the center of the round window (RW) and ignore the basal-most portion of the BM in the hook region. Measuring the size and morphology of the BM in the hook region can improve CDL measurements and our understanding of cochlear tonotopy. Methods Ten cadaveric human cochleae underwent synchrotron radiation phase-contrast imaging. The length of the BM through the hook region and CDL were measured. Two different CDL measurements were obtained for each sample, with starting points at the center of the RW (CDLRW) and the basal-most tip of the BM (CDLHR). Regression analysis was performed to relate CDLRW to CDLHR. A three-dimensional polynomial model was determined to describe the average BM hook region morphology. Results The mean CDLRW value was 33.03 ± 1.62 mm, and the mean CDLHR value was 34.68 ± 1.72 mm. The following relationship was determined between CDLRW and CDLHR: CDLHR = 1.06(CDLRW)-0.26 (R2 = 0.99). Conclusion The length and morphology of the hook region was determined. Current measurements underestimate CDL in the hook region and can be corrected using the results herein.

The human cochlea transforms sound waves into electrical signals in the acoustic nerve fibers with high acuity. This transformation occurs via vibrating anisotropic membranes (basilar and tectorial membranes) and frequency-specific hair cell receptors. Frequency-positions can be mapped within the cochlea to create a tonotopic chart which fits an almost-exponential function with lowest frequencies positioned apically and highest frequencies positioned at the cochlear base (Bekesy 1960, Greenwood 1961). To date, models of frequency positions have been based on a two-dimensional analysis with inaccurate representations of the cochlear hook region. In the present study, the first three-dimensional frequency analysis of the cochlea using dendritic mapping to obtain accurate tonotopic maps of the human basilar membrane/organ of Corti and the spiral ganglion was performed. A novel imaging technique, synchrotron radiation phase-contrast imaging, was used and a spiral ganglion frequency function was estimated by nonlinear least squares fitting a Greenwood-like function (F = A (10ax − K)) to the data. The three-dimensional tonotopic data presented herein has large implications for validating electrode position and creating customized frequency maps for cochlear implant recipients.

Background and objective The size of the cochlea varies a lot among the human population bringing the necessity for electrode arrays to be available in various lengths irrespective of the cochlear implant (CI) brand. This research software helps in the estimation of the patient's cochlear duct length (CDL) which is then used for the simulation of the correct length electrode array matching the patient's cochlear size and as well in getting the patient specific cochlear frequency map. Methods Visual Studio Express 2012 for Windows Desktop is used in the architecture of this research software. The basal turn diameter of the cochlea (“A” value) needs to be measured from the pre-operative computed tomography (CT) image of the patient's temporal bone. This “A” will be taken as the input for the CDL equations proposed by Alexiades et al for estimating the CDL along the basilar membrane for various insertion depths. Greenwood's equation is then used in combination with the CDL for the full length of the cochlea in getting the patient specific frequency map. Results The research software with the help of the “A” value as input, with few button clicks, gives the patient specific CDL for various insertion depths and the Greenwood's frequency map. The users have the choice to select any electrode array of their choice and place it under the frequency map to see how good it fits to that particular patient's cochlea. Also, given the possibility to drag and move the electrode array picture to mimic the post-operative actual electrode insertion depth. Conclusions This research software simplifies the overall process of CDL estimation and in getting the patient specific cochlear frequency map. The clinicians get the chance to simulate placing the various electrode array lengths in patient cochlea in identifying the best fit electrode. This could help in pushing the CI field into the concept of individualized CI electrode array solution that ultimately benefits the patients.

The purpose of this study is to develop a mathematical model of the spiral basilar membrane in the center of the cochlea, which plays an important role in the mammalian auditory system. The basilar membrane transmits sound vibrations, which are converted into electrical potential changes by the inner hair cells. The basilar membrane is thought to lie on a locally undistorted curved surface because the inner hair cells, which are arranged in an orderly fashion on the basilar membrane, respond to their location-specific frequencies. In mammals, the number of rotations of this surface and the rate of change of its width with each rotation are different. It turns out that by modifying the right helicoid, we can obtain a mathematical model that satisfies these points. In conclusion, even though the three-dimensional structure of the basilar membrane varies among species, this model can reproduce this structure. This further suggests that there are common genetic determinants of cochlear development in mammals. From a practical standpoint, this may be useful for creating cochlear implants.

OBJECTIVE To describe the first cochlear array insertions using a robot-assisted technique, with different types of straight or precurved electrode arrays, compared with arrays manually inserted into the cochlea. STUDY DESIGN Retrospective review. SETTING Tertiary otologic center. PATIENTS Twenty cochlear implantations in the robot-assisted group and 40 in the manually inserted group. INTERVENTIONS Cochlear implantations using a robot-assisted technique (RobOtol) with straight (eight Cochlear CI522/622, and eight Advanced Bionics Hifocus Slim J) or precurved (four Advanced Bionics Hifocus Mid-Scala) matched to manual cochlear implantations. Three-dimensional reconstruction images of the basilar membrane and the electrode array were obtained from pre- and postimplantation computed tomography. MAIN OUTCOME MEASURES Rate and localization of scalar translocations. RESULTS For straight electrode arrays, scalar translocations occurred in 19% (3/16) of the robot-assisted group and 31% (10/32) of the manually inserted group. Considering the number of translocated electrodes, this was lower in the robot-assisted group (7%) than in the manually inserted group (16%) (p

Introduction Meniere's disease is a clinical entity with no definitive objective testing. It has been hypothesized that underlying endolymphatic hydrops stiffens the basilar membrane leading to increased speed of the acoustic stimulus, therefore traveling wave velocity has been proposed as an objective test to aid in the diagnosis. The objective of this study is to compare electrocochleography frequency-specific action potential latency, basilar membrane traveling wave time, and summation to action potential (SP/AP) ratio in Meniere's and non-Meniere's patients. Methods Tympanic electrocochleography was performed with frequency-specific action potential latency time and SP/AP ratio recorded. Patient demographics, symptoms, audiogram data, AAO-HNS classification of Meniere's disease, management interventions, and follow-up were recorded. Statistical analysis was performed to compare outcome measures across patient groups, demographics, and clinical data. Results Ninety-one patients (182 ears) were included. There was a significant difference between a "definite" Meniere's diagnosis and an "unlikely" or "probable" diagnosis by an average of 13 dB HL for the pure-tone thresholds at 250 Hz on the affected side (p = 0.006). There was no significant difference in pure-tone thresholds at any other frequency, AP latency at any frequency, or AP/SP ratio between the different Meniere's classification groups. Conclusions Our study fails to show significance of the traveling wave velocity as an objective test for Meniere's disease. A significant correlation was found with low-frequency hearing loss between AAO-HNS Meniere's classification groups.

For a deeper understanding of the inner ear dynamics, a Finite-Element model of the human cochlea is developed. To describe the unsteady, viscous creeping flow of the liquid, a pressure-displacement-based Finite-Element formulation is used. This allows one to efficiently compute the basilar membrane vibrations resulting from the fluid-structure interaction leading to hearing nerve stimulation. The results show the formation of a travelingwave on the basilar membrane propagating with decreasing velocity towards the peaking at a frequency dependent position. This tonotopic behavior allows the brain to distinguish between sounds of different frequencies. Additionally, not only the middle ear, but also the transfer behavior of the cochlea contributes to the frequency dependence of the auditory threshold. Furthermore, the fluid velocity and pressure fields show the effect of viscous damping forces and allow us to deeper understand the formation of the pressure difference, responsible to excite the basilar membrane.

Human speech primarily contains low frequencies. It is well established that such frequencies maximally excite the cochlea near its apex. But, the micromechanics that precede and are involved in this transduction are not well understood. We measured vibrations from the low-frequency, second turn in intact gerbil cochleae using optical coherence tomography (OCT). The data were used to create spatial maps that detail the sound-evoked motions across the sensory organ of Corti complex (OCC). These maps were remarkably similar across animals and showed little variation with frequency or level. We identify four, anatomically distinct, response regions within the OCC: the basilar membrane (BM), the outer hair cells (OHC), the lateral compartment (lc), and the tectorial membrane (TM). Results provide evidence that active processes in the OHC play an important role in the mechanical interplay between different OCC structures which increases the amplitude and tuning sharpness of the traveling wave. The angle between the OCT beam and the OCC makes that we captured radial motions thought to be the effective stimulus to the mechano-sensitive hair bundles. We found that TM responses were relatively weak, arguing against a role in enhancing mechanical hair bundle deflection. Rather, BM responses were found to closely resemble the frequency selectivity and sensitivity found in auditory nerve fibers (ANF) that innervate the low-frequency cochlea.

After Békésy the stapes base moves around two axes: for weaker sounds - rotates around its transverse axis; in case of a strong sound - it moves around its longitudinal axis. Békésy’s place theory cannot alone explain the frequency-distinguishing ability of the ear. However, the existence of active amplification further sharpens the frequency-analysing ability of the cochlea. In addition, the different frequency sensitivity of afferent nerve fibres of inner hair cells synergizes with the mechanisms above. Peaked resonance curves are consequences of different threshold sensitivities of nerves connecting to individual hair cells. The frequency, which belongs to the lowest stimulus threshold, is called the characteristic frequency of a nerve. This place assignment of nerve frequencies are formed by the following mechanism in the cochlea. The place of amplitude maxima of progressive waves excited in the basilar membrane shows slight frequency dependence. The mechanism of active amplification forming in outer hair cells amplifies and sharpens the resonances of the basilar membrane. In 1961, nobleman Georg von Békésy received the Nobel Prize in Medicine: “for his discoveries of the physical mechanisms of stimulation within the cochlea”.

The effects of cochlear implants on residual hearing loss is investigated through a finite element model of human auditory periphery consisting of the cochlea and middle ear. The simulation results show that a round window stiffness is the dominant factor in residual hearing loss. The increased round window stiffness to five times caused over 4 dB residual hearing loss at low frequencies below 500 Hz. Without considering round window ossification, inserting a cochlear implant can show at most 4 dB difference of residual hearing loss in magnitude from the no-implant case although the cochlear implant's geometry and position has been varied. If the stiffness of the round window is the same, the simulation results suggest to use a thin-straight-cochlear implant inserted into the lateral side in order to preserve residual hearing at frequencies below 700 Hz. In addition, when the distance between the basilar membrane and a cochlear implant is closer, the residual hearing loss becomes severe at high frequencies above 1 kHz. The results would be helpful for choice of a cochlear implant depending on a patient's condition.

The mammalian hearing organ, the cochlea, contains an active amplifier to boost the vibrational response to low level sounds. Hallmarks of this active process are sharp location-dependent frequency tuning and compressive nonlinearity over a wide stimulus range. The amplifier relies on outer hair cell (OHC)-generated forces driven in part by the endocochlear potential, the ∼+80 mV potential maintained in scala media, generated by the stria vascularis. We transiently eliminated the endocochlear potential in vivo by an intravenous injection of furosemide and measured the vibrations of different layers in the cochlea’s organ of Corti using optical coherence tomography. Distortion product otoacoustic emissions were also monitored. After furosemide injection, the vibrations of the basilar membrane lost the best frequency (BF) peak and showed broad tuning similar to a passive cochlea. The intra-organ of Corti vibrations measured in the region of the OHCs lost the BF peak and showed low-pass responses but retained nonlinearity. This strongly suggests that OHC electromotility was operating and being driven by nonlinear OHC current. Thus, although electromotility is presumably necessary to produce a healthy BF peak, the mere presence of electromotility is not sufficient. The BF peak recovered nearly fully within 2 h, along with the recovery of odd-order distortion product otoacoustic emissions. The recovery pattern suggests that physical shifts in operating condition are a critical step in the recovery process.

International audience; Cochlear implantation consists in electrically stimulating the auditory nerve by inserting an electrode array inside the cochlea, a bony structure of the inner ear. In the absence of any visual feedback, the insertion results in many cases of damages of the internal structures. This paper presents a feasibility study on intraoperative imaging and identification of cochlear structures with high-frequency ultrasound (HFUS). 6 ex-vivo guinea pig cochleae were subjected to both US and microcomputed tomography (µCT) we respectively referred as intraoperative and preoperative modalities. For each sample, registration based on simulating US from the scanner was performed to allow a precise matching between the visible structures. According to two otologists, the procedure led to a Target Registration Error (TRE) of 0.32 mm ± 0.05. Thanks to referring to a better preoperative anatomical representation, we were able to intraoperatively identify the modiolus, both scalae vestibuli and tympani and deduce the location of the basilar membrane, all of which is of great interest for cochlear implantation. Our main objective is to extend this procedure to the human case and thus provide a new tool for inner ear surgery.

In this study, inspired from human cochlea, we propose an artificial basilar membrane structure based on an array of gold electrodes microfabricated along the opposite surfaces of a piezoelectric continuum. The proposed piezoelectric continuum features an isosceles trapezoidal geometry and is situated atop an elastomer matrix with embedded electrode grooves and a duct. At first, a detailed analytical model is presented, which formulates the continuum’s planar deflection equation, governing its elastodynamic behavior. Subsequently, in order to verify the analytical outcomes, a multiphysics finite-element analysis is performed in COMSOL®. Both analytical and numerical models demonstrate desired frequency selectivity akin to the capability of a biological basilar membrane. Subsequently, a proof-of-concept model of the proposed structure is custom-fabricated through standard photo- and soft lithography techniques using Polyvinylidene Difluoride (PVDF), gold, and Polydimethylsiloxane (PDMS) materials. Finally, the fabricated artificial basilar membrane that is intended to be used as a broad band sensor, and artificial cochlea for seamless human-robot interaction is experimentally characterized using a custom-built acoustic exciter, and its effective performance is validated within the frequency range of 3 kHz to 8 kHz.

As an organ that is sensitive to pressure changes, the ear is often damaged when a person is subjected to blast exposures resulting in hearing loss due to tissue damage in the middle ear and cochlea. While observation of middle ear damage is non-invasive, examining the damage to the cochlea is difficult to quantify. Previous works have modeled the cochlear response often when subjected to an acoustic pressure input, but the inner ear mechanics have rarely been studied when the ear is exposed to a blast wave. In this study we aim to develop a finite element (FE) model of the entire ear, particularly the cochlea, for predicting the blast wave transmission from the ear canal to cochlea. We utilized a FE model of the ear, which includes the ear canal, middle ear, and uncoiled two-chambered cochlea, to simulate the cochlear response to blast overpressure (BOP) at the entrance of the ear canal with ANSYS Mechanical and Fluent in a fluid–structure interface coupled analysis in the time domain. This model was developed based on previous middle and inner ear models, and the cochlea was remeshed to improve BOP simulation performance. The FE model was validated using experimentally measured blast pressure transduction from the ear canal to the middle ear and cochlea in human cadaveric temporal bones. Results from the FE model showed significant displacements of the tympanic membrane, middle ear ossicles, and basilar membrane (BM). The stapes footplate displacement was observed to be as high as 60 µm, far exceeding the displacement during normal acoustic stimulation, when the 30 kPa (4.35 psi, 183 dB (SPL), Sound Pressure Level) of BOP was applied at the ear canal entrance. The large stapes movement caused pressures in the cochlea to exceed the physiological pressure level [

A passive three-dimensional model of the human cochlea is described and analysed in the present article. One of its features is the implementation of a thermo-viscous boundary layer as a physically approved mechanism of mechanical damping. The model is solved numerically with the finite element method in ANSYS® and the simulation results are analysed with the help of MATLAB®. In this way curves of the basilar membrane's amplitude, phase and velocity for frequencies between 1000Hz and 8000Hz are calculated. A traveling wave develops on the basilar membrane and is damped after reaching its frequency-dependent maximum due to the boundary layer damping. A plot of the frequency-to-space transformation can be obtained which fits to the experimental data found in the literature. Furthermore, the study shows an energy analysis of the simulation verifying the boundary layer damping as a relevant physical effect for 3D-models of the cochlea.

Cochlear hair cells are critical for the conversion of acoustic into electrical signals and their dysfunction is a primary cause of acquired hearing impairments, which worsen with aging. Piezoelectric materials can reproduce the acoustic-electrical transduction properties of the cochlea and represent promising candidates for future cochlear prostheses. The majority of piezoelectric hearing devices so far developed are based on thin films, which have not managed to simultaneously provide the desired flexibility, high sensitivity, wide frequency selectivity, and biocompatibility. To overcome these issues, we hypothesized that fibrous membranes made up of polymeric piezoelectric biocompatible nanofibers could be employed to mimic the function of the basilar membrane, by selectively vibrating in response to different frequencies of sound and transmitting the resulting electrical impulses to the vestibulocochlear nerve. In this study, poly(vinylidene fluoride-trifluoroethylene) piezoelectric nanofiber-based acoustic circular sensors were designed and fabricated using the electrospinning technique. The performance of the sensors was investigated with particular focus on the identification of the resonance frequencies and acoustic-electrical conversion in fibrous membrane with different size and fiber orientation. The voltage output (1-17 mV) varied in the range of low resonance frequency (100-400 Hz) depending on the diameter of the macroscale sensors and alignment of the fibers. The devices developed can be regarded as a proof-of-concept demonstrating the possibility of using piezoelectric fibers to convert acoustic waves into electrical signals, through possible synergistic effects of piezoelectricity and triboelectricity. The study has paved the way for the development of self-powered nanofibrous implantable auditory sensors. ispartof: ACS APPLIED MATERIALS & INTERFACES vol:12 issue:31 pages:34643-34657 ispartof: location:United States status: published

The classic view of cochlear partition (CP) motion, generalized to be for all mammals, was derived from basal-turn measurements in laboratory animals. Recently, we reported motion of the human CP in the cochlear base that differs substantially from the classic view. We described a human soft tissue "bridge" (non-existent in the classic view) between the osseous spiral lamina (OSL) and basilar membrane (BM), and showed how OSL and bridge move in response to sound. Here, we detail relevant human anatomy to better understand the relationship between form and function. The bridge and BM have similar widths that increase linearly from base to apex, whereas the OSL width decreases from base to apex, leading to an approximately constant total CP width throughout the cochlea. The bony three-dimensional OSL microstructure, reconstructed from unconventionally thin, 2-μm histological sections, revealed thin, radially wide OSL plates with pores that vary in size, extent, and distribution with cochlear location. Polarized light microscopy revealed collagen fibers in the BM that spread out medially through the bridge to connect to the OSL. The long width and porosity of the OSL may explain its considerable bending flexibility. The similarity of BM and bridge widths along the cochlea, both containing continuous collagen fibers, may make them a functional unit and allow maximum CP motion near the bridge-BM boundary, as recently described. These anatomical findings may help us better understand the motion of the structures surrounding the organ of Corti and how they shape the input to the cochlear sensory mechanism.

Cochlear amplification of basilar membrane traveling waves is thought to occur between a tone’s characteristic frequency (CF) place and within one octave basal of the CF. Evidence for this view comes only from the cochlear base. Stimulus-frequency otoacoustic emissions (SFOAEs) provide a noninvasive alternative to direct measurements of cochlear motion that can be measured across a wide range of CF regions. Coherent reflection theory indicates that SFOAEs arise mostly from the peak region of the traveling wave, but several studies using far-basal suppressor tones claimed that SFOAE components originate many octaves basal of CF. We measured SFOAEs while perfusing guinea pig cochleas from apex to base with salicylate or KCl solutions that reduced outer-hair-cell function and SFOAE amplification. Solution effects on inner hair cells reduced auditory nerve compound action potentials (CAPs) and provided reference times for when solutions reached the SFOAE-frequency CF region. As solution flowed from apex to base, SFOAE reductions generally occurred later than CAP reductions and showed that the effects of cochlear amplification usually peaked ∼1/2 octave basal of the CF region. For tones ≥2 kHz, cochlear amplification typically extended ∼1.5 octaves basal of CF, and the data are consistent with coherent reflection theory. SFOAE amplification did not extend to the basal end of the cochlea, even though reticular lamina motion is amplified in this region, which indicates that reticular lamina motion is not directly coupled to basilar membrane traveling waves. Previous reports of SFOAE-frequency residuals produced by suppressor frequencies far above the SFOAE frequency are most likely due to additional sources created by the suppressor. For some tones

Hair cells in both the auditory and vestibular systems receive efferent innervation. A number of prior studies have indicated that efferent regulation serves to diminish the overall sensitivity of the auditory system. The efferent pathway is believed to affect the sensitivity and frequency selectivity of the hair cell by modulating its membrane potential. However, its effect on the mechanical response of the hair cell has not been established. We explored how stimulation of the efferent neurons affects the mechanical responsiveness of an individual hair bundle. We tested this effect onin vitropreparations of hair cells in the sacculi of American bullfrogs of both genders. Efferent stimulation routinely resulted in an immediate increase of the frequency of hair bundle spontaneous oscillations for the duration of the stimulus. Enlarging the stimulus amplitude and pulse length, or conversely, decreasing the interpulse interval led to oscillation suppression. Additionally, we tested the effects of efference on the hair bundle response to mechanical stimulation. The receptive field maps of hair cells undergoing efferent actuation demonstrated an overall desensitization with respect to those of unstimulated cells.SIGNIFICANCE STATEMENTThe efferent system is an important aide for the performance of the auditory system. It has been seen to contribute to sound detection and localization, ototoxicity prevention, and speech comprehension. Although measurements have demonstrated that efference suppresses basilar membrane movement, there is still much unknown about how efferent activity affects hearing mechanics. Here, we explore the mechanical basis for the efferent system's capabilities at the level of the hair bundle. We present optical recordings, receptive field maps, and sensitivity curves that show a hair bundle is desensitized by efferent stimulation. This supports the hypothesis that efferent regulation may be a biological control parameter for tuning the hair bundle's mechanical sensitivity.

HYPOTHESIS The objective was to evaluate the effect of cochlear implant (CI) insertion technique on electrode insertion forces and intracochlear trauma. We hypothesize that robotics-assisted insertions will reduce insertion forces and intracochlear trauma compared with manual insertions. BACKGROUND Variability in CI outcomes exists across patients, implant centers, surgeons, and electrode types. While surgical techniques that reduce electrode insertion trauma are well established, insertion trauma remains one contributing factor to variability in CI outcomes. Previous work demonstrates that micromechanically controlled insertion tools reduce both maximum insertion forces and insertion variability compared with manual insertions. METHODS CI electrode insertions were performed either by hand (n = 12) or utilizing a robotics-assisted tool (n = 12) in fresh frozen, human cadaveric cochleae using electrodes from four different CI manufacturers. Electrodes array insertion forces were additionally evaluated in benchtop cochlea models. Following cadaveric insertions, samples were imaged via high resolution x-ray microscopy to evaluate electrode position and intracochlear trauma events based on a modified Eshraghi scale. RESULTS Electrode array insertions performed by robotics-assisted system showed significantly lower insertion forces and variability. Manual electrode array insertions had a significantly higher overall trauma score of 3.1 ± 2.0 compared with 0.9 ± 1.0 for robotics-assisted insertions. Robotics-assisted insertions had higher rate of basilar membrane elevations while manual insertions showed higher rates of severe trauma events. CONCLUSIONS The robotic-assisted insertion system reduced trauma events associated with CI electrode insertions in cadaveric cochleae compared with manual insertions. Surgical devices which help to precisely and more consistently insert electrodes may improve CI outcomes and hearing preservation.

The cochlear basilar membrane (CBM) contains inner hair cells and outer hair cells that convert sound waves into electrical signals and transmit them to the central auditory system. Cochlear aging, the primary reason of age-related hearing loss, can reduce the signal transmission capacity. There is no ideal in vitro aging model of the CBM. In this study, we cultured the CBM, which was dissected from the cochlea of the C57BL/6 mice 5 days after birth, in a medium containing 20 mg/mL, 40 mg/mL, or 60 mg/mL d-galactose (d-gal). Compared with the control group, the levels of senescence-associated β-galactosidase were increased in a concentration-dependent manner in the CBM of the d-gal groups. In addition, levels of the mitochondrial superoxide and patterns of an age-related mitochondrial DNA3860-bp deletion were significantly increased. The ATP levels and the membrane potential of the mitochondrial were significantly decreased in the CBM of the D-gal groups compared with the control group. Furthermore, in comparison with the control group, damaged hair cell stereocilia and a loss of inner hair cell ribbon synapses were observed in the CBM of the d-gal groups. A loss of hair cells and activation of caspase-3-mediated outer hair cell apoptosis were also observed in the CBM of the high-dose d-gal group. These insults induced by D-gal in the CBM in vitro were similar to the ones that occur in cochlear natural aging in vivo. Thus, we believe that this is a successful in vitro aging model using cultured CBM. These results demonstrate the effects of mitochondrial oxidative damage on presbycusis and provide a reliable aging model to study the mechanisms of presbycusis in vitro.

Objective The intracochlear position of an electrode array may influence the outcome after cochlear implantation. The design of the electrode array can increase the risk of trauma causing penetration of the basilar membrane or shift of the electrode array into the scala vestibuli. The aim of the present study was to identify a scalar shift after implantation of two different electrode arrays developed by one manufacturer. Study design Retrospective analysis. Setting Tertiary referral center. Patients and intervention Cochlear implant recipients implanted between 2010 and 2014 and receiving either a mid-scala (n = 30) or a perimodiolar (n = 30) electrode array. Main outcome measure Occurrence of scalar shift in association with the electrode type. Results Scalar shift occurred in 26.7% (8 of 30) of the patients implanted with a perimodiolar electrode array and in 6.7% (2 of 30) of the patients implanted with the mid-scala electrode array. The mean insertion depth in the patients experiencing scalar shift after implantation of the mid-scala electrode was much deeper (21.59 ± 0.34 mm) when compared with the mean insertion depth of the patients with scalar shift after implantation with a perimodiolar electrode array (17.85 ± 2.19 mm). There tends to be a correlation between the cochlear length and the occurrence of a scalar shift. However, the number of patients with scalar shift in the mid-scala group is rather small. Conclusion Based on the presented data, more patients implanted with a perimodiolar electrode array have a scalar shift when compared with the midscalar electrode array.

According to the World Health Organization (WHO), approximately 5% of the world’s population has a hearing loss disability caused by various reasons. The cochlea is a spiral-shaped bone found in the inner ear that is capable of doing exceptional sound analysis, in terms of both frequency and intensity which allows the perception of sound frequency in the range of 20 Hz to 20 kHz. An artificial basilar membrane having various shapes has been developed but none of those covers the whole human audible frequency range. This paper compares the mechanical characteristics of the rectangular and taper piezoelectric cantilever to develop an artificial basilar membrane that mimics the human cochlea with high sensitivity. The cantilever beam is made up of molybdenum (Mo), aluminum nitride (AlN), tungsten (W) and the desired frequency range is obtained by varying the length and thickness of the cantilever beams. The 3D design and simulations were performed by COMSOL Multiphysics to study the Eigen frequency, displacement, and stress measurements of the cantilever. The Eigen frequency is observed to be increased with an increase in the thickness and decrease in the length for both rectangular and taper cantilever beam. The rectangular beam showed higher sensitivity and lower stresses compared to the taper beam. Therefore, the rectangular cantilever beam is more suitable to mimic the basilar membrane of the human cochlea.

Introduction: Auditory brainstem response (ABR) is one of the commonly used methods in clinical settings to evaluate the hearing sensitivity and auditory function. The current ABR measurement usually adopts click sound as the stimuli. However, there may be partial ABR amplitude attenuation due to the delay characteristics of the cochlear traveling wave along the basilar membrane. To solve that problem, a swept-tone method was proposed, in which the show-up time of different frequency components was adjusted to compensate the delay characteristics of the cochlear basilar membrane; therefore, different ABR subcomponents of different frequencies were synchronized. Methods: The normal hearing group, moderate sensorineural hearing loss group, and severe sensorineural hearing loss group underwent click ABR and swept-tone ABR with different stimulus intensities. The latencies and amplitudes of waves I, III, and V in 2 detections were recorded. Results: It was found that the latency of each of the recorded I, III, and V waves detected by swept-tone ABR was shorter than that by click ABR in both the control group and experimental groups. In addition, the amplitude of each of the recorded I, III, and V waves, except V waves under 60 dB nHL in the moderate sensorineural hearing loss group, detected by swept-tone ABR was larger than that by click ABR. The results also showed that the swept-tone ABR could measure the visible V waves at lower stimulus levels in the severe sensorineural hearing loss group. Conclusion: Swept-tone improves the ABR waveforms and helps to obtain more accurate threshold to some extent. Therefore, the proposed swept-tone ABR may provide a new solution for better morphology of ABR waveform, which can help to make more accurate diagnosis about the hearing functionality in the clinic.

Recent observations of sound-evoked vibrations of the cochlea’s sensory organ of Corti (ooC) using optical coherence tomography (OCT) have revealed unanticipated and complex motions. Interpreting these results in terms of the micromechanical inner-ear processes that precede hair-cell transduction is not trivial since OCT only measures a projection of the true motion, which may include transverse and longitudinal displacements. We measure ooC motions at multiple OCT beam angles relative to the longitudinal axis of the basilar membrane (BM) by using the cochlea’s natural curvature and find that the relative phase between outer hair cells (OHC) and BM varies with this angle. This includes a relatively abrupt phase reversal where OHC lead (lag) the BM by ~0.25 cycles for negative (positive) beam angles, respectively. We interpret these results as evidence for significant longitudinal motion within the ooC, which should be considered when interpreting (relative) ooC vibrations in terms of inner-ear sound processing.

Objectives Temporal bone (TB) studies are essential during the development of new arrays. Postoperative cochlear histology is still regarded as golden standard for the assessment of electrode localization and trauma though it is time consuming, expensive and technically very demanding. The aim of this study is to investigate whether pre-operative evacuation of perilymph improve the assessment of electrode localization and insertion trauma in TBs applying fusion imaging. The results were compared to a prior validated image fusion technique based on the quantification of the electrode placement. Materials and methods 12 prototype electrodes were implanted in fresh frozen TBs. The perilymph was evacuated from the scale prior to pre-operative cone-beam computer tomography (CBCT). The TB were then immersed in Ringer solution to rehydrated both scalae. After electrode insertion post-operative CBCT were obtained. 3D fusions of the pre- and postoperative registration were reconstructed. The electrode localization with respect to the basilar membrane was visually assessed. Results The visualization of the BM on the pre-operative scans was achieved beyond the second turn in all TBs. The visual assessment was found to be as accurate as the previously validated fusion technique. There was no statistically significant difference between the methods (p=0.564). The image reconstructions and evaluations, however, were faster to perform and the insertion results are immediately available. Conclusion CBCT in combination with pre- and postoperative image fusion is an accurate method for the post-operative assessment of insertion trauma in TBs. This new application facilitates the identification of the BM and allows for a visual assessment of insertion trauma.

The outer hair cells in the mammalian cochlea are cellular actuators essential for sensitive hearing. The geometry and stiffness of the structural scaffold surrounding the outer hair cells will determine how the active cells shape mammalian hearing by modulating the organ of Corti (OoC) vibrations. Specifically, the tectorial membrane and the Deiters cell are mechanically in series with the hair bundle and soma, respectively, of the outer hair cell. Their mechanical properties and anatomic arrangement must determine the relative motion among different OoC structures. We measured the OoC mechanics in the cochleas acutely excised from young gerbils of both sexes at a resolution fine enough to distinguish the displacement of individual cells. A three-dimensional finite element model of fully deformable OoC was exploited to analyze the measured data in detail. As a means to verify the computer model, the basilar membrane deformations because of static and dynamic stimulations were measured and simulated. Two stiffness ratios have been identified that are critical to understand cochlear physics, which are the stiffness of the tectorial membrane with respect to the hair bundle and the stiffness of the Deiters cell with respect to the outer hair cell body. Our measurements suggest that the Deiters cells act like a mechanical equalizer so that the outer hair cells are constrained neither too rigidly nor too weakly.SIGNIFICANCE STATEMENTMammals can detect faint sounds thanks to the action of mammalian-specific receptor cells called the outer hair cells. It is getting clearer that understanding the interactions between the outer hair cells and their surrounding structures such as the tectorial membrane and the Deiters cell is critical to resolve standing debates. Depending on theories, the stiffness of those two structures ranges from negligible to rigid. Because of their perceived importance, their properties have been measured in previous studies. However, nearly all existing data were obtainedex situ(after they were detached from the outer hair cells), which obscures their interaction with the outer hair cells. We quantified the mechanical properties of the tectorial membrane and the Deiters cellin situ.

Cochlear distortions afford researchers and clinicians a glimpse into the conditions and properties of inner ear signal processing mechanisms. Until recently, our examination of these distortions has been limited to measuring the vibration of the basilar membrane or recording acoustic distortion output in the ear canal. Despite its importance, the generation mechanism of cochlear distortion remains a substantial task to understand. The ability to measure the vibration of the reticular lamina in rodent models is a recent experimental advance. Surprising mechanical properties have been revealed. These properties merit both discussion in context with our current understanding of distortion, and appraisal of the significance of new interpretations of cochlear mechanics. This review focusses on some of the recent data from our research groups and discusses the implications of these data on our understanding of vocalization processing in the periphery, and their influence upon future experimental directions. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.

A WKB solution to the cochlear wave equation is derived, which results from the interaction between the passive dynamics of the basilar membrane and the 1D fluid coupling in the scalae, including both fluid viscosity and compressibility. The effect of various nondimensional parameters on the form of this solution is discussed. A nondimensional damping parameter and a nondimensional phase-shift parameter are shown to have the greatest influence on the response under normal conditions in the cochlea, with the fluid viscosity and compressibility only playing a minor role. It is then shown that in the case of an acoustic rainbow sensor, comprised of a discrete series of Helmholtz resonators in a duct, the governing wave equation in the continuous limit has the same form as the cochlear wave equation. The nondimensional compressibility parameter in this case is governed by the ratio of the Helmholtz resonator volume to that of the connecting duct and this parameter can be much larger than in the cochlea, and so plays a more dominant role in determining the response.

When the air of warm summer nights is buzzing and whirring with the songs of male bushcrickets (also known as katydids), our ears perform a series of tasks enabling us to perceive these acoustic communication signals. Airborne sound waves travel through the ear canal of the outer ear and impinge on the tympanic membrane, causing mechanical vibrations. These are transformed via the three ossicles in the middle ear into fluid vibrations of the inner ear cochlea, which in turn, activate sensory receptor cells, thereby transforming the mechanical energy into electrical signals (1). In our ears, this transduction process involves an ∼25-mm-long ear canal, a tympanic membrane 8 to 10 mm in diameter, and ∼3,500 inner hair cells distributed along the 35-mm-long basilar membrane (2). Female bushcrickets, the males’ intended audience, have to perform essentially the same feat but with miniature hearing organs located not on the head but on the upper tibia of the forelegs. These ears are typically only around 1 to 2 mm in size and contain rarely more than 100 neurons (3). Nevertheless, these tiny insect ears share a surprising amount of structural and functional similarities with our ears, some of which Vavakou et al. (4) uncover. Each bushcricket ear consists of two ear drums—the anterior tympanic membrane (ATym) and the posterior tympanic membrane (PTym)—located on opposite sides of the leg. Both tympana are backed internally by two branches of an air-filled tube connecting the ear to a large spiracular opening at the thorax. This acoustic trachea fulfils the role of an (outer ear) ear canal, with sound traveling from the acoustic spiracle to the back of the tympana (Fig. 1) (5). Because sound waves are both amplified and slowed down while traversing the ear canal, the internal tracheal input provides more sound pressure to the (middle … [↵][1]1Email: thorin.jonsson{at}uni-graz.at. [1]: #xref-corresp-1-1

We present a 3-D finite element (FE) model of the chinchilla's inner ear consisting of the entire cochlea structure and the vestibular system. The reaction of the basilar membrane to the head rotation and the reaction of ampulla to the stapes movement were investigated. These results demonstrate the existence of hearing-vestibular system interaction. They provide an explanation to the clinical finding on the coexistence between hearing loss and equilibration dysfunction. It is a preliminary, yet critical step toward the development of a comprehensive FE model of an entire ear for mechano-acoustic analysis.

According to coherent reflection theory, otoacoustic emissions (OAE) evoked with clicks (clicked-evoked, CE) or tones (stimulus frequency, SF) originate via the same mechanism. We test this hypothesis in gerbils by investigating the similarity of CE- and SFOAEs across a wide range of stimulus levels. The results show that OAE transfer functions measured in response to clicks and sweeps have nearly equivalent time–frequency characteristics, particularly at low stimulus levels. At high stimulus levels, the two OAE types are more dissimilar, reflecting the different dynamic properties of the evoking stimulus. At mid to high stimulus levels, time–frequency analysis reveals contributions from at least two OAE source components of varying latencies. Interference between these components explains the emergence of strong spectral microstructure. Time–frequency filtering based on mean basilar-membrane (BM) group delays (τ(BM)) shows that late-latency OAE components (latency ~ 1.6τ(BM)) dominate at low stimulus intensities and exhibit highly compressive growth with increasing stimulus intensity. In contrast, early-latency OAE components (~ 0.7τ(BM)) are small at low stimulus levels but can come to dominate the overall response at higher intensities. Although the properties of long-latency OAEs are consistent with an origin via coherent reflection near the peak of the traveling wave, the generation place and/or mechanisms responsible for the early-latency OAE components warrant further investigation. Because their delay remains in constant proportion to τ(BM) across sound intensity, long-latency OAEs, whether evoked with tones or clicks, can be used to predict characteristics of cochlear processing, such as the sharpness of frequency tuning, even at high stimulus levels.

Meniere's disease is an inner ear disorder, associated with episodes of vertigo, fluctuant hearing loss, tinnitus, and aural fullness. Meniere's disease is associated with endolymphatic hydrops. Clinical evidences show that this disease is often incapacitating, negatively affecting the patients' everyday life. The pathogenesis of Meniere's disease is still not fully understood and remains unclear. Previous numerical studies available in the literature related with endolymphatic hydrops, are very scarce. The present work applies the finite element method to investigate the consequences of endolymphatic hydrops in the normal hearing, associated with the Meniere's disease. The obtained results for the steady state dynamics analysis are in accordance with clinical evidences. The results show that the basilar membrane is not affected in the same intensity along its length and that the lower frequencies are more affected by the endolymphatic hydrops. From a clinical point of view, this work shows the relationship between the increasing of the endolymphatic pressure and the development of hearing loss.

The similarity of acoustic tasks performed by odontocete (toothed whale) and microchiropteran (insectivorous bat) biosonar suggests they may have common ultrasonic signal reception and processing mechanisms. However, there are also significant media and prey dependent differences, notably speed of sound and wavelengths in air vs. water, that may be reflected in adaptations in their auditory systems and peak spectra of out-going signals for similarly sized prey. We examined the anatomy of the peripheral auditory system of two species of FM bat (big brown bat Eptesicus fuscus; Japanese house bat Pipistrellus abramus) and two toothed whales (harbor porpoise Phocoena phocoena; bottlenose dolphin Tursiops truncatus) using ultra high resolution (11–100 micron) isotropic voxel computed tomography (helical and microCT). Significant differences were found for oval and round window location, cochlear length, basilar membrane gradients, neural distributions, cochlear spiral morphometry and curvature, and basilar membrane suspension distributions. Length correlates with body mass, not hearing ranges. High and low frequency hearing range cut-offs correlate with basilar membrane thickness/width ratios and the cochlear radius of curvature. These features are predictive of high and low frequency hearing limits in all ears examined. The ears of the harbor porpoise, the highest frequency echolocator in the study, had significantly greater stiffness, higher basal basilar membrane ratios, and bilateral bony support for 60% of the basilar membrane length. The porpoise’s basilar membrane includes a “foveal” region with “stretched” frequency representation and relatively constant membrane thickness/width ratio values similar to those reported for some bat species. Both species of bats and the harbor porpoise displayed unusual stapedial input locations and low ratios of cochlear radii, specializations that may enhance higher ultrasonic frequency signal resolution and deter low frequency cochlear propagation.

We built a flexible platform to study the mechanical operation of the organ of Corti (OoC) in the transduction of basilar membrane (BM) vibrations to oscillations of an inner hair cell bundle (IHB). The anatomical components that we consider are the outer hair cells (OHCs), the outer hair cell bundles, Deiters cells, Hensen cells, the IHB and various sections of the reticular lamina. In each of the components we apply Newton's equations of motion. The components are coupled to each other and are further coupled to the endolymph fluid motion in the subtectorial gap. This allows us to obtain the forces acting on the IHB, and thus study its motion as a function of the parameters of the different components. Some of the components include a nonlinear mechanical response. We found that slight bending of the apical ends of the OHCs can have a significant impact on the passage of motion from the BM to the IHB, including critical oscillator behaviour. In particular, our model implies that the components of the OoC could cooperate to enhance frequency selectivity, amplitude compression and signal to noise ratio in the passage from the BM to the IHB. Since the model is modular, it is easy to modify the assumptions and parameters for each component., Comment: A similar version was posted in bioRxiv

Objectives: Misplacement of the electrode array is associated with impaired speech perception in patients with cochlear implants (CIs). Translocation of the electrode array is the most common misplacement. When a CI is translocated, it crosses the basilar membrane from the scala tympani into the scala vestibuli. The position of the implant can be determined on a postoperative CT scan. However, such a scan is not obtained routinely after CI insertion in many hospitals, due to radiation exposure and processing time. Previous studies have shown that impedance measures might provide information on the placement of the electrode arrays. The electrode impedance was measured by dividing the plateau voltage at the end of the first phase of the pulse by the injected current. The access resistance was calculated using the so-called access voltage at the first sampled time point after the start of the pulse divided by the injected current. In our study, we obtained the electrode impedance and the access resistance to detect electrode translocations using electrical field imaging. We have investigated how reliably these two measurements can detect electrode translocation, and which method performed best. Design: We calculated the electrode impedances and access resistances using electrical field imaging recordings from 100 HiFocus Mid-Scala CI (Advanced Bionics, Sylmar, CA) recipients. We estimated the normal values of these two measurements as the baselines of the implant placed in the cochlea without translocation. Next, we calculated the maximal electrode impedance deviation and the maximal access-resistance deviation from the respective baselines as predictors of translocation. We classified these two predictors as translocations or nontranslocations based on the bootstrap sampling method and receiver operating characteristics curves analysis. The accuracy could be calculated by comparing those predictive results to a gold standard, namely the clinical CT scans. To determine which measurement more accurately detected translocation, the difference between the accuracies of the two measurements was calculated. Results: Using the bootstrap sampling method and receiver operating characteristics–based optimized threshold criteria, the 95% confidence intervals of the accuracies of translocation detections ranged from 77.8% to 82.1% and from 89.5% to 91.2% for the electrode impedance and access resistance, respectively. The accuracies of the maximal access-resistance deviations were significantly larger than that of the maximal electrode impedance deviations. The location of the translocation as predicted by the access resistance was significantly correlated with the result derived from the CT scans. In contrast, no significant correlation was observed for the electrode impedance. Conclusions: Both the electrode impedance and access resistance proved reliable metrics to detect translocations for HiFocus Mid-Scala electrode arrays. The access resistance had, however, significantly better accuracy and it also reliably detected the electrode-location of translocations. The electrode impedance did not correlate significantly with the location of translocation. Measuring the access resistance is, therefore, the recommended method to detect electrode-array translocations. These measures can provide prompt feedback for surgeons after insertion, improving their surgical skills, and ultimately reducing the number of translocations. In the future, such measurements may allow near-real-time monitoring of the electrode array during insertion, helping to avoid translocations.