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At least 271 records · Page 15Linked to original sources
PubMed2000

Speech evaluation of partially implantable piezoelectric middle ear implants in vivo.

OBJECTIVE: Cochlear microphonic responses (CMs) were measured in a rabbit model in the intact ear (CM1) and in ears with a partially implantable piezoelectric middle ear implant (P-MEI) (CM2) to investigate the characteristics of speech transmission of the P-MEI in vivo. DESIGN: The spectra of pure tones, voices, and elicited CM1 and CM2 obtained from the round window before and after the implantation of a P-MEI device were calculated by using fast Fourier transform. Frequency response functions of CM1 and CM2 were used to demonstrate the functional similarity between the implanted P-MEI and the normal ossicular chain. The coherence functions between the voices and CM1 and between CM1 and CM2 were evaluated to characterize speech transmission of the P-MEI in vivo. Ten rabbit ears were used in this study. Pure tones, six Chinese vowels, and six Chinese characters were the acoustic stimuli. The CMs elicited by a list of bisyllabic words were tape-recorded and then recognized by subjects with normal hearing. RESULTS: Using pure tones at the same intensity of 90 dB SPL, frequency response functions of the CMs between the two states (the intact ear with normal hearing and ears with a P-MEI device at the medium volume) were calculated showing great resemblance in shape. Compared with that at 1 kHz, gain factors were 10 and 20 dB, respectively, at higher frequencies. The correlation and spectral analyses of the vocalizations, CM1 and CM2, demonstrated that the harmonics of CM1 were approximately identical as those of the voices between 0.5 and 5.0 kHz with coherence functions of about 0.7 to approximately 1 at the formants' frequencies, whereas the harmonics of CM2 between 0.5 and 2.5 kHz were enhanced with the coherences near to unity at the formants' frequencies, and others <0.5 kHz and >2.5 kHz were attenuated. The recognition score of the CMs elicited by a list of bisyllabic words was >90% using subjects with normal hearing. CONCLUSIONS: Data from this study suggest that cochlear microphonic potentials can be used as an important tool to evaluate objectively whether the implantation of a P-MEI device is successful and whether the quality in speech transmission of the P-MEI is satisfactory. Thus, the method would be of significance to clinically ascertain the performance of the device in vivo.

Animals↗
PubMed2006

Auditory neuropathy characteristics in children with cochlear nerve deficiency.

OBJECTIVE: To describe a group of children exhibiting electrophysiologic responses characteristic of auditory neuropathy (AN) who were subsequently identified as having absent or small cochlear nerves (i.e., cochlear nerve deficiency). DESIGN: A retrospective review of the clinical records, audiological testing results, and magnetic resonance imaging (MRI) studies. Fifty-one of 65 children with AN characteristics on auditory brain stem response (ABR) testing had MRI available for review. Nine (18%) of these 51 children with ABR characteristic of AN have been identified as having small (N = 2; 4%) or absent (N = 7; 14%) cochlear nerves on MRI. RESULTS: Of the nine children with cochlear nerve deficiency, five (56%) were affected unilaterally and four (44%) bilaterally. Eight of nine presented after failing a newborn infant hearing screening, whereas one presented at 3 yr of age. On diagnostic ABR testing, all 9 children (9 of 13 affected ears; 69%) had evidence of a cochlear microphonic (CM) and absent neural responses in at least one ear. In the unilateral cases, AN characteristics were detected in all affected ears. In bilateral cases, at least one of the ears in each child demonstrated the AN phenotype, whereas the contralateral ear had no CM identified. Only one ear with cochlear nerve deficiency had present otoacoustic emissions as measured by distortion-product otoacoustic emissions. In children with appropriate available behavioral testing results, all ears without cochlear nerves were identified as having a profound hearing loss. Only 4 (31%) of the 13 ears with cochlear nerve deficiency had a small internal auditory canal on MRI. CONCLUSIONS: Children with cochlear nerve deficiency can present with electrophysiologic evidence of AN. These children frequently refer on newborn screening examinations that use ABR-based testing methods. Similar to other causes of AN, diagnostic ABR testing will show a CM with absent neural responses. Given that 9 (18%) of 51 children with available MRI and electrophysiologic characteristics of AN in our program have been identified as having cochlear nerve deficiency makes this a relatively common diagnosis. These findings suggest that MRI is indicated for all children diagnosed with AN. Moreover, electrophysiologic evidence of unilateral AN in association with a profound hearing loss should make the clinician highly suspicious for this problem. Although children with cochlear nerve deficiency who have a small nerve may benefit from cochlear implantation or amplification, these interventions are obviously contraindicated in children with completely absent cochlear nerves.

Audiometry, Pure-Tone↗
PubMed1980

Basilar-membrane motion in the alligator lizard: its relation to tonotopic organization and frequency selectivity.

In the alligator lizard the entire basilar membrane is accessible for measurements of its velocity by the Mössbauer method. Tests of the method indicate (1) the Mössbauer source can be placed on the basilar membrane without altering the signal-transmission properties of the cochlea, and (2) the source adheres to the basilar membrane. Isovelocity curves (IVCs) were constructed by plotting (as a function of tone frequency) the sound-pressure level at the tympanic membrane required to produce a specified velocity amplitude. IVCs from 21 lizards for source locations spanning the length of the basilar membrane indicate that basilar-membrane velocity does not vary systematically with longitudinal location as it does in mammalian cochleas. Measurements of velocity waveforms in two lizards do not indicate substantial nonlinearity in the inner-ear mechanical system. The frequency dependence of the basilar-membrane velocity is similar to that of the extrastapes velocity over the range 0.4 to 2 kHz. Thus, the tonotopic organization and frequency selectivity, which have been previously demonstrated in this species in responses of both auditory-nerve fibers and cells of the receptor organ, are apparently not primarily determined by basilar-membrane motion.

Animals↗
PubMed1990

Middle-ear response in the chinchilla and its relationship to mechanics at the base of the cochlea.

The responses of the malleus and the stapes to sinusoidal acoustic stimulation have been measured in the middle ears of anesthetized chinchillas using the Mössbauer technique. With "intact" bullas (i.e., closed except for venting via capillary tubing), the vibrations of the tip of the malleus reach a maximal peak velocity of about 2 mm/s in responses to 100-dB SPL tones in the frequency range 500-6000 Hz; vibration velocity diminishes toward lower frequencies with a slope of about 6 dB/oct. Opening the bulla widely increases the responses to low-frequency stimuli by as much as 16 dB. At low frequencies, malleus response sensitivity with either open or intact bullas far exceeds all previous measurements in cats and matches or exceeds such measurements in guinea pigs. Whether measured in open or intact bullas, phase-versus-frequency curves closely approximate those predicted from the magnitude-versus-frequency curves by minimum phase theory. The stapes responses are similar to those of the malleus, except that stapes response magnitude is lower, on the average, by 7.5 dB at frequencies below 2 kHz and 10.7 dB at 2 kHz and above. Comparison of the responses of the middle ear with those of the basilar membrane at a site 3.5 mm from the stapes indicates that, at frequencies below 150 Hz, the basilar membrane displacement is proportional to stapes acceleration. At frequencies between 150 and 2000 Hz, basilar membrane displacement is proportional to stapes velocity.

Acoustic Impedance Tests↗
PubMed1990

The representation of the spectra and fundamental frequencies of steady-state single- and double-vowel sounds in the temporal discharge patterns of guinea pig cochlear-nerve fibers.

Psychophysical results using double vowels imply that subjects are able to use the temporal aspects of neural discharge patterns. To investigate the possible temporal cues available, the responses of fibers in the cochlear nerve of the anesthetized guinea pig to synthetic vowels were recorded at a range of sound levels up to 95 dB SPL. The stimuli were the single vowels /i/ [fundamental frequency (f0) 125 Hz], /a/ (f0, 100 Hz), and /c/ (f0, 100 Hz) and the double vowels were /a(100),i(125)/ and /c(100),i(125)/. Histograms synchronized to the period of the double vowels were constructed, and locking of the discharge to individual harmonics was estimated from them by Fourier transformation. One possible cue for identifying the f0's of the constituents of a double vowel is modulation of the neural discharge with a period of 1/f0. Such modulation was found at frequencies between the formant peaks of the double vowel, with modulation at the periods of 100 and 125 Hz occurring at different places in the fiber array. Generation of a population response based on synchronized responses [average localized synchronized rate (ALSR): see Young and Sachs [J. Acoust. Soc. Am. 66, 1381-1403 (1979)] allowed estimation of the f0's by a variety of methods and subsampling the population response at the harmonics of the f0 of the constituent vowel achieved a good reconstruction of its spectrum. Other analyses using interval histograms and autocorrelation, which overcome some problems associated with the ALSR approach, also allowed f0 identification and vowel segregation. The present study has demonstrated unequivocally that the timing of the impulses in auditory-nerve fibers provides copious possible cues for the identification of the fundamental frequencies and spectra associated with each of the constituents of double vowels.

Animals↗
PubMed1992

The effect of olivocochlear bundle transection on tuning curves and acoustic distortion products.

A growing body of research suggests that the efferent innervation to the cochlea, the olivocochlear bundle (OCB), may modulate the mechanical function of the cochlea. However, the role of tonic OCB input in cochlear function remains poorly understood. The purpose of this study was to determine the influence of tonic efferent input on cochlear mechanics, by transecting the entire OCB in guinea pigs, and observing changes in tuning curves and acoustic distortion products. The OCB was transected by avulsing the inferior vestibular nerve as it enters the internal auditory canal of the right bulla. Auditory brainstem response (ABR) thresholds, ABR tuning curves, and acoustic distortion products were measured before and after surgery. Successful transection of the OCB was verified histochemically. Results revealed no consistent changes in tuning curves or in the growth functions of the distortion products. To the extent that these measures reflect cochlear mechanical nonlinearities, it is concluded that tonic OCB input is not necessary for grossly normal cochlear mechanical function in the 10-kHz region of the guinea pig cochlea. It thus seems unlikely that the efferents are involved in establishing a "set point" for cochlear operation.

Animals↗
PubMed2005

Wiener kernels of chinchilla auditory-nerve fibers: verification using responses to tones, clicks, and noise and comparison with basilar-membrane vibrations.

Responses to tones, clicks, and noise were recorded from chinchilla auditory-nerve fibers (ANFs). The responses to noise were analyzed by computing the zeroth-, first-, and second-order Wiener kernels (h0, h1, and h2). The h1s correctly predicted the frequency tuning and phases of responses to tones of ANFs with low characteristic frequency (CF). The h2s correctly predicted the frequency tuning and phases of responses to tones of all ANFs, regardless of CF. Also regardless of CF, the kernels jointly predicted about 77% of the features of ANF responses to "frozen" samples of noise. Near-CF group delays of kernels and signal-front delays of responses to intense rarefaction clicks exceeded by 1 ms the corresponding basilar-membrane delays at both apical and basal sites of the chinchilla cochlea. This result, confirming that synaptic and neural processes amount to 1 ms regardless of CF, permitted drawing a map of basilar-membrane delay as a function of position for the entire length of the chinchilla cochlea, a first for amniotic species.

Acoustic Stimulation↗
PubMed1988

Delay-tuned combination-sensitive neurons in the auditory cortex of the vocalizing mustached bat.

1. FM-FM neurons in the auditory cortex of the mustached bat are sensitive to a pair of frequency-modulated (FM) sounds that simulates an FM component of the orientation sound and an FM component of the echo. These neurons are tuned to particular delays between the two FM components, suggesting an encoding of target range information. The response properties of these FM-FM neurons, however, have previously been studied only with synthesized orientation sounds and echoes delivered from a loud-speaker as substitutes for the bat's own orientation sounds and corresponding echoes. In this study, the combination sensitivity and delay tuning of FM-FM neurons were examined while the bat was actively vocalizing. 2. When the bat produced orientation sounds in an anechoic environment, or synthesized single FM echoes were delivered to a silent bat, the FM-FM neurons showed weak or no response. In contrast, when synthesized FM echoes were delivered with a particular delay from the FM component of the vocalized orientation sounds, the FM-FM neurons exhibited strong facilitative responses. 3. In both the vocalizing bats and the silent bats with substituted synthesized orientation sounds, all FM-FM neurons tested responded preferentially to the same echo harmonic (FM2, FM3, or FM4). 4. In vocalizing bats, FM-FM neurons showed maximum response to an echo FM component delivered with a particular delay (best delay) from an FM component in the orientation sound. Best delays measured with vocalized orientation sounds were nearly the same as those measured with synthesized orientation sounds. 5. The equivalent effect of a vocalized orientation sound and a synthesized FM1 component on the activity of FM-FM neurons indicates that, during echolocation, the FM1 component in the vocalized orientation sound stimulates the auditory system and conditions the FM-FM neurons to be sensitive to echoes with particular delays from the vocalized orientation sounds. 6. The amount of vocal self-stimulation to the inner ear by the bat's own vocalized sounds was measured by recording cochlear microphonic potentials (CMs). Spectral analysis of CM indicated that the amount of vocal self-stimulation by each harmonic of an orientation sound was equivalent to a sound of 70 dB sound pressure level (SPL) for the first harmonic (H1), 91 dB SPL for H2, 83 dB SPL for H3, and 70 dB SPL for H4, when the amplitude of the vocalized sound was 117 dB SPL at 5 cm in front of the bat's mouth.

Animals↗
PubMed1999

Development of acetylcholine-induced responses in neonatal gerbil outer hair cells.

Cochlear outer hair cells (OHCs) are dominantly innervated by efferents, with acetylcholine (ACh) being their principal neurotransmitter. ACh activation of the cholinergic receptors on isolated OHCs induces calcium influx through the ionotropic receptors, followed by a large outward K+ current through nearby Ca2+-activated K+ channels. The outward K+ current hyperpolarizes the cell, resulting in the fast inhibitory effects of efferent action. Although the ACh receptors (AChRs) in adult OHCs have been identified and the ACh-induced current responses have been characterized, it is unclear when the ACh-induced current responses occur during development. In this study we attempt to address this question by determining the time of onset of the ACh-induced currents in neonatal gerbil OHCs, using whole cell patch-clamp techniques. Developing gerbils ranging in age from 4 to 12 days were used in these experiments, because efferent synaptogenesis and functional maturation of OHCs occur after birth. Results show that the first detectable ACh-induced current occurred at 6 days after birth (DAB) in 12% of the basal turn cells with a small outward current. The fraction of responsive cells and the size of outward currents increased as development progressed. By 11 DAB, the fraction of responsive cells and the current size were comparable with those of adult OHCs. The results indicate that the maturation of the ACh-induced response begins around 6 DAB. It appears that the development of ACh-induced responses occur during the same time period when OHCs develop motility but before the onset of auditory function, which is around 12 DAB when cochlear microphonic potentials can first be evoked with acoustic stimulation in gerbils.

Acetylcholine↗
PubMedDate not supplied

Cochlear and brain stem responses in hearing loss following neonatal hyperbilirubinemia.

The site of lesion in hearing loss following neonatal hyperbilirubinemia is unclear. Histopathological studies have implicated the brain stem auditory nuclei while other investigations have hinted at a lesion in the cochlea. In order to clarify this issue, attempts were made to record responses from the auditory pathway in 13 patients with hearing loss following neonatal hyperbilirubinemia. The neural response from the auditory nerve was absent in 11 of the 13 patients and present only in response to high intensity stimuli in 2 patients. However, the response of the cochlear hair cells (cochlear microphonic potential) was present in 9 of the 13 patients. In most other cases of sensorineural hearing loss, with no history of hyperbilirubinemia, the hair cell response was absent. This is functional evidence for auditory nerve damage in cases of hearing loss following neonatal hyperbilirubinemia while the hair cells are spared.

Adult↗
PubMedDate not supplied

Generators of the frequency-following response in the guinea pig.

Generators of the frequency-following response (FFR) were assessed in 13 guinea pigs by cooling of the whole body and by experimental lesions of the brain stem. In the temperature study, the amplitude-temperature function of the FFR contained a significant cubic component that was absent from that of the cochlear microphonic potential (CM) recorded from the round window. The phase shift of the FFR increased with decreasing body temperature. In experimental lesions of the brain stem, a significant phase shift of the FFR was obtained following contralateral postcollicular section. The FFR amplitude with transection of the auditory nerve was similar to that found before surgical sections of the brain stem. The duration of the FFR after the transection corresponded precisely to that of the round window CM. These results indicate that the origin of the FFR contains both nonneural (ie, cochlea) and neural (ie, involving the inferior colliculus) generators.

Animals↗
PubMed2005

Auditory neuropathy/dys-synchrony and its perceptual consequences.

Auditory neuropathy/dys-synchrony is a form of hearing impairment in which cochlear outer hair cell function is spared but neural transmission in the auditory pathway is disordered. This condition, or group of conditions with a common physiologic profile, accounts for approximately 7% of permanent childhood hearing loss and a significant (but as yet undetermined) proportion of adult impairment. This paper presents an overview of the mechanisms underlying auditory neuropathy/dys-synchrony-type hearing loss and the clinical profile for affected patients. In particular it examines the perceptual consequences of auditory neuropathy/dys-synchrony, which are quite different from those associated with sensorineural hearing loss, and considers currently available, and future management options.

Adult↗
PubMed2000

Basic and clinical physiology of the inner ear receptors and their neural pathways in the brain.

The six receptors of the inner ear (cochlea, two otolith organs and three semicircular canals) share a common transduction unit made up of a sensory hair cell, a first order sensory neuron and the synapse between them. Displacement of the stereocilia in a particular direction leads to excitation of the hair cell and activation of the neuron. Electrical and mechanical reflections of these stages of transduction can be recorded non-invasively in humans and in animals. These include cochlear microphonic potentials, otoacoustic emissions, auditory and vestibular evoked potentials. The ability to record these activities can be used to track the development of inner ear function in the fetus and neonate and to study the effects of various ototoxic agents (e.g. noise) and drugs.

Animals↗
PubMed1975

[Evoked response audiometry of the guinea pig before and after drop in hearing induced by furosemid (author's transl)].

Using particular surface electrodes evoked response audiometry (ERA) can be applied to small laboratory animals without any sedation or anaesthesia. In addition to other methods we have studied in this way the influence of extreme doses of Furosemid on the guinea pig inner ear. 6-20 mg Furosemid per 100 g of bodyweight (about 100 times the human therapy dose) were applicated i.v. within 5 min resulting in a drop of hearing immediately. For the anaesthesized animal the cochlear microphonic potentials (CM) decrease simultaneously, indicating Furosemid to act at the inner ear itself. By both methods recovery of inner ear function is seen to start about 10 min later according to the little biological half life of Furosemid. As being restricted in respect of time for the CM-measurements we are sure about reversibility only by the ERA-method.

Animals↗
PubMed1989

[Frequency-dependent cochlear microphonics in inner ear hearing loss with various pitch thresholds].

Promontory recordings of the cochlear microphonics (CM) after stimulation with 0.5, 1 and 2 kHz tone bursts at 120 dB SPL were performed on normal subjects and patients with various, levels of sensory hearing loss. A significant correlation was found between frequency-related CM amplitudes and the configuration of the pure-tone audiogram. Such recordings provide objective information on hearing abilities at low and middle frequencies and are thus a relevant tool in clinical audiometry.

Auditory Threshold↗
PubMed1986

[The promontory test and electrocochleography in deafness caused by mumps].

Contradictory histological findings in patients with deafness following mumps led us to conduct electrophysiological investigations. Promontory testing (PT) and measurement of cochlear microphonics (CM) enabled us to distinguish between neural and sensory deafness. On the basis of a careful history and serological tests in 19 cases of unilateral deafness we found that the hearing loss was probably caused by mumps. In all patients except one auditory sensations could be obtained by electric stimulation of the acoustic nerve whereas no CM were detectable even with strong stimuli of 100 dB tonepips. In view of the electrophysiological findings, doubt is cast on the neural genesis of deafness following mumps as assumed by Lehnhardt (1962).

Audiometry, Evoked Response↗