Cochlear Microphonic Response Research Articles

Intracochlear electrocochleography findings in cochlear implant recipients with auditory neuropathy spectrum disorder.

This study aimed to compare intracochlear electrocochleography (ECochG) findings in a group of cochlear implant (CI) recipients with auditory neuropathy spectrum disorder (ANSD) with a group of CI recipients with sensorineural hearing loss (SNHL). Auditory outcome and spectral resolution findings were also compared among CI recipients with and without cochlear microphonic (CM) responses. This single-center, prospective cohort study was undertaken at a tertiary referral center. CM responses by the intracochlear ECochG test were recorded in CI recipients at 0.25-2kHz. Speech, spatial, and hearing quality (SSQ) outcomes and spectral resolution measured with the spectral-temporally modulated ripple test were obtained for each recipient. The study included 62 implanted ears in 46 recipients, of which 59% (n=27) were male and 41% (n=19) were female. Twenty-nine ears with ANSD and 33 ears with SNHL were included. The mean age of the participants was 11 years. The results compared the intracochlear ECochG findings of the ANSD group with those of the SNHL group. Participants were divided into two groups with and without obtainable CM responses. CM responses were obtained in 13 of 29 ears in the ANSD group and 14 of 33 ears in the SNHL group. CM thresholds obtained were better according to behavioral audiometric responses in some frequencies in the ANSD group. No significant difference was found in the auditory outcome and spectral resolution among CI recipients with and without CM responses. Intracochlear ECochG has a limited potential clinical value for monitoring ANSD. CM thresholds obtained using ECochG may not reflect behavioral hearing thresholds.

Gom1 Mutant Mice as a Model of Otitis Media.

Otitis media (OM) disease is a common cause of hearing loss that is primarily the result of middle ear infection. At present, our understanding of the mechanisms leading to OM is limited due to the lack of animal models of OM with effusion (OME). Here, we report that the mice with genetic otitis media one (gom1) mutants are prone to OM. gom1 Mice were produced by the N-ethyl-N-nitrosourea (ENU) mutagenesis program as an animal model to study OM. These mice demonstrate many common features of OM, such as middle ear effusion and hearing impairment. We revealed that gom1 mice display various signs of middle ear and inner ear dysfunctions, including elevated thresholds of auditory-evoked brainstem response (ABR) and lack of cochlear microphonic responses. Decreased compliance intympanometrymeasurements indicates tympanic membrane and ossicular chain malfunction. We confirmed through histological examinations of middle ear structures that 34/34 (100 %) of the mutant mice suffered from severe OME. While individual ears had different levels of effusion and inflammatory cells in the middle ear cavity, all had thickened middle ear mucosa and submucosa compared to control mice (B6). Moreover, the mutant mice displayed cochlear hair cell loss. These observations also suggested the craniofacial abnormalities in the gom1 mouse model. Together, these results indicate that gom1 mice could be valuable for investigating the genetic contribution to the development of middle ear disease.

Auditory neuropathy spectrum disorder in two siblings with congenital cytomegalovirus infections: Two rare cases

Auditory neuropathy spectrum disorder (ANSD) is a rare hearing disorder when signal transmission is disrupted on the auditory pathway. Infection is one of the multifactorial causes of ANSD. Only a few researchers have reported the cases of ANSD caused by congenital cytomegalovirus (CMV) infection, and fewer have presented cases involving siblings. In our study, the two patients were siblings, aged 3 years and 7 months and 8 months. They were born prematurely, had microcephaly; anti-CMV IgG levels were reactive. Distortion product otoacoustic emissions test was normal. A click auditory brainstem response showed that no wave was detected with an 80 dB stimulus, and a cochlear microphonic response was obtained. No abnormality in the middle ear was observed, and negative acoustic reflexes were noted. Hearing habilitation with a low-gain hearing aid, speech therapy, and motoric habilitation was planned, and the patients were referred to the pediatric neurology for CMV management.

Retro-labyrinthine Lesion Site Detected by Galvanic Vestibular Stimulation Elicited Vestibular-evoked Myogenic Potentials in Patients with Auditory Neuropathy.

Auditory neuropathy (AN) is a unique pattern of hearing loss with preservation of hair cell function. The condition is characterized by the presence of otoacoustic emissions (OAE) or cochlear microphonic (CM) responses with severe abnormalities of the auditory brainstem response (ABR). The vestibular branches of the VIII cranial nerve and the structures innervated by it can also be affected. However, the precise lesion sites in the vestibular system are not well characterized in patients with AN. The air-conducted sound (ACS) vestibular-evoked myogenic potentials (VEMPs) and galvanic vestibular stimuli (GVS)-VEMPs were examined in 14 patients with AN. On examination of VEMPs (n=14, 28 ears), the absent rates of ACS-cervical VEMP (cVEMP), ACS-ocular VEMP (oVEMP), GVS-cVEMP, GVS-oVEMP and caloric test were 92.9% (26/28), 85.7% (24/28), 67.9% (19/28), 53.6% (15/28), and 61.5% (8/13), respectively. Impaired functions of the saccule, inferior vestibular nerve, utricle, superior vestibular nerve, and horizontal semicircular canal were found in 25.0% (7/28), 67.9% (19/28), 32.1% (9/28), 53.6% (15/28) and 61.5% (8/13) patients, respectively. On comparing the elicited VEMPs parameters of AN patients with those of normal controls, both ACS-VEMPs and GVS-VEMPs showed abnormal results in AN patients (such as, lower presence rates, elevated thresholds, prolonged latencies, and decreased amplitudes). The study suggested that patients with AN often have concomitant vestibular disorders. Retro-labyrinthine lesions were more frequently observed in this study. GVS-VEMPs combined with ACS-VEMPs may help identify the lesion sites and facilitate detection of areas of vestibular dysfunction in these patients.

Electrocochleography Observations in a Series of Cochlear Implant Electrode Tip Fold-Overs.

Tip fold-over is a rare but serious complication of cochlear implant (CI) surgery. The purpose of this study was to present intraoperative electrocochleography (ECochG) observations in a series of CI electrode tip fold-overs. Five pediatric subjects undergoing CI surgery through a round window (RW) approach with a perimodiolar electrode array, who were diagnosed with either auditory neuropathy spectrum disorder or enlarged vestibular aqueduct. Intraoperative RW ECochG during CI surgery: tone burst stimuli were presented from 95 to 110 dB SPL. Magnitude and phase characteristics of ECochG responses obtained intraoperatively before and immediately after electrode insertion were examined for patients with and without tip fold-over. Three subjects presented with tip fold-over and two formed the control group. Among fold-over cases, one participant exhibited an inversion in the starting phase of the cochlear microphonic response and a decrease in spectral magnitude from pre- to postinsertion. Both subjects who did not exhibit a change in phase had an increase in the ECochG-total response (ECochG-TR) magnitude. No case in the control group exhibited a change in starting phase. In regard to the ECochG-TR, all controls showed a decrease in the magnitude. Despite the small number of patients, heterogeneous ECochG response patterns were observed within the fold-over group. Though these results are not conclusive, they can serve as a framework to begin to understand ECochG's utility in detecting intraoperative tip fold-over.

Postoperative Intracochlear Electrocochleography in Pediatric Cochlear Implant Recipients: Association to Audiometric Thresholds and Auditory Performance.

The aim of this study was to compare intracochlear-recorded cochlear microphonics (CM) responses to behavioral audiometry thresholds in young children, with congenital hearing loss, 2 to 5 years after cochlear implantation early in life. In addition, differences in speech and auditory outcomes were assessed among children with and without residual hearing. The study was conducted at a tertiary, university-affiliated, pediatric medical center. CM responses by intracochlear electrocochleography technique were recorded from 102 implanted ears of 60 children and those responses correlated to behavioral audiometry thresholds at 0.125 to 2 kHz frequencies. All children had received Advanced Bionics cochlear implant with High Focus J1 or MidScala electrodes, along with extensive auditory rehabilitation before and after implantation, including the use of conventional hearing aids. Speech Spatial and Hearing Qualities, Category of Auditory Performance scale, and educational settings information were obtained for each participant. Those cochlear implantation (CI) outcomes were compared between children with or without residual CM responses. Two distinctive CM responses patterns were found among the implanted children. Of all ears diagnosed with cochlear hearing loss (n = 88), only in 29 ears, clear CM responses were obtained. In all other ears, no CM responses were obtained at the maximum output levels. The CM responses were highly correlated with coefficients ranging from 0.7 to 0.83 for the audiometric behavioral thresholds at 0.125 to 2 kHz frequency range. Of all ears diagnosed with auditory neuropathy syndrome disorder (n = 14), eight ears had residual hearing and recordable CM postimplantation. The other six ears showed no recordable CM responses at maximum output levels for all tested frequencies. Those showed supposedly better CM responses than the behavioral audiometry threshold, however with poor correlations with tested frequency thresholds. Children with residual hearing showed significantly better auditory outcomes with CI, compared with those without residual hearing. In children with congenital cochlear hearing loss, the objective CM intracochlear responses can reliably predict the residual audiometric threshold. However, in children with auditory neuropathy syndrome disorder, the CM thresholds did not match the behavioral audiometric responses. Postoperatively, children with recordable CM responses, showing preserved residual hearing, demonstrated better CI outcomes.

A novel variant in diaphanous homolog 1 (DIAPH1) as the cause of auditory neuropathy in a Chinese family

ObjectivesTo determine the genetic cause of non-syndromic autosomal dominant deafness segregating in a Chinese Auditory neuropathy (AN) family. IntroductionAN is a genetically related rare disease characterized by sensorineural hearing loss and retention of hair cell function. Diaphanous Homolog 1 (DIAPH1) is the causative gene of DFNA1. To date, no evidence has been detected to reveal the connection between gene DIAPH1 and AN. Material and methodsAudiological and imageological examinations, genome-wide linkage analysis, and whole exome sequencing (WES) were carried out on the family members. ResultsIn the 13-member branch of the family, 4 patients with preserved otoacoustic emission or cochlear microphonic and abnormal auditory brainstem responses were diagnosed with AN. Linkage analysis detected an interval with a LOD (log odds) score >4 on chr5:138.845–149.509 cM. Using WES we identified a novel frameshift variant c.3551_3552del (p.Glu1184AlafsTer11) in exon 26 of DIAPH1 located in the linkage region. The variant was co-segregated with hearing impairment phenotype in the family except 4 members below the average age of onset. We have found sufficient evidence conforming with the American College of Medical Genetics and Genomics Guideline to consider c.3551_3552del as the genetic cause of the family patients. ConclusionIt is the first report to expand DIAPH1-related phenotypic spectrum to include AN. Our findings could facilitate the clinical diagnosis and genetic counselling for AN, especially for those with DIAPH1 variants.

An Objective Estimation of Air-Bone-Gap in Cochlear Implant Recipients with Residual Hearing Using Electrocochleography.

Although, cochlear implants (CI) traditionally have been used to treat individuals with bilateral profound sensorineural hearing loss, a recent trend is to implant individuals with residual low-frequency hearing. Notably, many of these individuals demonstrate an air-bone gap (ABG) in low-frequency, pure-tone thresholds following implantation. An ABG is the difference between audiometric thresholds measured using air conduction (AC) and bone conduction (BC) stimulation. Although, behavioral AC thresholds are straightforward to assess, BC thresholds can be difficult to measure in individuals with severe-to-profound hearing loss because of vibrotactile responses to high-level, low-frequency stimulation and the potential contribution of hearing in the contralateral ear. Because of these technical barriers to measuring behavioral BC thresholds in implanted patients with residual hearing, it would be helpful to have an objective method for determining ABG. This study evaluated an innovative technique for measuring electrocochleographic (ECochG) responses using the cochlear microphonic (CM) response to assess AC and BC thresholds in implanted patients with residual hearing. Results showed high correlations between CM thresholds and behavioral audiograms for AC and BC conditions, thereby demonstrating the feasibility of using ECochG as an objective tool for quantifying ABG in CI recipients.

The auditory characteristics of children with inner auditory canal stenosis

Conclusions This study shows that the prevalence of auditory neuropathy spectrum disorder (ANSD) in the children with inner auditory canal (IAC) stenosis is much higher than those without IAC stenosis, regardless of whether they have other inner ear anomalies. In addition, the auditory characteristics of ANSD with IAC stenosis are significantly different from those of ANSD without any middle and inner ear malformations. Objectives To describe the auditory characteristics in children with IAC stenosis as well as to examine whether the narrow inner auditory canal is associated with ANSD. Method A total of 21 children, with inner auditory canal stenosis, participated in this study. A series of auditory tests were measured. Meanwhile, a comparative study was conducted on the auditory characteristics of ANSD, based on whether the children were associated with isolated IAC stenosis. Results Wave V in the ABR was not observed in all the patients, while cochlear microphonic (CM) response was detected in 81.1% ears with stenotic IAC. Sixteen of 19 (84.2%) ears with isolated IAC stenosis had CM response present on auditory brainstem responses (ABR) waveforms. There was no significant difference in ANSD characteristics between the children with and without isolated IAC stenosis.

The Effects of Urethane on Rat Outer Hair Cells.

The cochlea converts sound vibration into electrical impulses and amplifies the low-level sound signal. Urethane, a widely used anesthetic in animal research, has been shown to reduce the neural responses to auditory stimuli. However, the effects of urethane on cochlea, especially on the function of outer hair cells, remain largely unknown. In the present study, we compared the cochlear microphonic responses between awake and urethane-anesthetized rats. The results revealed that the amplitude of the cochlear microphonic was decreased by urethane, resulting in an increase in the threshold at all of the sound frequencies examined. To deduce the possible mechanism underlying the urethane-induced decrease in cochlear sensitivity, we examined the electrical response properties of isolated outer hair cells using whole-cell patch-clamp recording. We found that urethane hyperpolarizes the outer hair cell membrane potential in a dose-dependent manner and elicits larger outward current. This urethane-induced outward current was blocked by strychnine, an antagonist of the α9 subunit of the nicotinic acetylcholine receptor. Meanwhile, the function of the outer hair cell motor protein, prestin, was not affected. These results suggest that urethane anesthesia is expected to decrease the responses of outer hair cells, whereas the frequency selectivity of cochlea remains unchanged.

Auditory Fatigue

Introduction and objectivesGiven the relevance of possible hearing losses due to sound overloads and the short list of references of objective procedures for their study, we provide a technique that gives precise data about the audiometric profile and recruitment factor.Our objectives were to determine the peripheral fatigue, through the cochlear microphonic response to sound pressure overload stimuli, as well as to measure recovery time, establishing parameters for differentiation with regard to current psychoacoustic and clinical studies. Material and methodWe used specific instruments for the study of cochlear microphonic response, plus a function generator that provided us with stimuli of different intensities and harmonic components. In Wistar rats, we first measured the normal microphonic response and then the effect of auditory fatigue on it. ResultsUsing a 60dB pure tone acoustic stimulation, we obtained a microphonic response at 20dB. We then caused fatigue with 100dB of the same frequency, reaching a loss of approximately 11dB after 15min; after that, the deterioration slowed and did not exceed 15dB. By means of complex random tone maskers or white noise, no fatigue was caused to the sensory receptors, not even at levels of 100dB and over an hour of overstimulation. ConclusionsNo fatigue was observed in terms of sensory receptors. Deterioration of peripheral perception through intense overstimulation may be due to biochemical changes of desensitisation due to exhaustion. Auditory fatigue in subjective clinical trials presumably affects supracochlear sections. The auditory fatigue tests found are not in line with those obtained subjectively in clinical and psychoacoustic trials.

Fatiga auditiva

Introduction and objectivesGiven the relevance of possible hearing losses due to sound overloads and the short list of references of objective procedures for their study, we provide a technique that gives precise data about the audiometric profile and recruitment factor.Our objectives were to determine peripheral fatigue, through the cochlear microphonic response to sound pressure overload stimuli, as well as to measure recovery time, establishing parameters for differentiation with regard to current psychoacoustic and clinical studies. Material and methodWe used specific instruments for the study of cochlear microphonic response, plus a function generator that provided us with stimuli of different intensities and harmonic components. In Wistar rats, we first measured the normal microphonic response and then the effect of auditory fatigue on it. ResultsUsing a 60dB pure tone acoustic stimulation, we obtained a microphonic response at 20dB. We then caused fatigue with 100dB of the same frequency, reaching a loss of approximately 11dB after 15minutes; after that, the deterioration slowed and did not exceed 15dB. By means of complex random tone maskers or white noise, no fatigue was caused to the sensory receptors, not even at levels of 100dB and over an hour of overstimulation. ConclusionsNo fatigue was observed in terms of sensory receptors. Deterioration of peripheral perception through intense overstimulation may be due to biochemical changes of desensitisation due to exhaustion. Auditory fatigue in subjective clinical trials presumably affects supracochlear sections. The auditory fatigue tests found are not in line with those obtained subjectively in clinical and psychoacoustic trials.

Erratum to: Conductive Hearing Loss Induced by Experimental Middle-Ear Effusion in a Chinchilla Model Reveals Impaired Tympanic Membrane-Coupled Ossicular Chain Movement

Otitis media with effusion (OME) occurs when fluid collects in the middle-ear space behind the tympanic membrane (TM). As a result of this effusion, sounds can become attenuated by as much as 30-40 dB, causing a conductive hearing loss (CHL). However, the exact mechanical cause of the hearing loss remains unclear. Possible causes can include altered compliance of the TM, inefficient movement of the ossicular chain, decreased compliance of the oval window-stapes footplate complex, or altered input to the oval and round window due to conduction of sound energy through middle-ear fluid. Here, we studied the contribution of TM motion and umbo velocity to a CHL caused by middle-ear effusion. Using the chinchilla as an animal model, umbo velocity (V U) and cochlear microphonic (CM) responses were measured simultaneously using sinusoidal tone pip stimuli (125 Hz-12 kHz) before and after filling the middle ear with different volumes (0.5-2.0 mL) of silicone oil (viscosity, 3.5 Poise). Concurrent increases in CM thresholds and decreases in umbo velocity were noted after the middle ear was filled with 1.0 mL or more of fluid. Across animals, completely filling the middle ear with fluid caused 20-40-dB increases in CM thresholds and 15-35-dB attenuations in umbo velocity. Clinic-standard 226-Hz tympanometry was insensitive to fluid-associated changes in CM thresholds until virtually the entire middle-ear cavity had been filled (approximately >1.5 mL). The changes in umbo velocity, CM thresholds, and tympanometry due to experimentally induced OME suggest CHL arises primarily as a result of impaired TM mobility and TM-coupled umbo motion plus additional mechanisms within the middle ear.

Conductive Hearing Loss Induced by Experimental Middle-Ear Effusion in a Chinchilla Model Reveals Impaired Tympanic Membrane-Coupled Ossicular Chain Movement

Otitis media with effusion (OME) occurs when fluid collects in the middle-ear space behind the tympanic membrane (TM). As a result of this effusion, sounds can become attenuated by as much as 30-40dB, causing a conductive hearing loss (CHL). However, the exact mechanical cause of the hearing loss remains unclear. Possible causes can include altered compliance of the TM, inefficient movement of the ossicular chain, decreased compliance of the oval window-stapes footplate complex, or altered input to the oval and round window due to conduction of sound energy through middle-ear fluid. Here, we studied the contribution of TM motion and umbo velocity to a CHL caused by middle-ear effusion. Using the chinchilla as an animal model, umbo velocity (V U) and cochlear microphonic (CM) responses were measured simultaneously using sinusoidal tone pip stimuli (125Hz-12kHz) before and after filling the middle ear with different volumes (0.5-2.0mL) of silicone oil (viscosity, 3.5 Poise). Concurrent increases in CM thresholds and decreases in umbo velocity were noted after the middle ear was filled with 1.0mL or more of fluid. Across animals, completely filling the middle ear with fluid caused 20-40-dB increases in CM thresholds and 15-35-dB attenuations in umbo velocity. Clinic-standard 226-Hz tympanometry was insensitive to fluid-associated changes in CM thresholds until virtually the entire middle-ear cavity had been filled (approximately >1.5mL). The changes in umbo velocity, CM thresholds, and tympanometry due to experimentally induced OME suggest CHL arises primarily as a result of impaired TM mobility and TM-coupled umbo motion plus additional mechanisms within the middle ear.

A new auditory threshold estimation technique for low frequencies: proof of concept.

Presently available nonbehavioral methods to estimate auditory thresholds perform less well at frequencies below 1 kHz than at 1 kHz and above. For many uses, such as providing accurate infant hearing aid amplification for low-frequency vowels, an accurate nonbehavioral method to estimate low-frequency thresholds is needed. A novel technique was developed to estimate low-frequency cochlear thresholds based on the use of a previously reported waveform. It was determined how well the method worked by comparing the resulting thresholds to thresholds from onset-response compound action potentials (CAPs) and single-auditory-nerve (AN)- fibers in cats. A long-term goal is to translate this technique for use in humans. An electrode near the cochlea records a combination of cochlear microphonic (CM) and neural responses. In response to low-frequency, near threshold-level tones, the CM is almost sinusoidal whereas the neural responses occur preferentially at one phase of the tone. If the tone is presented again but with its polarity reversed, the neural response keeps the same shape, but shifts ½ cycle in time. Averaging responses to tones presented separately at opposite polarities overlaps and interleaves the neural responses and yields a waveform in which the CM is canceled and the neural response appears twice each tone cycle, that is, the resulting neural response is mostly at twice the tone frequency. The resultant waveform is referred to as "the auditory nerve overlapped waveform" (ANOW). In this study, ANOW level functions were measured in anesthetized cats from 10 to 80 dB SPL in 10 dB steps using tones between 0.3 and 1 kHz. As a response metric, the magnitude of the ANOW component was calculated at twice the tone frequency (ANOW2f). The ANOW threshold was the sound level where the interpolated ANOW2f crossed a statistical criterion that was higher than 95% of the noise floor distribution. ANOW thresholds were compared with onset-CAP thresholds from the same recordings and single-AN-fiber thresholds from the same animals. ANOW and onset-CAP level functions were obtained for 0.3 to 1 kHz tones, and single-AN-fiber responses from cats. Except at 1 kHz, typical ANOW thresholds were mostly 10 to 20 dB more sensitive than onset-CAP thresholds and 10 to 20 dB less sensitive than the most sensitive single-AN-fiber thresholds. ANOW provides frequency-specific estimates of cochlear neural thresholds over a frequency range that is important for hearing but is not well accessed by nonbehavioral, objective methods. Results suggest that with further targeted development, the ANOW low-frequency threshold estimation technique can be useful both clinically in humans and in basic-science animal experiments.

Different Manifestations of Auditory Neuropathy

Auditory neuropathy (AN) is characterized by a range of auditory deficits including elevated pure tone thresholds, reduced speech recognition scores, absence of auditory brainstem responses (ABR), and preservation of evoked otoacoustic emissions and the cochlear microphonic (CM) response. With increased advocacy for early implantation, patients with auditory neuropathy may be considered for implantation at or before one year of age. The decision for early implantation of very young patients with clinical test results that suggest AN should be made cautiously as a subset of patients presenting with the clinical constellation of AN may demonstrate reversible hearing loss over time.

Effects of isoflurane on auditory evoked potentials in the cochlea and brainstem of guinea pigs

Electrophysiological recordings of the auditory system are commonly performed in deeply anesthetized animals. This study evaluated the effects of various concentrations of the volatile anesthetic isoflurane (1–3%) on the compound action potential (CAP), cochlear microphonic (CM) and auditory brainstem response (ABR). Recordings were initiated in the awake, lightly restrained animal. Anesthesia was induced with a single dose of Hypnorm® (fentanyl and fluanisone). After tracheostomy increasing isoflurane concentrations were applied in N 2O/O 2 via controlled ventilation. Data were compared to recordings in the awake animal using repeated measures ANOVA and Dunnett’s post hoc test. On average, isoflurane dose-dependently suppressed the amplitude and increased the latency of the CAP. CM amplitude was suppressed. These effects were most profound at high frequencies and were typically significant at isoflurane concentrations of 2.5% and 3%. Amplitude and latency of the second negative peak of the CAP (N 2) were affected to a greater extent compared to the first peak (N 1). On average, isoflurane dose-dependently reduced the amplitude and increased the latency of the ABR. These effects were typically significant at an isoflurane concentration of 2%. Effects on peak IV and V were more pronounced compared to the early peaks I and III.

Deafness and Permanently Reduced Potassium Channel Gene Expression and Function in HypothyroidPit1dwMutants

The absence of thyroid hormone (TH) during late gestation and early infancy can cause irreparable deafness in both humans and rodents. A variety of rodent models have been used in an effort to identify the underlying molecular mechanism. Here, we characterize a mouse model of secondary hypothyroidism, pituitary transcription factor 1 (Pit1(dw)), which has profound, congenital deafness that is rescued by oral TH replacement. These mutants have tectorial membrane abnormalities, including a prominent Hensen's stripe, elevated beta-tectorin composition, and disrupted striated-sheet matrix. They lack distortion product otoacoustic emissions and cochlear microphonic responses, and exhibit reduced endocochlear potentials, suggesting defects in outer hair cell function and potassium recycling. Auditory system and hair cell physiology, histology, and anatomy studies reveal novel defects of hormone deficiency related to deafness: (1) permanently impaired expression of KCNJ10 in the stria vascularis of Pit1(dw) mice, which likely contributes to the reduced endocochlear potential, (2) significant outer hair cell loss in the mutants, which may result from cellular stress induced by the lower KCNQ4 expression and current levels in Pit1(dw) mutant outer hair cells, and (3) sensory and strial cell deterioration, which may have implications for thyroid hormone dysregulation in age-related hearing impairment. In summary, we suggest that these defects in outer hair cell and strial cell function are important contributors to the hearing impairment in Pit1(dw) mice.

Auditory pathology in cri‐du‐chat (5p‐) syndrome: phenotypic evidence for auditory neuropathy

5p-(cri-du-chat syndrome) is a well-defined clinical entity presenting with phenotypic and cytogenetic variability. Despite recognition that abnormalities in audition are common, limited reports on auditory functioning in affected individuals are available. The current study presents a case illustrating the auditory functioning in a 22-month-old patient diagnosed with 5p- syndrome, karyotype 46,XX,del(5)(p13). Auditory neuropathy was diagnosed based on abnormal auditory evoked potentials with neural components suggesting severe to profound hearing loss in the presence of cochlear microphonic responses and behavioral reactions to sound at mild to moderate hearing levels. The current case and a review of available reports indicate that auditory neuropathy or neural dys-synchrony may be another phenotype of the condition possibly related to abnormal expression of the protein beta-catenin mapped to 5p. Implications are for routine and diagnostic specific assessments of auditory functioning and for employment of non-verbal communication methods in early intervention.

Evoked cochlear potentials in the barn owl

Gross electrical responses to tone bursts were measured in adult barn owls, using a single-ended wire electrode placed onto the round window. Cochlear microphonic (CM) and compound action potential (CAP) responses were evaluated separately. Both potentials were physiologically vulnerable. Selective abolishment of neural responses at high frequencies confirmed that the CAP was of neural origin, while the CM remained unaffected. CAP latencies decreased with increasing stimulus frequency and CAP amplitudes were correlated with known variations in afferent fibre numbers from the different papillar regions. This suggests a local origin of the CAP along the tonotopic gradient within the basilar papilla. The audiograms derived from CAP and CM threshold responses both showed a broad frequency region of optimal sensitivity, very similar to behavioural and single-unit data, but shifted upward in absolute sensitivity. CAP thresholds rose above 8 kHz, while CM responses showed unchanged sensitivity up to 10 kHz.