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Background: This study aims to evaluate the effectiveness of recording cochlear microphonics (CM) using auditory brainstem response (ABR) protocols by comparing them with those obtained using electrocochleography (ECochG) protocols. To achieve this objective, 30 healthy participants aged 15–25 years were recruited. CM recordings were recorded using both ABR and ECochG protocols, utilizing three different stimuli (500-Hz tone burst (10 ms & 18 ms) and a 0.1-ms click), each presented at 100-dB SPL through insert earphones. In the ABR protocol, the non-inverting electrode was placed on the mastoid of the test ear, while in the ECochG protocol, a TipTrode was inserted inside the ear canal. The inverting electrode was placed on the mastoid of the non-test ear, and the ground electrode was positioned on the upper forehead for both protocols. The amplitude and onset latency of the recorded CM were then analyzed. Results: The study found that CM was detectable in 100% of subjects in both ABR and ECochG protocols when 500-Hz tone bursts were utilized. However, CM was recorded in 86.7% of ears using click stimuli in the ECochG protocol and in 80% of ears using the ABR protocol. The CM amplitude recorded with the ECochG protocol was significantly higher than that recorded with the ABR protocol. Additionally, CM amplitude elicited by tone bursts was significantly higher than that evoked by click stimuli in both protocols. The onset latency of CM evoked by click stimuli showed no significant differences between both protocols. However, the onset latency of CM evoked by 500-Hz tone bursts recorded via the ECochG protocol was significantly earlier compared to that recorded via the ABR protocol. Conclusion: The findings of the study suggest that the CM could be recorded using the scalp electrode with ABR protocol also, and this could lead to a cost- and time-effective procedure where audiologists can simultaneously record both cochlear potentials and neural responses. Findings also demonstrate that these recordings could be optimized and more reliably detected across subjects using 500-Hz tone bursts. These insights can guide clinical and research applications in auditory diagnostics and assessments. [ABSTRACT FROM AUTHOR]

Objectives: During cochlear implant (CI) electrode placement, single low-frequency (e.g., 500 Hz) cochlear microphonics (CM) measurements are used to monitor hair-cell function and provide feedback to avert insertion trauma. However, it can be difficult to differentiate between trauma and the electrode's progression through the cochlea when monitored with a single frequency. Multi-frequency CM measurements, while more complex to analyze, can provide more accurate feedback by measuring CM from various locations along the basilar membrane. Methods: A new algorithm was developed to analyze multi-frequency CM tracings by comparing amplitude and phase changes across different test frequencies. The new algorithm was evaluated as to its ability to identify drop-alarm instances with the multi-frequency approach, as compared to single-frequency 500 Hz tracings. Results: The algorithm presented in this manuscript uses the relationship between CM amplitude and phase changes across frequencies to provide real-time feedback during CI electrode placement. The results show that multi-frequency CM tracings raised an alarm only 0.5 times, as compared to 2.8 instances of alarm raised for the single-frequency 500 Hz CM measurements. Conclusions: Multi-frequency CM tracings can help reduce the number of alarms which may be false positives prompting unnecessary electrode manipulations, thereby minimizing the risk of insertion trauma. [ABSTRACT FROM AUTHOR]

BACKGROUND: Despite cochlear microphonic's potential clinical application, especially in ANSD diagnosis, the optimal parameters to record cochlear microphonics and the effect of various stimulus parameters are not well understood yet, which makes its recording a difficult procedure. The present study was undertaken to determine the effect of stimulus polarity, rate, stimulus type, and stimulus frequency on different aspects of cochlear microphonics, which could help to decide an optimal stimulus parameter that can be used to record CM. METHODS: The study involved 32 normal-hearing adults. CM was recorded from these individuals using extratympanic CM measurement from the ear canal independently for tone burst frequencies (500 Hz, 1 kHz, 4 kHz & 8 kHz) and click stimuli having rarefaction and condensation polarity at 30.1/sec and 59.1/sec repetition rates. Amplitude and latency were measured from the recorded waveforms and compared across and between stimulus conditions. RESULTS: Results reveal that stimulus frequency and stimulus type have a significant effect on different parameters of CM. However, there was no significant effect of stimulus polarity and rate of stimulus on the amplitude and latency of cochlear microphonics. The amplitude and latency of the cochlear microphonics are inversely proportional to the stimulus frequency. CONCLUSION: Hence, the study suggests the use of low-frequency tone burst (500 Hz/1 kHz) to elicit robust CM, which has greater application in the assessment of cochlear functioning over OAE as the latter gets affected by environmental and physiological noise and also due to middle ear pathology. [ABSTRACT FROM AUTHOR]

Abstract Background This study aims to evaluate the effectiveness of recording cochlear microphonics (CM) using auditory brainstem response (ABR) protocols by comparing them with those obtained using electrocochleography (ECochG) protocols. To achieve this objective, 30 healthy participants aged 15–25 years were recruited. CM recordings were recorded using both ABR and ECochG protocols, utilizing three different stimuli (500-Hz tone burst (10 ms & 18 ms) and a 0.1-ms click), each presented at 100-dB SPL through insert earphones. In the ABR protocol, the non-inverting electrode was placed on the mastoid of the test ear, while in the ECochG protocol, a TipTrode was inserted inside the ear canal. The inverting electrode was placed on the mastoid of the non-test ear, and the ground electrode was positioned on the upper forehead for both protocols. The amplitude and onset latency of the recorded CM were then analyzed. Results The study found that CM was detectable in 100% of subjects in both ABR and ECochG protocols when 500-Hz tone bursts were utilized. However, CM was recorded in 86.7% of ears using click stimuli in the ECochG protocol and in 80% of ears using the ABR protocol. The CM amplitude recorded with the ECochG protocol was significantly higher than that recorded with the ABR protocol. Additionally, CM amplitude elicited by tone bursts was significantly higher than that evoked by click stimuli in both protocols. The onset latency of CM evoked by click stimuli showed no significant differences between both protocols. However, the onset latency of CM evoked by 500-Hz tone bursts recorded via the ECochG protocol was significantly earlier compared to that recorded via the ABR protocol. Conclusion The findings of the study suggest that the CM could be recorded using the scalp electrode with ABR protocol also, and this could lead to a cost- and time-effective procedure where audiologists can simultaneously record both cochlear potentials and neural responses. Findings also demonstrate that these recordings could be optimized and more reliably detected across subjects using 500-Hz tone bursts. These insights can guide clinical and research applications in auditory diagnostics and assessments.

Objective: It has recently been discussed whether hearing screening and hearing threshold assessment can accurately be completed using automated ASSR methods for children with auditory neuropathy spectrum disorder (ANSD). Possible causes for the claimed potential failures were investigated here. Design: The study is based on the analysis of stored ASSR raw data. Study sample: This study reviewed raw ASSR data from 274 patients with a total of 5809 individual recordings. Results: Cochlear microphonics (CM) were found in 18 of the 274 patient records. Four of these 18 were obtained from patients with ANSD. One patient with ANSD without click auditory brainstem responses up to 100 dBnHL demonstrated clear ASSR responses from 65 dBnHL upwards. Where click stimulation suggests an auditory nerve defect, narrow-band chirps were shown to evoke ASSR in certain patients. CMs are elicited by narrow-band chirps in the same way as by broadband stimuli. CM residuals as well as a presumed enlarged wave I with absent neural responses, always accompanied by CM, were found as possible causes of misinterpretation at high stimulus levels. A CM detector was created. Conclusions: The CM detector, indicating the presence of CM, will prevent misinterpretation of clinical ASSR results. [ABSTRACT FROM AUTHOR]

Auditory neuropathy spectrum disorder (ANSD) is a heterogenous group of disorder characterized by abnormalities in auditory brainstem responses (ABR) with preserved otoacoustic emissions and/or cochlear microphonics. The aim of the study is to estimate the prevalence and evaluate the audiological characteristics of ANSD in adult population with sensory neural hearing loss. A prospective study was conducted on the adult population (≥ 18 years) attending ENT outpatients clinic at Rajiv Gandhi Government General Hospital, Chennai. All patients reported to the department with auditory and vestibular symptoms underwent case history, otoscopic examination, and routine audiological evaluation (pure tone audiometry, speech audiometry and immittance audiometry). Patients with indications of ANSD in case history and routine audiological evaluation were further evaluated using distortion product otoacoustic emissions and ABR. A total of 8682 adult population was evaluated during the period of 2017 to 2018. Out of 8682 patients, 1343 (15.46%) of them had sensory neural hearing loss of varying degrees. Out of 1343 adults with sensory neural hearing loss, 24 (1.78%) adults were diagnosed as ANSD. The prevalence of ANSD in adult population with sensory neural hearing loss in our study is 1.32% per 1000 adults. The clinical characteristics of ANSD shows impairment in speech perception irrespective of degree of hearing loss, preserved cochlear functions and abnormal ABR. Hence ANSD is not a rare clinical finding in adults with sensory neural hearing loss, but its prevalence was estimated to be lower in Indian population. Often young females are affected causing significant impairment in speech perception and disability. [ABSTRACT FROM AUTHOR]

Introduction: Electrocochleography (ECochG) is increasingly used in cochlear implant (CI) surgery, in order to monitor the effect of insertion of the electrode array aiming to preserve residual hearing. However, obtained results are often difficult to interpret. Here we aim to relate changes in ECochG responses to acute trauma induced by different stages of cochlear implantation by performing ECochG at multiple time points during the procedure in normal-hearing guinea pigs. Materials and methods: Eleven normal-hearing guinea pigs received a gold-ball electrode that was fixed in the round-window niche. ECochG recordings were performed during the four steps of cochlear implantation using the gold-ball electrode: (1) Bullostomy to expose the round window, (2) hand-drilling of 0.5- 0.6 mm cochleostomy in the basal turn near the round window, (3) insertion of a short flexible electrode array, and (4) withdrawal of electrode array. Acoustical stimuli were tones varying in frequency (0.25-16 kHz) and sound level. The ECochG signal was primarily analyzed in terms of threshold, amplitude, and latency of the compound action potential (CAP). Midmodiolar sections of the implanted cochleas were analyzed in terms of trauma to hair cells, modiolar wall, osseous spiral lamina (OSL) and lateral wall. Results: Animals were assigned to cochlear trauma categories: minimal (n = 3), moderate (n = 5), or severe (n = 3). After cochleostomy and array insertion, CAP threshold shifts increased with trauma severity. At each stage a threshold shift at high frequencies (4-16 kHz) was accompanied with a threshold shift at low frequencies (0.25-2 kHz) that was 10-20 dB smaller. Withdrawal of the array led to a further worsening of responses, which probably indicates that insertion and removal trauma affected the responses rather than the mere presence of the array. In two instances, CAP threshold shifts were considerably larger than threshold shifts of cochlear microphonics, which could be explained by neural damage due to OSL fracture. A change in amplitudes at high sound levels was strongly correlated with threshold shifts, which is relevant for clinical ECochG performed at one sound level. Conclusion: Basal trauma caused by cochleostomy and/or array insertion should be minimized in order to preserve the low-frequency residual hearing of CI recipients. [ABSTRACT FROM AUTHOR]

Intraoperative electrocochleography (ECOG) is performed using a single low-frequency acoustic stimulus (e.g., 500 Hz) to monitor cochlear microphonics (CM) during cochlear implant (CI) electrode insertion. A decrease in CM amplitude is commonly associated with cochlear trauma and is used to guide electrode placement. However, advancement of the recording electrode beyond the sites of CM generation can also lead to a decrease in CM amplitude and is sometimes interpreted as cochlear trauma, resulting in unnecessary electrode manipulation and increased risk of cochlear trauma during CI electrode placement. In the present study, multi-frequency ECOG was used to monitor CM during CI electrode placement. The intraoperative CM tracings were compared with electrode scan measurements, where CM was measured for each of the intracochlear electrodes. Comparison between the peak CM amplitude measured during electrode placement and electrode scan measurements was used to differentiate between different mechanisms for decrease in CM amplitude during CI electrode insertion. Analysis of the data shows that both multi-frequency electrocochleography and electrode scan could potentially be used to differentiate between different mechanisms for decreasing CM amplitude and providing appropriate feedback to the surgeon during CI electrode placement. [ABSTRACT FROM AUTHOR]

IntroductionElectrocochleography (ECochG) is increasingly used in cochlear implant (CI) surgery, in order to monitor the effect of insertion of the electrode array aiming to preserve residual hearing. However, obtained results are often difficult to interpret. Here we aim to relate changes in ECochG responses to acute trauma induced by different stages of cochlear implantation by performing ECochG at multiple time points during the procedure in normal-hearing guinea pigs.Materials and methodsEleven normal-hearing guinea pigs received a gold-ball electrode that was fixed in the round-window niche. ECochG recordings were performed during the four steps of cochlear implantation using the gold-ball electrode: (1) Bullostomy to expose the round window, (2) hand-drilling of 0.5–0.6 mm cochleostomy in the basal turn near the round window, (3) insertion of a short flexible electrode array, and (4) withdrawal of electrode array. Acoustical stimuli were tones varying in frequency (0.25–16 kHz) and sound level. The ECochG signal was primarily analyzed in terms of threshold, amplitude, and latency of the compound action potential (CAP). Midmodiolar sections of the implanted cochleas were analyzed in terms of trauma to hair cells, modiolar wall, osseous spiral lamina (OSL) and lateral wall.ResultsAnimals were assigned to cochlear trauma categories: minimal (n = 3), moderate (n = 5), or severe (n = 3). After cochleostomy and array insertion, CAP threshold shifts increased with trauma severity. At each stage a threshold shift at high frequencies (4–16 kHz) was accompanied with a threshold shift at low frequencies (0.25–2 kHz) that was 10–20 dB smaller. Withdrawal of the array led to a further worsening of responses, which probably indicates that insertion and removal trauma affected the responses rather than the mere presence of the array. In two instances, CAP threshold shifts were considerably larger than threshold shifts of cochlear microphonics, which could be explained by neural damage due to OSL fracture. A change in amplitudes at high sound levels was strongly correlated with threshold shifts, which is relevant for clinical ECochG performed at one sound level.ConclusionBasal trauma caused by cochleostomy and/or array insertion should be minimized in order to preserve the low-frequency residual hearing of CI recipients.

NGLY1 deficiency is a rare in which affected individuals show developmental delay/intellectual disability in the mild to profound range, epilepsy, auditory neuropathy, abnormal liver function, complex hyperkinetic movement disorder and poor growth. Here, we present the follow-up results of hearing status in a patient with NGLY1 deficiency. [ABSTRACT FROM AUTHOR]

• Wireless EcochG is a feasible way to record high-quality signals reflecting receptor and neural activity from the cochlea. • Spontaneous auditory-nerve activity was modulated by visual crossmodal stimulation. The discovery and development of electrocochleography (ECochG) in animal models has been fundamental for its implementation in clinical audiology and neurotology. In our laboratory, the use of round-window ECochG recordings in chinchillas has allowed a better understanding of auditory efferent functioning. In previous works, we gave evidence of the corticofugal modulation of auditory-nerve and cochlear responses during visual attention and working memory. However, whether these cognitive top-down mechanisms to the most peripheral structures of the auditory pathway are also active during audiovisual crossmodal stimulation is unknown. Here, we introduce a new technique, wireless ECochG to record compound-action potentials of the auditory nerve (CAP), cochlear microphonics (CM), and round-window noise (RWN) in awake chinchillas during a paradigm of crossmodal (visual and auditory) stimulation. We compared ECochG data obtained from four awake chinchillas recorded with a wireless ECochG system with wired ECochG recordings from six anesthetized animals. Although ECochG experiments with the wireless system had a lower signal-to-noise ratio than wired recordings, their quality was sufficient to compare ECochG potentials in awake crossmodal conditions. We found non-significant differences in CAP and CM amplitudes in response to audiovisual stimulation compared to auditory stimulation alone (clicks and tones). On the other hand, spontaneous auditory-nerve activity (RWN) was modulated by visual crossmodal stimulation, suggesting that visual crossmodal simulation can modulate spontaneous but not evoked auditory-nerve activity. However, given the limited sample of 10 animals (4 wireless and 6 wired), these results should be interpreted cautiously. Future experiments are required to substantiate these conclusions. In addition, we introduce the use of wireless ECochG in animal models as a useful tool for translational research. [ABSTRACT FROM AUTHOR]

To date, objective measurements and psychophysical experiments have been used to measure frequency dependent basilar membrane (BM) delays in humans; however, in vivo measurements have not been made. This study aimed to measure BM delays by performing intracochlear electrocochleography in cochlear implant recipients. Sixteen subjects with various degrees of hearing abilities were selected. Postoperative Computer Tomography was performed to determine electrode locations. Electrical potentials in response to acoustic tone pips at 0.25, 0.5, 1, 2, and 4 kHz and clicks were recorded with electrodes at the frequency specific region. The electrode array was inserted up to the characteristic cochlear frequency region of 250 Hz for 6 subjects. Furthermore, the array was inserted in the region of 500 Hz for 15 subjects, and 1, 2, and 4 kHz were reached in all subjects. Intracochlear electrocochleography for each frequency-specific tone pip and clicks showed detectable responses in all subjects. The latencies differed among the cochlear location and the cochlear microphonic (CM) onset latency increased with decreasing frequency and were consistent with click derived band technique. Accordingly, BM delays in humans could be derived. The BM delays increased systematically along the cochlea from basal to apical end and were in accordance with Ruggero and Temchin, 2007. [ABSTRACT FROM AUTHOR]

UNLABELLED: The aim of this work was to assess the hearing impairment in patients with hereditary motor and sensory neuropathy (HMSN). Elevation of pure tone thresholds in the presence of preserved inner ear function as suggested by cochlear microphonics (CM), absent or markedly abnormal brainstem auditory evoked potentials (BAEP), and elevation of speech perception out of proportion to the pure tone loss were found in the patients. From 28 members of a Gypsy family, we examined two siblings aged 31 and 30 years and their nephew aged 20 years, all suffering from HMSN that was associated with auditory neuropathy. All three affected members with difficulty of understanding speech had following investigations: pure tone and speech audiograms, BAEP, cochlear microphonics, and nerve conduction studies (NCV). RESULTS: the older two siblings had a flat 80 dB audiogram, whereas the younger one has flat 20 dB audiogram on the Lt. ear and 30 dB audiogram on the Rt. ear. All had no speech comprehension and no BAEP. Two patients had preserved cochlear microphonics on one ear. Peripheral nerves were electrically not elicitable, however, at the beginning of the disease nerve conduction was slow. CONCLUSION: in all three affected members with distinct clinical picture of HMSN their hearing impairment was proved to be due to severe auditory neuropathy in the presence of preserved inner ear function.

UNLABELLED: The aim of this work was to assess the hearing impairment in patients with hereditary motor and sensory neuropathy (HMSN). Elevation of pure tone thresholds in the presence of preserved inner ear function as suggested by cochlear microphonics (CM), absent or markedly abnormal brainstem auditory evoked potentials (BAEP), and elevation of speech perception out of proportion to the pure tone loss were found in the patients. From 28 members of a Gypsy family, we examined two siblings aged 31 and 30 years and their nephew aged 20 years, all suffering from HMSN that was associated with auditory neuropathy. All three affected members with difficulty of understanding speech had following investigations: pure tone and speech audiograms, BAEP, cochlear microphonics, and nerve conduction studies (NCV). RESULTS: the older two siblings had a flat 80 dB audiogram, whereas the younger one has flat 20 dB audiogram on the Lt. ear and 30 dB audiogram on the Rt. ear. All had no speech comprehension and no BAEP. Two patients had preserved cochlear microphonics on one ear. Peripheral nerves were electrically not elicitable, however, at the beginning of the disease nerve conduction was slow. CONCLUSION: in all three affected members with distinct clinical picture of HMSN their hearing impairment was proved to be due to severe auditory neuropathy in the presence of preserved inner ear function.

Background: The detection of precise hearing thresholds in infants and children with auditory neuropathy (AN) is challenging with current objective methods, especially in those younger than six months of age. Purpose: The aim of this study was to compare the thresholds using auditory steady-state response (ASSR) and cochlear microphonics (CM) in children with AN and children with normal hearing. Research Design: The thresholds of CM, ASSR, and visual reinforcement audiometry (VRA) tests were recorded; the ASSR and VRA frequencies used were 250, 500, 1000, 2000, and 4000 Hz. Study Sample: The participants in this study were 15 children with AN (27 ears) (1-7.6 years, median age 4.1 years) and ten children with normal hearing (20 ears) (1-8 years, median age four years). Data Collection and Analysis: The thresholds of the three methods were compared, and histograms were used to represent frequency distributions of threshold differences obtained from the three methods. Results: In children with normal hearing, the average CM thresholds (84.5 dB) were significantly higher than the VRA thresholds (10.0-10.8 dB); in children with AN, both CM and VRA responses were seen at high signal levels (88.9 dB and 70.6-103.4 dB, respectively). In normal children, the difference between mean VRA and ASSR thresholds ranged from 17.5 to 30.3 dB, which was significantly smaller than the difference seen between the mean CM and VRA thresholds (71.5-72.3 dB). The correlation between VRA and ASSR in children with normal hearing ranged from 0.38 to 0.48, whereas no such correlation was seen in children with AN at any frequency (0.03-0.19). Conclusions: Our results indicated that ASSR and CM were poor predictors of the conventional behavioral threshold in children with AN. [ABSTRACT FROM AUTHOR]

Objective measurements of the ossicular mobility have not been commonly performed during the surgery, and the assessment of ossicular mobility is made by palpation in most cases. Palpation is inherently subjective and may not always be reliable, especially in milder degrees of ossicular fixation and in the case of multiple fixation. Although several devices have been developed to quantitatively measure the ossicular mobility during surgery, they have not been widely used. In this study, a new system with a hand-held probe which enables intraoperative quantitative measurements of ossicular mobility has been developed. This system not only measures the ossicular mobility, but also investigates "local" transmission characteristics of the middle ear by directly applying vibration to the ossicles and measuring cochlear microphonic. The basic performance of this system was confirmed by measuring the mobility of artificial ossicles and cochlear microphonics in an animal experiment. Our system may contribute to selection of a better surgical method and reducing the risks of revision surgery. • A new system with a hand-held probe which enables intraoperative quantitative measurements of ossicular mobility has been developed. • This system also estimates "local" transmission characteristics of the middle ear by directly applying vibration to the ossicles and measuring cochlear microphonic. • The basic performance of the system was confirmed by measuring the mobility of artificial ossicles and cochlear microphonics in an animal experiment. [ABSTRACT FROM AUTHOR]

In vestibular-schwannoma (VS) surgery, hearing-preservation rate remains low. Besides damage to the cochlear nerve, intraoperative cochlear ischemia is a potential cause of hearing loss. Here, we used non-invasive cochlear microphonic (CM) recordings to detect the cochlear vascular events of VS surgery. Continuous intraoperative CM monitoring, in response to 80-95 dB SPL, 1-kHz tone-bursts, was performed in two samples of patients undergoing retrosigmoid cerebellopontine-angle surgery: one for VS ( n = 31) and one for vestibular neurectomy or vasculo-neural conflict causing intractable trigeminal neuralgia, harmless to hearing ( n = 19, control group). Preoperative and postoperative hearings were compared as a function of intraoperative CM changes and their chronology. Monitoring was possible throughout except for a few tens of seconds when drilling or suction noises occurred. Four patterns of CM time course were identified, eventless, fluctuating, abrupt or progressive decrease. Only the VS group displayed the last two patterns, mainly during internal-auditory-canal drilling and the ensuing tumor dissection, always with postoperative loss of hearing as an end result. Conversely, eventless and fluctuating CM patterns could be associated with postoperative hearing loss when the cochlear nerve had been reportedly damaged, an event that CM is not meant to detect. Cochlear ischemia is a frequent event in VS surgery that leads to deafness. The findings that CM decrease raised no false alarm, and that CM fluctuations, insignificant in control cases, were easily spotted, suggest that CM intraoperative monitoring is a sensitive tool that could profitably guide VS surgery. [ABSTRACT FROM AUTHOR]

The presence of ringing cochlear microphonics (CM) with an absence of auditory brainstem response (ABR) is an indicator of auditory neuropathy spectrum disorder (ANSD). The duration of CM may vary based on the stimuli used to elicit the response. Generally, ABR is recorded using clicks with very limited use of tonebursts. Thus, this study aims to understand the duration of CM in individuals with ANSD and normal hearing in response to clicks, 500 Hz toneburst, and 4000 Hz toneburst using ABR. Results show that individuals with ANSD have a longer duration of CM than those with normal hearing. The presence of CM was more evident in response to toneburst stimuli than clicks, with 500 Hz being commonly eliciting more CM in both groups. The difference in duration of CM was statistically significant in individuals with ANSD with longer duration obtained for 500 Hz followed by clicks and 4000 Hz toneburst. The duration of the stimuli used plays an important role in revealing the CM while recording ABR. This indicates that the use of toneburst, particularly low frequency such as 500 Hz, will be clinically useful in identifying ANSD especially when otoacoustic emissions are compromised., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2023, Sasidharan et al.)

Objective: It is agreed that the cochlear microphonic (CM) arises mainly from the normal outer hair cells (OHCs) in cochlea. The aim of this research is to study the CM characteristics in different hearing profiles and reflect the usefulness of recording CM simultaneously during Auditory Brainstem Response (ABR) threshold testing in children. Methods: This is a retrospective study that included 33 cases comprised of children with autism spectral disorders (ASD), children with cochlear sensorineural hearing loss (SNHL), children with auditory neuropathy spectrum disorder (ANSD) and 41 normal hearing healthy children as controls. The children's ages ranged from 0.5 to 96 months. Both the CM and ABR waves were simultaneously recorded using alternating split polarity ABR. Results: CM amplitudes and thresholds in normal hearing children with ASD did not significantly differ from normal hearing healthy children. CM were preserved in children with ANSD despite the absence of distortion product OAE responses, but in a significantly lower amplitude than those with DPOAE. There was no statistically significant correlation between the children's ages and CM amplitude at any intensity level and in any of the different child groups, except in the controls where there was a statistically significant negative correlation between the children's ages and CM amplitude at 70dBnHL, while there was a statistically significant positive correlation between the children's ages and CM threshold. There were no differences in the CM amplitude between the two ears at any intensity level in all of the different groups of children. Conclusion: Children with ASD showed comparable outer hair cell function to normal hearing healthy children, reflecting absence of any peripheral hyperacusis due to loudness recruitment. CM should always be searched for when testing young children when there is absence of ABR response with absence or presence of otoacoustic emissions, to avoid any false negative results for ANSD. CM can be preserved in children with SNHL with loudness recruitment. This finding could be confused with ANSD, so CM should be traced down to its threshold for an appropriate diagnosis. [ABSTRACT FROM AUTHOR]

Auditory neuropathy spectrum disorder (ANSD) is a type of hearing disorder which is challenging for assessment and rehabilitation. This disorder has been studied over a decade and prevalence of the disorder is variable. The study aimed at estimating the prevalence and audiological characteristics of ANSD in children. A retrospective study was conducted from the medical records of pediatric patients evaluated at Rajiv Gandhi Government General Hospital and Madras Medical College, Chennai to estimate the prevalence of ANSD. Medical records of 2,624 children evaluated during the period of November 2010 to October 2012 within the age range of 6 months to 12 years were analyzed. Out of 2,624 pediatric population assessed 217 (8.26 %) of them had unilateral or bilateral sensory neural hearing loss with varying degrees. Out of 217 children with sensory neural hearing loss 5.06 % (N = 11) had ANSD. Audiological characteristics varied among the group. Children with ANSD had varied degree of hearing thresholds from normal to profound hearing impairment. All of them had 'A' type tympanogram with absent stapedial reflexes. DPOAEs or TEOAEs were observed in 54 % of population with ANSD. All of them had abnormal auditory brainstem responses (ABR). Replicable cochlear microphonics was observed in 46 % of children with ANSD. These results indicate that ANSD is not a rare condition among children and we emphasize the use of objective tests like tympanometry, Stapedial Reflex test, otoacoustic emissions and ABR in routine hearing assessment procedure for all children to identify ANSD. [ABSTRACT FROM AUTHOR]

Introduction The early diagnosis of AS/AN in children remains challenging because it exclusively relies on the detection of OAE and/or CM, while ABR are pathologically changed or missing. The aim of our study was to ensure the diagnosis of AS/AN, demarcate it to an outer hair cell damage and possibly differentiate between pre- and postsynaptic pathologies. Methods We retrospectively evaluated the transtympanic ECochG results of ten children with AS/AN and compared them to a matched group with SNHL and without any signs of AS/AN. We analyzed the thresholds, latencies and – as a new parameter – the amplitude ratio between CAP and SP. Results CM and SP thresholds were significantly lower than CAP thresholds in AS/AN patients and significantly lower than SP and CM thresholds in SNHL patients with comparable CAP thresholds. The CAP/SP ratio of amplitudes in SNHL children was more than three times (significantly) higher than in AS/AN children. The cutoff value was set at 1.0 in order to differentiate between both groups with a 80–90% sensitivity and specifity. It was not possible to differentiate between a pre- and postsynaptic type of AS/AN in our collective. Summary and conclusion The ECochG can add valuable information for a precise differential diagnosis of AS/AN, especially in babyhood. We identified the CAP/SP ratio as a new parameter for differentiation between AS/AN and SNHL. When the CAP/SP ratio falls below 1.0, patients can be diagnosed AS/AN with high specificity and sensitivity. Significantly smaller SPL are needed to evoke SP and CM in the AS/AN group, thus showing the preserved hair cell function. [ABSTRACT FROM AUTHOR]

This study investigates changes in amplitude and delays in low-frequency toneburst cochlear microphonic (CM) waveforms recorded at the ear canal in response to different stimulus intensities. Ten volunteers aged 20-30 were recruited. Low-frequency CM waveforms at 500 Hz in response to a 14-ms toneburst were recorded from an ear canal electrode using electrocochleography techniques. The data was statistically analyzed in order to confirm whether the differences were significant in the effects of stimulus intensity on the amplitudes and delays of the low-frequency CM waveforms. Electromagnetic interference artifacts can jeopardize CM measurements but such artifacts can be avoided. The CM waveforms can be recorded at the ear canal in response to a toneburst which is longer than that used in ABR measurements. The CM waveforms thus recorded are robust, and the amplitude of CM waveforms is intensity-dependent. In contrast, the delay of CM waveforms is intensity-independent, which is different from neural responses as their delay or latency is intensity-dependent. These findings may be useful for development of the application of CM measurement as a supplementary approach to otoacoustic emission (OAE) measurement in the clinic which is severely affected by background acoustic noise. The development of the application in the assessment of low-frequency cochlear function may become possible if a further series of studies can verify the feasibility, but it is not meant to be a substitute for audiometry or OAE measurements. The measurement of detection threshold of CM waveform responses using growth function approach may become possible in the clinic. The intensity-independent nature of CMs with regards to delay measurements may also become an impacting factor for differential diagnoses and for designing new research studies.

Conclusion: Our study demonstrates that the regulation of D2 receptors may be frequency specific. The reduction in cochlear microphonics (CM) and distortion product otoacoustic emission (DPOAE) amplitudes after perfusion with a D2 antagonist suggests that this receptor plays a role in the regulation of cochlear hair cell activation. Objectives: Dopaminergic terminals are subject to negative feedback from dopamine D2 receptors. In the present study we investigated whether the regulation of dopamine D2 receptor is frequency specific and evaluated changes in CM in guinea pig cochlea. Methods: A total of 30 male guinea pigs were randomly assigned to 3 groups and perfused with artificial perilymph (AP), AP containing ethanol (0.1%), or a D2 antagonist (L741626) for 2 h. In each group, compound action potentials (CAPs) evoked by a 1, 2, 4, 8, 16 or 24 kHz tone pip, CM evoked by 4 kHz tone bursts, and DPOAEs were measured before and 2 h after perilymphatic perfusion. Results: Perfusion with the D2 antagonist resulted in increased CAP thresholds compared with the other two groups at high frequencies (4, 8, 16, 24 kHz, p < 0.05); however, no significant increase was observed at low frequencies (1, 2 kHz, p > 0.05). There was a significant reduction in DPOAEs and CM amplitudes after the 2 h perfusion with the D2 antagonist. A CM input/output (I/O) function curve plotted with the stimulating level as input and the CM relative amplitude as output indicated obvious nonlinearity after the 2 h perfusion in all three groups. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Auditory neuropathy spectrum disorder (ANSD) has become a well accepted clinical entity. ANSD has now become easy to recognize with advent of test battery approach for hearing loss evaluation. However, little is known about its epidemiology and aetiology, especially its prevalence and incidence in India. This study was conducted to determine the prevalence and audiological characteristics of ANSD in our tertiary care hospital at New Delhi, India. Methods: We prospectively enrolled all the paediatric cases i.e. less than 12years of age referred to our outpatient department for hearing evaluation. All the cases were evaluated using complete audiological test battery consisting of pure tone audiometry (PTA), impedance audiometry, acoustic reflexes, otoacoustic emissions (OAE), and brain stem evoked response audiometry (BERA). The instrument used was GSI Audera. BERA with both condensation and rarefaction polarity was performed in cases with absent wave V even at highest intensity levels. The criteria used for diagnosis of ANSD was normal or near normal cochlear hair cells (sensory) function (preservation of otoacoustic emissions and/or cochlear microphonics) and absent or abnormal auditory nerve function (absent or severely abnormal auditory brainstem potentials). A repeat test battery was performed after 3months on the diagnosed cases of auditory neuropathy. Based on their behavioural findings the appropriate management programme was formulated. Results: A total of 487 paediatric cases were referred for hearing evaluation. 183 (37.6%) cases showed absent BERA and 26(5.3%) cases fulfilled the diagnostic criteria for ANSD. Repeat examination after 3months revealed presence of OAE''s in 57.6% (15/26) cases while cochlear microphonics were present in all the 26 cases. Conclusion: The prevalence of ANSD in our study is 5.3% and in children diagnosed with severe to profound hearing loss is 14%. Presence of cochlear microphonics with absent BERA seems to be reliable criteria for diagnosing ANSD. [Copyright &y& Elsevier]

Conclusions: Cochlear microphonics (CMs) play an important role in the diagnosis of auditory neuropathy (AN). It is necessary and helpful to diagnose the sites-of-lesion in infants and children with AN by analyzing the patterns of CM amplitudes and I/O functions together. Objectives: To investigate the characteristics and clinical significance of CMs in the diagnosis of AN among infants and children. Methods: A total of 36 infants and children (16 males and 20 females) were divided into two groups. Group A included 15 children (30 ears) with auditory brainstem response (ABR) absent and distortion product otoacoustic emissions (DPOAEs) present and group B included 21 children (30 ears) with ABR absent and DPOAEs absent. Fifteen normal-hearing infants (30 ears) made up the control group. Click eliciting CMs were recorded at stimulus levels of 100, 90, 80, and 70 dB nHL for each ear using a button electrode placed at the top of the forehead. A tube-clamping method was used to distinguish CMs from artifacts, and an averaging algorithm was used to obtain a clear CM waveform. The time delay and amplitude of CMs were measured in both children with AN and normal-hearing infants on (C-R)/2 waveforms, and an I/O function curve for each group was plotted with the stimulating level as input and the CM amplitude as output. Results: The largest identifiable CMs were generally found between 0.5 and 0.8 ms after stimulation with mean delay of 0.63 ± 0.04 ms in both group A and the control group, and 0.63 ± 0.07 ms in group B. There was no significant difference between the AN group and the control group in CM time delay. There was no significant difference (p > 0.05) between group A (AN with OAEs present, 0.47 ± 0.15 μV) and the control group (0.45 ± 0.13 μV) in CM amplitude, while CM amplitudes in children with AN with DPOAEs absent (0.24 ± 0.08 μV) were significantly lower than those in either the control group or group A (p < 0.01). The amplitude of CMs reduced with stimulus intensity in all the subjects. There was obvious nonlinearity in group A and the control group, while there was a more linear tendency in amplitude increasing on the I/O function curve in group B [ABSTRACT FROM AUTHOR]

Conclusions: The majority of the patients with unilateral auditory neuropathy spectrum disorder (UANSD) were pediatric and mostly showed a great degree of hearing loss when diagnosed. Abnormal auditory brainstem response (ABR) and preserved otoacoustic emissions (OAEs) and/or cochlear microphonics (CM) were important features to differentiate it from common sensorineural deafness and central nerve hearing loss. Objective: To identify the clinical characteristics of patients with UANSD. Methods: This was a retrospective study involving 14 patients diagnosed as having UANSD between 2004 and 2010 in the Chinese PLA Hospital. Results: In all, 50% of the cases were males (1:1 sex ratio) and the average age of onset was 4.1 years. Of the 14 affected ears with UANSD in these cases, 6 were left-sided, while 8 were right-sided. Of the 14 contralateral ears, 4 presented with sensorineural hearing loss, while the other 10 showed normal hearing. The degree of hearing loss in the 14 affected ears varied, including moderate in 1, moderately severe in 4, severe in 5, and profound in 4. ABRs were absent in the 14 affected ears, while the OAEs, and/or CM were present. [ABSTRACT FROM AUTHOR]

'Auditory neuropathy' (AN), the term used to codify a primary degeneration of the auditory nerve, can be linked directly or indirectly to mitochondrial dysfunction. These observations are based on the expression of AN in known mitochondrial-based neurological diseases (Friedreich's ataxia, Mohr-Tranebjærg syndrome), in conditions where defects in axonal transport, protein trafficking, and fusion processes perturb and/or disrupt mitochondrial dynamics (Charcot-Marie-Tooth disease, autosomal dominant optic atrophy), in a common neonatal condition known to be toxic to mitochondria (hyperbilirubinemia), and where respiratory chain deficiencies produce reductions in oxidative phosphorylation that adversely affect peripheral auditory mechanisms. This body of evidence is solidified by data derived from temporal bone and genetic studies, biochemical, molecular biologic, behavioral, electroacoustic, and electrophysiological investigations. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: The structures of cochlear transduction include stereocilia at the apical surface of hair cells and their connection to the tectorial membrane. The transduction site is one of the loci for noise-induced cochlear damage. Although stereocilia are susceptible to noise, it has been found that in the inner ears of avians, this fragile structure is largely self-repairing and is associated with recovery of hearing sensitivity after noise exposure, as observed in the difference between the temporal threshold shift (TTS) and the permanent threshold shift (PTS). In the mammalian cochleae, however, threshold shifts measured in the auditory brainstem responses (ABR) did not parallel the chronological changes in the stereocilia on hair cells. It is unclear how the morphological recovery of the stereocilia on the mammalian hair cells is correlated with the changes in cochlear transduction that can be assessed by measuring receptor potential. In the present study, guinea pigs were exposed to a broadband noise of 110dBSPL for 2h. Auditory sensitivity was evaluated using ABR and cochlear transduction was assessed using cochlear microphonics (CM). Stereocilia morphology was quantified at different time points after the noise and compared with the control. The noise produced a TTS of 55.69±14.13dB in frequency-averaged ABR thresholds. The threshold shift was reduced to 9.58±11.75dBSPL 1month later with virtually no loss of hair cells. Damage to the stereocilia immediately after noise exposure was found to be associated with depression of CM amplitude. Virtually no abnormal stereocilia were observed 1month after the noise in association with a fully recovered CM. [Copyright &y& Elsevier]

Cochlear microphonics are electrical stimulus responses of the inner ear. They are generated by mechanical displacement of the hair cells caused by acoustic stimulation and can be recorded from the cochlear promontory via a needle electrode. In individuals with post-meningitic deafness, fibrous obliteration or ossification of the cochlea may occur. The aim of the present investigation was to establish whether obliteration or ossification leads to any alteration in the extent to which cochlear microphonics can be recorded (as compared with that in patients with a fluid-filled cochlea whose deafness was not post-meningitic), as an indication of changes in the mechanical displacement of the remaining hair cells. Cochlear microphonics in 15 individuals with proven obliteration or ossification of the cochlea were compared with those in 15 control subjects (deaf individuals whose hearing loss was not post-meningitic, and who had a fluid-filled cochlea). Our findings reveal no statistically significant differences between the two groups in the degree to which cochlear microphonics can be recorded. This study does not demonstrate evidence of a change in this property due to ossification or obliteration of the cochlea. [ABSTRACT FROM AUTHOR]

Abstract: 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 N2O/O2 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 (N2) were affected to a greater extent compared to the first peak (N1). 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. [Copyright &y& Elsevier]

Test results and management data are summarized for 260 patients with diagnoses of Auditory Neuropathy Spectrum Disorder (ANSD). Hearing aids were tried in 85 of these patients, and 49 patients tried cochlear implants. Approximately 15% reported some benefit from hearing aids for language learning, while improvement in speech comprehension and language acquisition was reported in 85% of patients who were implanted. Approximately 5% (13/260) of the total population developed normal speech and language without intervention. Patients were diagnosed at our laboratory (n=66) or referred from other sites (n=194), and all showed absent/grossly abnormal auditory brainstem responses (ABR), often ‘ringing’ cochlear microphonics, and the presence or history of otoacoustic emissions. Etiologies and co-existing conditions included genetic (n=41), peripheral neuropathies (n=20), perinatal jaundice and/or anoxia and/or prematurity (n=74). These patients comprise 10% or more of hearing impaired patients; their language acquisition trajectories are generally unpredictable from their audiograms. Sumario Se resumen los resultados de las pruebas y los datos del tratamiento de 260 pacientes con diagnóstico de Espectro de desórdenes de la Neuropatía Auditiva (ANSD). En 85 de estos pacientes se probó el uso de auxiliares auditivos y 49 pacientes recibieron un implante coclear. Aproximadamente 15% reportaron algún beneficio con los auxiliares auditivos para la adquisición del lenguaje mientras que el 85% de los que recibieron un implante reportaron una mejoría en la comprensión y la adquisición del lenguaje. Aproximadamente 5% (13/260) de la población total desarrolló lenguaje normal sin intervención. Los paciente fueron diagnosticados en nuestro laboratorio (n=66) o referidos de algún otro lado (n=194) y todos mostraron ausencia o anormalidad importante de los potenciales evocados (ABR), frecuentemente con una microfónica coclear “timbrante” y con presencia o historia de emisiones otoacústicas. La etiología o las condiciones co-existentes incluidas fueron: genéticas (n=41), neuropatías periféricas (n=20), ictericia perinatal y/o anoxia y/o prematurez (n=74). Estos pacientes representan 10% o más de los pacientes con hipoacusia; su trayectoria en el proceso de adquisición del lenguaje es generalmente impredecible a partir de sus audiogramas. [ABSTRACT FROM AUTHOR]

Test results and management data are summarized for 260 patients with diagnoses of Auditory Neuropathy Spectrum Disorder (ANSD). Hearing aids were tried in 85 of these patients, and 49 patients tried cochlear implants. Approximately 15% reported some benefit from hearing aids for language learning, while improvement in speech comprehension and language acquisition was reported in 85% of patients who were implanted. Approximately 5% (13/260) of the total population developed normal speech and language without intervention. Patients were diagnosed at our laboratory (n=66) or referred from other sites (n=194), and all showed absent/grossly abnormal auditory brainstem responses (ABR), often ‘ringing’ cochlear microphonics, and the presence or history of otoacoustic emissions. Etiologies and co-existing conditions included genetic (n=41), peripheral neuropathies (n=20), perinatal jaundice and/or anoxia and/or prematurity (n=74). These patients comprise 10% or more of hearing impaired patients; their language acquisition trajectories are generally unpredictable from their audiograms. Sumario Se resumen los resultados de las pruebas y los datos del tratamiento de 260 pacientes con diagnóstico de Espectro de desórdenes de la Neuropatía Auditiva (ANSD). En 85 de estos pacientes se probó el uso de auxiliares auditivos y 49 pacientes recibieron un implante coclear. Aproximadamente 15% reportaron algún beneficio con los auxiliares auditivos para la adquisición del lenguaje mientras que el 85% de los que recibieron un implante reportaron una mejoría en la comprensión y la adquisición del lenguaje. Aproximadamente 5% (13/260) de la población total desarrolló lenguaje normal sin intervención. Los paciente fueron diagnosticados en nuestro laboratorio (n=66) o referidos de algún otro lado (n=194) y todos mostraron ausencia o anormalidad importante de los potenciales evocados (ABR), frecuentemente con una microfónica coclear “timbrante” y con presencia o historia de emisiones otoacústicas. La etiología o las condiciones co-existentes incluidas fueron: genéticas (n=41), neuropatías periféricas (n=20), ictericia perinatal y/o anoxia y/o prematurez (n=74). Estos pacientes representan 10% o más de los pacientes con hipoacusia; su trayectoria en el proceso de adquisición del lenguaje es generalmente impredecible a partir de sus audiogramas. [ABSTRACT FROM AUTHOR]

Summary: The diagnostic dilemma surrounding the presence of cochlear microphonics (CM) coupled with significantly elevated auditory brainstem response (ABR) thresholds in babies failing the newborn hearing screening is highlighted. A case report is presented where initial electo-diagnostic assessment could not help in differentiating between Auditory Neuropathy/Auditory Dys-synchrony (AN/AD) and sensorineural hearing loss (SNHL). In line with the protocol and guidelines provided by the national Newborn Hearing Screening Programme in the UK (NHSP) AN/AD was suspected in a baby due to the presence of CM at 85dBnHL along with click evoked ABR thresholds of 95dBnHL in one ear and 100dBnHL in the other ear. Significantly elevated thresholds for 0.5 and 1kHz tone pip ABR fulfilled the audiological diagnostic criteria for AN/AD. However, the possibility of a SNHL could not be ruled out as the 85dBnHL stimuli presented through inserts for the CM would have been significantly enhanced in the ear canals of the young baby to exceed the threshold level of the ABR that was carried out using headphones. SNHL was eventually diagnosed through clinical and family history, physical examination and imaging that showed enlarged vestibular aqueducts. Presence of CM in the presence of very high click ABR thresholds only suggests a pattern of test results and in such cases measuring thresholds for 0.5 and 1kHz tone pip ABR may not be adequate to differentiate between SNHL and other conditions associated with AN/AD. There is a need for reviewing the existing AN/AD protocol from NHSP in the UK and new research to establish parameters for CM to assist in the differential diagnosis. A holistic audiological and medical approach is essential to manage babies who fail the newborn hearing screening. [Copyright &y& Elsevier]

Abstract: Several animal models of auditory neuropathy (AN) have been produced by employing pharmacological agents to damage auditory neurons or hair cells selectively. The specificity of pharmacological lesions is generally assessed by observation of visible structural damage but it is difficult to localize the delivery, which could lead to functional side effects in other anatomical structures. Although genetic analyses of human AN patients have provided important information on the pathophysiology of AN, specific genetic defects have not been fully correlated with functional deficits in the auditory nervous system. To address this problem, we compressed rat auditory nerves to assess neural degeneration for up to 35 weeks. The method produced a good model of auditory neuropathy, including profound deterioration of the auditory brainstem response and preservation of both cochlear microphonics and distortion product otoacoustic emissions. Histological examination revealed that in spite of profound degeneration of the auditory nerve, the hair cells remained intact. The model provides a complementary alternative to those based on pharmacological lesions and genetic analyses of AN patients and should allow analysis of the pathophysiology of auditory neuropathy with less risk of the results being confounded by unknown deficits in other cell types. [Copyright &y& Elsevier]

It is generally accepted that during periods of attention to specific stimuli there are changes in the neural activity of central auditory structures; however, it is controversial whether attention can modulate auditory responses at the cochlear level. Several studies performed in animals as well as in humans have attempted to find a modulation of cochlear responses during visual attention with contradictory results. Here, we have appraised cochlear sensitivity in behaving chinchillas by measuring, with a chronically implanted round-window electrode, sound-evoked auditory-nerve compound action potentials and cochlear microphonics, a measure of outer hair cell function, during selective attention to visual stimuli. Chinchillas were trained in a visual discrimination or in an auditory frequency discrimination two-choice task. We found a significant decrease of cochlear sensitivity during the period of attention to visual stimuli in the animals performing the visual discrimination task, but not in those performing the auditory task, demonstrating that this physiological effect is related to selective attention to visual stimuli rather than to an increment in arousal level. Furthermore, the magnitude of the cochlear-sensitivity reductions increased in sessions performed with shorter target-light durations (4-0.5 s), suggesting that this effect is stronger for higher attentional demands of the task. These results demonstrate that afferent auditory activity is modulated by selective attention as early as at sensory transduction, possibly through activation of olivocochlear efferent fibers. [ABSTRACT FROM AUTHOR]

The aim of the experiment was to determine the effect of whole-body vibration on the inner ear. The investigations were carried out on 40 guinea pigs, subjected to sinusoidal vibration (10 Hz/5 mm/1.4 g rms) for 1 to 6 months in a noiseless apparatus. Cochlear microphonic measurements were done with a phase-sensitive detection technique for the levels 70, 80 and 90 dB and the frequencies of 0.26, 0.5, 1 and 2 kHz from the apex of the cochlea and for 4 and 8 kHz from the region of the round window. Analysis of 1,440 measurements suggested the possibility of damage appearing in the upper turnings of the cochlea. The subsequent morphological analysis was based on the estimation of the state of the hair cells (a three-degree scale of injury) in a Zeiss DSM 950 scanning microscope and of the structure of the fibers of the acoustic nerve in a Zeiss EM 900 transmission microscope. Vibration-induced changes were seen in all the examined inner ears of the experimental groups. Hair-cell damage was more often seen in the region of the apex, spreading gradually in the direction of the base and from the circumference (outer hair cells of the third row) to the modiolus. The most characteristic vibrational changes of the acoustic nerve fibers occurred in 100% of the examined myelin sheaths and were visible as decreases in their electrodensity. The changes in both the assessed elements of the inner ear appeared simultaneously but independently and were directly connected with the duration of the experiment. The results obtained allow an explanation of the mechanism of hearing loss in persons subjected to whole-body vibration. The damages done to the inner ear structures may cause a worsening of hearing there, especially in the low and medium frequencies. [ABSTRACT FROM AUTHOR]

The primary goal of this study was to compare the characteristics of the post-implant evoked potentials with pre-implant evoked potentials in patients with auditory neuropathy (AN) or dys-synchrony. AN is typically characterized by sensorineural hearing loss, reduced speech perception, abnormal temporal processing, and unusual patterns of results with various objective audiological tests. In some cases, these patients may be appropriate candidates for a cochlear implant. In this article, we highlight evoked potential findings in two children diagnosed with AN who were provided with multichannel cochlear implants. Preoperative, interoperative and postoperative evoked potential measures show that the restoration of neural synchrony may occur at multiple levels of the auditory pathways in patients with AN when appropriate diagnostic tests, cochlear implantation and rehabilitation are provided. [ABSTRACT FROM AUTHOR]

The influence of the crossed medial efferent system on cochlear mechanics of the mustached bat was tested by measuring delayed evoked otoacoustic emissions (DEOAEs), cochlear microphonics, distortion product otoacoustic emissions (DPOAEs) and stimulus frequency otoacoustic emissions. Contralaterally delivered sinusoids, broadband noise and bat echolocation calls were used for acoustic stimulation of the efferent system. With all four measures we found a level-dependent suppression under stimulation with both broadband noise and echolocation calls. In addition, the sharply tuned cochlear resonance of the mustached bat which is involved in processing echolocation signals at 61 kHz shifted upward in frequency by several 100 Hz. Presentation of sinusoids did not have any significant effect. DEOAEs and DPOAEs were in some cases enhanced during contralateral presentation of the bat calls at moderate intensities. The most important function of the efferent system in the mustached bat might be the control of the extraordinarily fine-tuned resonator of this species, which is close to instability as evident from the very pronounced evoked otoacoustic emissions which sometimes convert into spontaneous otoacoustic emissions of high level. [Copyright &y& Elsevier]

Objectives Because endolymphatic hydrops causes cochlear malfunction, and both otoacoustic emissions and cochlear microphonics measure specific cochlear activities, some insight into the pathology of Meniere's disease might be gained by using these two test modalities. Specifically, the involvement of cochlear outer hair cells in patients with endolymphatic hydrops may be detected. Furthermore, it is hoped that these two tests might help determine which regions of the cochlea are affected by endolymphatic hydrops, as well as where along the auditory pathway abnormalities are present. Study Design Data were gathered prospectively on patients presenting to a private, tertiary referral otology/neurotology practice. Methods From February 1999 to April 2000, clinical information was collected on patients presenting with vertigo, hearing loss (HL), sudden HL, fluctuant HL, aural fullness, and/or tinnitus. Data included demographics, diagnosis, pure-tone and speech audiometry, tympanometry, summating potential, action potential, cochlear microphonic, and distortion-product otoacoustic emissions. Descriptive statistics were calculated, and relationships between distortion-product otoacoustic emissions and cochlear microphonics in patients with hydrops (defined as summating potential to action potential ratio ≥0.40) and without hydrops were analyzed. Results Distortion-product otoacoustic emissions were present more often and had larger amplitudes at the lower frequencies. No differences were found in the presence of distortion-product otoacoustic emissions across the frequencies for the two groups, but larger mean amplitudes were found for hydropic ears at 7966 Hz. As hearing levels worsened, both hydropic and nonhydropic ears were less likely to have emissions present; however, 18% of hydropic ears had emissions unexpectedly present when the pure-tone thresholds were ≥50 dB. The cochlear microphonic from the hydrops group tended to be smaller, but this was not statistically significant. Analysis of variance showed a small negative correlation between summating potential to action potential ratio and level of emission at 1968 Hz in hydropic ears; otherwise, there was no relationship between the ratio and emissions. The only statistically significant finding when analyzing the relationship between cochlear microphonic and otoacoustic emission was a small positive correlation between level of microphonic and level of emission at 1406 Hz in hydropic ears. No significant relationships were found between hearing thresholds and emissions or microphonics. Conclusions Even though both distortion-product otoacoustic emissions (DPOAEs) and cochlear microphonics (CMs) measure specific cochlear activities, they were not found to be useful for differentiating patients with hydrops from those without. In some patients, however, unexpected distortion-product otoacoustic emissions were present. This may represent localizing information about which regions of the cochlea are being affected by hydrops in these patients. Also, a small positive correlation between the CM and the DPOAE at 1406 Hz was detected in the hydrops group, which may represent the effects of endolymphatic hydrops on the outer hair cell. Future investigations involving hydropic patients with unexpected DPOAEs and studies looking for more DPOAE and CM correlations at frequencies surrounding 1406 Hz are being planned. [ABSTRACT FROM AUTHOR]

The ever-expanding arsenal of genetically modified mice has created experimental models for studying various mechanisms of deafness. Electrocochleography (ECochG) is a recording technique of cochlear potentials evoked by sound stimulation, which was widely used to evaluate the cochlear hearing function. However, there is currently a lack of information on long-term recording technology of ECochG in mice. We describe in detail the surgical procedure of implanting electrode into the facial nerve canal in C57BL/6J mice for ECochG recording. The results of ECochG recorded by electrode in the facial nerve canal were compared with ECochG guided by electrode on the round window niche. The surgical method of inserting the electrode into the facial nerve canal is relatively simple and can be completed within 15 min. The electrode inserted into the elongated facial nerve canal is stable and close to the auditory nerve trunk, so it is conducive to long-term auditory function monitoring. Hence, the ECochG guided by the electrode from the facial nerve canal can maintain a stable response for more than two weeks. In contrast, the ECochG guided by the electrode in the round window niche can only be maintained for a maximum of 20 min. In mice, existing recording techniques of ECochG from round window niche is limited by conductive hearing loss due to middle ear effusion or surgical damage. ECochG recording from the facial nerve canal is suitable for long-term recording in mice. This electrode approach provides a repeatable and reliable measurement of ECochG. • ECochG recording from the electrode in the facial nerve canal in C57BL/6J mice. • The CM, CAP and SP recording. • Comparison between recording from facial nerve canal and round window niche. [ABSTRACT FROM AUTHOR]

Electrophysiological methods were applied to 160 healthy adult male guinea pigs in order to investigate the effects of pure-tone exposure for 24 h on the inner ear. A reduction in cochlear microphonics (CM), action potential (AP) and endocochlear potential was observed following exposure to 110 dB at 100 Hz, 100 dB at 200 and 600 Hz and 95 dB at 2 kHz. The observed K endolymphatic concentration during 40 min anoxia remained unchanged. In contrast K+ decreased in control animals and following exposure to pure tones varying from 110 dB at 60 Hz to 85 dB at 2 kHz. These findings indicate that high frequency tones have a greater effect on inner ear functions than those of lower frequency, decreasing the maximum output voltage of CM and AP but not changing K endolymphatic concentration. [ABSTRACT FROM AUTHOR]

Using 97 male albino guinea pigs and applying electrophysiological methods, the effects of a 6 kHz tone were investigated at a moderate sound pressure level to the inner ear during a 24-h exposure time. Following exposure to the 6 kHz tone at 90 dB, cochleas showed decreased maximum output voltage of cochlear microphonics (CM) and action potential (AP). In the endolymph, K ion and Na ion concentrations remained unchanged during 40 min anoxia and 90 dB tone exposure. At 80 dB sound exposure decreases in maximum output voltage of CM and AP and decreases in the absolute value of EP could not be detected. Endolymph K-ion Na-ion concentrations were also unchanged. These findings indicate that diffusion potentials are induced at the same time as decreases of maximum output voltage in CM induced by exposure to sound at 90 dB. [ABSTRACT FROM AUTHOR]

By examining 218 albino guinea pigs, electrophysiological methods were used to investigate the effects of low frequency ultrasound at moderate sound pressure levels after long-term exposure to the inner ear. From 10 kHz to 28 kHz, low frequency ultrasound below 100 dB SPL induced significant changes in cochlear microphonics, elevated thresholds and decreased maximum output voltage of action potentials and decreased absolute values of negative potentials of the endocochlear potentials. [ABSTRACT FROM AUTHOR]

Alterations in inner ear fluid pressure and cochlear microphonics (CM) associated with increased cerebrospinal fluid (CSF) pressure were studied in the guinea pig. Hydrostatic pressure in the endolymph and perilymph of the cochlea were measured by use of a servo-controlled micropipet system. Endolymphatic and perilymphatic pressure increased in a linear manner with little or no time lag following pressure increases of 0-50 mm Hg. There was no pressure gradient between the endolymph and perilymph. CM in response to 500 Hz and 4000 Hz tone bursts was recorded before, during and after CSF pressurization. The input-output function of CM showed suppression of 2-8 dB in both maximum output and sensitivity unless the increase in CSF pressure exceeded a level which reduced the cochlear blood flow. [ABSTRACT FROM AUTHOR]

The effect of perilymphatic pressure on the cochlear microphonics (CM) threshold was examined in guinea pigs with experimentally induced hydrops. When a pressure of 300 mm H20 was applied to the scala tympani of the basal turn, the 500 Hz CM threshold shifts in ears during the 1st week following obliteration of the endolymphatic sac and duct were significantly smaller when compared with shifts in normal ears. Larger threshold shifts were then regained at 4-12 weeks after surgery. When acetazolamide was administered to hydropic animals, the effect of the increase of perilymphatic pressure on the CM threshold was also investigated. During the 1st postoperative week (4-7 days after surgery), CM threshold shifts were larger when compared to changes in hydropic animals without medication. The CM depression as the result of pressure is probably due to a mechanical effect on the intracochlear partition. [ABSTRACT FROM AUTHOR]