Predicting Postoperative Speech Perception and Audiometric Thresholds Using Intracochlear Electrocochleography in Cochlear Implant Recipients.

OBJECTIVES: Electrocochleography (ECochG) appears to offer the most accurate prediction of post-cochlear implant hearing outcomes. This may be related to its capacity to interrogate the health of underlying cochlear tissue. The four major components of ECochG (cochlear microphonic [CM], summating potential [SP], compound action potential [CAP], and auditory nerve neurophonic [ANN]) are generated by different cochlear tissue components. Analyzing characteristics of these components can reveal the state of hair and neural cell in a cochlea. There is limited evidence on the characteristics of intracochlear (IC) ECochG recordings measured across the array postinsertion but compared with extracochlear recordings has better signal to noise ratio and spatial specificity. The present study aimed to examine the relationship between ECochG components recorded from an IC approach and postoperative speech perception or audiometric thresholds. DESIGN: In 113 human subjects, responses to 500 Hz tone bursts were recorded at 11 IC electrodes across a 22-electrode cochlear implant array immediately following insertion. Responses to condensation and rarefaction stimuli were then subtracted from one another to emphasize the CM and added to one another to emphasize the SP, ANN, and CAP. Maximum amplitudes and extracochlear electrode locations were recorded for each of these ECochG components. These were added stepwise to a multi-factor generalized additive model to develop a best-fit model predictive model for pure-tone audiometric thresholds (PTA) and speech perception scores (speech recognition threshold [SRT] and consonant-vowel-consonant phoneme [CVC-P]) at 3- and 12-month postoperative timepoints. This best-fit model was tested against a generalized additive model using clinical factors alone (preoperative score, age, and gender) as a null model proxy. RESULTS: ECochG-factor models were superior to clinical factor models in predicting postoperative PTA, CVC-P, and SRT outcomes at both timepoints. Clinical factor models explained a moderate amount of PTA variance ( r2 = 45.9% at 3-month, 31.8% at 12-month, both p < 0.001) and smaller variances of CVC-P and SRT ( r2 range = 6 to 13.7%, p = 0.008 to 0.113). Age was not a significant predictive factor. ECochG models explained more variance at the 12-month timepoint ( r2 for PTA = 52.9%, CVC-P = 39.6%, SRT = 36.4%) compared with the 3-month one timepoint ( r2 for PTA = 49.4%, CVC-P = 26.5%, SRT = 22.3%). The ECochG model was based on three factors: maximum SP deflection amplitude, and electrode position of CM and SP peaks. Adding neural (ANN and/or CAP) factors to the model did not improve variance explanation. Large negative SP deflection was associated with poorer outcomes and a large positive SP deflection with better postoperative outcomes. Mid-array peaks of SP and CM were both associated with poorer outcomes. CONCLUSIONS: Postinsertion IC-ECochG recordings across the array can explain a moderate amount of postoperative speech perception and audiometric thresholds. Maximum SP deflection and its location across the array appear to have a significant predictive value which may reflect the underlying state of cochlear health.

Cochlear Microphonics in Hearing Preservation Cochlear Implantees.

OBJECTIVES: The intracochlear electrocochleography (ECoG) could be recorded directly from the cochlear implant (CI) electrode in CI recipients with residual hearing. The primary objective of this study is to identify the most sensitive frequency to record cochlear microphonics (CM) in CI users with a wide degree of hearing abilities and deep electrode insertion. The secondary objective is to identify the optimum location within the cochlea to record intracochlear potentials. MATERIALS AND METHODS: CMs were recorded from the CI electrodes in eight females and eight males implanted with CIs Pulsar, Concerto, or Sonata, Med-El Corp. RESULTS: Among the tone pips of various frequencies, 1k or 500 Hz were the most sensitive for CI users. The most sensitive place in the cochlea to record the CM potentials depended on the tone frequency used. The deeper into the cochlea the mean maximum CM peak-to-peak amplitude was measured, the lower the stimulating tone frequency was. CONCLUSION: The most optimal recording parameters identified for intracochlear CM recording can be useful for intraoperative and postoperative monitoring of cochlear health in CI users with residual hearing.

An analytic approach to identifying the sources of the low-frequency round window cochlear response.

The cochlear microphonic, traditionally thought of as an indication of electrical current flow through hair cells, in conjunction with suppressing high-pass noise or tones, is a promising method of assessing the health of outer hair cells at specific locations along the cochlear partition. We propose that the electrical potential recorded from the round window in gerbils in response to low-frequency tones, which we call cochlear response (CR), contains significant responses from multiple cellular sources, which may expand its diagnostic purview. In this study, CR is measured in the gerbil and modeled to identify its contributing sources. CR was recorded via an electrode placed in the round window niche of sixteen Mongolian gerbils and elicited with a 45 Hz tone burst embedded in 18 high-pass filtered noise conditions to target responses from increasing regions along the cochlear partition. Possible sources were modeled using previously-published hair cell and auditory nerve response data, and then weighted and combined using linear regression to produce a model response that fits closely to the mean CR waveform. The significant contributing sources identified by the model are outer hair cells, inner hair cells, and the auditory nerve. We conclude that the low-frequency CR contains contributions from several cellular sources.

The Effect of Test, Electrode, and Rate on Electrocochleography Measures.

BACKGROUND: Electrocochleography (ECochG) is the measurement of stimulus-related cochlear potentials and the compound action potential (AP). Its primary clinical application is with the assessment of inner ear disorders. There are few studies examining the variability of ECochG measures. PURPOSE: The objective of the study was to examine the effect of test (i.e., initial versus retest), electrode (i.e., extratympanic versus tympanic), and stimulus rate (i.e., 7.7 versus 77.7/sec) on ECochG indices (i.e., summating potential [SP] amplitude, AP latency, AP amplitude, SP/AP amplitude ratio, and SP/AP area ratio). RESEARCH DESIGN: Correlational and three-factor repeated measures designs were employed. STUDY SAMPLE: Eighteen normal-hearing young adults participated. DATA COLLECTION AND ANALYSIS: ECochG responses were obtained with 90 dB nHL click stimuli for an initial test and retest at two stimulus rates with a commercially available extratympanic (TIPtrode™) and tympanic (Lilly TM-Wick) electrode. Separate repeated measures linear mixed-model analysis of variance examined the effect of test, electrode, and rate for all ECochG indices. Test-retest variability was also examined with correlation analyses; an examination of mean test-retest differences and their 95% confidence intervals (CI); and construction of Bland-Altman plots. RESULTS: The presence of SP and AP responses varied across experimental conditions. Electrode and rate were statistically significant predictors (p < 0.05) of SP and AP responses: SP and AP responses were more likely to be present with the tympanic electrode and at the slow rate. Statistically significant correlations (p < 0.05) were found between initial tests and retests with all ECochG indices with both electrodes with the exception of SP amplitude with the TIPtrode™ electrode. There were no significant main effects of test (initial versus retest) or interactions of test and electrode or rate for any of the ECochG indices (p > 0.05). The 95% CI of the mean test-retest differences contained 0 confirming that the effect of test was not statistically significant. There was a statistically significant main effect of electrode (p < 0.05) on three ECochG measures. The Lilly TM-Wick electrode produced larger SP amplitudes, AP amplitudes, and SP/AP area ratios than TIPtrode™ electrodes. A statistically significant main effect of rate (p < 0.05) was identified for all ECochG measures. The effect of rate on AP latency and amplitude was expected. Increasing the stimulus rate prolonged the AP latency and decreased AP amplitude. SP amplitude was larger for the faster rate. CONCLUSIONS: There was no difference between electrodes with regard to test-retest measures. However, considering the higher likelihood of ECochG SP and AP responses and larger SP amplitude, SP/AP amplitude ratio, and SP/AP area ratio indices, the tympanic electrode placement is recommended for clinical practice. The addition of a fast stimulus rate may be considered for enhanced SP amplitude, SP/AP amplitude ratio, and SP/AP area ratio albeit with the consideration of the loss of SP and AP responses in some individuals.

Spectral Ripples in Round-Window Cochlear Microphonics: Evidence for Multiple Generation Mechanisms.

The cochlear microphonic (CM) results from the vector sum of outer hair cell transduction currents excited by a stimulus. The classical theory of CM generation-that the response measured at the round window is dominated by cellular sources located within the tail region of the basilar membrane (BM) excitation pattern-predicts that CM amplitude and phase vary little with stimulus frequency. Contrary to expectations, CM amplitude and phase-gradient delay measured in response to low-level tones in chinchillas demonstrate a striking, quasiperiodic pattern of spectral ripples, even at frequencies > 5 kHz, where interference with neurophonic potentials is unlikely. The spectral ripples were reduced in the presence of a moderate-level saturating tone at a nearby frequency. When converted to the time domain, only the delayed CM energy was diminished in the presence of the saturator. We hypothesize that the ripples represent an interference pattern produced by CM components with different phase gradients: an early-latency component originating within the tail region of the BM excitation and two delayed components that depend on active cochlear processing near the peak region of the traveling wave. Using time windowing, we show that the early, middle, and late components have delays corresponding to estimated middle-ear transmission, cochlear forward delays, and cochlear round-trip delays, respectively. By extending the classical model of CM generation to include mechanical and electrical irregularities, we propose that middle components are generated through a mechanism of "coherent summation" analogous to the production of reflection-source otoacoustic emissions (OAEs), while the late components arise through a process of internal cochlear reflection related to the generation of stimulus-frequency OAEs. Although early-latency components from the passive tail region typically dominate the round-window CM, at low stimulus levels, substantial contributions from components shaped by active cochlear processing provide a new avenue for improving CM measurements as assays of cochlear health.

Validation of methods for prediction of clinical output levels of active middle ear implants from measurements in human cadaveric ears.

Today, the standard method to predict output levels of active middle ear implants (AMEIs) before clinical data are available is stapes vibration measurement in human cadaveric ears, according to ASTM standard F2504-05. Although this procedure is well established, the validity of the predicted output levels has never been demonstrated clinically. Furthermore, this procedure requires a mobile and visually accessible stapes and an AMEI stimulating the ossicular chain. Thus, an alternative method is needed to quantify the output level of AMEIs in all other stimulation modes, e.g. reverse stimulation of the round window. Intracochlear pressure difference (ICPD) is a good candidate for such a method as it correlates with evoked potentials in animals and it is measurable in cadaveric ears. To validate this method we correlated AMEI output levels calculated from ICPD and from stapes vibration in cadaveric ears with outputs levels determined from clinical data. Output levels calculated from ICPD were similar to output levels calculated from stapes vibration and almost identical to clinical data. Our results demonstrate that both ICPD and stapes vibration can be used as a measure to predict AMEI clinical output levels in cadaveric ears and that ICPD as reference provided even more accurate results.

Resistance of Gerbil Auditory Function to Reversible Decrease in Cochlear Blood Flow.

The objective was to design in gerbils a model of reversible decrease in cochlear blood flow (CBF) and analyze its influence on cochlear function. In Mongolian gerbils injected with ferromagnetic microbeads, a magnet placed near the porus acusticus allowed CBF to be manipulated. The cochlear microphonic potential (CM) from the basal cochlea was monitored by a round-window electrode. In 13 of the 20 successfully injected gerbils, stable CBF reduction was obtained for 11.5 min on average. The CM was affected only when CBF fell to less than 60% of its baseline, yet remained >40% of its initial level in about 2/3 of such cases. After CBF restoration, CM recovery was fast and usually complete. Reduced CM came with a 35- to 45-dB threshold elevation of neural responses determined by compound action potentials. This method allowing reversible changes of CBF confirms the robustness of cochlear function to decreased CBF. It can be used to study whether a hypovascularized cochlea is abnormally sensitive to stress.

A connexin30 mutation rescues hearing and reveals roles for gap junctions in cochlear amplification and micromechanics.

Accelerated age-related hearing loss disrupts high-frequency hearing in inbred CD-1 mice. The p.Ala88Val (A88V) mutation in the gene coding for the gap-junction protein connexin30 (Cx30) protects the cochlear basal turn of adult CD-1Cx30A88V/A88V mice from degeneration and rescues hearing. Here we report that the passive compliance of the cochlear partition and active frequency tuning of the basilar membrane are enhanced in the cochleae of CD-1Cx30A88V/A88V compared to CBA/J mice with sensitive high-frequency hearing, suggesting that gap junctions contribute to passive cochlear mechanics and energy distribution in the active cochlea. Surprisingly, the endocochlear potential that drives mechanoelectrical transduction currents in outer hair cells and hence cochlear amplification is greatly reduced in CD-1Cx30A88V/A88V mice. Yet, the saturating amplitudes of cochlear microphonic potentials in CD-1Cx30A88V/A88V and CBA/J mice are comparable. Although not conclusive, these results are compatible with the proposal that transmembrane potentials, determined mainly by extracellular potentials, drive somatic electromotility of outer hair cells.

Study of cochlear microphonic potentials in auditory neuropathy / Estudo do microfonismo coclear na neuropatia auditiva

Abstract Introduction: Auditory Neuropathy/Dyssynchrony is a disorder characterized by the presence of Otoacoustic Emissions and Cochlear Microphonic Potentials, an absence or severe alteration of Brainstem Evoked Auditory Potential, auditory thresholds incompatible with speech thresholds and altered acoustic reflexes. The study of the Cochlear Microphonic Potential appears to be the most important tool for an accurate diagnosis of this pathology. Objective: Determine the characteristics of the Cochlear Microphonic in Auditory Neuropathy/Dyssynchrony using an integrative review. Methods: Bibliographic survey of Pubmed and Bireme platforms and MedLine, LILACS and SciELO data banks, with standardized searches up to July 2014, using keywords. Criteria were established for the selection and assessment of the scientific studies surveyed, considering the following aspects: author, year/place, degree of recommendation/level of scientific evidence, objective, sample, age range, mean age, tests, results and conclusion. Results: Of the 1959 articles found, 1914 were excluded for the title, 20 for the abstract, 9 for the text of the article, 2 for being repeated and 14 were selected for the study. Conclusion: The presence of the Cochlear Microphonic is a determining finding in the differential diagnosis of Auditory Neuropathy/Dyssynchrony. The protocol for the determination of Cochlear Microphonic must include the use of insert earphones, reverse polarity and blocking the stimulus tube to eliminate electrical artifact interference. The amplitude of the Cochlear Microphonic in Auditory Neuropathy/Dyssynchrony shows no significant difference from that of normal individuals. The duration of the Cochlear Microphonic is longer in individuals with Auditory Neuropathy/Dyssynchrony.

Resumo Introdução: A Neuropatia/Dessincronia Auditiva é uma doença caracterizada pela presença das Emissões Otoacústicas e do Microfonismo Coclear, com ausência ou grave alteração do Potencial Evocado Auditivo de Tronco Encefálico, limiares auditivos incompatíveis com limiares vocais e reflexos acústicos alterados. O estudo do Microfonismo Coclear parece ser a ferramenta mais importante para um diagnóstico preciso desta patologia. Objetivo: Verificar por meio de uma revisão integrativa as características do Microfonismo Coclear na Neuropatia/Dessincronia Auditiva. Método: Levantamento bibliográfico nas plataformas Pubmed e Bireme e nas bases de dados MedLine, LILACS e SciELO, com buscas padronizadas até julho de 2014, utilizando-se palavraschave. Para a seleção e avaliação dos estudos científicos levantados, foram estabelecidos critérios, contemplando os aspectos: autor, ano/local, grau de recomendação/nível de evidência científica, objetivo, amostra, faixa etária, média de idade em anos, testes, resultados e conclusão. Resultados: Dos 1959 artigos encontrados, 1914 foram excluídos pelo título, 20 pelo resumo, nove pela leitura do artigo, dois eram repetidos e 14 foram selecionados para o estudo. Conclusão: A presença do Microfonismo Coclear é um achado determinante no diagnóstico diferencial da Neuropatia/Dessincronia auditiva. O protocolo de registro do Microfonismo Coclear deve contar com o uso de fones de inserção, a inversão da polaridade e o bloqueio do tubo do estímulo para impedir a interferência de artefato elétrico. A amplitude do Microfonismo Coclear na Neuropatia/Dessincronia auditiva não apresenta diferença significante entre a amplitude do Microfonismo Coclear em ouvintes normais. A duração do Microfonismo Coclear é maior em indivíduos com Neuropatia/Dessincronia auditiva.

The potential use of low-frequency tones to locate regions of outer hair cell loss.

Current methods used to diagnose cochlear hearing loss are limited in their ability to determine the location and extent of anatomical damage to various cochlear structures. In previous experiments, we have used the electrical potential recorded at the round window -the cochlear response (CR) -to predict the location of damage to outer hair cells in the gerbil. In a follow-up experiment, we applied 10 mM ouabain to the round window niche to reduce neural activity in order to quantify the neural contribution to the CR. We concluded that a significant proportion of the CR to a 762 Hz tone originated from phase-locking activity of basal auditory nerve fibers, which could have contaminated our conclusions regarding outer hair cell health. However, at such high concentrations, ouabain may have also affected the responses from outer hair cells, exaggerating the effect we attributed to the auditory nerve. In this study, we lowered the concentration of ouabain to 1 mM and determined the physiologic effects on outer hair cells using distortion-product otoacoustic emissions. As well as quantifying the effects of 1 mM ouabain on the auditory nerve and outer hair cells, we attempted to reduce the neural contribution to the CR by using near-infrasonic stimulus frequencies of 45 and 85 Hz, and hypothesized that these low-frequency stimuli would generate a cumulative amplitude function (CAF) that could reflect damage to hair cells in the apex more accurately than the 762 stimuli. One hour after application of 1 mM ouabain, CR amplitudes significantly increased, but remained unchanged in the presence of high-pass filtered noise conditions, suggesting that basal auditory nerve fibers have a limited contribution to the CR at such low frequencies.

Study of cochlear microphonic potentials in auditory neuropathy.

INTRODUCTION: Auditory Neuropathy/Dyssynchrony is a disorder characterized by the presence of Otoacoustic Emissions and Cochlear Microphonic Potentials, an absence or severe alteration of Brainstem Evoked Auditory Potential, auditory thresholds incompatible with speech thresholds and altered acoustic reflexes. The study of the Cochlear Microphonic Potential appears to be the most important tool for an accurate diagnosis of this pathology. OBJECTIVE: Determine the characteristics of the Cochlear Microphonic in Auditory Neuropathy/Dyssynchrony using an integrative review. METHODS: Bibliographic survey of Pubmed and Bireme platforms and MedLine, LILACS and SciELO data banks, with standardized searches up to July 2014, using keywords. Criteria were established for the selection and assessment of the scientific studies surveyed, considering the following aspects: author, year/place, degree of recommendation/level of scientific evidence, objective, sample, age range, mean age, tests, results and conclusion. RESULTS: Of the 1959 articles found, 1914 were excluded for the title, 20 for the abstract, 9 for the text of the article, 2 for being repeated and 14 were selected for the study. CONCLUSION: The presence of the Cochlear Microphonic is a determining finding in the differential diagnosis of Auditory Neuropathy/Dyssynchrony. The protocol for the determination of Cochlear Microphonic must include the use of insert earphones, reverse polarity and blocking the stimulus tube to eliminate electrical artifact interference. The amplitude of the Cochlear Microphonic in Auditory Neuropathy/Dyssynchrony shows no significant difference from that of normal individuals. The duration of the Cochlear Microphonic is longer in individuals with Auditory Neuropathy/Dyssynchrony.

Cochlear Implant Stimulation of a Hearing Ear Generates Separate Electrophonic and Electroneural Responses.

Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in clinical practice. However, little is known about the properties of electrically induced responses in the hearing cochlea. In the present study, normal-hearing guinea pig cochleae underwent cochlear implantation through a cochleostomy without significant loss of hearing. Using recordings of unit activity in the midbrain, we were able to investigate the excitation patterns throughout the tonotopic field determined by acoustic stimulation. With the cochlear implant and the midbrain multielectrode arrays left in place, the ears were pharmacologically deafened and electrical stimulation was repeated in the deafened condition. The results demonstrate that, in addition to direct neuronal (electroneuronal) stimulation, in the hearing cochlea excitation of the hair cells occurs ("electrophonic responses") at the cochlear site corresponding to the dominant temporal frequency components of the electrical stimulus, provided these are < 12 kHz. The slope of the rate-level functions of the neurons in the deafened condition was steeper and the firing rate was higher than in the hearing condition at those sites that were activated in the two conditions. Finally, in a monopolar stimulation configuration, the differences between hearing status conditions were smaller than in the narrower (bipolar) configurations. SIGNIFICANCE STATEMENT: Stimulation with cochlear implants and hearing aids is becoming more widely clinically used in subjects with residual hearing. The neurophysiological characteristics underlying electroacoustic stimulation and the mechanism of its benefit remain unclear. The present study directly demonstrates that cochlear implantation does not interfere with the normal mechanical and physiological function of the cochlea. For the first time, it double-dissociates the electrical responses of hair cells (electrophonic responses) from responses of the auditory nerve fibers (electroneural responses), with separate excited cochlear locations in the same animals. We describe the condition in which these two responses spatially overlap. Finally, the study implicates that using the clinical characteristics of stimulation makes electrophonic responses unlikely in implanted subjects.

Using a concha electrode to measure response patterns based on the amplitudes of cochlear microphonic waveforms across acoustic frequencies in normal-hearing subjects.

OBJECTIVES: Compared to a conventional click-evoked cochlear microphonic (CM) in an electrocochleogram, a tone-burst evoked CM waveform (CMW) is unconventional and the frequency band is narrower. Furthermore, compared to conventional CM measurement techniques such as the use of a tympanic or a canal electrode, the use of a concha electrode is the least invasive and an unconventional technique in the measurement of CMs. Finally, compared to CM responses measured by conventional approaches, the response pattern obtained from the amplitude of far-field recorded CMWs across acoustic frequencies is unconventional. Our objective is to combine these three unconventional elements together into a unique approach, which may provide potential benefits for clinical diagnosis and cochlear research. DESIGN: Using a concha electrode, CMWs in response to a 14 msec tone burst were recorded in seven normal-hearing subjects. The CMW amplitudes recorded over different acoustic frequencies were compared to each other to produce a frequency response pattern. RESULTS: Two features were observed in the response pattern: the CMW amplitude decreased upon an increase in frequency of a tone burst stimulus, and the decrease occurred faster at lower frequencies than at higher frequencies. CONCLUSIONS: We confirmed a measurable CMW response pattern using the concha electrode. We propose that the pattern's features may be partly due to variation along the cochlea of the activities and volume of hair cells and possibly also the physical properties of the basilar membrane. The clinical importance of these results may be related mainly to seven features of the CMW, including electrode locations, response patterns, inclusion of low frequencies, and uniqueness of CMWs (versus otoacoustic emissions, auditory brainstem responses, shorter stimulus, and audiograms). Limitations, such as signal to noise ratio, also exist. After further study, the concha electrode may be used in the clinic and in research, and the response pattern may be used to interpret the CMW measurement.

Effects of salicylate on sound-evoked outer hair cell stereocilia deflections.

Hearing depends on sound-evoked deflections of the stereocilia that protrude from the sensory hair cells in the inner ear. Although sound provides an important force driving stereocilia, forces generated through mechanically sensitive ion channels and through the motor protein prestin have been shown to influence stereocilia motion in solitary hair cells. While a possible influence of prestin on mechanically sensitive ion channels has not been systematically investigated, a decrease in transducer currents is evident in solitary hair cells when prestin is blocked with salicylate, raising the question of whether a reduced prestin activity or salicylate itself affected the mechanotransduction apparatus. We used two- and three-dimensional time-resolved confocal imaging to visualize outer hair cell stereocilia during sound stimulation in the apical turn of cochlear explant preparations from the guinea pig. Surprisingly, following application of salicylate, outer hair cell stereocilia deflections increased, while cochlear microphonic potentials decreased. However, when prestin activity was altered with the chloride ionophore tributyltin, both the cochlear microphonic potential and the stereocilia deflection amplitude decreased. Neither positive nor negative current stimulation abolished the bundle movements in the presence of salicylate, indicating that the observed effects did not depend on the endocochlear potential. These data suggest that salicylate may alter the mechanical properties of stereocilia, decreasing their bending stiffness.

Electrocochleography in children with auditory synaptopathy/neuropathy: diagnostic findings and characteristic parameters.

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 specificity. 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.

[Cochlear microphonic latency]. / Latencia de los microfónicos cocleares.

INTRODUCTION AND OBJECTIVE: By using appropriate instrumentation, we have found that cochlear microphonics (CM) advance or delay their appearance, depending on the sound pressure that generates them. This time variation is on the order of microseconds. We have not found any reference to this behaviour, which is why we make the finding known. MATERIAL AND METHOD: We used the standard instrumentation specified for the study of CM. The method was based on the phase shift function of the CM according to the intensity of the stimulus. RESULTS: Latency was observed in CM, and we determined that latency time diminishes as the intensity of the stimulus increases. CONCLUSIONS: From the sound stimulus to the bioelectric potential transduction, there is a time period of microseconds, the shorter the more powerful the stimulus. This suggests that electromechanical transduction is not a simple mechanical process.

Comparison of auditory responses determined by acoustic stimulation and by mechanical round window stimulation at equivalent stapes velocities.

Active middle ear implants (AMEIs) have been studied to overcome the limitations of conventional hearing aids such as howling, occlusion, and social discrimination. AMEIs usually drive the oval window (OW) by means of transmitting vibrational force through the ossicles and the vibrational force corresponding to sound is generated from a mechanical actuator. Recently, round window (RW) stimulation using an AMEI such as a floating mass transducer (FMT) to deliver sound to the cochlea has been introduced and hearing improvement in clinical use has been reported. Although previous studies demonstrated that the auditory response to RW stimulation was comparable to a sound-evoked auditory response, few studies have investigated the quantification of the physiologic performance of an AMEI through RW stimulation on the inner ear in vivo. There is no established relationship between the cochlear responses and mechanical stimulation to RW. The aim of this study is to assess the physiologic response in RW stimulation by an AMEI. The transferred energy through the RW to the inner ear could estimate the response corresponding to acoustic stimulation in order to quantify the AMEI output in the ossicular chain or OW stimulation. The parameters of the auditory brainstem responses (ABRs) were measured and compared based on stapes velocities similar enough to be regarded as the same for acoustic stimulation to the external auditory canal (EAC) and mechanical stimulation to the RW in an in vivo system. In conclusion, this study showed that the amplitudes and latencies of the ABRs of acoustic and RW stimulation showed significant differences at comparable stapes velocities in an in vivo system. These differences in the ABR amplitudes and latencies reflect different output functions of the cochlea in response to different stimulation pathways. Therefore, it is necessary to develop a new method for quantifying the output of the cochlea in the case of RW stimulation.

Twelve months of active musical training in 8- to 10-year-old children enhances the preattentive processing of syllabic duration and voice onset time.

Musical training has been shown to positively influence linguistic abilities. To follow the developmental dynamics of this transfer effect at the preattentive level, we conducted a longitudinal study over 2 school years with nonmusician children randomly assigned to music or to painting training. We recorded the mismatch negativity (MMN), a cortical correlate of preattentive mismatch detection, to syllables that differed in vowel frequency, vowel duration, and voice onset time (VOT), using a test-training-retest procedure and 3 times of testing: before training, after 6 months and after 12 months of training. While no between-group differences were found before training, enhanced preattentive processing of syllabic duration and VOT, as reflected by greater MMN amplitude, but not of frequency, was found after 12 months of training in the music group only. These results demonstrate neuroplasticity in the child brain and suggest that active musical training rather than innate predispositions for music yielded the improvements in musically trained children. These results also highlight the influence of musical training for duration perception in speech and for the development of phonological representations in normally developing children. They support the importance of music-based training programs for children's education and open new remediation strategies for children with language-based learning impairments.

Modelling the generation of the cochlear microphonic.

The cochlear microphonic (CM) is one of the electrical signals generated by the human ear in response to sound stimulus. Difficulty in recording this signal and inadequate understanding of its origin have restricted its use for human auditory research. Modelling can help to improve our understanding of this signal. In this paper, an electromechanical model for the generation of the cochlear microphonic is proposed. The results of the model can also explain discrepancies between the basilar membrane and CM tuning curves.