The spatial organization of ascending auditory pathway microstructural maturation from infancy through adolescence using a novel fiber tracking approach.

Auditory perception is established through experience-dependent stimuli exposure during sensitive developmental periods; however, little is known regarding the structural development of the central auditory pathway in humans. The present study characterized the regional developmental trajectories of the ascending auditory pathway from the brainstem to the auditory cortex from infancy through adolescence using a novel diffusion MRI-based tractography approach and along-tract analyses. We used diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) to quantify the magnitude and timing of auditory pathway microstructural maturation. We found spatially varying patterns of white matter maturation along the length of the tract, with inferior brainstem regions developing earlier than thalamocortical projections and left hemisphere tracts developing earlier than the right. These results help to characterize the processes that give rise to functional auditory processing and may provide a baseline for detecting abnormal development.

[A study of mismatched negative in normal hearing patients of different ages].

Objective:To study the characteristics of Mismatch negativity（MMN） in normal hearing patients of different ages, and to compare the MMN of normal hearing subjects at different ages to explore the differences in MMN between different ages. Methods:MMN test was performed on both ears using the classic Oddball mode. A frequency of 1 000 Hz（standard stimuli） and 2 000 Hz（deviant stimuli） was used to evoked the MMN. According to different age groups: the juvenile group（7-17 years old）, the youth group（18-44 years old）, the middle-aged group（45-59 years old）, and the elderly group（60-75 years old）, with 25 cases in each group. The MMN characteristics of normal hearing subjects in different age groups were analyzed statistically and the differences between groups were compared. All subjects underwent pure tone threshold test, tympanic reactance test and ABR test before MMN test. Results:MMN waveform could be elicited from both ears of 100 subjects. Among them, the average latency of the juvenile group was（159.70±20.34） ms while the average amplitude was（4.34±2.26） µV, For the youth group, the average latency was（166.01±28.67） ms and the average amplitude was（3.70±2.28） µV. Then in the middle-aged group, the average latency was（175.16±37.24） ms, meanwhile, the average amplitude was（2.69±0.84） µV. Finally, the elderly group has an average latency of（178.03±14.37） ms and an average amplitude of（2.11±0.70） µV. Therefore, there was no statistical difference in latency and amplitude between all groups（P>0.05）, and there was no statistical difference in latency and amplitude between left and right ears among all subjects as a whole（P>0.05）. However, when the left and right ears of all groups were compared, it was found that the latency between the left and right ears of the Juvenile group had statistical significance（P<0.05）, and the amplitude difference was not statistically significant（P>0.05）, while the latency and amplitude differences between the left and right ears of other groups had no statistical significance（P>0.05）. There were also no significant differences in latency and amplitude between men and women（P>0.05）. Conclusion:There was no statistically significant difference in the latency and amplitude of mismatched negative among normal hearing subjects of different ages, and no statistically significant difference in the MMN latency and amplitude between the left and right ears of subjects and between men and women. Therefore, the study inferred that the auditory cerebral cortex of subjects aged 7-75 years old maintained a stable state for a long time after maturity, and the latency and amplitude of mismatched negative waves were relatively stable. It is not affected by age, gender and ear side, and can stably reflect the auditory cortex function of the subjects. It has broad application prospects in clinical practice, and provides a reliable detection means for future research on the changes of the auditory cerebral cortex of patients, which is worthy of our further research and clinical promotion.

Soft Tissue Conduction Activates the Auditory Pathway in the Brain.

Soft tissue conduction is a mode of hearing which differs from air and bone conduction since the soft tissues of the body convey the audio-frequency vibrations to the ear. It is elicited by inducing soft tissue vibrations with an external vibrator applied to sites on the body or by intrinsic vibrations resulting from vocalization or the heartbeat. However, the same external vibrator applied to the skin sites also excites cutaneous mechanoreceptors, and attempts have been made to assist patients with hearing loss by audio-tactile substitution. The present study was conducted to assess the contribution of the auditory nerve and brainstem pathways to soft tissue conduction hearing. The study involved 20 normal hearing students, equipped with ear plugs to reduce the possibility of their response to air-conducted sounds produced by the external vibrator. Pure tone audiograms and speech reception (recognition) thresholds were determined in response to the delivery of the stimuli by a clinical bone vibrator applied to the cheek, neck and shoulder. Pure tone and speech recognition thresholds were obtained; the participants were able to repeat the words they heard by soft tissue conduction, confirming that the auditory pathways in the brain had been stimulated, with minimal involvement of the somatosensory pathways.

Multielectrode array use in insect auditory neuroscience to unravel the spatio-temporal response pattern in the prothoracic ganglion of Mecopoda elongata.

Mechanoreceptors in hearing organs transduce sound-induced mechanical responses into neuronal signals, which are further processed and forwarded to the brain along a chain of neurons in the auditory pathway. Bushcrickets (katydids) have their ears in the front leg tibia, and the first synaptic integration of sound-induced neuronal signals takes place in the primary auditory neuropil of the prothoracic ganglion. By combining intracellular recordings of the receptor activity in the ear, extracellular multichannel array recordings on top of the prothoracic ganglion and hook electrode recordings at the neck connective, we mapped the timing of neuronal responses to tonal sound stimuli along the auditory pathway from the ears towards the brain. The use of the multielectrode array allows the observation of spatio-temporal patterns of neuronal responses within the prothoracic ganglion. By eliminating the sensory input from one ear, we investigated the impact of contralateral projecting interneurons in the prothoracic ganglion and added to previous research on the functional importance of contralateral inhibition for binaural processing. Furthermore, our data analysis demonstrates changes in the signal integration processes at the synaptic level indicated by a long-lasting increase in the local field potential amplitude. We hypothesize that this persistent increase of the local field potential amplitude is important for the processing of complex signals, such as the conspecific song.

A Central Auditory Test reveals differences between drug treatment regimens in adults living with HIV.

OBJECTIVE: This exploratory study examined whether central auditory tests show differences between people living with HIV (PLWH) treated with two predominant antiretroviral drug therapy (ART) regimens. DESIGN: Cross-sectional. STUDY SAMPLE: 253 PLWH (mean age 39.8 years) from the Shanghai Public Health Clinical Centre, China. METHODS: The Hearing in Noise Test speech reception threshold (SRT) assessed central auditory function and the Montreal Cognitive Assessment (MoCA) assessed cognition. The relationship between ART regimen and SRT was evaluated with multivariable linear regression incorporating age, HIV duration, and peripheral hearing ability. Multivariable logistic regression was used to ascertain if SRT and ART regimen predicted MoCA impairment. RESULTS: The two predominant ART regimens differed by one drug (zidovudine or tenofovir). Participants taking the zidovudine-containing regimen had poorer SRT performance (p=.012) independent of age and hearing thresholds. MoCA scores did not differ between drug regimens, but a negative relationship was found between SRT and MoCA impairment (p=.048). CONCLUSIONS: ART regimens differed in their association with central auditory test performance likely reflecting neurocognitive changes in PLWH taking the zidovudine-containing regimen. Central auditory test performance also marginally predicted cognitive impairment, supporting further assessment of central auditory tests to detect neurocognitive deficits in PLWH.

Multiple Concurrent Predictions Inform Prediction Error in the Human Auditory Pathway.

The key assumption of the predictive coding framework is that internal representations are used to generate predictions on how the sensory input will look like in the immediate future. These predictions are tested against the actual input by the so-called prediction error units, which encode the residuals of the predictions. What happens to prediction errors, however, if predictions drawn by different stages of the sensory hierarchy contradict each other? To answer this question, we conducted two fMRI experiments while female and male human participants listened to sequences of sounds: pure tones in the first experiment and frequency-modulated sweeps in the second experiment. In both experiments, we used repetition to induce predictions based on stimulus statistics (stats-informed predictions) and abstract rules disclosed in the task instructions to induce an orthogonal set of (task-informed) predictions. We tested three alternative scenarios: neural responses in the auditory sensory pathway encode prediction error with respect to (1) the stats-informed predictions, (2) the task-informed predictions, or (3) a combination of both. Results showed that neural populations in all recorded regions (bilateral inferior colliculus, medial geniculate body, and primary and secondary auditory cortices) encode prediction error with respect to a combination of the two orthogonal sets of predictions. The findings suggest that predictive coding exploits the non-linear architecture of the auditory pathway for the transmission of predictions. Such non-linear transmission of predictions might be crucial for the predictive coding of complex auditory signals like speech.Significance Statement Sensory systems exploit our subjective expectations to make sense of an overwhelming influx of sensory signals. It is still unclear how expectations at each stage of the processing pipeline are used to predict the representations at the other stages. The current view is that this transmission is hierarchical and linear. Here we measured fMRI responses in auditory cortex, sensory thalamus, and midbrain while we induced two sets of mutually inconsistent expectations on the sensory input, each putatively encoded at a different stage. We show that responses at all stages are concurrently shaped by both sets of expectations. The results challenge the hypothesis that expectations are transmitted linearly and provide for a normative explanation of the non-linear physiology of the corticofugal sensory system.

Signal processing and stimulation potential within the ascending auditory pathway: a review.

The human auditory system encodes sound with a high degree of temporal and spectral resolution. When hearing fails, existing neuroprosthetics such as cochlear implants may partially restore hearing through stimulation of auditory neurons at the level of the cochlea, though not without limitations inherent to electrical stimulation. Novel approaches to hearing restoration, such as optogenetics, offer the potential of improved performance. We review signal processing in the ascending auditory pathway and the current state of conventional and emerging neural stimulation strategies at various levels of the auditory system.

Suboptimal postnatal function of brainstem auditory pathway in late preterm infants who do not have major perinatal and postnatal complications.

OBJECTIVES: To examine postnatal functional status of the brainstem auditory pathway in late preterm infants and detect any postnatal auditory abnormality. METHODS: Thirty preterm infants born at 33-36 weeks gestation were studied three months after term. None had major perinatal and postnatal complications to minimize confounding effects. Brainstem auditory evoked responses were recorded with 21-91/s clicks. RESULTS: Compared with postnatal age-matched normal term infants, the late preterm infants did not manifest any major abnormalities in brainstem auditory evoked responses at conventionally used 21/s clicks. At higher click rates, however, the late preterm infants manifested a moderate prolongation in BAER wave V latency. All interpeak intervals tended to be prolonged at higher click rates. The I-V interval was significantly prolonged at 51/s and particularly at 91/s clicks. Both the I-III and III-V intervals were significantly prolonged at 91/s. The late preterm infants also manifested reduced amplitudes of BAER waves III and V at most click rates. CONCLUSION: The central components of the brainstem auditory evoked responses were abnormal at higher click rates three months after term in the late preterm infants. Postnatal brainstem auditory function is suboptimal in late preterm infants without major complications. This suboptimal brainstem auditory function may not be clearly shown at term or an earlier stage, but can be shown later. Late preterm infants, although they may not have major complications, should be followed for later auditory development, providing valuable information for improving postnatal care.

Detection of Spatially Localized Sounds Is Robust to Saccades and Concurrent Eye Movement-Related Eardrum Oscillations (EMREOs).

Hearing is an active process, and recent studies show that even the ear is affected by cognitive states or motor actions. One example are movements of the eardrum induced by saccadic eye movements, known as "eye movement-related eardrum oscillations" (EMREOs). While these are systematically shaped by the direction and size of saccades, the consequences of saccadic eye movements and their resulting EMREOs for hearing remain unclear. We here studied their implications for the detection of near-threshold clicks in human participants. Across three experiments, sound detection was not affected by their time of presentation relative to saccade onset, by saccade amplitude or direction. While the EMREOs were shaped by the direction and amplitude of the saccadic movement, inducing covert shifts in spatial attention did not affect the EMREO, suggesting that this signature of active sensing is restricted to overt changes in visual focus. Importantly, in our experiments, fluctuations in the EMREO amplitude were not related to detection performance, at least when monaural cues are sufficient. Hence, while eye movements may shape the transduction of acoustic information, the behavioral implications remain to be understood.SIGNIFICANCE STATEMENT Previous studies suggest that oculomotor behavior may influence how we perceive spatially localized sounds. Recent work has introduced a new perspective on this question by showing that eye movements can directly modulate the eardrum. Yet, it remains unclear whether this signature of active hearing accounts for behavioral effects. We here show that overt but not covert changes in visual attention modulate the eardrum, but these modulations do not interfere with the detection of sounds. Our results provide a starting point to obtain a deeper understanding about the interplay of oculomotor behavior and the active ear.

Impact of inner ear malformation and cochlear nerve deficiency on the development of auditory-language network in children with profound sensorineural hearing loss.

Profound congenital sensorineural hearing loss (SNHL) prevents children from developing spoken language. Cochlear implantation and auditory brainstem implantation can provide partial hearing sensation, but language development outcomes can vary, particularly for patients with inner ear malformations and/or cochlear nerve deficiency (IEM&CND). Currently, the peripheral auditory structure is evaluated through visual inspection of clinical imaging, but this method is insufficient for surgical planning and prognosis. The central auditory pathway is also challenging to examine in vivo due to its delicate subcortical structures. Previous attempts to locate subcortical auditory nuclei using fMRI responses to sounds are not applicable to patients with profound hearing loss as no auditory brainstem responses can be detected in these individuals, making it impossible to capture corresponding blood oxygen signals in fMRI. In this study, we developed a new pipeline for mapping the auditory pathway using structural and diffusional MRI. We used a fixel-based approach to investigate the structural development of the auditory-language network for profound SNHL children with normal peripheral structure and those with IEM&CND under 6 years old. Our findings indicate that the language pathway is more sensitive to peripheral auditory condition than the central auditory pathway, highlighting the importance of early intervention for profound SNHL children to provide timely speech inputs. We also propose a comprehensive pre-surgical evaluation extending from the cochlea to the auditory-language network, showing significant correlations between age, gender, Cn.VIII median contrast value, and the language network with post-implant qualitative outcomes.

mRNA Abundance of Neurogenic Factors Correlates with Hearing Capacity in Auditory Brainstem Nuclei of the Rat.

Neural stem cells (NSCs) have previously been described up to the adult stage in the rat cochlear nucleus (CN). A decreasing neurogenic potential was observed with critical changes around hearing onset. A better understanding of molecular factors affecting NSCs and neurogenesis is of interest as they represent potential targets to treat the cause of neurologically based hearing disorders. The role of genes affecting NSC development and neurogenesis in CN over time on hearing capacity has remained unclear. This study investigated the mRNA abundance of genes influencing NSCs and neurogenesis in rats' CN over time. The CN of rats on postnatal days 6, 12, and 24 were examined. Real-time quantitative polymerase chain reaction arrays were used to compare mRNA levels of 84 genes relevant to NSCs and neurogenesis. Age- and hearing-specific patterns of changes in mRNA abundance of neurogenically relevant genes were detected in the rat CN. Additionally, crucial neurogenic factors with significant and relevant influence on neurogenesis were identified. The results of this work should contribute to a better understanding of the molecular mechanisms underlying the neurogenesis of the auditory pathway.

Effect of Contralateral Acoustic Stimulation on Temporal Processing Abilities in Individuals with Normal Hearing.

The aim of the article was to compare the conditions of silent and contralateral noise on the temporal processing parameters. A total of 40 participants (20 males and 20 females) were enrolled in the study with a mean age of 21.7 years, participants with normal hearing thresholds and no history of middle ear pathology were enrolled for the study. The temporal processing tests such as duration discrimination test, gap detection test, and temporal modulation transfer function tests were carried out in these 40 individuals in the two conditions of silent and contralateral noise using MATLAB. Statistical analysis was carried out using the SPSS version 25.0 were descriptive and inferential statistics were carried out. Data was normally distributed on the Shapiro-Wilk's test of normality due to which a paired t test was carried out to establish the nature of significance between the silent and contralateral noise condition. Results reveal the presence of significant difference (p < 0.01) between the groups for all the parameters of temporal resolution with contralateral noise condition performing better than silent condition for the parameters. There is a positive effect of the efferent auditory pathway on the temporal resolution parameters thus implying that speech perception in noise is improved in the presence of background noise for normal hearing individuals due to this effect.

Neurogenic Stem Cell Niche in the Auditory Thalamus: In Vitro Evidence of Neural Stem Cells in the Rat Medial Geniculate Body.

The medial geniculate body (MGB) is a nucleus of the diencephalon representing a relevant segment of the auditory pathway and is part of the metathalamus. It receives afferent information via the inferior brachium of the inferior colliculus and transmits efferent fibers via acoustic radiations to the auditory cortex. Neural stem cells (NSCs) have been detected in certain areas along the auditory pathway. They are of great importance as the induction of an adult stem cell niche might open a regenerative approach to a causal treatment of hearing disorders. Up to now, the existence of NSCs in the MGB has not been determined. Therefore, this study investigated whether the MGB has a neural stem cell potential. For this purpose, cells were extracted from the MGB of PND 8 Sprague-Dawley rats and cultured in a free-floating cell culture assay, which showed mitotic activity and positive staining for stem cell and progenitor markers. In differentiation assays, the markers ß-III-tubulin, GFAP, and MBP demonstrated the capacity of single cells to differentiate into neuronal and glial cells. In conclusion, cells from the MGB exhibited the cardinal features of NSCs: self-renewal, the formation of progenitor cells, and differentiation into all neuronal lineage cells. These findings may contribute to a better understanding of the development of the auditory pathway.

Effect of Electromagnetic Radiation from Mobile Phones on Auditory Brainstem Response.

Mobile phones are being used by around 70% of the global population. A simple non-invasive procedure to detect early impairment of the acoustic nerve and auditory pathway is by auditory brainstem response (ABR). It's a response to the sound stimulus generated from the brainstem in the form of electrical impulses. To determine the effect of long-term usage of mobile phones on auditory brainstem responses (ABRs). This Epidemiological, cross-sectional study was undertaken at a tertiary care hospital and includes 865 individuals aged between 18 to 45 years using mobile phone for > 2 years. Users were categorized into various groups according to the minutes of mobile usage per day, years of mobile usage and total duration of mobile phone use in dominant (mobile using) and non-Dominant (non-mobile using) ears. The changes in ABR were studied in each ear to ascertain the effect of EMF exposure due to chronic mobile phone use. Mean age of subjects was 27.01 years. (M: F = 1.57:1.0). Range of mobile phone usage was from 4 to 900 min/day, with mean as 85.94 min/day. No significant differences were seen between dominant and non-dominant ears in regard to amplitudes of wave I, III and V, latencies of wave I and V and Inter peak latency (IPL) of wave I-III, III-V and I-V. No statistically significant difference for I-III, III-V and I-V IPL were found b/w two groups/ears except for usage of mobile phone for > 180 min/day in wave I-V, usage for 0-4 years in wave I-III and I-V and net hours usage for > 1500 h in wave I-V. The mean IPL in all the waves increases with the increase in years of mobile usage and is maximum in all waves in > 12 years mobile users. The long-term exposure to EMF does induce measurable changes in ABRs. Amplitude and IPLs of ABR were found comparable between the dominant and non-dominant ears using mobile phones, except for those using mobile usage for > 180 min/day and with increasing years of usage of mobile phone. Therefore, prudent use of mobile phone should be encouraged for a shorter period of time and for essential purpose only.

Short-Term and Long-Term Stability of Medial Olivocochlear Reflex in Adults with Typical Hearing.

This study aimed to assess the stability of Medial Olivocochlear Reflex (MOCR) function in typical hearing adults with the use of Contralateral Suppression (CS) of Distortion Product Otoacoustic Emissions (DPOAEs). This study included fifty-three (90 ears) participants between the ages of 18-30. Participants were divided into 3 groups (Group A-daily stability, Group B-short-term stability, and Group C- long-term stability). For each group, 4 measurements (30 × 4 = 120sessions) were taken. Group A measurements were taken daily, Group B measurements were taken weekly and Group C measurements were taken monthly. DPOAEs and Contralateral Suppression of DPOAEs were measured for each group. Analyses indicated that Medial Olivocochlear Reflex (MOCR) measured through contralateral suppression of DPOAE was unstable. This result indicates a DPOAE-based measure of the MOCR was not repeated across time. A great deal has been learned using CS of DPOAEs to study medial efferent activation, but several unresolved methodological issues that could impact the data to produce poor stability across time. Those methodological issues need to be explored and researched in the future.

Evaluation of Auditory Temporal Discrimination Thresholds in Migraine Patients.

INTRODUCTION: Although vestibular migraine is well defined, the effects of migraine on the auditory system have not been clearly identified yet. The aim of this study was to determine the effect of migraine on the auditory system. METHODS: Migraine patients without hearing loss were included in the study. Group 1 consisted of patients with migraine pain, group 2 consisted of patients with migraine in the interictal period, and group 3 consisted of healthy volunteers with similar demographic characteristics to groups 1 and 2. Random gap detection test was applied to all 3 groups. Additionally, group 2 and group 3 patients were evaluated with the auditory cortical potentials and the mismatch negativity test. RESULTS: There was a statistically significant difference between the 3 groups in the random gap detection test. There was no statistically significant difference in auditory cortical potentials between group 2 and group 3; however, a statistically significant difference was found between the groups in terms of mismatch negativity test latency. CONCLUSION: An auditory pathway may be affected in migraine patients, although hearing tests are normal. This interaction continues between attacks, being more evident during the pain period. Therefore, disorders of hearing or speech perception in migraine patients should be evaluated by further audiological tests.

Hallazgos en los potenciales evocados auditivos del tallo cerebral en pacientes menores de 2 años con antecedente de hemorragia intraventricular / Findings in brainstem auditory evoked potentials in patients under 2 years of age with a history of intraventricular haemorrhage

Introducción: Existen pocos estudios que describan los resultados de la evaluación de la vía auditiva en pacientes con antecedente de hemorragia intraventricular (HIV) durante los primeros años de vida. La hipoacusia puede presentarse desde los grados iniciales de la HIV. Los potenciales evocados auditivos del tallo cerebral (PEATC) son una herramienta útil para diagnosticar alteraciones de la vía auditiva en la infancia temprana. El objetivo del presente estudio fue describir los hallazgos en los PEATC en pacientes menores de 2 años con antecedente de HIV. Pacientes y métodos: Es un estudio observacional retrospectivo realizado en pacientes menores de 2 años con antecedente de HIV enviados a nuestro hospital para la realización de PEATC en un período de tres años. Se excluyó a pacientes con síndromes genéticos asociados a hipoacusia. A través de los PEATC se evaluó la presencia o la ausencia de respuesta bioeléctrica y latencias de las ondas I, III y V, así como de los intervalos I-III, III-V y I-V, además de su morfología, amplitud, sincronía y la replicabilidad. Se realizó un análisis de tipo descriptivo con cálculo de frecuencias y porcentajes. Resultados: Se incluyó a un total de 122 pacientes. El 51% de ellos tenía antecedente de HIV de grado I; el 42%, de grado II; y el 7%, de grados III o IV. La respuesta bioeléctrica se obtuvo en 243 vías auditivas (99,6%). La morfología se encontró alterada en el 6,2% de las vías auditivas, mientras que las amplitudes estuvieron disminuidas en el 2,5% de las evaluadas. Las latencias para las ondas I y III se encontraron prolongadas en el 2%, y, para la onda V, en el 3,6% de los pacientes. El umbral auditivo fue normal en el 64,8%, y el 35,2% de los casos presentó hipoacusia. Conclusiones: La prevalencia de la hipoacusia fue alta en la muestra analizada. Se recomienda realizar el seguimiento mediante PEATC de forma sistemática con la finalidad de detectar y atender oportunamente problemas...(AU)

Introduction: There are few studies that describe the results of auditory pathway assessment in patients with a history of intraventricular haemorrhage (IVH) during the early years of life. Hypoacusis can occur from the earliest stages of IVH. Brainstem auditory evoked potentials (BAEPs) are a useful tool for diagnosing auditory pathway disorders in early childhood. The aim of the present study was to describe the BAEPs findings in patients under 2 years of age with a history of IVH. Patients and methods: We conducted a retrospective observational study in patients under 2 years of age with a history of IVH referred to our hospital for BAEPs over a period of three years. Patients with genetic syndromes associated with hypoacusis were excluded. BAEPs were used to evaluate the presence or absence of any bioelectrical response and latencies of waves I, III and V, as well as of the intervals I-III, III-V and I-V, and also their morphology, amplitude, synchrony and reproducibility. A descriptive analysis was carried out with the calculation of frequencies and percentages. Results: A total of 122 patients were included. Fifty-one per cent of them had a history of Grade I IVH; 42%, Grade II; and 7%, Grades III or IV. A bioelectrical response was obtained in 243 auditory pathways (99.6%). The morphology was found to be altered in 6.2% of the auditory pathways, while amplitudes were decreased in 2.5% of those tested. Latencies for waves I and III were found to be prolonged in 2% and for wave V in 3.6% of patients. The hearing threshold was normal in 64.8%, and 35.2% of cases presented hypoacusis.Conclusions: The prevalence of hypoacusis was high in the sample analysed. Systematic follow-up using BAEPs is recommended in order to detect and treat problems in the auditory pathway in patients with IVH in a timely manner.(AU)

The effect of cochlear size on electrically evoked auditory brainstem responses in deaf children.

Objectives: To investigate the relationship between auditory pathway function and cochlear size in deaf children with a radiologically normal inner ear or Mondini malformation. Methods: Thirty-five deaf children without inner ear malformations (IEMs) and forty cases with Mondini malformation were included in this study. The electrically evoked auditory brainstem responses (EABRs) evoked by electrical stimulation at the round window niche (RWN) and round window membrane (RWM) were recorded during cochlear implantation (CI) surgery. The anatomical parameters of the cochlea were assessed by high-resolution computed tomography and OTOPLAN 3-D construction software. Correlations between EABRs and cochlear sizes were analyzed. Results: The EABR thresholds and/or latencies were negatively correlated with the basal cochlear diameter, cochlear width and/or cochlear duct length in both patients without IEMs and those with Mondini malformation. Conclusion: The physiological function of the peripheral auditory system depends on the anatomical structure of the cochlea to an extent. A larger cochlear size appears to be associated with better auditory conduction function. Our findings may be beneficial to selection of the proper electrode type and prediction of postoperative auditory rehabilitation. Level of Evidence: Level 4.

Stability of complex sound representations in the auditory midbrain across the lifespan despite age-related brainstem delays.

The extent to which aging of the central auditory pathway impairs auditory perception in the elderly independent of peripheral cochlear decline is debated. To cause auditory deficits in normal hearing elderly, central aging needs to degrade neural sound representations at some point along the auditory pathway. However, inaccessible to psychophysical methods, the level of the auditory pathway at which aging starts to effectively degrade neural sound representations remains poorly differentiated. Here we tested how potential age-related changes in the auditory brainstem affect the stability of spatiotemporal multiunit complex speech-like sound representations in the auditory midbrain of old normal hearing CBA/J mice. Although brainstem conduction speed slowed down in old mice, the change was limited to the sub-millisecond range and only minimally affected temporal processing in the midbrain (i.e. gaps-in-noise sensitivity). Importantly, besides the small delay, multiunit complex temporal sound representations in the auditory midbrain did not differ between young and old mice. This shows that although small age-related neural effects in simple sound parameters in the lower brainstem may be present in aging they do not effectively deteriorate complex neural population representations at the level of the auditory midbrain when peripheral hearing remains normal. This result challenges the widespread belief of 'pure' central auditory decline as an automatic consequence of aging, at least up to the inferior colliculus. However, the stability of midbrain processing in aging emphasizes the role of undetected 'hidden' peripheral damage and accumulating effects in higher cortical auditory-cognitive processing explaining perception deficits in 'normal hearing' elderly.

Effect of perinatal and postnatal thiamine deficiency on auditory pathway of the Wistar-Albino rats

Abstract Objective: In this study, we created an animal model to demonstrate the effects of thiamine on the hearing pathways of new-borns during pregnancy and lactation by inducing a dietary thiamine deficiency in the mother. Methods: The study included 16 female Wistar albino rats. The animals were separated into four groups and provided the appropriate amounts of dietary thiamine according to their groups during pre-pregnancy, pregnancy, and lactation periods. Three pups from each mother were included in the study, and 12 pups were selected from each group. On the fortieth day after birth, the auditory pathways of 48 pups in the 4 groups were examined electro physiologically and ultra-structurally. Results: In Group N-N, morphology of hair cells stereocilia degeneration was not obtained in all turns of cochlea. In Group N-T, Inner Hair Cells (IHCs) and Outher Hair Cells (OHCs) stereocilia didn't show degeneration in all turns of cochlea but had rupture inrows of HCs stereocilia. In group T-N IHCs stereocilia less degeneration was observed in all turns of cochlea. OHC stereocilia partial loss was observed only in basal turn of cochlea. In Group T-T IHCs stereocilia was observed less degeneration and rupture in all turns of cochlea. Conclusion: Thiamine is vital for the development of cochlear hair cells during both prenatal and postnatal periods. Even partial deficiency of thiamine causes significant degeneration to the auditory pathway. Level of evidence: The level of evidence of this article is 5. This article is an experimental animal and laboratory study.