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Results for “Cochlear Microphonic Potentials”

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At least 19 recordsLinked to original sources
PubMed1981

[Study of the mechanism of auditory adaptation by simultaneous recording of cortical auditory evoked potentials and cochlear microphonic potentials].

Auditory adaptation, apart from the effect of the neurotropic drugs, galanthamine, GABA and nanophyn on this adaptation, was examined in 35 rabbits exposed to white noise (90 dB, re 2.10(-5) Pa, 10 min) by concurrent recording of evoked potentials of the brain and microphonic potentials of the cochlea. The results suggest that the mechanism of auditory adaptation is determined by the processes that occur in the synapses of the auditory system central parts and is monitored by the sympathetic nervous system.

Adaptation, Physiological↗
PubMed1977

[Microphonic cochlear potentials in the cat during exposure to 2-tons harmonic signals with different phase spectra].

Cochlear microphonic potentials (CM), i. e. the round window responses, evoked by the two-tone sound complexes consisting of the 1st and 2nd harmonics with different phase relation between the components were studied in cats. The spectral analysis of the CM responses showed high sensitivity of the CM potentials to phase changes in the complex sound stimuli. The 1st harmonic in the range of 350--750 Hz could be reduced at a certain phase shift of the 2nd harmonic in the complex signal. The phase and frequency limits of this phenomenon are described.

Animals↗
PubMed1976

Recording of the cochlear microphonic potential with surface electrodes.

The cochlear microphonic potential was recorded in human subjects with surface electrodes (earlobe clip and scalp vertex disc) and an averaging procedure. Special precautions were taken to identify and separate artefactual, neural and microphonic components. These included shielding of the earphone, a rubber tube to introduce a time delay between artefact and biological response and white noise to mask the neural component. The cochlear microphonic potential was larger in amplitude in response to low frequency sounds and had a high threshold. Two clinical cases of cochlear hearing loss are presented, both lacking neural responses. The cochlear microphonic potential was present in one of them (i.e., neural hearing loss) and absent in the other (i.e., sensory hearing loss).

Adult↗
PubMedDate not supplied

[New method for recording human cochlear microphonic potentials].

The use of invasive methods to record cochlear microphonic potentials preclude its use in routine clinical diagnosis in humans. We present an instrument and method used to obtain cochlear microphonics recordings using external electrodes in human beings. Biological and technical tests were performed before application. Stimulation with a pure, continuous and defined tone yielded cochlear microphonics that can be interpreted easily. This new method allows human cochlear physiology and pathophysiology to be studied non-invasively.

Acoustic Stimulation↗
PubMedDate not supplied

Surface-recorded cochlear microphonic potentials during temporary threshold shifts in man.

Cochlear microphonic potentials (CM) were recorded, by means of surface electrodes, before, during and after white-noise-induced temporary threshold shifts (TTS) in human volunteers. The behavioural threshold shift was not accompanied by a change in amplitude of CM. These findings indicate that in humans, the site affected by the noise exposure and which probably gives rise to the TTS is central to the site of generation of CM. In a previous study, the compound action potential generated in the auditory nerve was found to be of lower amplitude and longer latency during TTS, and it is thus proposed that the site affected is peripheral to the generation of conducted action potentials. The synapse between hair cells and the auditory nerve fibres is the most likely candidate to be the affected site.

Acoustic Stimulation↗
PubMed1987

Variations of cochlear microphonic potential after sectioning efferent fibers to the cochlea.

Cochlear microphonic (CM) potentials were recorded, in guinea pig, with differential electrodes before and after sectioning the medial efferent innervation at the level of the brainstem. Sectioning the crossed part of the medial efferent innervation did not change the CM whatever the frequency or level of stimulation used. Sectioning the medial--crossed and uncrossed--efferent fibers diminished CM amplitude at frequencies above 2 kHz. Thus, the ipsilateral medial efferent tract seems to be involved, through a tonic action, in controlling outer hair cell micromechanics.

Acoustic Stimulation↗
PubMedDate not supplied

[Cochlear microphonic potentials with surface electrodes in the diagnosis of sensorineural hearing loss].

Cochlear microphonic potentials have only been used experimentally because of technical difficulties and the need for inserting transtympanic electrodes. We present the results of a study of 70 ears, 40 with sensorineural hearing loss and 30 with normal hearing. Cochlear microphonics were recorded with surface electrodes. The stimulus was a pure, continuous tone. Statistical analysis disclosed a difference in cochlear microphonic threshold between the two groups. The normal threshold was defined as 83.73 dB and the most significant frequency was 4,000 Hz. The present report shows that this new method can be useful in diagnosing sensorineural hearing loss.

Adolescent↗
PubMed2001

Cochlear microphonic potentials: a new recording technique.

A new instrumentation and a particular method for detecting and recording cochlear microphonic potentials (CMPs) are described here. The CMPs were recorded in rats by means of pure tones (4,000, 2,000, 1,000, 500, and 250 Hz) and intraepidermic electrodes; the electrocochleography technique was avoided. An experimental design that included the use of a glutamatergic agonist (kainic acid [KA]) and an aminoglycoside antibiotic (kanamycin [KANA]) was carried out to demonstrate the origin of the recorded potential. Morphological studies showed that KA selectively eliminated the afferent type I dendrites of the spiral ganglion, while the administration of KANA resulted in the absence of outer hair cells. When CMPs were recorded after KA administration, no alterations were detected. In contrast, KANA administration resulted in the absence of any selective electrophysiological activity corresponding to CMPs. All these results were compared with the recording of the compound action potential of the eighth nerve obtained by electrocochleography. These findings and the great specificity of the reproduction of the sound stimulus confirm that the CMPs can be recorded by the new equipment.

Acoustic Stimulation↗
PubMedDate not supplied

Cochlear microphonic potentials in patients with vestibular schwannomas.

We evaluated the cochlear function of 44 patients with unilateral vestibular schwannomas by measuring cochlear microphonic potentials (CM) in electrocochleography. We used short tone bursts with 0.5-, 1-, 2-, and 4-kHz frequencies as acoustic stimuli to evoke CMs, and determined CM detection thresholds. The CM detection thresholds in vestibular schwannomas ranged from normal to no response. Cochlear dysfunction was seen in 35 (79.5%) of the 44 cases; these patients had higher CM detection thresholds than normal subjects. Although a significant correlation was found between mean hearing level (0.5-4 kHz) and mean CM detection threshold (0.5-4 kHz), 20 patients had lower CM detection thresholds than were found using audiometry. This suggests that there is an additional retrocochlear component responsible for this hearing loss.

Adult↗
PubMed1997

[Study on cochlear microphonic potentials obtained by adaptive filtering technique].

In order to delete the contamination of acoustic stimulus artefact in average evoked cochlear microphonics by surface recording, an application of adaptive filtering technique for cancelling the stimulus artefact from the cochlear microphonics was proposed. The results demonstrated that in normal hearing ears, the cochlear microphonic potentials (CM) which was obtained by adaptive filtering technique was later than the ipsilateral response, whereas the AP response could be seen in the ipsilateral response to 2 kHz, 4 kHz and 8 kHz stimuli. In 31(77.5%) ears with profound sensorineural hearing loss and 29(27.5%) ears with moderate to severe sensorineural hearing loss, the CM was absent, but in the other ears the CM was as clear as in ears with normal hearing. It suggests that by this technique sensorineural hearing loss can be further differentiated into two kinds: neural hearing loss and sensory hearing loss.

Action Potentials↗
PubMed1982

Cochlear microphonic potentials elicited by biosonar signals in flying bats, Pteronotus p. parnellii.

Cochlear microphonic (CM) potentials were recorded from the bat, Pteronotus p. parnellii during tethered flight and during simulated flight on a pendulum. For each emitted signal the frequency of the ca. 61 kHz constant frequency (CF) component was compared with the frequency response characteristics of the animals's ear. The majority of "resting pulses' had CF components with the maximum frequency approximately 200 Hz below the best frequency (BF) of the CM audiogram. Doppler shift compensation occurred only during forward swings of the pendulum and in such a way that the echo CF components were always maintained near the BF, but on the low frequency slope of the CM audiogram. CM responses to emitted pulses were usually small in amplitude and in some animals no responses were seen. Echoes Doppler shifted upward, however, evoked high amplitude potentials. Echo CF components estimated to be at least 43 dB fainter than the emitted pulses evoked higher amplitude CM potentials than the loud emitted pulses. Echoes from large surfaces up to 4.5-5.0 meters away evoked CM potentials as high in amplitude as those elicited by emitted pulses, even when there was no Doppler shift. Beats in the CM were observed on many occasions and occurred as a result of pulse-echo and echo-echo interactions.

Animals↗
PubMed1975

Frequency dependent changes in the amplitude of the cochlear microphonic potential of the pigeon ear during transient anoxia.

The effect of transient anoxia on the cochlear microphonic potential at different sound frequencies was investigated. The microphonic potential was recorded with glass microelectrodes in the ductus cochlearis of the pigeon ear. Transient anoxia had different effects, related to frequency, on the amplitude and the relative phase angle of the microphonic potential recorded from one place in the ductus cochlearis. At frequencies equal to and higher than the best frequency the amplitude of the microphonic potential was more sensitive to anoxia than it was at lower frequencies. Microphonic potential at 1 kHz lower than the best frequency was often enlarged in amplitude during transient anoxia. The results suggest that this frequency-dependent effect is a positional one. Changes in the phase were largest around the best frequency. It is inferred that anoxia causes complex changes in the pattern of vibration in the cochlear partition. The observed changes in amplitude and also changes in phase are caused by the combined effects of reduction of the endolymphatic potential and changes in vibration pattern.

Acoustic Stimulation↗
PubMed2006

Cochlear microphonic potential recorded by transtympanic electrocochleography in normally-hearing and hearing-impaired ears.

The cochlear microphonic is a receptor potential believed to be generated primarily by outer hair cells. Its detection in surface recordings has been considered a distinctive sign of outer hair cell integrity in patients with auditory neuropathy. This report focuses on the results of an analysis performed on cochlear microphonic recorded by transtympanic electrocochleography in response to clicks in 502 subjects with normal hearing threshold or various degrees of hearing impairment, and in 20 patients with auditory neuropathy. Cochlear microphonics recorded in normally-hearing and hearing-impaired ears showed amplitudes decreasing by the elevation of compound action potential Cochlear microphonic responses were clearly detected in ears with profound hearing loss. After separating recordings according to the presence or absence of central nervous system pathology (CNS+ and CNS-, respectively), cochlear microphonic amplitude was significantly higher in CNS+ than in CNS- subjects with normally-hearing ears and at 70 dB nHL compound action potential threshold. Cochlear microphonic responses were detected in all auditory neuropathy patients, with similar amplitudes and thresholds to those calculated for normally-hearing CNS- subjects. Cochlear microphonic duration was significantly higher in auditory neuropathy and normally-hearing CNS+ patients compared to CNS- subjects. Our results show that: 1. cochlear microphonic detection is not a distinctive feature of auditory neuropathy; 2. CNS+ subjects showed enhancement in cochlear microphonic amplitude and duration, possibly due to efferent system dysfunction; 3. long-lasting, high frequency cochlear microphonics with amplitudes comparable to those obtained from CNS- ears were found in auditory neuropathy patients. This could result from a variable combination of afferent compartment lesion, efferent system dysfacilitation and loss of outer hair cells.

Adolescent↗
PubMed1988

Concomitant changes in the acoustic impedance and the cochlear microphonic potentials during twitch contractions of the middle ear muscles in cats.

The effect of twitch contractions of the middle ear muscles in cats on sound transmission through the middle ear (as measured by the cochlear microphonic potential of the inner ear) was compared with the simultaneous changes in the acoustic input impedance of the middle ear at the same frequency. It was found that decreases in impedance were related to an increase in the amplitude of the cochlear microphonics and vice versa. This may imply that decreases in impedance measured during the initial phase of the acoustic reflex in man are true decreases and are not due to transient decoupling of the ossicular chain at any point.

Acoustic Impedance Tests↗