Lack of correlation between medial olivocochlear reflex strength and sentence recognition in noise.

OBJECTIVE: The medial olivocochlear (MOC) reflex provides unmasking of sounds in noise, but its contribution to speech-in-noise perception remains unclear due to conflicting results. This study determined associations between MOC reflex strength and sentence recognition in noise in individuals with normal hearing. DESIGN: MOC reflex strength was assessed using contralateral inhibition of transient-evoked otoacoustic emissions (TEOAEs). Scores on the AzBio sentence task were quantified at three signal-to-noise ratios (SNRs). Additionally, slope and threshold of the psychometric function were computed. Associations between MOC reflex strength and speech-in-noise outcomes were assessed using Spearman rank correlations. STUDY SAMPLE: Nineteen young adults with normal hearing participated, with data from 17 individuals (mean age = 21.8 years) included in the analysis. RESULTS: Contralateral noise significantly decreased the amplitude of TEOAEs. A range of contralateral inhibition values was exhibited across participants. Scores increased significantly with increasing SNR. Contrary to hypotheses, there were no significant correlations between MOC reflex strength and score, nor were there any significant correlations between MOC reflex strength and measures of the psychometric function. CONCLUSIONS: Results found no significant monotonic relationship between MOC reflex strength and sentence recognition in noise. Future work is needed to determine the functional role of the MOC reflex.

Analysis of Newborn Hearing Screening Results in South Korea after National Health Insurance Coverage: A Nationwide Population-Based Study.

Newborn hearing screening (NHS) has been covered by national health insurance since October 2018 in Korea. However, the results of the NHS are not reported due to the absence of a follow-up tracking system. This study analyzed the status and the predicted referral rates of NHS after the Korean national health insurance coverage by analyzing the National Health Insurance Service database in 2019 and 2020. The NHS coverage was 91.7% of total birth in 2019 and 92.1% in 2020. The predicted referral rate of NHS calculated by the duplicated NHS cases was 1.05% in 2019 and 0.99% in 2020. However, another predicted referral rate calculated by the number of diagnostic auditory brainstem responses (ABRs) performed was 1.44% in 2019 and 1.43% in 2020. The first NHS was performed within one day of birth for 96.5% of the babies and within three days of birth for 97%. However, diagnostic ABR was adequately performed within three months of birth for only 4.3%, while 82.3% performed the test after six months which delays appropriate intervention for hearing loss. National support such as national coordinators, follow-up tracking, and data management systems are needed for early hearing detection and intervention of newborns and infants in Korea.

Characterizing the Relationship Between Reflection and Distortion Otoacoustic Emissions in Normal-Hearing Adults.

Otoacoustic emissions (OAEs) arise from one (or a combination) of two basic generation mechanisms in the cochlea: nonlinear distortion and linear reflection. As a result of having distinct generation processes, these two classes of emissions may provide non-redundant information about hair-cell integrity and show distinct sensitivities to cochlear pathology. Here, we characterize the relationship between reflection and distortion emissions in normal hearers across a broad frequency and stimulus-level space using novel analysis techniques. Furthermore, we illustrate the promise of this approach in a small group of individuals with mild-moderate hearing loss. A "joint-OAE profile" was created by measuring interleaved swept-tone stimulus-frequency OAEs (SFOAEs) and 2f1-f2 distortion-product OAEs (DPOAEs) in the same ears using well-considered parameters. OAE spectra and input/output functions were calculated across five octaves. Using our specific recording protocol and analysis scheme, SFOAEs in normal hearers had higher levels than did DPOAEs, with the most pronounced differences occurring at the highest stimulus levels. Also, SFOAE compression occurred at higher stimulus levels (than did DPOAE compression) and its growth in the compressed region was steeper. The diagnostic implications of these findings and the influence of the measurement protocol on both OAEs (and on their relationship) are discussed.

Evaluation of Medial Olivocochlear Neural Efferent Pathway in Tinnitus Perception in Normal-hearing Individuals.

OBJECTIVE: The objective of this study is to investigate a possible role of the Medial Olivocochlear (MOC) efferent neural pathway and neural connections responsible for tinnitus generation in silence/sensory deprivation. DESIGN: By placing normal hearing participants in a sound booth for 10 minutes, silence/sensory deprivation was created. This offered assessment of MOC neural pathway in normal hearing participants in silence. Hyperactivity of MOC neural pathway was assessed by its more suppressive effect on Transient Otoacoustic Emissions (TEOAEs) in silence. The required auditory measurements were recorded in the sound booth using recommended diagnostic protocols to ensure the effect of 'only silence' on auditory structures. TEOAE were recorded from the right ear and suppression was measured by placing noise in the left ear. Fifty-eight normal hearing male individuals between age 18-35 years were recruited as participants in this study. RESULTS: Approximately, forty-one percent of the participants perceived some type of tinnitus during/after 10 minutes of silence. No statistically significant difference was found in the total TEOAE amplitude and TEOAE suppression amplitude before and after ten minutes of silence. Post silence total TEOAE suppression between tinnitus perceiving and non-perceiving tinnitus participants were not statistically significantly different. CONCLUSION: These results suggest that the medial olivocochlear efferent pathway or lower brain stem area does not appear to play a role in the emergence of temporary tinnitus in silence however indicate the involvement of higher central auditory nervous system structures in perception of the tinnitus which support the well-accepted notion that tinnitus is the central auditory processing phenomenon.

The effect of coffee on contralateral suppression of transient evoked otoacoustic emissions.

Background: Coffee is a popular non-alcoholic beverage consumed by humans across the world. It contains caffeine, which is a type of stimulant of the central nervous system. In the auditory system, it has a positive effect on auditory brainstem response and perception of speech in noise. Further, caffeine has an inhibitory effect in the cochlea, but studies have rarely investigated its effect on otoacoustic emissions (OAEs) in humans. OAEs are low-intensity sounds produced by the cochlea, which could be recorded in the ear canal. The present study was carried out to investigate the effect of coffee on transient evoked otoacoustic emission (TEOAE) and contralateral suppression of TEOAE. Method: A total of 52 young adults participated in the study. A cross-over study design was used for the present investigation. The TEOAE and contralateral suppression of TEOAE were recorded before and after consumption of coffee and milk. The contralateral suppression of TEOAE was measured by presenting white noise to the contralateral ear at 40, 50, and 60 dB sound pressure level (SPL). Results: The mean amplitude of TEOAE before and after consumption of coffee was similar in both ears. Further, the mean contralateral suppression of TEOAE was slightly larger after consumption of coffee in both ears. However, the mean difference was not significant in both the ears. Conclusions: Based on the findings of present study, coffee has no significant effect on the amplitude of TEOAE and contralateral suppression of TEOAE.

Conversion of amplitude modulation to phase modulation in the human cochlea.

When an amplitude modulated signal with a constant-frequency carrier is fed into a generic nonlinear amplifier, the phase of the carrier of the output signal is also modulated. This phenomenon is referred to as amplitude-modulation-to-phase-modulation (AM-to-PM) conversion and regarded as an unwanted signal distortion in the field of electro-communication engineering. Herein, we offer evidence that AM-to-PM conversion also occurs in the human cochlea and that listeners can use the PM information effectively to process the AM of sounds. We recorded otoacoustic emissions (OAEs) evoked by AM signals. The results showed that the OAE phase was modulated at the same rate as the stimulus modulation. The magnitude of the AM-induced PM of the OAE peaked generally around the stimulus level corresponding to the compression point of individual cochlear input-output functions, as estimated using a psychoacoustic method. A computational cochlear model incorporating a nonlinear active process replicates the abovementioned key features of the AM-induced PM observed in OAEs. These results indicate that AM-induced PM occurring at the cochlear partition can be estimated by measuring OAEs. Psychophysical experiments further revealed that, for individuals with higher sensitivity to PM, the PM magnitude is correlated with AM-detection performance. This result implies that the AM-induced PM information cannot be a dominant cue for AM detection, but listeners with higher sensitivity may partly rely on the AM-induced PM cue.

Medial olivocochlear reflex effects on amplitude growth functions of long- and short-latency components of click-evoked otoacoustic emissions in humans.

Functional outcomes of medial olivocochlear reflex (MOCR) activation, such as improved hearing in background noise and protection from noise damage, involve moderate to high sound levels. Previous noninvasive measurements of MOCR in humans focused primarily on otoacoustic emissions (OAEs) evoked at low sound levels. Interpreting MOCR effects on OAEs at higher levels is complicated by the possibility of the middle-ear muscle reflex and by components of OAEs arising from different locations along the length of the cochlear spiral. We overcame these issues by presenting click stimuli at a very slow rate and by time-frequency windowing the resulting click-evoked (CE)OAEs into short-latency (SL) and long-latency (LL) components. We characterized the effects of MOCR on CEOAE components using multiple measures to more comprehensively assess these effects throughout much of the dynamic range of hearing. These measures included CEOAE amplitude attenuation, equivalent input attenuation, phase, and slope of growth functions. Results show that MOCR effects are smaller on SL components than LL components, consistent with SL components being generated slightly basal of the characteristic frequency region. Amplitude attenuation measures showed the largest effects at the lowest stimulus levels, but slope change and equivalent input attenuation measures did not decrease at higher stimulus levels. These latter measures are less commonly reported and may provide insight into the variability in listening performance and noise susceptibility seen across individuals.NEW & NOTEWORTHY The auditory efferent system, operating at moderate to high sound levels, may improve hearing in background noise and provide protection from noise damage. We used otoacoustic emissions to measure these efferent effects across a wide range of sound levels and identified level-dependent and independent effects. Previous reports have focused on level-dependent measures. The level-independent effects identified here may provide new insights into the functional relevance of auditory efferent activity in humans.

Association between Spontaneous Otoacoustic Emission and Psychoacoustic measures.

AIM: The aim of the present study was to evaluate the association of presence and absence of spontaneous otoacoustic emissions (SOAEs) on different psycho-acoustic measures such as intensity discrimination, gap detection test, duration discrimination test, modulation detection for sinusoidal amplitude modulated noise at 8, 20, 60, and 100 Hz. METHOD: Sixty adults with hearing sensitivity within normal limits were divided into two groups; group 1 consisted of participants with SOAEs present and group 2 consisted of participants with SOAEs absent. All the participants were tested for presence of SOAEs and different psycho-acoustic measures. RESULTS: The present study results showed no significant difference on intensity discrimination, gap detection test, duration discrimination test, modulation detection for sinusoidal amplitude modulated noise at 8, 20, 60, and 100 Hz in presence and absent of SOAE. CONCLUSION: The findings reveals that the presence or absence of SOAE did not influence or enhance the psychophysical performance at most comfortable level in individuals having normal hearing.

Use of custom-moulded earmoulds to improve repeatability of DPOAE map measurements.

OBJECTIVE: Distortion product otoacoustic emission (DPOAE) mapping characterises cochlear function, can include both the 2f1-2f2 and 2f2-2f1 DPOAEs, and shows promise for tracking cochlear changes. DPOAE amplitude measurements are not as repeatable longitudinally as pure-tone audiometry, likely due in part to probe placement sensitivity. We hypothesised that DPOAE level map variation over multiple testing sessions could be minimised by replacing traditional rubber tips with custom-moulded probe tips. DESIGN: Traditional rubber tips (TRT) and custom-moulded probes tips (CMPT) were used to measure DPOAE level maps repeatedly over five sessions. Probe placement was assessed using a frequency sweep in the ear canal. Repeatability of the DPOAE level maps was assessed using a Bland-Altman analysis. Overall map repeatability was assessed by measuring differences in distortion product amplitude over sessions. STUDY SAMPLE: Crossover study with a convenience sample size of six adults. RESULTS: The CMPT frequency sweeps showed reduced variability in probe placement. The repeatability coefficient for individual DPOAEs measurements improved from 6.9 dB SPL with the TRT to 5.1 dB SPL with the CMPT. Map repeatability improved for most subjects with the CMPT.

Detection of Age-Related Hearing Losses (ARHL) via Transient-Evoked Otoacoustic Emissions.

PURPOSE: The objective of the study was to identify subjects presenting hearing deficits, specifically age-related hearing losses (ARHL), via objective assessment methodologies. MATERIALS AND METHODS: Initially, 259 subjects (165 men, 94 women) were enrolled in the study. After the application of inclusion criteria, the final number was reduced to 88 subjects (49.8 ± 19.1 ys) subdivided into 64 normal and 83 ARHL cases. The subjects were assessed with traditional audiometry tests and with transiently evoked otoacoustic emissions (TEOAEs). Since each ear has its own acoustic signature, the TEOAE analyses were conducted in terms of ears and not subjects. The TEOAE data were processed by traditional and recurrence quantification analyses, leading to the estimation of the WWR (whole waveform reproducibility) and the new RAD2D (2-dimensional radius) parameters. A plot of WWR vs RAD2D was used to optimize the classification of the cases presenting ARHL. RESULTS: By using a WWR value of 70% as a classifier, the sensitivity of TEOAEs was estimated as 75.9% and the specificity as 89.1%. By using the RAD2D parameter (with a cut-off value of 1.78), a sensitivity value of 80.7% and a specificity value of 71.9% were obtained. When both parameters were used, a sensitivity value of 85.5% and a specificity value of 92.2% were estimated. In the latter classification paradigm, the number of false negatives decreased from 20 to 12 out of 83 ears (14%). CONCLUSION: In adult hearing screening assessments, the proposed method optimizes the identification of subjects with a hearing impairment correlated to the presence of age-related hearing loss.

Human medial olivocochlear reflex: Contralateral activation effect on low and high frequency cochlear response.

The role of the medial olivocochlear (MOC) reflex has been investigated by assessing changes of cochlear responses (CR) in humans. The CR consists of pre-neural and neural potentials originating from the inner ear, and at high signal levels is dominated by cochlear microphonic (CM). The CM originates from the outer hair cells, where the MOC fibers synapse, and there is little research about using it to investigate the MOC reflex in humans. The current study aimed to investigate the effect of contralateral activation of the MOC reflex on the CR in humans. The CR was recorded in female adults (n = 16) to 500 and 2000 Hz tone burst stimuli presented at 80 dB nHL with and without contralateral broadband noise (CBBN) at 40 dB SPL. Two different methods were utilized to quantify and analyze the CR data: peak amplitude and power spectrum. Results revealed enhancement of the CR amplitude with activation of the MOC reflex. Furthermore, on average, enhancement in the CR amplitude was observed to 500 Hz, but not 2000 Hz stimulus. The CR power spectrum findings revealed similar findings to the peak amplitude. These findings indicate the MOC effect is measurable when using a low frequency stimulus, but not high frequency. Moreover, the CR could be used as a potential tool to study the MOC reflex in humans.

[Study protocol of the monocentric prospective randomized placebo-controlled double-blind phase II study to explore the protective effects of the ginkgo biloba extract EGb 761® from temporary noise-induced hearing loss]. / Prüfplan für die monozentrische prospektive randomisierte placebokontrollierte doppelblinde Phase-II-Studie zur Exploration protektiver Effekte des Ginkgo-biloba-Spezialextrakts EGb 761® vor einer vorübergehenden Hörschädigung durch Lärm.

BACKGROUND: Hearing loss is frequently induced by occupational noise exposure and leads to rising hearing thresholds as well as reduced otoacoustic emissions (OAE), mostly caused by metabolic hair cell decompensation. OBJECTIVE: Primary endpoint is the increase in average pure tone thresholds after noise exposure, secondary endpoints are loss of distortion product and click-evoked OAE as well as reduction of their contralateral suppression. PARTICIPANTS AND METHODS: The present study design describes the verification of the anti-oxidant and neuroprotective properties of EGb 761® by evaluation of cochlear protection from noise impact as well as its safety and tolerance in 202 healthy male participants distributed equally to verum and placebo groups in a double-blind manner. Participants were assessed, medicated, exposed to noise, and then examined at timepoints up to 10 min and 4 weeks thereafter. CONCLUSION: This summary of the verification study protocol highlights the complexity of diligent and precise planning according to the European Medicines Agency criteria for controlled trials (EudraCT). Key points are the intervention rationale, definitions of in- and exclusion criteria, estimation of subject numbers, and examination method setting in terms of optimum endpoint description.

Analysis of probe fitting stimulus properties on transient evoked otoacoustic emissions.

Objective: The objectives of the current study are first, to evaluate the subjective evaluation of probe fitting stimulus properties, and second, to analyse the effects of different probe fittings on transient evoked otoacoustic emission (TEOAE) response and noise amplitudes in subjects.Design: The Q methodology was used to sort 48 probe fittings differing in stimulus properties in seven categories from totally unacceptable to certainly acceptable. Further, TEOAE response and noise amplitudes were measured in one baseline condition with optimal probe fitting and eight experimental conditions with less than optimal probe fittings.Study sample: The probe fittings were ranked by 18 participants, while the repeated measures design was performed in 34 ear.Results: First, it was found that only 19.61% of all distributions of the probe fittings by the participants had a mutual correlation of at least 70.00%. Almost 60% of the variance of distributions was explained by 83.33% of the participants, although most probe fittings significantly differed from other fittings based on spectral broadness. Second, significant differences in TEOAE response and especially noise amplitudes between conditions were found. Further, TEOAE response and noise amplitudes between the baseline and experimental conditions were significantly different depending on ringing and spectral flatness of the stimulus.Conclusion: A substantial amount of subjectivity during TEOAE measurements is involved with regard to the evaluation of probe fitting stimulus properties. TEOAE response but especially noise amplitudes are influenced by varying stimulus parameters which stresses the importance of inspecting these parameters prior to or during EOAE measurements. Although more research is needed, some guidelines regarding these parameters are given which could improve the accuracy of TEOAEs in practice.

Establishing critical differences in ear-canal stimulus amplitude for detecting middle ear muscle reflex activation during olivocochlear efferent measurements.

Objective: Assessments of the medial olivocochlear reflex (MOCR) may have clinical utility. The MOCR is measured using contralateral inhibition of otoacoustic emissions but concurrent activation of the middle ear muscle reflex (MEMR) confounds test interpretation. MEMR activation can be detected using the change in ear-canal stimulus amplitude without versus with an MOCR elicitor. This study provides a description of how critical differences in ear-canal stimulus amplitude can be established.Design: Clicks were presented in right ears without and with a contralateral MOCR elicitor. Ear-canal stimulus amplitudes were measured. Two measurements without an elicitor were used to develop critical differences. MEMR activation was considered present if the difference in ear-canal stimulus amplitude without versus with an elicitor exceeded the critical difference.Study sample: Forty-six normal-hearing adults (mean age = 23.4 years, 35 females) participated, with data from 44 participants included in the final analysis.Results: Two participants exceeded the 95% critical difference. The 80, 90 and 99% critical differences are also reported for reference.Conclusions: Results suggest that the contralateral elicitor can evoke the MEMR in a small number of participants. The methods described in this paper can be used for developing equipment- and clinic-specific critical differences for detecting MEMR activation.

Análise das emissões otoacústicas transitórias por banda de frequência em adolescentes com diabetes mellitus tipo 1 / Transient otoacoustic emissions analysis by frequency bands in adolescents with type 1 diabetes mellitus

Introdução: A associação entre perda auditiva e Diabetes Mellitus tipo 1 (DM1) é ainda pouco estudada. A perda auditiva é uma das complicações crônicas relacionadas ao grau de controle glicêmico, que os pacientes podem apresentar com a progressão da doença. Objetivo: Investigar o comprometimento auditivo por meio das emissões otoacústicas transitórias (EOAT) por banda de frequência em adolescentes com DM1 e relação com o controle glicêmico. Métodos: Foram incluídos 80 adolescentes, 50% do gênero masculino, entre 10 e 19 anos de idade: 40 com DM1 e 40 controles saudáveis, pareados por gênero e idade. Os dados clínicos e laboratoriais foram pesquisados nos prontuários médicos. O controle glicêmico foi avaliado por meio dos exames de hemoglobina glicada e os pacientes com DM1 analisados de acordo com o controle glicêmico. A avaliação auditiva foi realizada por meio da imitanciometria, audiometria, e posteriormente EOAT, em sala tratada acusticamente, pelo protocolo "TE Test" de clique não-linear (1 KHz a 4 kHz) a 80 dB NPS de intensidade (AuDX - Biologic). Resultados: As respostas às EOAT foram ausentes em 5,12% em pacientes com DM1, com diferença significativa em relação aos controles (p=0,04). A análise das EOAT por bandas de frequência mostrou maior proporção de alteração nos adolescentes com DM1 mal controlados quando comparados aos bem controlados, nas frequências de 1000Hz, 2000Hz e 3000Hz (p<0,05). Conclusão: As EOAT por bandas de frequência permitiram a identificação precoce de comprometimento auditivo em adolescentes com DM1 e mostraram associação entre DM1 mal controlado e perda auditiva. (AU)

Introduction: The association between hearing loss and type 1 diabetes mellitus (DM1) is still poorly studied. Hearing loss is one of the chronic complications related to the degree of glycemic control that patients may present with the progression of the disease. Objective: To investigate auditory impairment through transient otoacoustic emissions (TEOAE) by frequency band in adolescents with DM1 and in relation to glycemic control. Methods: Were included 80 adolescents, 50% males, between 10 and 19 years of age: 40 with DM1 and 40 healthy controls, matched by gender and age. Clinical and laboratory data were taken from the medical records. Glycemic control was evalueted by glycated hemoglobin and the patients with DM1 were analyzed according to glycemic control. To the auditory evaluation were used the immittance and audiometry, and the TEOAE. The test was performed in the acoustically treated room, the non-linear TE test protocol (1 KHz to 4 kHz) at 80 dB SPL (AuDX - Biologic ). Results: TEOAE responses were absent in 5.12% of patients with DM1, with a significant difference in relation to controls (p = 0.04). The analysis of TEOAE by frequency bands showed a higher proportion of alteration in adolescents with DM1 poorly controlled when compared to well controlled ones, in the frequencies of 1000Hz, 2000Hz and 3000Hz (p <0.05). Conclusion: TEOAE by frequency bands allowed the early identification of auditory impairment in adolescents with DM1 and showed an association between poorly controlled DM1 and hearing loss. (AU)

Swept-Tone Stimulus-Frequency Otoacoustic Emissions in Human Newborns.

Several types of otoacoustic emissions have been characterized in newborns to study the maturational status of the cochlea at birth and to develop effective tests of hearing. The stimulus-frequency otoacoustic emission (SFOAE), a reflection-type emission elicited with a single low-level pure tone, is the least studied of these emissions and has not been comprehensively characterized in human newborns. The SFOAE has been linked to cochlear tuning and is sensitive to disruptions in cochlear gain (i.e., hearing loss) in adult subjects. In this study, we characterize SFOAEs evoked with rapidly sweeping tones in human neonates and consider the implications of our findings for human cochlear maturation. SFOAEs were measured in 29 term newborns within 72 hr of birth using swept tones presented at 2 oct/s across a four-octave frequency range (0.5­8 kHz); 20 normal-hearing young adults served as a control group. The prevalence of SFOAEs in newborns was as high as 90% (depending on how response "presence" was defined). Evidence of probe-tip leakage and abnormal ear-canal energy reflectance was observed in those ears with absent or unmeasurable SFOAEs. Results in the group of newborns with present stimulus-frequency emissions indicate that neonatal swept-tone SFOAEs are adult-like in morphology but have slightly higher amplitude compared with adults and longer SFOAE group delays. The origin of these nonadult-like features is probably mixed, including contributions from both conductive (ear canal and middle ear) and cochlear immaturities.

The Medial Olivocochlear Reflex Is Unlikely to Play a Role in Listening Difficulties in Children.

The medial olivocochlear reflex (MOCR) has been implicated in several auditory processes. The putative role of the MOCR in improving speech perception in noise is particularly relevant for children who complain of listening difficulties (LiD). The hypothesis that the MOCR may be impaired in individuals with LiD or auditory processing disorder has led to several investigations but without consensus. In two related studies, we compared the MOCR functioning of children with LiD and typically developing (TD) children in the same age range (7-17 years). In Study 1, we investigated ipsilateral, contralateral, and bilateral MOCR using forward-masked click-evoked otoacoustic emissions (CEOAEs; n = 17 TD, 17 LiD). In Study 2, we employed three OAE types: CEOAEs (n = 16 TD, 21 LiD), stimulus frequency OAEs (n = 21 TD, 30 LiD), and distortion product OAEs (n = 17 TD, 22 LiD) in a contralateral noise paradigm. Results from both studies suggest that the MOCR functioning is not significantly different between the two groups. Some likely reasons for differences in findings among published studies could stem from the lack of strict data quality measures (e.g., high signal-to-noise ratio, control for the middle ear muscle reflex) that were enforced in the present study. The inherent variability of the MOCR, the subpar reliability of current MOCR methods, and the heterogeneity in auditory processing deficits that underlie auditory processing disorder make detecting clinically relevant differences in MOCR function impractical using current methods.

Protective Effect of Melatonin on Cisplatin-induced Ototoxicity in Rats.

BACKGROUND/AIM: Cisplatin is a highly effective chemotherapeutic agent that is used to treat solid tumors; however, its severe side effects remain a limitation. In particular, the high incidence of cisplatin-induced ototoxicity has attracted interest. Melatonin has been shown to decrease the toxic effects of cisplatin due to its antioxidant activity, and could increase the efficacy of cancer chemotherapy. The aim of this study was to determine the effect of melatonin against ototoxicity in rats treated with cisplatin. MATERIALS AND METHODS: Rats were randomly divided into four groups (saline, melatonin, cisplatin+saline, and melatonin+cisplatin). Distortion-product otoacoustic emission (DPOAE) measurements were carried out on days 1 and 8. RESULTS: There was a decrease in DPOAE amplitudes in the animals that received cisplatin (10 mg/kg); however, the group treated with cisplatin+melatonin presented DPOAE amplitudes comparable to those of the control groups. CONCLUSION: Melatonin can be used as an adjuvant tumor treatment due to its ability to decrease cisplatin-induced ototoxicity.

Distortion product otoacoustic emissions: Sensitive measures of tympanic -membrane perforation and healing processes in a gerbil model.

Distortion product otoacoustic emissions (DPOAEs) evoked by two pure tones carry information about the mechanisms that generate and shape them. Thus, DPOAEs hold promise for providing powerful noninvasive diagnostic details of cochlear operations, middle ear (ME) transmission, and impairments. DPOAEs are sensitive to ME function because they are influenced by ME transmission twice, i.e., by the inward-going primary tones in the forward direction and the outward traveling DPOAEs in the reverse direction. However, the effects of ME injuries on DPOAEs have not been systematically characterized. The current study focused on exploring the utility of DPOAEs for examining ME function by methodically characterizing DPOAEs and ME transmission under pathological ME conditions, specifically under conditions of tympanic-membrane (TM) perforation and spontaneous healing. Results indicated that DPOAEs were measurable with TM perforations up to ∼50%, and DPOAE reductions increased with increasing size of the TM perforation. DPOAE reductions were approximately flat across test frequencies when the TM was perforated about 10% (<1/8 of pars tensa) or less. However, with perforations greater than 10%, DPOAEs decreased further with a low-pass filter shape, with ∼30 dB loss at frequencies below 10 kHz and a quick downward sloping pattern at higher frequencies. The reduction pattern of DPOAEs across frequencies was similar to but much greater than, the directly measured ME pressure gain in the forward direction, which suggested that reduction in the DPOAE was a summation of losses of ME ear transmission in both the forward and reverse directions. Following 50% TM perforations, DPOAEs recovered over a 4-week spontaneously healing interval, and these recoveries were confirmed by improvements in auditory brainstem response (ABR) thresholds. However, up to 4-week post-perforation, DPOAEs never fully recovered to the levels obtained with normal intact TM, consistent with the incomplete recovery of ABR thresholds and ME transmission, especially at high-frequency regions, which could be explained by an irregularly dense and thickened healed TM. Since TM perforations in patients are commonly caused by either trauma or infection, the present results contribute towards providing insight into understanding ME transmission under pathological conditions as well as promoting the application of DPOAEs in the evaluation and diagnosis of deficits in the ME-transmission system.

Effects of selective auditory-nerve damage on the behavioral audiogram and temporal integration in the budgerigar.

Auditory-nerve fibers are lost steadily with age and as a possible consequence of noise-induced glutamate excitotoxicity. Auditory-nerve loss in the absence of other cochlear pathologies is thought to be undetectable with a pure-tone audiogram while degrading real-world speech perception (hidden hearing loss). Perceptual deficits remain unclear, however, due in part to the limited behavioral capacity of existing rodent models to discriminate complex sounds. The budgerigar is an avian vocal learner with human-like behavioral sensitivity to many simple and complex sounds and the capacity to mimic speech. Previous studies in this species show that intracochlear kainic-acid infusion reduces wave 1 of the auditory brainstem response by 40-70%, consistent with substantial excitotoxic auditory-nerve damage. The present study used operant-conditioning procedures in trained budgerigars to quantify kainic-acid effects on tone detection across frequency (0.25-8 kHz; the audiogram) and as a function of duration (20-160 ms; temporal integration). Tone thresholds in control animals were lowest from 1 to 4 kHz and decreased with increasing duration as in previous studies of the budgerigar. Behavioral results in kainic-acid-exposed animals were as sensitive as in controls, suggesting preservation of the audiogram and temporal integration despite auditory-nerve loss associated with up to 70% wave 1 reduction. Distortion-product otoacoustic emissions were also preserved in kainic-acid exposed animals, consistent with normal hair-cell function. These results highlight considerable perceptual resistance of tone-detection performance with selective auditory-nerve loss. Future behavioral studies in budgerigars with auditory-nerve damage can use complex speech-like stimuli to help clarify aspects of auditory perception impacted by this common cochlear pathology.