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PubMed2005

Neural response telemetry results with the nucleus 24 contour in a perimodiolar position.

OBJECTIVE: The purpose of the study was to analyze changes in neural response telemetry using the Cochlear Nucleus 24 Contour before and after stylet removal in a human model. STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: Twelve patients (23-72 years old) undergoing cochlear implantation, using the Nucleus 24 Contour implant, secondary to congenital and age-related hearing loss. INTERVENTION: Cochlear implantation with Cochlear Nucleus 24 Contour implant. MAIN OUTCOME MEASURE: Neural response telemetry thresholds were recorded initially with the stylet in and then with the stylet out during the implant procedure. RESULTS: Stimulus levels to obtain neural response telemetry threshold after stylet removal were statistically lower after the stylet was removed. CONCLUSION: The Nucleus 24 Contour achieves a perimodiolar position once the stylet is removed, and this leads to reduction in the current required to elicit a threshold neural response telemetry response.

Action Potentials↗

PubMed2006

Inner ear dysplasia is common in children with Down syndrome (trisomy 21).

OBJECTIVES/HYPOTHESIS: Middle and external ear anomalies are well recognized in Down syndrome (DS, trisomy 21). Inner ear anomalies are much less frequently described. This study reviews inner ear morphology on imaging to determine the prevalence of cochlear and vestibular anomalies in children with DS. STUDY DESIGN: The authors conducted a retrospective review of imaging features of (DS) inner ear structures. METHODS: Fifty-nine sequential patients with DS with imaging of the inner ear were identified by a radiology report text search program. Quantitative biometric assessment of the inner ear was performed on patients with high-resolution computed tomography or magnetic resonance images of the petrous bone. Petrous imaging was performed for evaluation of inflammatory disease or hearing loss. Spinal imaging, which included petrous views, was performed in most cases to exclude C1 to 2 dislocation, a potential complication of DS. Measurements were compared with normative data. RESULTS: Inner ear dysplasia is much more common in DS than previously reported. Inner ear structures are universally hypoplastic. Vestibular malformations are particularly common and a small bony island of the lateral semicircular canal (<3 mm in diameter) appears highly typical. Additional findings in some patients were persistent lateral semicircular anlage with fusion of the lateral semicircular canal and vestibule into a single cavity, vestibular aqueduct and endolymphatic sac fossa enlargement, cochlear nerve canal hypoplasia, and stenosis or duplication of the internal auditory canal. Stenosis of the external meatus, poor mastoid pneumatization, middle ear and mastoid opacification, and cholesteatoma were common, as expected.

Adolescent↗

PubMed2006

Developmental expression and localization of KCNJ10 K+ channels in the guinea pig inner ear.

The inward rectifier Kir4.1, composed of KCNJ10 K channel subunits, plays an essential role in inner ear K homeostasis. We have investigated the developmental expression and localization of KCNJ10 (Kir4.1) in the guinea pig inner ear using semi-quantitative reverse transcription polymerase chain reaction and immunohistochemistry. Kcnj10 was expressed at low levels from embryonic day 30 (E30), increased from E45, and persisted from E50 to adulthood. KCNJ10 channel protein was detected in spiral ganglion satellite cells of the basal turn at E40, and at E45 its expression proceeded with a base-to-apex gradient along the cochlear spiral. KCNJ10 protein was enriched in the myelin sheath around the cochlear nerve between E40 and E45 and disappeared gradually with age. In the strial intermediate cells, KCNJ10 channel expression was first observed at E50, and lagged behind that of the spiral ganglion. In addition, KCNJ10 channel protein was expressed and localized in vestibular transitional cells. Differential expression of KCNJ10 channel protein suggests roles for KCNJ10 channels in inner ear development and onset of auditory function.

Animals↗

PubMed1977

Electrocochleographic changes in acoustic neuroma: some experimental findings.

Reversible experimental lesions were produced in the central end of the cochlear nerve at the IAM of guinea pigs by various procedures, including the instillation of KCl (0.1 or 0.01 M). As a result the usual diphasic AP waveforms seen in guinea pigs (when click stimuli are used) were transformed into monophasic, widened negative waves. This change, attributed to a neural block, was reversible, e.g. when the instilled KCl was dispersed by irrigation with normal saline. It is suggested that the widened monophasic negative AP's observed at ECochG in cases of acoustic neuroma or similar lesions, are produced in this way.

Action Potentials↗

PubMed1977

Juvenile diabetes mellitus, optic atrophy, hearing loss, diabetes insipidus, atonia of the urinary tract and bladder, and other abnormalities (Wolfram syndrome). A review of 88 cases from the literature with personal observations on 3 new patients.

A review of 88 cases from the literature with personal observations on 3 new patients is given of the syndrome featured by juvenile diabetes mellitus, optic atrophy, hearing loss, diabetes insipidus, atonia of the urinary tract and bladder and other abnormalities. The postmortem in one of our cases is mentioned. The pattern of inheritance is autosomal recessive. The interpretation of the data on diabetes insipidus from the literature and in our three patients is also discussed. It can only be stated that neurohypophyseal diabetes insipidus can be a component of the syndrome and that in many cases--particularly in the presence of lesions of the efferent urinary tract--the possibility of nephrogenous diabetes insipidus can not be excluded with certainty. It seems probable that the same mechanism can be held responsible for the lesions of the olfactory, optic, vestibular and cochlear nerves, the hypophyseal form of diabetes insipidus, retarded sexual maturation, abnormal pupillary reaction, myelopathy and the electro-encephalographic, electroneurological and electromyographic changes in the Wolfram syndrome. The process underlying this affection of neural structures remains obscure.

Adolescent↗

PubMed2006

Time-course of the human medial olivocochlear reflex.

The time-course of the human medial olivocochlear reflex (MOCR) was measured via its suppression of stimulus-frequency otoacoustic emissions (SFOAEs) in nine ears. MOCR effects were elicited by contralateral, ipsilateral or bilateral wideband acoustic stimulation. As a first approximation, MOCR effects increased like a saturating exponential with a time constant of 277+/-62 ms, and decayed exponentially with a time constant of 159+/-54 ms. However, in ears with the highest signal-to-noise ratios (4/9), onset time constants could be separated into "fast," tau= approximately 70 ms, "medium," tau = approximately 330 ms, and "slow," tau = approximately 25 s components, and there was an overshoot in the decay like an under-damped sinusoid. Both the buildup and decay could be modeled as a second order differential equation and the differences between the buildup and decay could be accounted for by decreasing one coefficient by a factor of 2. The reflex onset and offset delays were both approximately 25 ms. Although changing elicitor level over a 20 dB SPL range produced a consistent systematic change in response amplitude, the time course did not show a consistent dependence on elictor level, nor did the time-courses of ipsilaterally, contralaterally, and bilaterally activated MOCR responses differ significantly. Given the MOCR's time-course, it is best suited to operate on acoustic changes that persist for 100's of milliseconds.

Acoustic Stimulation↗

PubMed2006

Virtual pitch in a computational physiological model.

A computational model of nervous activity in the auditory nerve, cochlear nucleus, and inferior colliculus is presented and evaluated in terms of its ability to simulate psychophysically-measured pitch perception. The model has a similar architecture to previous autocorrelation models except that the mathematical operations of autocorrelation are replaced by the combined action of thousands of physiologically plausible neuronal components. The evaluation employs pitch stimuli including complex tones with a missing fundamental frequency, tones with alternating phase, inharmonic tones with equally spaced frequencies and iterated rippled noise. Particular attention is paid to differences in response to resolved and unresolved component harmonics. The results indicate that the model is able to simulate qualitatively the related pitch-perceptions. This physiological model is similar in many respects to autocorrelation models of pitch and the success of the evaluations suggests that autocorrelation models may, after all, be physiologically plausible.

Auditory Threshold↗

PubMed1989

A closed-form solution for removing the dead time effects from the poststimulus time histograms.

Discharge patterns from cochlear nerve fibers contain important information about acoustic stimuli and encoding schemes of the peripheral auditory system. Yet these patterns are distorted due to refractory or dead time effects. By modeling discharges from peripheral auditory nerves as a self-exciting Poisson process, the effects of dead time on a poststimulus time histogram can be determined, assuming the recovery time does not depend on acoustic stimuli. If the recovery function is known, a closed-form formula is available to remove the dead time distortions from the poststimulus time histogram.

Action Potentials↗

PubMed1994

Recognition of plosive syllables in noise: comparison of an auditory model with human performance.

Some of the effects of noise on the perception of plosive-vowel syllables have been investigated. It was found that noise added to the syllables for the duration of the speech had a more deleterious effect on perception than noise of the same intensity played continuously. Physiological experiments have shown that the response thresholds of cochlear nerve fibers to tones are raised by continuous background noise but not by short bursts of noise. It is suggested that this may be responsible for the speech perception results. In order to investigate this, an auditory model was developed which incorporated response threshold shifts. This was interfaced to a hidden Markov model recognizer and tested with the same sounds that were employed in the human perception experiments. The recognition scores were greater with the threshold shifts than without them.

Acoustic Stimulation↗

PubMed1996

The normalized correlation: accounting for binaural detection across center frequency.

Bernstein and Trahiotis [L. R. Bernstein and C. Trahiotis, J. Acoust. Soc. Am. 100, 1754-1763 (1996)] recently reported the results of experiments designed to determine the form of interaural correlation that accounts for listeners' sensitivities to interaural disparities within high-frequency stimuli. Overall, those results demonstrated that listeners' abilities to discriminate changes in the interaural correlation of the envelope (from a base correlation of 1.0) were well accounted for by the use of the normalized correlation. The purpose of this study was to determine how well the normalized correlation computed subsequent to half-wave rectification and low-pass filtering could account for binaural detection data at low, intermediate, and high frequencies, respectively. In a four-interval, two-alternative task, listeners detected which interval contained a tone (between 500 Hz and 2 kHz) added antiphasically to diotic, 100-Hz-wide, noise (NoS pi). "Nonsignal" intervals contained the tone added homophasically (NoSo). Performance was measured for signal-to-noise ratios between -30 and +30 dB. Results indicated that a low-pass filter function based on physiological measures of synchrony in cochlear nerve fibers in conjunction with the assumption of half-wave, square-law rectification, accounted for typically 80% of the variance in the behavioral data.

Humans↗

PubMed1979

Tectorial membrane: a possible effect on frequency analysis in the cochlea.

Mathematical analysis and computer and network simulations of the cochlea show that, given appropriate values of specific physical constants, radial shear motion between the tectorial membrane and the reticular lamina may provide the sharpening of frequency analysis observed in cochlear nerve fibers in comparison with the mechanical amplitude distribution on the basilar membrane. According to the analysis, the sharpening occurs through an interaction of the longitudinal mechanical propagation constant of the tectorial membrane with the wavelength on the basilar membrane.

Basilar Membrane↗

PubMedDate not supplied

Sensorineural hearing loss in children.

A variety of pathologic conditions cause sensorineural hearing loss in infants and children. Modern imaging techniques such as high-resolution computed tomography (CT) and magnetic resonance (MR) imaging have made it possible to identify a specific cause of pediatric hearing loss in many cases. A classification system has been developed that groups these abnormalities into three anatomic locations along the cochlear nerve: the labyrinth, the internal auditory canal, and the brain stem and cerebrum. Unenhanced high-resolution CT remains the imaging modality of choice in evaluating most cases of pediatric sensorineural hearing loss. In general, CT is the preferred modality in cases of trauma and nonacute congenital otic capsular dysplasias, whereas contrast material-enhanced MR imaging is preferred in cases of inflammatory and neoplastic disorders. Documented acute hearing loss in an older child or adolescent should also be studied with contrast-enhanced MR imaging. Reliable radiologic evaluation requires accurate clinical information as well as knowledge of normal inner ear anatomy and abnormal imaging findings.

Brain↗

PubMed1996

Hearing loss.

Nearly 30 million Americans have hearing loss. Audiograms are used to determine if hearing loss is sensorineural (SNHL), conductive (CHL), or mixed (MHL). SNHL indicates dysfunction of the cochlea, cochlear nerve, or brain. The study of choice for adults with SNHL is gadolinium-enhanced magnetic resonance imaging, which is used to look for acoustic neuromas, abnormal labyrinth signal intensity or enhancement, and brain disease. In children with SNHL, computed tomography (CT) performed with bone algorithms demonstrates inner ear dysplasias. SNHL from trauma is best evaluated with CT studies. CHL indicates disease in the external auditory canal, tympanic membrane, or middle ear; CT with thin bone algorithms is the best study. Causes of CHL include external canal atresia and neoplasms, myringosclerosis, middle ear anomalies, effusion, cholesteatomas, and neoplasms. MHL is a combination of SNHL and CHL. Dysplasias such as otosclerosis and osteogenesis imperfecta, the most frequent diseases with radiologic findings, are best assessed on CT images. The combination of patient age and type of hearing loss determines the best imaging study.

Adult↗

PubMed2006

Development of spontaneous miniature EPSCs in mouse AVCN neurons during a critical period of afferent-dependent neuron survival.

During a critical period prior to hearing onset, cochlea ablation leads to massive neuronal death in the mouse anteroventral cochlear nucleus (AVCN), where cell survival is believed to depend on glutamatergic input. We investigated the development of spontaneous miniature excitatory postsynaptic currents (mEPSCs) in AVCN neurons using whole cell patch-clamp techniques during [postnatal day 7 (P7)] and after (P14, P21) this critical period. We also examined the effects of unilateral cochlea ablation on mEPSC development. The two main AVCN neuron types, bushy and stellate cells, were distinguished electrophysiologically. Bushy cell mEPSCs became more frequent and faster between P7 and P14/P21 but with little change in amplitude. Dendritic filtering of mEPSCs was not detected as indicated by the lack of correlation between 10 and 90% rise times and decay time constants. Seven days after cochlea ablation at P7 or P14, mEPSCs in surviving bushy cells were similar to controls, except that rise and decay times were positively correlated (R = 0.31 and 0.14 for surgery at P7 and P14, respectively). Consistent with this evidence for a shift of synaptic activity from the somata to the dendrites, SV2 staining (a synaptic vesicle marker) forms a ring around somata of control but not experimental bushy cells. In contrast, mEPSCs of stellate cells showed few significant changes over these ages with or without cochlea ablation. Taken together, mEPSCs in mouse AVCN bushy cells show dramatic developmental changes across this critical period, and cochlea ablation may lead to the emergence of excitatory synaptic inputs impinging on bushy cell dendrites.

Action Potentials↗

PubMed1994

Phase-locked response characteristics of single neurons in the frog "cochlear nucleus" to steady-state and sinusoidal-amplitude-modulated tones.

1. We made extracellular recordings from 164 single neurons in the frog dorsal medullary nucleus (DMN), a homologue of the cochlear nucleus. Phase-locked responses to tones at the unit's characteristic frequency (CF) and to off-CF tones were evaluated. We also stimulated units with tones at CF that were amplitude modulated sinusoidally between 5 and 1,000 Hz and examined responses to these stimuli. 2. Results showed that single neurons in the frog DMN displayed phase-locked discharges to tones at frequencies < or = 800 Hz. Phase-locking was robust at low frequencies (< 400 Hz) and became poorer at higher frequencies; the variation of the synchronization coefficient (SC) with frequency typically showed a low-pass characteristic. 3. The capacity of phase-locking to tones was correlated with the functional classification of a DMN neuron and the firing rate of its CF response. Primarylike neurons exhibited various degrees of phase-locked discharges to tones at off-CF frequencies. The average upper cutoff frequency, i.e., the frequency at which the SC dropped to 0.5 of maximum value, differed for the three classes of primarylike neurons. The average cutoff frequency was respectively 183, 325, and 536 Hz for primarylike neurons that displayed low (PL-1), intermediate (PL-2), and high (PL-3) steady-state firing rates to CF stimulation. The phasic neurons showed poor phase-locking capacities at all tone frequencies. 4. The frequency range of phase-locking to amplitude-modulated stimuli was also different for the different cell types, as evidenced by the units' modulation transfer functions (MTFs). The primarylike neurons exhibited mostly all-pass or low-pass sync-based MTFs. The mean upper cutoff frequencies for primarylike neurons having low-pass MTFs were 155 Hz for PL-1 neurons, 176 Hz for PL-2 neurons, and 218 Hz for PL-3 neurons. Pauser, chopper, phasic, and phasic-burst neurons gave mostly low-pass MTFs having a mean upper cutoff frequency of 219, 235, 242, and 251 Hz, respectively. 5. The phase-locking ability of DMN neurons to tones and to amplitude-modulated stimuli are compared with those of frog's primary afferent fibers and with those of avian and mammalian cochlear nucleus neurons. The significance of results in terms of sound localization and sound pattern recognition is discussed.

Animals↗

PubMed1997

Stochastic threshold characterization of the intensity of active channel dynamical action potential generation.

Stochastic threshold characterization of the intensity of active channel dynamical action potential generation. J. Neurophysiol. 78: 2616-2630, 1997. This paper develops a stochastic intensity description for action potential generation formulated in terms of stochastic processes, which are direct analogues of the physiological processes of the pre- and postsynaptic complex of the cochlear nerve: 1) neurotransmitter release is modeled as an inhomogeneous Poisson counting process with release intensity mu t, 2) the excitatory postsynaptic conductance (EPSC) process is modeled as a marked, linearly filtered Poisson process resulting from the linear superposition of standard shaped postsynaptic conductances of size G, and 3) action potential generation is modeled as resulting from the EPSC exceeding a random threshold determined by active channel dynamics of the Hodgkin-Huxley type. The random threshold is defined to be the least upper bound in the size of a standard-shaped neurotransmitter release injected at time t given the previous action potential time and the number of releases occurring in a short preconditioning time increment. The action potential process is modeled as a self-exciting point process with stochastic intensity resulting from the probability that the random threshold process crosses the threshold in some small time increment that is a function of time since previous action potential, release intensity, and the probability that a single synaptic event exceeds the stochastic threshold. The stochastic intensity model is consistent with a direct simulation of the nonlinear Hodgkin-Huxley differential equations over a variety of parameters for the vesicle release intensity, vesicle size, vesicle duration, and temperatures. Results are presented showing that the regularity properties seen in the vestibular primary afferent in the lizard, Calotes versicolor, associated with a slow-to-activate potassium channel resulting in a long afterhyperpolarization can be accommodated directly by the stochastic intensity description. The stimulus dependence of the model is attributed to synaptic transmission and the probabilistic nature to the threshold conductance process, which is dependent upon the EPSC process. The stochastic intensity is seen to have a form consistent with the phenomenologically based Siebert-Gaumond model, a stimulus-related function of time multiplied by a refractory-related function of time since previous action potential.

Action Potentials↗

PubMedDate not supplied

Structural recovery from sound and aminoglycoside damage in the avian cochlea.

Hair cell regeneration in the mature avian cochlea occurs in response to trauma that causes the death of some or all of the existing hair cell population. In general, this trauma has been introduced experimentally by either sound overexposure or treatment of the bird with high doses of aminoglycoside antibiotics. When injured hair cells are ejected from the sensory epithelium, the nonsensory supporting cells respond by re-entering the cell cycle and proliferating or by transdifferentiating directly into hair cells without a mitotic event. The new hair cells mature in a manner similar to that seen during embryonic development. They make connections with the overlying tectorial membrane and the afferent and efferent cochlear nerve processes within the sensory epithelium. This structural regeneration is accompanied by a significant recovery of auditory function and thus allows the animal to regain its hearing ability. This hair cell regeneration is presumably quite beneficial to birds, whose primary means of communication is based on vocalizations and the ability to hear and comprehend them. The prevalence of hearing loss in our society and the isolating impact it has on affected individuals makes the potential for finding ways to induce a similar hair cell regeneration in humans a very tempting goal. Studies of hair cell regeneration over the last 12 years have focused on the mechanisms that regulate the process and how they could be controlled. This review will examine the structural events involved in regenerating hair cells in the avian cochlea after sound damage and aminoglycoside treatment. It will define how hair cells and nerve endings are lost and the tectorial membrane is damaged by the traumatizing stimuli and how the supporting cells and nerve fibers respond by producing new hair cells, a new tectorial membrane and new synaptic connections during recovery. Finally, it will focus on mechanisms that control the proliferation and transdifferentiation of supporting cells and the differentiation of new hair cells. This structural review is accompanied by a companion review that covers the fundamental issues concerning functional recovery in the avian cochlea associated with hair cell regeneration.

Aminoglycosides↗

PubMedDate not supplied

Roles of fibroblast growth factors in the inner ear.

The basic biology of the fibroblast growth factor (FGF) receptors and their splice variants is first reviewed, followed by a review of the known roles of FGFs in the inner ear. They include induction of the otocyst by FGF19, followed by FGF3 in further development of the otocyst. In later development, FGF3 or FGF10 acting on FGF receptor 2b is likely to be involved in development of the walls of the cochlear spaces, while FGF receptor 3 is involved in differentiation of the pillar cells of the organ of Corti. FGF1 and FGF2 act as trophic factors for the developing cochlear nerve fibres.

Animals↗