Auditory Brainstem Response Waveforms Research Articles

Factors influencing auditory brainstem response changes in infants

BackgroundTo elucidate the factors influencing auditory brainstem response (ABR) threshold improvement in infants. MethodsThis retrospective study included 626 infants who underwent ABR at the our Health and Medical Center between 2016 and 2020. Preliminary assessment indicated that 352 infants had an ABR threshold ≥40 dBnHL in both ears. A second ABR examination was conducted 5 months after delivery. The participants were divided into the improved (improvement ≥20 dBnHL) and unchanged (improvement <20 dBnHL) groups. The associations between risk factors were evaluated. Furthermore, we measured and compared the latencies of waves I, III, and V between participants with normal hearing and those in the improved and unchanged groups. ResultsThe improved and unchanged groups consisted of 185 and 167 participants, respectively. ABR deterioration occurred in one infant with unilateral congenital cytomegalovirus-associated hearing loss. Binary logistic regression analysis revealed that the presence of otitis media with effusion and Down syndrome were factors contributing to ABR threshold improvement. In the ABR waveform analysis, patients in the improved group who had otitis media with effusion exhibited prolonged latencies of waves I, III, and V. Conversely, patients in the unchanged group who had Down syndrome showed shortened I–V interval. ConclusionsHalf of the infants tested the second time showed improvement in ABR threshold. Children with congenital syndromes (such as Down syndrome) or otitis media with effusion should undergo a second ABR examination or other auditory assessments to ensure an accurate diagnosis of hearing loss.

Computational model for synthesizing auditory brainstem responses to assess neuronal alterations in aging and autistic animal models.

This study presents a novel computational model of the auditory brainstem, capable of synthesizing auditory brainstem response (ABR) traces by simulating large-scale neuronal activities. Addressing limitations of traditional ABR measurements, the model links ABR waveform features to underlying neuronal properties. Validated using empirical ABRs from animal models of autism and aging, the model accurately reproduced observed ABR alterations, revealing influences of myelin deficits and hyperexcitability in Fragile X syndrome, and degraded inhibitory activity in aging. These findings, supported by experimental data, demonstrate the model's potential for predicting changes in auditory brainstem physiology and guiding further physiological investigations, thus advancing our understanding of auditory neural processes.

Auditory brainstem response audiometry in tauopathy mouse model of human Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder in which changes in hearing sensitivity precede cognitive decline. Despite a well-known link between dementia and hearing loss, few AD model mouse lines have hearing characterized. We screened for hearing loss using auditory brainstem responses (ABR) in young (3-4 months) and aging (9-10 months) mice with a P301S tauopathy (PS19 mice). Compared to wild types, aging PS19 mice did not show accelerated hearing loss but did show latency differences in centrally generated ABR waveform components. These results suggest that tauopathy causes mild central auditory dysfunction in the absence of overt hearing loss.

Automatic Recognition of Auditory Brainstem Response Waveforms Using a Deep Learning-Based Framework.

Recognition of auditory brainstem response (ABR) waveforms may be challenging, particularly for older individuals or those with hearing loss. This study aimed to investigate deep learning frameworks to improve the automatic recognition of ABR waveforms in participants with varying ages and hearing levels. The research used a descriptive study design to collect and analyze pure tone audiometry and ABR data from 100 participants. The research was conducted at a tertiary academic medical center, specifically at the Clinical Audiology Center of Tsinghua Chang Gung Hospital (Beijing, China). Data from 100 participants were collected and categorized into four groups based on age and hearing level. Features from both time-domain and frequency-domain ABR signals were extracted and combined with demographic factors, such as age, sex, pure-tone thresholds, stimulus intensity, and original signal sequences to generate feature vectors. An enhanced Wide&Deep model was utilized, incorporating the Light-multi-layer perceptron (MLP) model to train the recognition of ABR waveforms. The recognition accuracy (ACC) of each model was calculated for the overall data set and each group. The ACC rates of the Light-MLP model were 97.8%, 97.2%, 93.8%, and 92.0% for Groups 1 to 4, respectively, with a weighted average ACC rate of 95.4%. For the Wide&Deep model, the ACC rates were 93.4%, 90.8%, 92.0%, and 88.3% for Groups 1 to 4, respectively, with a weighted average ACC rate of 91.0%. Both the Light-MLP model and the Wide&Deep model demonstrated excellent ACC in automatic recognition of ABR waveforms across participants with diverse ages and hearing levels. While the Wide&Deep model's performance was slightly poorer than that of the Light-MLP model, particularly due to the limited sample size, it is anticipated that with an expanded data set, the performance of Wide&Deep model may be further improved.

Investigating the Effects of Level-Specific CE-Chirp on Auditory Brainstem Response Waves in Normal Hearing Infants.

Auditory brainstem response (ABR) to the level-specific (LS) CE-Chirp has been reported to provide optimum neural synchrony along cochlear partitions, theoretically improving ABR waveform resolution. Despite this promising finding, limited studies have been conducted to contrast the results between LS CE-Chirp and Click stimuli. The current study aimed to compare the results of ABR between the two stimuli (Click and LS CE-Chirp). Sixty-seven normal-hearing infants, both with and without risk factors, aged less than 7 months old, participated in this study. The ABR test was conducted at 70 dBnHL using 33.3 stimulus repetition rates with both Click and LS CE-Chirp stimuli. The signal averaging was stopped at a maximum fixed signal average of 2,500 sweeps. Data were statistically compared between the two stimuli using the Wilcoxon signed-rank test. The waves I and V ABRs elicited by LS CE-Chirp exhibited significantly larger amplitudes than the Click stimulus. However, the amplitude of wave III and absolute latencies were similar in both stimuli at a supra-threshold level. LS CE-Chirp has the advantage of larger amplitudes than the ABR from Click at the supra-threshold level (70 dBnHL) in normal-hearing infants.

Gaussian Processes for Hearing Threshold Estimation Using Auditory Brainstem Responses.

The Auditory Brainstem Response (ABR) plays an important role in diagnosing and managing hearing loss, but can be challenging and time-consuming to measure. Test times are especially long when multiple ABR measurements are needed, e.g., when estimating hearing threshold at a range of frequencies. While many detection methods have been developed to reduce ABR test times, the majority were designed to detect the ABR at a single stimulus level and do not consider correlations in ABR waveforms across levels. These correlations hold valuable information, and can be exploited for more efficient hearing threshold estimation. This was achieved in the current work using a Gaussian Process (GP), i.e., a Bayesian approach for non-linear regression. The function to estimate with the GP was the ABR's amplitude across stimulus levels, from which hearing threshold was ultimately inferred. Active learning rules were also designed to automatically adjust the stimulus level and efficiently locate hearing threshold. Simulation results show test time reductions of up to ∼50% for the GP compared to a sequentially applied Hotelling's T2 test, which does not consider correlations across ABR waveforms. A case study was also included to briefly assess the GP approach in ABR data from an adult volunteer.

Inter-rater reliability of auditory brainstem response waveforms elicited by complex stimuli

Abstract Objective: The objective of this study was to assess the inter-rater reliability of peak marking for the frequency following the response portion of auditory brainstem response (ABR) waveforms elicited by complex stimuli. Materials and Methods: ABR testing was carried out on 30 adult participants with normal hearing, which generated a data set of 60 click-evoked waveforms and 60/da/-evoked waveforms. Three audiologists marked peaks for both click and/da/evoked ABR waveform data, derived from 30 participants aged 18–30 years. To assess inter-rater reliability, a two-way, random effects, single-measure model was used to calculate the intraclass correlation coefficients (ICCs). Results: The ICCs were ≥0.89 for peaks I, III, and V of the click-evoked waveforms. For the/da/evoked waveforms, the ICCs were rated good to high (≥0.83) for peaks V, A, E, F, and O, fair (0.75) for peak D but poor (≥0.45) for peak C. Conclusion: Investigations of reliability of waveform marking should be undertaken before using complex stimuli for ABR testing to prevent premature adoption of screening or diagnostic tools.

Auditory brainstem response (ABR) waveform analysis program

Auditory brainstem responses (ABR) are a high-throughput assessment of auditory function. Many studies determine changes to the threshold at frequencies that span the normal hearing range of their test subjects, but fewer studies evaluate changes in waveform morphology. The goal of developing this program was to make a user-friendly semiautomatic peak-detection algorithm to encourage widespread analysis of the amplitudes and latencies of the ABR, which may yield informative details about the integrity of the auditory system with development, aging, genetic manipulations, or damaging conditions. This method incorporates automated peak detection with manual override and inter-rater validation to calculate the amplitude and latency for waves 1–5, as well as interpeak latencies and amplitude ratios between waves. The output includes raw data and calculations in a format compatible with graphical and statistical software.•The method yields a high-throughput peak-detection algorithm with manual override and inter-rater capabilities to streamline ABR waveform analysis.•Data output includes amplitudes, latencies, amplitude ratios, and interpeak latencies for generation of input-output curves.•While complete automation of peak detection with this tool is dependent on good signal-to-noise ratios, relevant amplitude and latency calculations are fully automated, and manual spot-checking is simplified to significantly reduce the time to analyze waveforms.

Aging leads to impairment of spatial hearing abilities in the Mongolian Gerbil

Aging in humans is known to affect spatial hearing and speech in noise recognition, often even when hearing thresholds are normal. The Mongolian Gerbil (Meriones unguiculatus) can provide a model organism to investigate these changes. We performed auditory brainstem responses (ABRs), prepulse inhibition of the acoustic startle (PPI) behavior, and cochlear histology to assess age-related changes of the gerbil auditory brainstem. Aging (&amp;gt;33month) gerbils showed reduced ABR waveform amplitudes compared to young gerbils (2-10 months). Aging gerbils also show a reduced amplitude of the binaural interaction component (BIC), a biomarker for spatial hearing. However, ABR thresholds were not significantly different between cohorts. Aging gerbils showed impaired performance in our behavior tasks: young gerbils detected shorter gaps in noise and smaller minimum audible angles than aging animals, indicating that aging impairs temporal and spatial hearing abilities. Cochlear histology revealed an increase in cochlear synaptopathy in aging animals, revealing a potential mechanism for age-related dysfunction in the auditory pathway. Taken together, these data reveal structural and physiological changes in the auditory brainstem that underlie spatial hearing deficits in the gerbil. [Work supported by R01-DC017924.]

A multi-channel EEG mini-cap can improve reliability for recording auditory brainstem responses in chinchillas

Background:Disabling hearing loss affects nearly 466 million people worldwide (World Health Organization). The auditory brainstem response (ABR) is the most common non-invasive clinical measure of evoked potentials, e.g., as an objective measure for universal newborn hearing screening. In research, the ABR is widely used for estimating hearing thresholds and cochlear synaptopathy in animal models of hearing loss. The ABR contains multiple waves representing neural activity across different peripheral auditory pathway stages, which arise within the first 10 ms after stimulus onset. Multi-channel (e.g., 32 or higher) caps provide robust measures for a wide variety of EEG applications for the study of human hearing. However, translational studies using preclinical animal models typically rely on only a few subdermal electrodes. New Method:We evaluated the feasibility of a 32-channel rodent EEG mini-cap for improving the reliability of ABR measures in chinchillas, a common model of human hearing. Results:After confirming initial feasibility, a systematic experimental design tested five potential sources of variability inherent to the mini-cap methodology. We found each source of variance minimally affected mini-cap ABR waveform morphology, thresholds, and wave-1 amplitudes. Comparison with Existing Method:The mini-cap methodology was statistically more robust and less variable than the conventional subdermal-needle methodology, most notably when analyzing ABR thresholds. Additionally, fewer repetitions were required to produce a robust ABR response when using the mini-cap. Conclusions:These results suggest the EEG mini-cap can improve translational studies of peripheral auditory evoked responses. Future work will evaluate the potential of the mini-cap to improve the reliability of more centrally evoked (e.g., cortical) EEG responses.

Quantitative Threshold Determination of Auditory Brainstem Responses in Mouse Models.

The auditory brainstem response (ABR) is a scalp recording of potentials produced by sound stimulation, and is commonly used as an indicator of auditory function. However, the ABR threshold, which is the lowest audible sound pressure, cannot be objectively determined since it is determined visually using a measurer, and this has been a problem for several decades. Although various algorithms have been developed to objectively determine ABR thresholds, they remain lacking in terms of accuracy, efficiency, and convenience. Accordingly, we proposed an improved algorithm based on the mutual covariance at adjacent sound pressure levels. An ideal ABR waveform with clearly defined waves I-V was created; moreover, using this waveform as a standard template, the experimentally obtained ABR waveform was inspected for disturbances based on mutual covariance. The ABR testing was repeated if the value was below the established cross-covariance reference value. Our proposed method allowed more efficient objective determination of ABR thresholds and a smaller burden on experimental animals.

Short-term outcomes of infants with hyperbilirubinemia-associated auditory neuropathy spectrum disorder in neonatal intensive care unit

Hyperbilirubinemia is a high-risk factor for auditory neuropathy spectrum disorder (ANSD) as well as hearing loss in general. This study described the outcomes of hyperbilirubinemia-associated ANSD infants diagnosed in hearing screening in the neonatal intensive care unit (NICU).A total of 578 children with hyperbilirubinemia admitted to the NICU between October 2020 and October 2021 were included in this study. The distortion product otoacoustic emission (DPOAE) and automatic auditory brainstem response (AABR) were combined for hearing screening, and those who failed the DPOAE or/and AABR underwent an auditory brainstem response (ABR) test. Infants with ANSD were followed up for 12 months.Forty infants (40/578, 6.9%) failed the DPOAE or/and AABR tests, of which, 13 (13/578, 2.2%) were diagnosed as ANSD, and 27 (27/578, 4.7%) were diagnosed as having sensorineural hearing loss (SNHL). Of the 13 ANSD infants followed up for 12 months, 7 recovered, 3 improved, 3 did not recover, and 1 was lost, equating to improved or recovered hearing in 75% (9/12) of ANSD infants at 12 months of age. Moreover, the maximum bilirubin in recovered or improved ANSD infants was 408.6 ± 129.0 μmol/L, while the maximum bilirubin in unrecovered ANSD infants was 749.3 ± 323.0 μmol/L. Furthermore, poorly differentiated and absent ABR waveforms were observed in 6 and 14 ears at 1 month, 2 ears were lost, 6 (6/6, 100.0%) and 6 (6/12, 50.0%) ears were recovered or improved at 12 months of age.s: The incidence of hyperbilirubinemia associated-ANSD was 2.2% of infants screened in the NICU. ANSD caused by hyperbilirubinemia may be transient, with most infants improving or recovering hearing by 12 months of age. Infants with poorly differentiated ABR waveforms and low bilirubin concentration are more likely to recover and hearing aids are not recommended in hyperbilirubinemia-associated ANSD below 12 months of age.

Auditory brainstem response in autistic children: implications for sensory processing

Purpose Autistic individuals frequently experience sensory processing difficulties. Such difficulties can significantly impact important functions and quality of life. We are only beginning to understand the neural mechanisms of atypical sensory processing. However, one established way to measure aspects of auditory function is the auditory brainstem response (ABR). While ABR has been primarily hypothesised thus far as a means of early detection/diagnosis in autism, it has the potential to aid in examining sensory processing in this population. Method Thus, we investigated standard ABR waveform characteristics in age-matched groups of autistic and typically developing children during various stimulus and intensity conditions. We also examined within ear waveform cross-correlations and inter-aural cross-correlations (IACC) to assess replicability and synchrony of participants’ ABRs, which was a novel approach to ABR analysis in this population. Results We observed longer peak latencies (esp. wave III and V) and interpeak latencies in the autism and typically developing groups in different conditions. There were no statistically significant results in cross-correlation or IACC. Conclusions These results suggest that brainstem auditory function may differ slightly, but is mostly similar, between autistic and typically developing children. We discuss these findings in terms of their implications for sensory processing and future utility.

Characteristics of auditory brainstem response in wild yellow grouper Epinephelus awoara

Auditory brainstem response (ABR) technology is used to set up a fish auditory threshold detection system, and the auditory threshold of wild yellow grouper Epinephelus awoara caught in the Taiwan Strait is studied. The ABRs of 10 wild yellow groupers (TL150-200 mm) to 12 different frequencies of sound stimulation from 100 to 2000 Hz are recorded and analyzed. The results show that the auditory threshold of wild yellow grouper fish increases with the increase of frequency in the frequency of 200-2000Hz. The fish is sensitive to low frequency sound signal of 100-300Hz with the most sensitive frequency of 200Hz, and the auditory threshold is 90 dB re 1μPa. The ABR waveform shows three periods: response period, real hearing period and extension period. In the range of 100-2000Hz, the response time decreases with the increase of frequency at the same sound pressure level. At the same frequency, the response time increases with the decrease of sound pressure level. The first amplitude sound pressure of real hearing period is between 50-150nv, and the real hearing period contains the greatest amplitude. When the greatest amplitude is about 50nv and the next sound pressure level is below 50nv, the sound pressure level is the auditory threshold. The extension period is proportional to the response period.

Assessing Medial Olivocochlear Reflex Strengths via Auditory Brainstem Response: Measurement and Variability in Normal-Hearing Individuals

Optimal measurement settings to measure the medial olivocochlear reflex (MOCR) in humans have not yet been defined. The purpose of this study was to advance the representation of the MOCR in auditory brainstem response (ABR) as an addition to the current diagnostic portfolio. Twelve female and 14 male normal-hearing adults participated in the study. Potential effects of a contralateral acoustic stimulus (CAS) on amplitude changes were investigated by recording ABR waveform profiles on the left side at click intensities of 50/60/70 dB nHL with and without CAS (60 dB SPL). Secondly, to detect potential chronological order influences, measurement settings were rearranged on the right side and measurements were repeated. Additionally, ABR thresholds were recorded with and without a CAS in 10 patients. When the effect of contralateral suppression was analyzed on the basis of amplitude changes, there was a change under administration of the CAS signal that was statistically significant. Interestingly, the order of recordings affected the degree of amplitude change. In three out of 10 patients, reproducible suppression effects on ABR thresholds were detectable upon CAS presentation. To our knowledge, this is the largest study dealing with the recording of the MOCR elicited by a contralateral noise via ABR in normal-hearing individuals. Effects of MOCR are measurable via amplitude changes upon CAS administration. Chronological orders influence the impact of this effect on amplitude changes. Optimal measurement settings have not yet been defined. However, experiments such as this study may help to further improve measurements, and thus advance the representation of the MOC reflex in ABR as an addition to the current diagnostic portfolio.

Towards Optimizing the Quality of Long-Term Physiological Signals Monitoring by Using Anhydrous Carbon Paste Electrode.

Long-term physiological signal monitoring is very important for the diagnosis of health conditions that occur randomly and cannot be easily detected by a short period of a hospital visit. However, the conventional wet electrodes suffered from the problem of signal quality degradation due to the gradual dehydration of the conductive gel. An anhydrous carbon paste electrode (CPE) constructed by a composite of carbon black and polydimethylsiloxane was proposed to enable long-term physiological signal monitoring without signal quality degradation as time elapses. The performance was systematically compared with conventional electrodes when measuring long-term physiological signals including electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG) and auditory brainstem response (ABR). The proposed CPE showed more stable skin-electrode impedance and higher signal qualities as the monitoring time increased up to 48 days, with signal-to-noise ratios (SNRs) of 16.43 ± 10.39 dB higher for ECG and 24.30 ± 7.79 dB higher for EMG when compared with wet electrodes. The CPE method could also obtain more consistent ABR waveform morphologies and could measure EEG under sweating conditions. It is believed that the proposed CPE could be a potential candidate for durable and robust wearable sensors systems on long-term physiological signal monitoring.

Semi-Automated Analysis of Peak Amplitude and Latency for Auditory Brainstem Response Waveforms Using R.

Many reports in the last 15 years have assessed changes in the auditory brainstem response (ABR) waveform after insults such as noise exposure. Common changes include reductions in the peak 1 amplitude and the relative latencies of the later peaks, as well as increased central gain, which is reflected by a relative increase in the amplitudes of the later peaks compared to the amplitude of peak 1. Many experimenters identify the peaks and troughs visually to assess their relative heights and latencies, which is a laborious process when the waveforms are collected in 5 dB increments throughout the hearing range for each frequency and condition. This paper describes free routines that may be executed in the open-source platform R with the RStudio interface to semi-automate the measurements of the peaks and troughs of auditory brainstem response (ABR) waveforms. The routines identify the amplitudes and latencies of peaks and troughs, display these on a generated waveform for inspection, collate and annotate the results into a spreadsheet for statistical analysis, and generate averaged waveforms for figures. In cases when the automated process misidentifies the ABR waveform, there is an additional tool to assist in correction. The goal is to reduce the time and effort needed to analyze the ABR waveform so that more researchers will include these analyses in the future.

Semi-Automated Analysis of Peak Amplitude and Latency for Auditory Brainstem Response Waveforms Using R

Semi Automated Analysis Peak Amplitude Latency For Auditory Brainstem - Video. JoVE publishes peer-reviewed scientific video protocols to accelerate biological, medical, chemical and physical research. Watch our scientific video articles. JoVE is the world-leading producer and provider of science videos with the mission to improve scientific research, scientific journals, and education. Millions of scientists, educators and students at thousands of universities, colleges, hospitals and biopharmaceutical companies worldwide use JoVE for their research, teaching and learning.

Visualizing Contralateral Suppression of Hearing Sensitivity via Acoustic and Electric Brainstem Audiometry in Bimodal Cochlear Implant Patients: A Feasibility Study

Introduction: The medial olivocochlear reflex (MOCR) is a part of the binaural processing strategies and influences the efferent auditory pathway in normal-hearing individuals. Patients with asymmetric hearing loss often benefit from a bimodal hearing solution with a cochlear implant (CI) and a hearing aid (HA). However, hearing performances may vary with some surprisingly high- or low-performing CI/HA users. A potential role of the MOCR among these patients warrants further investigation. Otoacustics emissions are an established method to visualize the reflex; however, this technique implies some disadvantages. To visualize the MOCR via auditory brainstem response (ABR) could be a promising alternative. Methods: Twenty-three bimodal CI/HA users were enrolled. Experimental setup was as follows: I. electrical ABR on the CI side was recorded with and without simultaneous contralateral noise signal at the HA side, II. acoustic ABR was recorded on the HA side with and without simultaneous contralateral noise at the CI side. Brainstem thresholds and amplitudes of waveforms I–V with and without contralateral noise were compared. Potential correlations of patient-related factors and hearing performances were analysed. Results: In four individuals, a reduction of brainstem audiometry thresholds could be observed at the acoustic brainstem audiometry. In these cases, results could be reproduced. Summarizing ABR measurements at the HA side of all individuals, no relevant changes of ABR thresholds (dB nHL) or waveform amplitude reductions (nV) could be observed irrespective of the presence or absence of a contralateral suppression signal. Conclusion: Threshold changes of acoustic ABR upon presentation of a contralateral suppression signal could not generally be measured in bimodal CI users. However, in a subgroup, a highly reproducible effect was demonstrated if a contralateral suppression signal was applied. A reactivated rather than rehabilitated MOCR may have accounted for this effect in this subgroup. One could speculate that in these patients, bimodal fitting could be affected by the MOCR efferents.

Longitudinal analysis of auditory dysfunction in Alzheimer’s disease mice 5xFAD

AbstractBackgroundThere is no cure for AD at this moment. All available therapies require accurate diagnosis and staging of AD to ensure proper strategy. Current diagnosis methods rely on high‐cost technologies with radioactive agents, and those are not necessarily included in regular health screenings. Thus, a low‐cost, non‐invasive approach of AD analysis is in great need. The comorbidity between Alzheimer’s disease and hearing loss has been shown to be significant. Beyond hearing loss, AD patients also showed auditory processing disorders. However, it remains unclear if auditory deficits can be a good biomarker for AD analysis, especially for early stages.Method5xFAD animals were bred in CBA/B6 hybrid background to compensate the hearing loss deficits in C57/B6 strain and only F1 animals were used in this study. The auditory features were monitored by Auditory Brainstem Response (ABR) test and Distortion Product Otoacoustic Emission (DPOAE) test at 3, 6, 9 and 12‐month‐old, which correlate to young ‐ middle age of human lifespan. Their anti‐masking ability was evaluated by masking ABR and notched noise ABR in 3 and 12‐month‐old animals. Fluorescent immunostaining was performed to evaluate anatomical change in cochlea.ResultAD animals showed accelerated age‐related hearing loss comparing to their WT littermates. The ABR threshold showed significant change at lower frequencies first, then extended to all testing frequencies. DPOAE threshold did not show significant change at any testing frequency. Aged AD animals showed significantly higher threshold increase in masking ABR and notched‐noise ABR. In addition to the increased hearing threshold, ABR waveform abnormalities were also observed in the AD animals. Longitudinal analysis revealed that ABR waveform abnormalities develop along with the progression of AD. Those abnormalities suggest auditory neuropathy and auditory processing deficits in AD animals. Histology analysis showed no significant change in synapse number or efference morphology.ConclusionAuditory dysfunction is a possible outcome of AD, and more likely reflecting the anatomical changes in central nervous system rather than periphery. Auditory dysfunction is a good candidate as a biomarker for AD progression at early stages.