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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 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 -
Hearing Research Jun 2011Sound localization requires precise and specialized neural circuitry. A prominent and well-studied specialization is found in the mammalian auditory brainstem. Globular... (Review)
Review
Sound localization requires precise and specialized neural circuitry. A prominent and well-studied specialization is found in the mammalian auditory brainstem. Globular bushy cells of the ventral cochlear nucleus (VCN) project contralaterally to neurons of the medial nucleus of the trapezoid body (MNTB), where their large axons terminate on cell bodies of MNTB principal neurons, forming the calyces of Held. The VCN-MNTB pathway is necessary for the accurate computation of interaural intensity and time differences; MNTB neurons provide inhibitory input to the lateral superior olive, which compares levels of excitation from the ipsilateral ear to levels of tonotopically matched inhibition from the contralateral ear, and to the medial superior olive, where precise inhibition from MNTB neurons tunes the delays of binaural excitation. Here we review the morphological and physiological aspects of the development of the VCN-MNTB pathway and its calyceal termination, along with potential mechanisms that give rise to its precision. During embryonic development, VCN axons grow towards the midline, cross the midline into the region of the presumptive MNTB and then form collateral branches that will terminate in calyces of Held. In rodents, immature calyces of Held appear in MNTB during the first few days of postnatal life. These calyces mature morphologically and physiologically over the next three postnatal weeks, enabling fast, high fidelity transmission in the VCN-MNTB pathway.
Topics: Aging; Animals; Auditory Pathways; Axons; Cochlear Nerve; Cochlear Nucleus; Embryonic Development; Humans; Pons; Synaptic Transmission; Time Factors
PubMed: 21093567
DOI: 10.1016/j.heares.2010.11.004 -
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 -
The Journal of Neuroscience : the... May 2023Modulations in both amplitude and frequency are prevalent in natural sounds and are critical in defining their properties. Humans are exquisitely sensitive to frequency...
Modulations in both amplitude and frequency are prevalent in natural sounds and are critical in defining their properties. Humans are exquisitely sensitive to frequency modulation (FM) at the slow modulation rates and low carrier frequencies that are common in speech and music. This enhanced sensitivity to slow-rate and low-frequency FM has been widely believed to reflect precise, stimulus-driven phase locking to temporal fine structure in the auditory nerve. At faster modulation rates and/or higher carrier frequencies, FM is instead thought to be coded by coarser frequency-to-place mapping, where FM is converted to amplitude modulation (AM) via cochlear filtering. Here, we show that patterns of human FM perception that have classically been explained by limits in peripheral temporal coding are instead better accounted for by constraints in the central processing of fundamental frequency (F0) or pitch. We measured FM detection in male and female humans using harmonic complex tones with an F0 within the range of musical pitch but with resolved harmonic components that were all above the putative limits of temporal phase locking (>8 kHz). Listeners were more sensitive to slow than fast FM rates, even though all components were beyond the limits of phase locking. In contrast, AM sensitivity remained better at faster than slower rates, regardless of carrier frequency. These findings demonstrate that classic trends in human FM sensitivity, previously attributed to auditory nerve phase locking, may instead reflect the constraints of a unitary code that operates at a more central level of processing. Natural sounds involve dynamic frequency and amplitude fluctuations. Humans are particularly sensitive to frequency modulation (FM) at slow rates and low carrier frequencies, which are prevalent in speech and music. This sensitivity has been ascribed to encoding of stimulus temporal fine structure (TFS) via phase-locked auditory nerve activity. To test this long-standing theory, we measured FM sensitivity using complex tones with a low F0 but only high-frequency harmonics beyond the limits of phase locking. Dissociating the F0 from TFS showed that FM sensitivity is limited not by peripheral encoding of TFS but rather by central processing of F0, or pitch. The results suggest a unitary code for FM detection limited by more central constraints.
Topics: Male; Humans; Female; Cochlear Nerve; Cochlea; Sound; Speech; Music; Acoustic Stimulation
PubMed: 37028932
DOI: 10.1523/JNEUROSCI.0995-22.2023 -
Journal of the Association For Research... Sep 2009Persons with a prosthesis implanted in a cochlea with residual acoustic sensitivity can, in some cases, achieve better speech perception with "hybrid" stimulation than...
Persons with a prosthesis implanted in a cochlea with residual acoustic sensitivity can, in some cases, achieve better speech perception with "hybrid" stimulation than with either acoustic or electric stimulation presented alone. Such improvements may involve "across auditory-nerve fiber" processes within central nuclei of the auditory system and within-fiber interactions at the level of the auditory nerve. Our study explored acoustic-electric interactions within feline auditory nerve fibers (ANFs) so as to address two goals. First, we sought to better understand recent results that showed non-monotonic recovery of the electrically evoked compound action potential (ECAP) following acoustic masking (Nourski et al. 2007, Hear. Res. 232:87-103). We hypothesized that post-masking changes in ANF temporal properties and responsiveness (spike rate) accounted for the ECAP results. We also sought to describe, more broadly, the changes in ANF responses that result from prior acoustic stimulation. Five response properties-spike rate, latency, jitter, spike amplitude, and spontaneous activity-were examined. Post-masking reductions in spike rate, within-fiber jitter and across-fiber variance in latency were found, with the changes in temporal response properties limited to ANFs with high spontaneous rates. Thus, our results suggest how non-monotonic ECAP recovery occurs for ears with spontaneous activity, but cannot account for that pattern of recovery when there is no spontaneous activity, including the results from the presumably deafened ears used in the Nourski et al. (2007) study. Finally, during simultaneous (electric+acoustic) stimulation, the degree of electrically driven spike activity had a strong influence on spike rate, but did not affect spike jitter, which apparently was determined by the acoustic noise stimulus or spontaneous activity.
Topics: Acoustic Stimulation; Action Potentials; Animals; Cats; Cochlear Nerve; Electric Stimulation; Evoked Potentials, Auditory; Models, Animal; Nerve Fibers
PubMed: 19205803
DOI: 10.1007/s10162-008-0154-7