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Results for “Cochlear Microphonic Potentials”

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PubMed2000

Low-frequency acoustic modulations generated by the high-frequency portion of the cochlea, noninvasively recorded from the scalp of mice (Mus musculus).

Vocalizations often contain low-frequency modulations of the envelope of a high-frequency sound. The high-frequency portion of the cochlear nerve of mice (Mus musculus) generates a robust phase-locked response to these low-frequency modulations, and it can be easily recorded from the surface of the scalp. The cochlea is most sensitive to envelope modulation frequencies of approximately 500 to 2000 Hz. These responses have detection thresholds that are approximately 10 dB more sensitive than auditory brainstem responses, and they are very sharply tuned. These measurements may provide a nontraumatic means of repeatedly assessing cochlear functions involved in sound localization and perception of vocalizations.

Animals↗

PubMed1992

[Evoked otoacoustic emissions and their modification by contralateral acoustic stimulation].

The active vibration of the basilar membrane as well as evoked otoacoustic emissions (EOAE) are probably based on the motile properties of cochlear outer hair cells (OHC). In the present study we examined the effects of contralateral acoustic stimulation on ipsilateral EOAE and thereby the active cochlear micromechanics. Contralateral white noise with intensities below 30 dB HL enhanced the EOAE amplitude, whereas higher sound levels reduced the evoked acoustic emissions. Similar effects of contralateral acoustic stimuli on ipsilateral EOAE were observed in patients with a conductive hearing loss. However, the required sound levels were higher compared to probands with normal hearing. In controls with unilateral deaf patients white noise up to 60 dB HL did not alter the EOAE amplitude. We concluded, that in patients with normal hearing or unilateral conductive hearing loss, effects of contralateral acoustic stimulation on evoked ipsilateral sound emissions may be due to the activation of crossed olivo-cochlear efferents reaching the OHCs.

Acoustic Stimulation↗

PubMed1992

[Evoked otoacoustic emissions in diagnosis of cochlear hearing disorders].

The authors consider the possibility of routine use of evoked otoacoustic emissions (EOE) in diagnosis of sensory hearing loss by comparison of EOE curves with relative curves obtained by pure tone audiometry. 180 ears with sensory hearing loss of different aetiologies were examined. EOE were obtained by application of Bray and Kemp's Evoked Otoacustic Measurement Package (ILO88). The results obtained show a close correlation between presence of EOE and real hearing losses of different frequencies obtained by pure tone audiometric evaluation. We could detect no EOE with hearing losses over 50 dB HL at 500 Hz, 40 dB HL at 1000 Hz, 50 dB HL at 2000 Hz and 85 dB HL at 4000 Hz. With a rate of middle hearing loss over 45 dB HL we also did not find EOE for the whole frequency range. On the base of this study, the authors conclude that EOE explore the functional integrity of those parts of the cochlea that correspond to the middle frequencies of hearing range. If EOE are not detectable, statements on the nature and extent of hearing loss on the base of this examination are not valid.

Adolescent↗

PubMed1989

[Prognostic indications within the scope of the selection of cochlear implant patients].

The common selection criteria for cochlear implant patients do not allow any prognostic indication on the final result. On the other hand, some postoperative data (threshold, TDL, dynamic range, duration of deafness) corresponds clearly with the results, some of them also correspond with the preoperative data. Preoperative TDL, dynamic range as well as duration of deafness can therefore be used as suitable prognostic indicators.

Auditory Threshold↗

PubMed1992

Influence of spontaneous otoacoustic emissions (SOAE) on acoustic distortion product input/output functions: does the medial efferent system act differently in the vicinity of an SOAE?

Otoacoustic emission (OAE) generation mechanisms reside in the active micromechanical properties of the organ of Corti, and especially in the outer hair cells (OHCs). OHCs are strongly innervated by medial efferent olivo-cochlear fibres. Decrease of the intensity of transiently evoked otoacoustic emissions (TOAEs) and modification of spontaneous otoacoustic emissions (SOAEs) during acoustic stimulation of the contralateral ear have already been shown in humans. Similar results were obtained in guinea pigs with a decrease of 2F1-F2 acoustic distortion products (DPOAEs) and a suppression of the effect with sectioning of the floor of the fourth ventricle. The present study sought to investigate the influence of contralateral auditory stimulation on DPOAEs recorded in humans. It shows a decrease in DPOAE intensity for all frequencies, at levels above 45 dB SPL of contralateral broad band noise. This effect was found at levels of contralateral BBN well below the acoustic reflex threshold, and in subjects without acoustic reflex. Moreover, the influence of transcranial transmission could be ruled out since no effect was found when contralateral BBN applied to the altered ear of totally unilaterally deaf patients. Thus, the contralateral acoustic stimulation effect on DPOAEs provides a new means of functional exploration of the medial efferent system in humans. The effect obtained is more ample at low primary frequency levels. Moreover, as DPOAEs are known to be stronger and to show more irregular input/output function patterns in the vicinity of an SOAE, the influence of contralateral auditory stimulation was studied for DPOAEs recorded at 10 Hz, 50 Hz and 150 Hz from an SOAE frequency.

Acoustic Stimulation↗

PubMed1992

Cochlear microphonics and recruitment.

In this study, bilateral cochlear microphonics (CM) were evoked by tone burst simultaneously. A speaker was put in head-food axis 2 m from the mid-point of a given line connecting the bilateral external meatus. Five normal persons and 68 cases (34 cases of Meniere's disease, 27 cases of sudden hearing loss, and 7 cases of low-tone sensory hearing loss without vertigo) with unilateral sensory hearing loss and recruitment, in addition to 2 cases of bilateral Meniere's disease with recruitment were examined. CM shifted in normal and hearing loss ears and was absent in profound and totally deaf ears. When recruitment was present, CM at corresponding frequencies were enlarged and prolongated in 60 cases. Some of the enlarged and prolongated CM decayed slowly, others quickly. Meanwhile the CM of the opposite normal ear decreased obviously. The presence of enlarged and prolongated CM may indicate an increase of abnormal excitability of the hair cells caused by some pathological stimulations. This would cause excitability of the hair cells in the opposite cochlea to be inhibited by the effect of the efferent system. In such a condition, the patients complained that the stimulating sound was heard louder in the disordered ear than that in the opposite normal ear. CM was slightly enlarged during sleep.

Adult↗

PubMed1999

Clinical findings for a group of infants and young children with auditory neuropathy.

OBJECTIVE: To examine the prevalence of auditory neuropathy in a group of infants at risk for hearing impairment and to present an overview of the clinical findings for affected children. DESIGN: Results for 20 subjects who showed repeatable cochlear microphonic potentials in the absence of click-evoked auditory brain stem responses are included in this study. Behavioral and steady state evoked potential thresholds were established in each case. Where possible, otoacoustic emission and speech perception results (unaided and aided) also were obtained. RESULTS: One in 433 (0.23%) of the children in our series had evidence of auditory neuropathy. The audiometric findings for these subjects varied significantly, with behavioral thresholds ranging from normal to profound levels. Discrimination skills were also variable. Approximately half of the subjects showed little understanding, or even awareness, of speech inputs in both the unaided and aided conditions. There were, however, a number of children who could score at significant levels on speech discrimination tasks and who benefited from the provision of amplification. CONCLUSION: The results suggest that auditory neuropathy is more common in the infant population than previously suspected. The effects of neuropathy on auditory function appear to be idiosyncratic, producing significant variations in both the detection and discrimination of auditory signals. As such, the management of children with this disorder must allow for individual differences.

Audiometry, Evoked Response↗

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↗

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↗

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↗

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↗