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At least 181 records · Page 10Linked to original sources
PubMed1995

A novel cholinergic "slow effect" of efferent stimulation on cochlear potentials in the guinea pig.

This report documents slow changes in cochlear responses produced by electrical stimulation of the olivocochlear bundle (OCB), which provides efferent innervation to the hair cells of the cochlea. These slow changes have time constants of 25-50 sec, three orders of magnitude slower than those reported previously. Such "slow effects" are similar to classically described "fast effects" in that (1) they comprise a suppression of the compound action potential (CAP) of the auditory nerve mirrored by an enhancement of the cochlear microphonic potential (CM) generated largely by the outer hair cells; (2) the magnitude of suppression decreases as the intensity of the acoustic stimulus increases; (3) they share the same dependence on OCB stimulation rate; (4) both are extinguished upon cutting the OCB; and (5) both are blocked with similar concentrations of a variety of cholinergic antagonists as well as with strychnine and bicuculline. These observations suggest that both fast and slow effects are mediated by the same receptor and are produced by conductance changes in outer hair cells. Slow effects differ from fast effects in that (1) fast effects are greatest for acoustic stimulus frequencies between 6 and 10 kHz, whereas slow effects peak for frequencies from 12 to 16 kHz, and (2) fast effects persist over long periods of OCB stimulation, whereas slow effects diminish after 60 sec of stimulation. The time course of the slow effects can be described mathematically by assuming that each shock-burst produces, in addition to a fast effect, a small decrease in CAP amplitude that decays exponentially with a time constant that is long relative to the intershock interval. The long time constant of the slow effect compared to the fast effect suggests that it may arise from a distinct intracellular mechanism, possibly mediated by second-messenger systems.

Acoustic Stimulation↗
PubMed1977

Identification and separation of acoustic frequency following responses (FFRS) in man.

Frequency following responses (FFRs) to monaural tone bursts were recorded in normal and hearing impaired subjects as the potential difference between an ipsilateral earlobe electrode and a scalp vertex electrode. Whenn the rubber tube coupler between the earphone and the subject's ear was clamped, a stimulus artefact FFR was occasionally recorded. The "biological" FFR had a latency of about 1 msec and an irregular wave form which was made more sinusoidal by the addition of white noise. When the responses to tone bursts of opposite onset phases were added together, a "double frequency" FFR was obtained which had a latency of about 6 msec and whose amplitude was appreciably reduced by white noise. In some hearing impaired subjects (with no neural responses to clicks), this longer latency double frequency component could not be recorded, while in those cases in which the cochlear microphonic potential could be recorded, the shorter latency FFR was also present. It is concluded that the FFR in normally hearing subjects is made up of a short latency cochlear microphonic component and a longer latency neural component.

Adolescent↗
PubMed1977

Usher's syndrome: electrophysiological tests of the visual and auditory systems.

The symptoms of Usher's syndrome - congenital hearing impairment and tapetoretinal dystrophy - are difficult to detect in young children. The electroretinogram (ERG), visual evoked potential (VEP), auditory nerve and brain-stem responses as well as the cochlear microphonic potentials were used to evaluate the defects of the visual and auditory systems in 20 patients, 3-45 years of age. This study demonstrates the usefulness, reliability and convenience of the electrophysiological tests for early diagnosis and functional evaluation of Usher's syndrome.

Adolescent↗
PubMedDate not supplied

[Acoustically guided behavior in the early ontogeny of the long-eared owl: the development of hearing sensitivity].

The development of hearing sensitivity was studied in 15 nestlings and 7 adult long eared owls by cochlear recording potentials. The dynamic of frequency threshold characteristics of cochlear microphonic, action potential of cochlear nerve, and electromyogram of reflectory contraction of middle ear muscle were followed from the 1st to 40 day posthatching. The upper limit of hearing determined by cochlear microphonic, was about 3 kHz on the 1st day after hatching, 7 kHz on the 6th day, and 10 kHz on the 11th. Within 11 days after hatching the low-frequency range of higher sensitivity was revealed (with the maximum at 0.5 kHz), which was the same as that of monotonic signals effective for stimulation of the feeding reaction. The middle frequency range of higher sensitivity corresponded to the spectrum of own vocalization of the nestlings. During the period of formation of the patterned vision there was a delay in development of low- and middle-frequency sensitivity of cochlear microphonic while the high-frequency thresholds continued to decrease. After this period the guiding stimulation for eliciting feeding reaction changes from the auditory for the visual. The action potential of the cochlear nerve could be recorded from the 6th day simultaneously with the appearance of locating head movements and the reflectory contraction of the middle ear muscle.

Acoustic Stimulation↗
PubMed1985

[Electrophysiologic studies on the course of the adaptation phase following noise stress].

It was the aim of this study to settle the problem whether the post-stimulatory pattern of the extent of excitation (amplitude, latency) registered with the cortical evoked potentials can be verified in the recovery phase via leads from the brain stem region and cochlea. In this context electrophysiological measurements with human and animal material were performed. After a five-minute stimulation with a wide-band noise of various intensity we examined in the post-stimulation phase the specific stimulus pattern of the evoked potentials during an interval of 5 minutes with a resolution of 5 sec. We determined the change in response patterns of evoked potentials. Finally, the relevance of the results with regard to various nuclei of the auditory pathway is compared with corresponding electrophysiological measurements of the cochlear microphonics potentials, the VIII nerve compound action potential, and evoked potentials of different units of the brain stem and brain.

Animals↗
PubMedDate not supplied

Bioelectric phenomena in the ototoxicity of nitrogen mustard.

The effects of nitrogen mustard on the electrical potentials of the inner ear were studied, and the results were correlated with the histopathologic findings which have been reported in nitrogen mustard ototoxicity. The endocochlear DC potential (EP) decreased rapidly after an injection of nitrogen mustard (NM). The amplitude of the cochlear microphonics potential (CM) diminished rapidly, and no substantial recoveries were observed. No significant changes in the magnitude of the negative potential of organ of Corti (NPOC) were observed. A large negative summating potential (SP) was recorded even when the amplitude of the CM had diminished.

Acoustic Stimulation↗
PubMed1986

Development of mammalian endocochlear potential: normal ontogeny and effects of anoxia.

The development of the positive endocochlear potential (EP), the negative anoxic EP, and the organ of Corti potential were measured at various postnatal ages in the Mongolian gerbil, beginning at 8 days after birth (DAB). The organ of Corti potential (OCP) was present at 8 DAB but averaged 21% less than the adult value. OCP increased regularly with age, reaching adult values of -90 mV by 14 DAB. The positive EP was first observed at 10 DAB, at which age it averaged only 2-3 mV. This potential increased monotonically between 10 and 20 DAB, by which time it had reached the adult value of 75 mV. Anoxia did not result in a negative EP until 12 DAB, at which age this potential averaged -7 mV. The negative anoxic EP matured more rapidly than the positive EP, achieving the adult value of 40 mV by 18 DAB. During development the positive EP appeared to closely parallel the maturation of glucose metabolism in the stria vascularis. The negative anoxic EP was more closely related temporally to the development of cochlear microphonic potential (CM) thresholds. It is hypothesized that changes which occur between 10 and 16 DAB in the apical membranes of the cochlear hair cells contribute to the maturation of both CM and the negative anoxic EP.

Animals↗
PubMed1999

A model of cochlear function assessment during reversible ischemia in the Mongolian gerbil.

An in vivo model in the Mongolian gerbil is used to assess the auditory changes during reversible cochlear ischemia. This model allows the recordings of cochlear potentials (microphonics, summating potential and compound action potential) and otoacoustic emissions (cubic difference tones, CDTs), together with laser Doppler cochlear blood flow (CBF) measurements, over reversible cochlear ischemia. Ischemia is achieved by compression of the eighth nerve complex at the porus of the internal acoustical meatus, whereas the compression release allows the reperfusion to occur. While CBF monitoring permits to objectively determine the degree of ischemia and reperfusion, the combined analysis of cochlear potentials and CDTs makes it possible to point out the preferential site of main functional damage within the cochlea, i.e., outer hair cells (OHCs), inner hair cells, or ganglia cells. At least three ischemia-reperfusion sequences can be used on one side, and sometimes both ears can serve for experiments. This model could be applicable for testing drugs with alleged protective effects against cochlear ischemia and/or reperfusion, in treated vs. non-treated animals.

Animals↗
PubMed1986

Vestibular microphonic potentials in pigeons.

Electrical responses to acoustic stimuli were measured by placing thin wire electrodes in the vestibular system of a pigeon model. Responses were measured after extirpation of the cochlea and the application of tetrodotoxin to the perilymphatic space. Responses seen were comparable to those of known cochlear microphonic potentials. These findings indicate that acoustic stimuli can evoke microphonic potentials in the vestibular system of the pigeon. We also found that vibrational amplitudes of less than 1 nm were sufficient to evoke a vestibular microphonic potential.

Acoustic Stimulation↗
PubMed1976

Changes in cochlear microphonic sensitivity after priming C57BL/6j mice at various ages for audiogenic seizures.

Groups of mice were briefly exposed to a one-octave band of noise at 14, 18, 28, 38, or 58 days of age. Five days later the groups were divided, and some mice were behaviorally tested for audiogenic seizures by reexposing them to the same sound. The round window cochlear microphonic potential was measured in the remaining animals and compared with that observed in unprimed control subjects. Seizure behavior occurred in all animals primed on Day 18 but rarely for subjects in the other age groups. Cochlear microphonic threshold curves in mice primed on Day 18 showed a 30-dB loss in sensitivity, while all other primed groups showed little change. These data were discussed in terms of the "disuse-supersensitivity" hypothesis previously proposed to account for the physiological effects of priming in mice.

Acoustic Stimulation↗
PubMedDate not supplied

Comparison of hearing threshold determined by auditory pathway electric responses and by behavioural responses.

In order to evaluate their reliability for determing the hearing threshold, the cochlear microphonic potentials, the auditory nerve and brain stem neural evoked responses as well as the cortical evoked responses were compared with the behavioural hearing thresholds of the same subjects in the same session. The threshold for recording the cochlear microphonic potnetial was found to be appreciably higher than the behavioral threshold. The threshold for recording the auditory nerve and brain stem responses was within a few decibels of the behavioural threshold. The thresold of the cortical evoked response was several decibels higher. It is concluded that (1) the auditory nerve and brain stem neural evoked responses are the best indicators of hearing threshold; (2) the cortical evoked responses are usually comparable, and (3) all types of evoked responses are indispensable aids in the evaluation of hearing and the determination of site of lesion in the auditory system.

Audiometry↗
PubMed1999

Hearing impairment in patients with acoustic neuroma--analysis by electrocochleography.

OBJECTIVE: In patients with acoustic neuroma, the site and severity of hearing impairment are important in discussing surgical approaches. Since the effectiveness of conventional auditory psychological testing is limited, we studied objectively hearing impairment of the cochlea and the cochlear nerve due to the tumor. METHODS: Electrocochleography (ECochG) was carried out in 21 patients with acoustic neuroma. Cochlear microphonic potential (CM) and action potential (AP) in ECochG evoked with clicks and short tone bursts were recorded through a transtympanic needle electrode technique. Cochlear function was studied using the detection thresholds of CM, and cochlear nerve involvement was analyzed by differences between AP and CM detection thresholds. RESULTS: The 1 kHz CM detection threshold was elevated in 17 (81.0%) of 21 patients indicating cochlear impairment. Of seven patients with normal hearing or mild sensorineural hearing loss in pure tone audiometry, three had a slightly elevated CM detection threshold. Of five patients with pronounced pure tone levels, four showed a CM response and were thought to have mild cochlear dysfunction. Cochlear nerve impairment was confirmed in three of four patients with well-developed CM based on elevated AP detection thresholds. Three patients had CM response but no AP response, suggesting severe cochlear nerve impairment. CONCLUSION: Disorders of the cochlea and the cochlear nerve can be evaluated with ECochG AP and CM measurement. The findings of ECochG are thought to be important information to judge hearing prognosis, thereby enhancing its clinical utility.

Adult↗
PubMed1986

Trimethyltin ototoxicity: evidence for a cochlear site of injury.

The environmental contaminant, trimethyltin (TMT), produces a profound elevation in tone intensity necessary to inhibit the acoustic startle reflex in laboratory animals which recovers over a prolonged period except at very high frequencies. The recovery that is observed does not begin until 3 to 5 weeks after a single acute administration depending upon dosage. As opposed to the very temporary threshold shifts by the salicylates and loop diuretics or the permanent and progressive ototoxicity resulting from aminoglycoside antibiotics the time course for recovery of acoustic startle reflex inhibition after TMT appears to be an anomaly for a chemical ototoxicant. In terms of the duration of loss only, this pattern appears similar to that sometimes observed after noise exposure. The current investigation replicates the finding that recovery of acoustic startle reflex inhibition after TMT is frequency related in that only the highest frequency impairment appears to be permanent. While this frequency dependence suggests a cochlear locus of injury, both the known neurotoxic effects of TMT and the time course of the behavioral impairment suggest a more central locus of injury. Compound action potential and cochlear microphonic recordings made from the round window in the current study confirm a preferential high frequency effect of TMT and demonstrate a significant cochlear component to the ototoxic effects of this agent.

Action Potentials↗
PubMed1962

Cochlear responses to condensation and rarefaction clicks.

Auditory nerve responses to condensation and rarefaction clicks (CC and RC) have been recorded over a wide intensity range with gross electrodes. At low intensities the RC responses are nearly identical to CC responses. At high intensities RC and CC response waveforms are similar, but the latency of the N(1) peak in the RC response is 0.2 msec. shorter than that for the corresponding CC response. At intermediate intensities the RC and CC response waveforms are quite different. These results can be interpreted in terms of a model in which there are two excitatory mechanisms for the neural response, which are operative in different intensity ranges. The cochlear microphonic potential and a "slow" potential are suggested as possible excitatory mechanisms.

Acoustic Stimulation↗
PubMed1983

Receptor potentials of lizard hair cells with free-standing stereocilia: responses to acoustic clicks.

Receptor potentials of single hair cells in the free-standing region of the basilar papilla of the anaesthetized alligator lizard were measured intracellularly with micropipettes. Stimuli were primarily acoustic pulses (clicks) delivered to the tympanic membrane. The receptor potential was independent of click repetition rate for the range 10-150 clicks/s. This property is presumed to be the basis of the rate independence of the extracellular cochlear microphonic potential. The receptor potential wave-form consisted of a fast oscillatory component (or oscillation) superimposed on a usually positive (depolarizing) slow component. Reversal of the stimulus polarity resulted in a reversal of the polarity of the oscillations; the polarity of the slow component remained unchanged. The relative magnitudes of the two components depended on click level. At the higher click levels the magnitudes of the slow and oscillatory components were comparable. The relation of the receptor potential to the stimulus was non-linear; the peak-to-peak magnitude of the receptor potential increased less than proportionately with increasing sound-pressure level, and reversal of the stimulus polarity did not result in a reversal of the receptor potential. The receptor-potential magnitude for high-level clicks ranged from 1-13 mV peak-to-peak with an average value of 3.5 mV. At the lower click levels the magnitude of the slow component was much smaller than that of the oscillatory component. The relation of the receptor potential to the acoustic stimulus approached that of a linear system, the magnitude of the receptor potential became approximately proportional to the sound-pressure level, and reversal of the stimulus polarity resulted in approximate reversal of the receptor potential. For low-level stimuli the frequency of the oscillations of the receptor potential in response to clicks was approximately equal to the frequency of maximal a.c. response to tones. Apparently, both phenomena reflect the frequency selectivity of the processes generating the receptor potential. The frequency of oscillations in the click response varied from one cell to another (range of 1.0-2.2 kHz in this study). The results are qualitatively consistent with a model (Weiss, Mulroy & Altmann, 1974) that contains a linear, band-pass filter followed by a rectifier followed by a low-pass filter.

Acoustic Stimulation↗
PubMed1981

The summating potential and Meniere's disease. I. Summating potential amplitude in Meniere and non-Meniere ears.

We investigated the relationship between Meniere's disease and the abnormally enlarged summating potential (SP) in a series of patients and normal subjects. Cochlear and auditory nerve responses to rectangular-pulse clicks, delivered at a rate of 8/s and an intensity of 115 dB peak-equivalent sound pressure level, were recorded from ear canal skin. We performed a parabolic regression for SP amplitudes as a function of auditory nerve action potential (AP) amplitudes in normal ears and obtained the 95% confidence interval (+/- 2 SD) for normal scatter around the fitted curve. Sixty-eight percent of SP amplitudes from ears with Meniere's disease exceeded the upper normal confidence limit. In contrast, only 7% of the cochlear ears and none of the retrocochlear ears had SP amplitudes above this normal upper limit. Cochlear microphonic potentials and APs from the ears with Meniere's disease also tended to be larger than normal, but this tendency was not strong enough to be of diagnostic use.

Action Potentials↗
PubMed1987

Modulation of the masking phenomenon by the crossed part of the medial olivocochlear bundle.

The masking phenomenon is used in clinical investigation of the inner ear to determine the frequency selectivity properties of the auditory system. Sectioning of the crossed part of the medial efferent bundle in a guinea pig model decreases the simultaneous masking phenomenon. The efferent effect seen in the forward masking varied with the masking paradigm used. When the masker onset precedes the maskee onset by more than 40 ms, masking diminishes after sectioning the crossed part of the medial efferent bundle. When this duration was shortest (30 ms), no effect was observed. This phenomenon could be explained by the time necessary to stimulate the medial efferent loop. Our results could explain some differences observed in the compound action potential masking curves with different masking paradigms.

Acoustic Stimulation↗