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Balkan Medical Journal Sep 2017Morphologically congenital sensorineural hearing loss can be investigated under two categories. The majority of congenital hearing loss causes (80%) are membranous...
Morphologically congenital sensorineural hearing loss can be investigated under two categories. The majority of congenital hearing loss causes (80%) are membranous malformations. Here, the pathology involves inner ear hair cells. There is no gross bony abnormality and, therefore, in these cases high-resolution computerized tomography and magnetic resonance imaging of the temporal bone reveal normal findings. The remaining 20% have various malformations involving the bony labyrinth and, therefore, can be radiologically demonstrated by computerized tomography and magnetic resonance imaging. The latter group involves surgical challenges as well as problems in decision-making. Some cases may be managed by a hearing aid, others need cochlear implantation, and some cases are candidates for an auditory brainstem implantation (ABI). During cochlear implantation, there may be facial nerve abnormalities, cerebrospinal fluid leakage, electrode misplacement or difficulty in finding the cochlea itself. During surgery for inner ear malformations, the surgeon must be ready to modify the surgical approach or choose special electrodes for surgery. In the present review article, inner ear malformations are classified according to the differences observed in the cochlea. Hearing and language outcomes after various implantation methods are closely related to the status of the cochlear nerve, and a practical classification of the cochlear nerve deficiency is also provided.
Topics: Classification; Cochlea; Cochlear Nerve; Ear, Inner; Hearing Loss, Sensorineural; Humans; Osteogenesis; Temporal Bone; Tomography, X-Ray Computed
PubMed: 28840850
DOI: 10.4274/balkanmedj.2017.0367 -
The Journal of Neuroscience : the... Nov 2009Overexposure to intense sound can cause temporary or permanent hearing loss. Postexposure recovery of threshold sensitivity has been assumed to indicate reversal of...
Overexposure to intense sound can cause temporary or permanent hearing loss. Postexposure recovery of threshold sensitivity has been assumed to indicate reversal of damage to delicate mechano-sensory and neural structures of the inner ear and no persistent or delayed consequences for auditory function. Here, we show, using cochlear functional assays and confocal imaging of the inner ear in mouse, that acoustic overexposures causing moderate, but completely reversible, threshold elevation leave cochlear sensory cells intact, but cause acute loss of afferent nerve terminals and delayed degeneration of the cochlear nerve. Results suggest that noise-induced damage to the ear has progressive consequences that are considerably more widespread than are revealed by conventional threshold testing. This primary neurodegeneration should add to difficulties hearing in noisy environments, and could contribute to tinnitus, hyperacusis, and other perceptual anomalies commonly associated with inner ear damage.
Topics: Acoustic Stimulation; Animals; Cell Death; Cochlear Nerve; Ear, Inner; Ganglia, Sensory; Hearing Loss, Noise-Induced; Male; Mice; Mice, Inbred CBA; Nerve Degeneration; Neurons; Neurons, Afferent; Noise; Otoacoustic Emissions, Spontaneous; Synapses; Vestibulocochlear Nerve Diseases
PubMed: 19906956
DOI: 10.1523/JNEUROSCI.2845-09.2009 -
Hearing Research Nov 2015In early tetrapods, it is assumed that the tympana were acoustically coupled through the pharynx and therefore inherently directional, acting as pressure difference... (Review)
Review
In early tetrapods, it is assumed that the tympana were acoustically coupled through the pharynx and therefore inherently directional, acting as pressure difference receivers. The later closure of the middle ear cavity in turtles, archosaurs, and mammals is a derived condition, and would have changed the ear by decoupling the tympana. Isolation of the middle ears would then have led to selection for structural and neural strategies to compute sound source localization in both archosaurs and mammalian ancestors. In the archosaurs (birds and crocodilians) the presence of air spaces in the skull provided connections between the ears that have been exploited to improve directional hearing, while neural circuits mediating sound localization are well developed. In this review, we will focus primarily on directional hearing in crocodilians, where vocalization and sound localization are thought to be ecologically important, and indicate important issues still awaiting resolution.
Topics: Alligators and Crocodiles; Animals; Behavior, Animal; Biological Evolution; Biophysical Phenomena; Birds; Cochlear Nerve; Ear; Evoked Potentials, Auditory, Brain Stem; Mammals; Reptiles; Sound Localization
PubMed: 26048335
DOI: 10.1016/j.heares.2015.05.009 -
Audiology & Neuro-otology 2022The rates of cochlear nerve abnormalities and cochlear malformations in pediatric unilateral hearing loss (UHL) are conflicting in the literature, with important...
INTRODUCTION
The rates of cochlear nerve abnormalities and cochlear malformations in pediatric unilateral hearing loss (UHL) are conflicting in the literature, with important implications on management. The aim of this study was to investigate the incidence of cochlear nerve deficiency (CND) in pediatric subjects with UHL or asymmetric hearing loss (AHL).
METHODS
A retrospective chart review of pediatric subjects <18 years of age evaluated for UHL or AHL with fine-cut heavily T2-weighted magnetic resonance imaging (MRI) between January 2014 and October 2019 (n = 291) at a tertiary referral center was conducted. MRI brain and computed tomography temporal bone were reviewed for the presence of inner ear malformations and/or CND. Status of the ipsilateral cochlear nerve and inner ear was evaluated. Pure tone average (PTA) at 500, 1,000 and 2,000 Hz was assessed.
RESULTS
204 subjects with UHL and 87 subjects with AHL were included. CND (aplasia or hypoplasia) was demonstrated in 61 pediatric subjects with UHL (29.9%) and 10 with AHL (11.5%). Ipsilateral cochlear malformations were noted in 25 subjects with UHL (12.3%) and 11 with AHL (12.6%), and ipsilateral vestibular malformations in 23 (11.3%) and 12 (13.8%) ears, respectively. Median PTA was statistically significantly higher in ears with CND (98.33) than ears with normal nerves (90.84).
DISCUSSION/CONCLUSION
Imaging demonstrated a high incidence of inner ear malformations, particularly CND, in pediatric subjects with UHL. Auditory findings indicated CND cannot be ruled out by thresholds alone as some CND ears did demonstrate measurable hearing. Radiologic evaluation by MRI should be performed in all patients within this population to guide counseling and management of hearing loss based on etiology, with implications on candidacy for cochlear implantation.
Topics: Child; Cochlear Implantation; Cochlear Nerve; Hearing; Hearing Loss, Sensorineural; Hearing Loss, Unilateral; Humans; Magnetic Resonance Imaging; Retrospective Studies
PubMed: 35344959
DOI: 10.1159/000522566 -
Journal of Neurology, Neurosurgery, and... Nov 1950
Topics: Cochlear Nerve; Humans; Neoplasms; Neuroma; Neuroma, Acoustic; Vestibulocochlear Nerve
PubMed: 14795242
DOI: 10.1136/jnnp.13.4.277 -
Trends in Amplification 2004More than 60,000 people worldwide use cochlear implants as a means to restore functional hearing. Although individual performance variability is still high, an average... (Review)
Review
More than 60,000 people worldwide use cochlear implants as a means to restore functional hearing. Although individual performance variability is still high, an average implant user can talk on the phone in a quiet environment. Cochlear-implant research has also matured as a field, as evidenced by the exponential growth in both the patient population and scientific publication. The present report examines current issues related to audiologic, clinical, engineering, anatomic, and physiologic aspects of cochlear implants, focusing on their psychophysical, speech, music, and cognitive performance. This report also forecasts clinical and research trends related to presurgical evaluation, fitting protocols, signal processing, and postsurgical rehabilitation in cochlear implants. Finally, a future landscape in amplification is presented that requires a unique, yet complementary, contribution from hearing aids, middle ear implants, and cochlear implants to achieve a total solution to the entire spectrum of hearing loss treatment and management.
Topics: Acoustic Stimulation; Cochlea; Cochlear Implantation; Cochlear Nerve; Cues; Deafness; Electric Stimulation; Engineering; Humans; Music; Pitch Perception; Postoperative Care; Preoperative Care; Prosthesis Fitting; Speech Perception; Telemetry; Time Factors; Time Perception
PubMed: 15247993
DOI: 10.1177/108471380400800102 -
Trends in Neurosciences Jan 2019Speech has long been recognized as 'special'. Here, we suggest that one of the reasons for speech being special is that our auditory system has evolved to encode it in... (Review)
Review
Speech has long been recognized as 'special'. Here, we suggest that one of the reasons for speech being special is that our auditory system has evolved to encode it in an efficient, optimal way. The theory of efficient neural coding argues that our perceptual systems have evolved to encode environmental stimuli in the most efficient way. Mathematically, this can be achieved if the optimally efficient codes match the statistics of the signals they represent. Experimental evidence suggests that the auditory code is optimal in this mathematical sense: statistical properties of speech closely match response properties of the cochlea, the auditory nerve, and the auditory cortex. Even more interestingly, these results may be linked to phenomena in auditory and speech perception.
Topics: Acoustic Stimulation; Animals; Auditory Cortex; Auditory Perception; Cochlear Nerve; Humans; Speech; Speech Perception
PubMed: 30297085
DOI: 10.1016/j.tins.2018.09.004 -
European Archives of... Jun 2022In pediatric audiology, objective techniques for hearing threshold estimation in infants and children with profound or severe hearing loss play a key role. Auditory...
Comparison of ABR and ASSR using narrow-band-chirp-stimuli in children with cochlear malformation and/or cochlear nerve hypoplasia suffering from severe/profound hearing loss.
OBJECTIVES
In pediatric audiology, objective techniques for hearing threshold estimation in infants and children with profound or severe hearing loss play a key role. Auditory brainstem responses (ABR) and auditory steady-state responses (ASSR) are available for frequency-dependent hearing threshold estimations and both techniques show strong correlations but sometimes with considerable differences. The aim of the study was to compare hearing threshold estimations in children with and without cochlear and cochlear nerve malformations.
METHODS
Two groups with profound or severe hearing loss were retrospectively compared. In 20 ears (15 children) with malformation of the inner ear and/or cochlear nerve hypoplasia and a control group of 20 ears (11 children) without malformation, ABR were measured with the Interacoustics Eclipse EP25 ABR system (Denmark) with narrow-band CE-chirps at 500, 1000, 2000 and 4000 Hz and compared to ASSR at the same center frequencies under similar conditions.
RESULTS
ABR and ASSR correlated significantly in both groups (r = 0.413 in malformation group, r = 0.82 in control group). The malformation group showed a significantly lower percentage of "equal" hearing threshold estimations than the control group. In detail, patients with isolated cochlear malformation did not differ significantly from the control group, whereas patients with cochlear nerve hypoplasia showed significantly greater differences.
CONCLUSION
ABR and ASSR should be used jointly in the diagnostic approach in children with suspected profound or severe hearing loss. A great difference in hearing threshold estimation between these techniques could hint at the involvement of cochlear nerve or cochlear nerve hypoplasia itself.
Topics: Acoustic Stimulation; Auditory Threshold; Child; Cochlear Nerve; Evoked Potentials, Auditory, Brain Stem; Hearing Loss; Humans; Infant; Retrospective Studies
PubMed: 34318333
DOI: 10.1007/s00405-021-06990-4 -
The Journal of Neuroscience : the... Sep 2020Multiple forms of homeostasis influence synaptic function under diverse activity conditions. Both presynaptic and postsynaptic forms of homeostasis are important, but...
Multiple forms of homeostasis influence synaptic function under diverse activity conditions. Both presynaptic and postsynaptic forms of homeostasis are important, but their relative impact on fidelity is unknown. To address this issue, we studied auditory nerve synapses onto bushy cells in the cochlear nucleus of mice of both sexes. These synapses undergo bidirectional presynaptic and postsynaptic homeostatic changes with increased and decreased acoustic stimulation. We found that both young and mature synapses exhibit similar activity-dependent changes in short-term depression. Experiments using chelators and imaging both indicated that presynaptic Ca influx decreased after noise exposure, and increased after ligating the ear canal. By contrast, Ca cooperativity was unaffected. Experiments using specific antagonists suggest that occlusion leads to changes in the Ca channel subtypes driving neurotransmitter release. Furthermore, dynamic-clamp experiments revealed that spike fidelity primarily depended on changes in presynaptic depression, with some contribution from changes in postsynaptic intrinsic properties. These experiments indicate that presynaptic Ca influx is homeostatically regulated to enhance synaptic fidelity. Homeostatic mechanisms in synapses maintain stable function in the face of different levels of activity. Both juvenile and mature auditory nerve synapses onto bushy cells modify short-term depression in different acoustic environments, which raises the question of what the underlying presynaptic mechanisms are and the relative importance of presynaptic and postsynaptic contributions to the faithful transfer of information. Changes in short-term depression under different acoustic conditions were a result of changes in presynaptic Ca influx. Spike fidelity was affected by both presynaptic and postsynaptic changes after ear occlusion and was only affected by presynaptic changes after noise-rearing. These findings are important for understanding regulation of auditory synapses under normal conditions and also in disorders following noise exposure or conductive hearing loss.
Topics: Animals; Auditory Perception; Calcium; Cochlear Nerve; Cochlear Nucleus; Female; Homeostasis; Male; Mice; Mice, Inbred CBA; Neuronal Plasticity; Noise; Presynaptic Terminals; Synaptic Potentials
PubMed: 32747441
DOI: 10.1523/JNEUROSCI.1175-19.2020 -
The Journal of Neuroscience : the... Mar 2022Sound-level coding in the auditory nerve is achieved through the progressive recruitment of auditory nerve fibers (ANFs) that differ in threshold of activation and in...
Sound-level coding in the auditory nerve is achieved through the progressive recruitment of auditory nerve fibers (ANFs) that differ in threshold of activation and in the stimulus level at which the spike rate saturates. To investigate the functional state of the ANFs, the electrophysiological tests routinely used in clinics only capture the first action potentials firing in synchrony at the onset of the acoustic stimulation. Assessment of other properties (e.g., spontaneous rate and adaptation time constants) requires single-fiber recordings directly from the nerve, which for ethical reasons is not allowed in humans. By combining neuronal activity measurements at the round window and signal-processing algorithms, we constructed a peristimulus time response (PSTR), with a waveform similar to the peristimulus time histograms (PSTHs) derived from single-fiber recordings in young adult female gerbils. Simultaneous recordings of round-window PSTR and single-fiber PSTH provided models to predict the adaptation kinetics and spontaneous rate of the ANFs tuned at the PSTR probe frequency. The predictive model derived from gerbils was then validated in female mice and finally applied to humans by recording PSTRs from the auditory nerve in normal-hearing patients who underwent cerebellopontine angle surgeries. A rapid adaptation time constant of ∼3 ms and a mean spontaneous rate of ∼22 spikes/s in the 4 kHz frequency range were found. This study offers a promising diagnostic tool to map the human auditory nerve, thus opening new avenues to better understanding auditory neuropathies, tinnitus, and hyperacusis. Neural adaptation in auditory nerve fibers corresponds to the reduction in the neuronal activity to prolonged or repeated sound stimulation. For obvious ethical reasons, single-fiber recordings from the auditory nerve are not feasible in humans, creating a critical gap in extending data obtained using animal models to humans. Using electrocochleography in rodents, we inferred adaptation kinetics and spontaneous discharge rates of the auditory nerve fibers in humans. Routinely used in basic and clinical laboratories, this tool will provide a better understanding of auditory disorders such as neuropathies, tinnitus, and hyperacusis, and will help to improve hearing-aid fittings.
Topics: Acoustic Stimulation; Animals; Cochlear Nerve; Evoked Potentials, Auditory; Female; Gerbillinae; Hearing; Humans; Mice; Nerve Fibers
PubMed: 35078924
DOI: 10.1523/JNEUROSCI.0858-21.2022