Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cochlear Microphonic Potentials”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources
PubMed2000

An analysis of the hydraulic conductivity of the extracisternal space of the cochlear outer hair cell.

The cylindrically shaped cochlear outer hair cell (OHC) plays an important role in the transduction of acoustic energy into electrical energy in the cochlea. The extracisternal space (ECiS) of the lateral wall of the OHC is the fluid-filled space between the plasma membrane (PM) and the intracellular subsurface cisterna (SSC). In the ECiS, an array of cylindrical micropillars extends from the SSC to the PM. We obtain equations for the pressure, osmotic concentration and fluid velocity in the ECiS from the Brinkman-Stokes equations for steady incompressible flow in a plane channel that encloses an array of cylinders and whose upper wall, i.e. the plasma membrane, has a hydraulic conductivity of P(PM). From these equations we obtain an estimate for the hydraulic conductivity of the ECiS, P(ECiS). We show that the ECiS geometry accounts for P(ECiS) being several orders of magnitude larger than P(PM) and that P(ECiS) increases with the width of the ECiS and decreases with the length of the ECiS.

Cochlea↗
PubMed1981

Plasticity of binaural interaction in the cat inferior colliculus.

Responses of single neurones in the inferior colliculus (IC) to acoustic interaural intensity difference (IID) were examined in normal, adult cats and in cats that had been reared for 3--4 months, either from birth or as adults, with unilateral ligation of the external meatus. There were significantly fewer units displaying IID sensitivity in either of the ligated groups than there were in the normal group. The loss of IID sensitivity in the ligated animals reflected a diminished inhibitory input from the non-ligated ear.

Aging↗
PubMed1989

Suppression of auditory nerve activity in the guinea pig cochlea by 1-(p-bromobenzoyl)-piperazine-2,3-dicarboxylic acid.

1-(p-Bromobenzoyl)-piperazine-2,3-dicarboxylic acid (pBB-PzDA; 0.03-5 mM), an excitatory amino acid antagonist, was perfused through the guinea pig cochlea while monitoring various cochlear potentials. pBB-PzDA (1-5 mM) reversibly suppressed the amplitude of the compound action potential of the auditory nerve (CAP) and increased the latency of N1 (the first negative wave of the CAP) at all sound intensities. pBB-PzDA had no detectable effect on N1 latency at CAP threshold or presynaptic potentials such as the cochlear microphonics and the summating potential. At the single-cell level pBB-PzDA (5 mM) reversibly suppressed the firing of single auditory nerve ganglion cells. pBB-PzDA appeared to have the same potency in the cochlea as kynurenic acid. We conclude that the mechanism of action of pBB-PzDA is consistent with an antagonism of the hair-cell transmitter at the afferent auditory nerve.

Acoustic Stimulation↗
PubMed1980

Far-field cochlear microphonic responses to continuous pure tones recorded from the scalps of cats.

The cochlear microphonic response to continuous pure tones has been recorded in the 'far field' from the scalps of anesthetized cats. Previous methods for scalp recording used tone pip transients only. Our experiments show that the observed wave forms are not due to electrical or mechanoelectrical artifacts. Neural responses such as brain stem responses or the frequency-following response have been excluded as major contributors to the observed wave forms, which are virtually identical to the round window cochlear microphonic response with respect to (1) wave shape with non-sinusoidal stimuli, (2) intensity-amplitude functions, (3) response phase, and (4) amplitude changes due to superimposed band-limited white noise. The methods of ruling out significant artifacts are applicable to non-invasive recordings from humans.

Animals↗
PubMed1990

Selectively eliminating cochlear microphonic contamination from the frequency-following response.

The frequency-following response (FFR) is the scalp recorded response to low frequency stimuli. As an electrophysiological method for determining auditory threshold, it has application in both clinical and research settings. However, the response is often contaminated with the cochlear microphonic (CM), reflecting the response of outer hair cells, rather than neural generators (i.e., auditory nerve, cochlear nucleus, superior olivary nucleus, inferior colliculus, etc.). The FFR needs to be a purely neural response to establish its clinical and experimental usefulness. The methods applied to date have failed to accomplish this. The present study demonstrates a method of deriving a pure neural response by subtracting a forward masked FFR, which contains only CM, from an unmasked FFR. To confirm that the residual response after forward masking is solely CM, one needs to record two forward masked responses with opposite phase probe stimuli. When the responses are added they will sum to zero only if the residual response with forward masking is pure CM. This study demonstrates that the traditional method for removing CM from FFR, by simple summation of unmasked responses recorded with stimuli of opposite phase, does not accurately reflect the amplitude or frequency of the FFR, while the proposed method provides an accurate assessment of the FFR amplitude free of CM contamination.

Acoustic Stimulation↗
PubMed1995

Influence of auditory stimulation and visual attention on otoacoustic emissions.

Transient Evoked otoacoustical Emissions (TEOAEs) express the micromechanical activity of the cochlear outer hair cells (OHCs). The inhibitory effects of contralateral acoustic stimulation and of visual attention tasks on TEOAE amplitude is well-established. Contralateral auditory stimulation and attention affect cochlear micromechanics via the medial olivocochlear efferent system. The present study is a quantitative comparison of the individual and combined effects of these two inhibitory phenomena in the same subjects. TEOAEs were recorded in seven normal-hearing subjects in absence of inhibitory stimulus (S1), under contralateral 95 dB SPL white-noise stimulation (S2), during a visual attention task (S3) and with simultaneous presentation of both forms of stimulus (S4). Significant reductions in TEOAE amplitude were found with contralateral stimulation (S2) and visual attention (S3) (p = 0.01 and 0.05 respectively, in confirmation of previous studies. The inhibitory effect of combined stimulation (S4) was found to be yet more significant (p = 0.004) than the inhibition obtained with each stimulation presented alone.

Acoustic Stimulation↗
PubMed1995

A statistically based method to generate response maps objectively.

One scheme to classify the physiological response properties of single units in the cochlear nucleus is based on the average discharge rate of the unit and is reflected in the distribution of excitatory and inhibitory regions in a frequency-level map (response map) that spans the unit's receptive area (e.g., Evans and Nelson, 1973; Young and Brownell, 1976; Young and Voigt, 1982; Shofner and Young, 1985, Spirou and Young, 1991). Typically, discharge rate versus level curves are acquired at many frequencies and the investigator determines that a unit is excited or inhibited at a given level if the driven rate is above or below a spontaneous rate estimate by a specified criterion (for example, 20%). The investigator then encloses regions of excitation and inhibition where responses over adjacent frequencies and levels are consistent. In the present report, we describe an objective 3-step computer-based method to generate response maps: raw driven and spontaneous rate estimates are smoothed with a low-pass spatial filter; a unit is said to be excited or inhibited at a given level if the filtered driven rate is above or below the mean filtered spontaneous rate for that frequency by a specified criterion (percentage or statistical); and resultant response maps are median spatial filtered to eliminate spurious regions. The results shown here demonstrate that use of a statistical criterion provides a more reliable detection of excitation and inhibition than a 20% criterion, particularly when the variance of the rate estimates is high. Further, the statistically based method permits unit classification based on response map data that are more rapidly acquired with shorter duration stimuli (32 vs. 200 ms). Although this method is applied to units recorded in the dorsal cochlear nucleus, the technique may be applicable to studies of receptive fields and their plasticity in other systems.

Acoustic Stimulation↗
PubMedDate not supplied

Experimental congenital cytomegalovirus labyrinthitis and sensorineural hearing loss.

Cytomegalovirus is a leading cause of human congenital viral infection and hearing loss. The pathogenesis of human congenital cytomegalovirus infection is poorly understood. We have developed a reproducible model of congenital cytomegalovirus-induced sensorineural hearing loss in guinea pigs. This report reviews our previously published results and provides additional new information about this model.

Animals↗
PubMedDate not supplied

Effect of electrical stimulation on middle latency response in the guinea pig.

A temporary threshold shift (TTS) has been demonstrated in the electrically evoked middle latency response (EMLR) following exposure to moderate levels of continuous electrical stimulation via a cochlear implant. The threshold at which the EMLR was elicited in chronically implanted guinea pigs was elevated by approximately 100% following 30 minutes of moderate intensity (200 microA or more) sinusoidal electrical stimulation of the cochlea. Results obtained under anesthesia varied unacceptably. In awake animals, EMLR thresholds were stable over time and consistent TTSs were observed. The threshold returned to prestimulation levels within 4 hours following termination of the stimulation. The possibility of histopathologic changes and the relevance of these findings in setting safe output levels for cochlear implant processors are discussed.

Animals↗
PubMedDate not supplied

Cochlear microphonics recorded from fetal and newborn sheep.

PURPOSE: Sounds present within the uterus stimulate the fetal inner ear and central auditory pathway. This study was undertaken to determine the efficiency of transmission of exogenous airborne stimuli to the fetal inner ear. In this way, we may quantify the extent to which the fetal auditory system is isolated from sounds produced outside the mother. MATERIALS AND METHODS: Cochlear microphonics were recorded from fetal and newborn sheep to evaluate the extent to which the fetus is isolated from sounds exogenous to the ewe. Electrodes were surgically placed in contact with the round window membrane in nine near-term fetal sheep. Cochlear microphonics were recorded in response to 1/3 octave-band noises (0.125 to 2.0 kHz) delivered through a loudspeaker 1.8 m from one side of the pregnant ewe. Sound pressure levels generated by the noises were simultaneously recorded ex utero with a microphone and in utero with a hydrophone previously sutured to the fetal neck. After cochlear microphonic amplitudes were recorded, the fetus was delivered through an abdominal incision. Recordings were repeated from the newborn lamb. Fetal sound isolation was calculated as the difference between the sound pressure levels that were necessary to evoke equal cochlear microphonic amplitudes from the fetus and from the newborn lamb. RESULTS: The sound attenuation observed was variable for all frequencies. The fetus was isolated from external sounds by 11.1 dB for 0.125 kHz, 19.8 dB for 0.25 kHz, 35.3 dB for 0.5 kHz, 38.2 dB for 1.0 kHz, and 45.0 dB for 2.0 kHz. CONCLUSIONS: Other investigators have demonstrated that the immature auditory system is more susceptible to damage produced by noise exposure than is the mature auditory system. Low-frequency noise produces damaged cells that later in life code higher frequencies. A possibility of fetal hearing loss produced by intense noise exposure needs more careful evaluation.

Animals↗
PubMed1979

Bone conduction mechanisms: Mössbauer measurements on the role of ossicular inertia.

The Mössbauer technique was used to measure displacements of the stapes footplate and adjacent temporal bone during bone conduction stimulation at frequencies from 250 to 400 Hz in anaesthetized guinea pigs. The stapes was found not to be driven at amplitudes or phases that differed significantly from those of the temporal bone. Measurement of stapes displacements during air conduction stimulation, and of temporal bone displacements during bone conduction stimulation producing matching cochlear microphonic amplitude, enabled calculation of limiting values of amplitude and phase difference necessary to produce the required relative displacement. The obtained values (less than 1 dB for amplitude and 1--4 degrees for phase) were beyond the resolution of the measurement system employed for reasonable nuclear counting times. The results provide quantitative estimates of the magnitude of inertial effects, but do not establish whether ossicular inertia is an important factor in bone conduction stimulation.

Acoustic Stimulation↗
PubMed1980

Effects of loud tones on the inner ear: a combined electrophysiological and ultrastructural study.

Guinea pigs were exposed to a 10 kHz pure tone and damage to the cochlea was investigated immediately after exposure, or after a recovery period ranging from 18-25 days. Structural damage was assessed using scanning electron microscopy and functional damage estimated using the N1 threshold audiogram. Exposure at 106 dB for 1 h caused obvious abnormalities of outer hair cell stereocilia. The location and extent of this damage was related to the immediate or long term deficits in the N1 threshold audiogram.

Acoustic Stimulation↗
PubMed1980

Some dualistic properties of the cochlear microphonic.

Within a small frequency range just above the characteristic frequency of a differential electrode pair, cochlear microphonic input-output functions are bimodal, exhibiting two maxima. The more sensitive, low-intensity response has a more limited linear operating range, and it is more labile due to acoustic fatigue or hypoxia. After fatigue or hypoxia, the high-intensity response is revealed. The latter operates 180 degrees out-of-phase with the former, presumably due to its being generated more basalward in the cochlea. The difference in the lability of the two components suggests that the two sources are different types of hair cells: i.e., outer and inner hair cells.

Acoustic Stimulation↗
PubMed1980

Effect of intermittent sound stimulation on cochlear microphonics and the possible preventive effect of coenzyme Q10.

Observations have been made on the effect of intermittent intense sound stimuli, using the CM as an index. Experiments were conducted regarding the effectiveness of the drug CoQ10 in ameliorating the acoustic injury due to this traumatization. The CM was measured by the differential electrode method from the basal turn of the cochlea. The individual differences between animals were monitored using intensity functions. Pure tones at a frequency of 4 kHz were used both for the traumatizing signal and the CM generating signal. Acoustic traumatizing signals lasted 1 min with a 5 min silent interval, and were repeated 10 times. Both the chronic depression and the transient depression of CM were measured after each traumatization. In control animals, the chronic depression progressed in an exponential manner and the transient depression was constant after each stimulation. In CoQ10 treated animals, the chronic depression was milder than that in the control animals. The transient depression was equivalent in the two groups. The effectiveness of CoQ10 on the acoustic injury was discussed on the basis of the results obtained with the present experiment.

Acoustic Stimulation↗
PubMed1980

Voltage-dependent elements are involved in the generation of the cochlear microphonic and the sound-induced resistance changes measured in scala media of the guinea pig.

The injection of d.c. current into scale media alters both the cochlear microphonic (CM) and the acoustically synchronized changing resistance (CR) measured in scala media. Positive current increases the CM and decreases the CR. The effect on the CM is greatest at high sound pressure level (SPL), whereas the effect on CR is greatest at low SPL. Negative current has a similar but opposite effect on both the CM and the CR. The results suggest that a voltage-dependent nonlinear element exists in cochlear hair cells.

Acoustic Stimulation↗
PubMed1981

Acoustical responses and suppression-period patterns in guinea pigs.

Acoustic responses to short sound stimuli have been measured in the external ear canal of guinea pigs. Unequivocal responses had frequencies between 1.8 and 3.2 kHz, latencies (to their peak pressures) of 2.8 to 4.5 ms and sound pressures up to -10 dB SPL. A set of criteria was developed to clearly distinguish acoustical responses from after-resonances of the stimuli. Added phase-locked, very-low-frequency tones were able under some conditions to totally suppress the acoustical responses. The suppression-period pattern thus produced strongly resemble those obtained for man and the masking-period patterns obtained with human subjects.

Acoustic Stimulation↗
PubMed1982

Intracellular and extracellular responses in the organ of Corti of the gerbil.

Techniques have been developed for recording from and staining cells in the organ of Corti of the Mongolian gerbil. Using physiological criteria as in the guinea pig, the cells were classified as either supporting cells or inner hair cells (IHCs). In addition, several IHCs were stained using HRP and identified in surface preparations. Extracellular responses in the vicinity of IHCs were tuned as sharply as auditory-nerve fibers. Intracellular tuning curves of IHCs were equally sharp near their tips. However, the tip-to-tail distances and sensitivities appeared to be somewhat reduced, presumably due to trauma caused by the recording electrode. Intensity functions, relating receptor depolarization to stimulus intensity level, were obtained for the IHCs. The functions have a consistent quantitative form for frequencies equal to or less than the characteristic frequency of a cell. At low stimulus levels the response increases in proportion to energy, i.e. the square of the sound pressure level. At high levels the response increases more slowly, but shows a greater operating range, and smaller effects of saturation, than do the steady-state responses of single auditory-nerve fibers.

Animals↗