Need for a noninvasive technique to measure cochlear responses.
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Basilar Membrane↗
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Effect of furosemide upon morphology of hair bundles in guinea pig cochlear hair cells.
Furosemide was administered by intraperitoneal injection and intracochlear perfusion. The peak-to-peak amplitude of the cochlear microphonic at high sound intensities was reduced however the drug was administered. After a period of time ranging from 1-4 h following drug application, cochleae were fixed and prepared for scanning electron microscopy to examine the hair cells. Changes in the hair bundles from basal turns tended to be more extensive than those of more apical turns. Initially there was an increase in the granularity of the surface of the stereociliary membrane and a tendency for cross-links to swell, stretch and break. Later, the surface texture of stereocilia became smoother than normal, and hair cells in the basal turns showed extensive erosion and fracture of cross-links. Tip links could survive even when extensively stretched. It is possible that the morphological changes in stereocilia reported here do not arise from direct actions of furosemide, but indirectly, from perturbations of the ionic composition of cochlear fluids induced by effects of the drug upon the stria vascularis.
Animals↗
Subclinical changes of auditory function in the aged.
Elderly normal hearing subjects were studied using tests for cochlear functions (remote masking, brief tone audiometry, critical ratio, evoked otoacoustic emission), for neural auditory function (tone decay) and for central auditory functions (ipsilateral vs. contralateral acoustic reflex, tonal masking level difference). The findings demonstrated that ageing can cause subclinical abnormalities, almost consistently localized to the inner ear vibrating structures and only occasionally to the sensory and/or neural elements.
Acoustic Impedance Tests↗
What is the cochlear place code for pitch?
The advent of cochlear implants has increased the clinical interest in the cochlear code for pitch. It is widely believed that pitch is determined by the location of the excitation maximum in the cochlea. However, direct recordings from cochlear hair cells indicate that, for a given sound frequency, the location changes appreciably with sound intensity, whereas the corresponding pitch remains approximately constant. Correlated with this constancy is a surprising constancy of the location of the high-frequency cutoff of cochlear excitation.
Acoustics↗
Effects of salicylate on shape, electromotility and membrane characteristics of isolated outer hair cells from guinea pig cochlea.
A reversible tinnitus and hearing loss have long been known to result from large doses of salicylate. Cochlear electrophysiology and otoacoustic emission studies suggest that the drug may interfere with outer hair cell electromotility. Exposure of isolated outer hair cells to sodium salicylate concentrations ranging from 0.05 to 10 mM reveals a dose dependent, reversible loss of turgidity and dimunition of electromotility. There was also a change in membrane conductance with salicylate superfusion that occurred later in time from the onset of shape and electromotility changes. There was no evidence of dose dependence for the change in membrane conductance, nor was the change reversible. The changes in shape and electromotility that we observe in vitro may impair cochlear partition movements in vivo and could account, at least in part, for the salicylate-induced hearing loss and effects on otoacoustic emissions.
Animals↗
Spontaneous otoacoustic emissions. Short-time stability.
We have examined 307 spontaneous otoacoustic emissions (SOAEs) from 59 ears. The short-time amplitude stability was very good, especially in the high-frequency region. A statistically significant trend for emissions to influence other emissions could not be demonstrated.
Acoustics↗
Medial olivo-cochlear system and tinnitus.
A possible role of the efferent system in the mechanisms of tinnitus generation has been put forward by several authors. A simple method for studying the functioning of this system is to compare the amplitudes of otoemissions with and without mild contralateral stimulation. In a recent communication, Veuillet et al. (1991) reported that, on the side of tinnitus, the efferent system of patients suffering from unilateral tinnitus seems to be less efficient than on the other side. The results presented here correspond to those obtained in the very first tinnitus patients submitted to a research protocol exploring systematically the efferent system. When possible, the effectiveness was tested in two ways: globally, using evoked otoacoustic emissions (EOAEs) and, very precisely in the frequency zone of the tinnitus, using cubic distortion product 2f1-f2. Preliminary results obtained in bilateral and unilateral tinnitus sufferers show that a majority of them exhibits, at least in the proximity of the tinnitus, a lack of effectiveness of the efferent system. In some of them, instead of the suppressive effect, an increasing one was even observed.
Adult↗
Age-related changes in evoked otoacoustic emission in normal-hearing ears.
The evoked otoacoustic emissions (e-OAEs) elicited by both tone-bursts and clicks were investigated in normal-hearing ears of three age groups: young age group (approximately 30 years), middle age group (31-50 years) and old age group (51 years approximately). The pseudothreshold of tone-burst e-OAE at stimulus frequencies between 500 Hz and 2 kHz was significantly elevated in the middle and old age groups compared with that in the young age group. When the relationship between averaged emission cochleograms drawn from the mean pseudothresholds of tone-burst e-OAEs at 6 stimulus frequencies between 500 Hz and 4 kHz and averaged pure-tone audiograms was analyzed, a clear difference was found among the three age groups in a frequency range between 500 Hz and 2 kHz. Total echo power, reproducibility, highest peak power and frequency area peak power up to 4 kHz in click e-OAE significantly decreased in the middle and old age groups compared with those in the young age group. These results indicate the possibility that the function of cochlear micromechanics deteriorates in all cochlear partitions with increasing age, even in normal-hearing ears.
Acoustic Stimulation↗
Pathophysiology of hearing impairment in acoustic neuroma with profound deafness: analysis by evoked otoacoustic emission and promontory stimulation test.
Evoked otoacoustic emissions (e-OAEs) were examined and promontory stimulus test (PST) done prior to tumor removal in 15 cases of surgically proven unilateral acoustic neuroma (AN) with more than 80 dB in pure-tone hearing level. The e-OAEs were elicited by tone-bursts at 1 kHz and 2 kHz, and an interaural difference in pseudothreshold of more than 10 dB was defined as a significant impairment of the cochlear function. In PST, electrical stimulation was applied by a burst mode at 6 stimulus frequencies between 50 Hz and 1600 Hz. The number of stimulus frequencies with a positive response was defined as the PST score. The results obtained were as follows; i) Mean interaural difference in e-OAE pseudothreshold was 16.0 dB at 1 kHz and 8.0 dB at 2 kHz, ii) Positive PST was found in only 40% of the subjects and the mean PST score was 0.93, iii). When the pathophysiology of hearing impairment was inferred from the combination of the findings in e-OAEs and PST, it was found that 33.3% of the subjects had pure cochlear impairment, 13.3% pure retrocochlear impairment and 46.7% cochlear-retrocochlear impairment. It is concluded that analysis of both e-OAEs and PST could clarify the pathophysiology of hearing impairment in AN with profound deafness, which cannot be determined by conventional psychoacoustic tests.
Acoustic Stimulation↗
Latency of contralateral sound-evoked auditory efferent suppression of otoacoustic emissions.
The suppression of transiently evoked otoacoustic emissions by contralateral sound stimulation is thought to occur as a result of the action of the efferent pathway from the superior olivary complex to the cochlea via the medial olivo-cochlear neurons. The purpose of this study was to determine the time taken for this pathway to activate the suppressive mechanism in response to contralateral sound in normal human subjects. The time for onset of suppression was found to be between 7 and 20 ms.
Acoustic Stimulation↗
Cochlear distribution of frequency-following response initiation. A high-pass masking noise study.
The cochlear initiation of the frequency-following response (FFR) to 500-Hz tone bursts was assessed in 6 normal-hearing subjects by measuring FFR amplitude as a function of the low-frequency cutoff of high-pass masking noise (3 550, 1 800, 900, and 450 Hz). The major fall off of FFR amplitude occurred when the masking noise began to mask the apical portion of the cochlea. This effect was especially apparent at low intensities. The results are interpreted as supporting the view that at low intensities, low-frequency tone bursts evoke the FFR primarily through the apical portion of the cochlea.
Adult↗
Influence of the stimulus repetition rate on brain-stem-evoked responses in man.
In order to record brain-stem-evoked responses as fast as possible, the influence of the stimulus repetition rate was investigated. The repetition frequency was varied from 2.5 to 80 Hz. The amplitudes of N2-N4 diminish uniformly with increasing stimulus rate. The repetition rate has little or no influence on the amplitude of N5; however, increasing the repetition frequency about 10 Hz causes an increase in the latencies of N2-N5. It seems that the decrease in the amplitude of N2-N4 and the increase in the latencies of N2-N5 are of cochlear origin, since the amplitude and the latency of the cochlear responses are influenced in the same way by the repetition rate as the above-mentioned brain stem responses.
Adult↗
Early auditory-evoked responses: spectral content.
Spectral analysis of the early auditory-evoked responses in man and in the cat has shown that the predominant contribution to the total power is contained in the band below 50-100 Hz. This low-frequency content is considerably reduced when the corresponding spontaneous brain activity spectrum is subtracted from the response spectrum. Under the latter circumstances, the dominant frequency contribution is found in the 500- to 2,500- Hz bandwidth.
Animals↗
Slow cortical responses and the diagnosis of central hearing loss in infants and young children.
To evaluate the usefulness of slow cortical responses (ERA) for threshold estimation in infants and young children, 83 children were investigated with combinations of pure-tone audiometry, electrocochleography (ECochG) and ERA. The deviations between ECochG/ and ERA thresholds were correlated to brain function in order to diagnose central hearing losses. By comparing corresponding values of 2 kHz pure-tone and ERA thresholds, 32% (10/31) errors were found, mainly below 35 dB HL. In a group of patients with no sign of brain disorder, an overall error rate of 37% (20/53) was found. Below 35 dB HL, 72% (11/15) errors were found. In a group of patients with brain dysfunction, the overall rate was 70% (21/30), below 35 dB HL it was 84% (21/25). In the range below 35 dB HL, no significant difference (p greater than 0.05) in errors was found between the groups with and without brain disorders. It is concluded that ERA is unreliable for the estimation of moderate hearing losses and cannot per se detect a central hearing dysfunction. Elevated ERA thresholds may indicate a central hearing loss, but to establish this topical diagnosis, ECochG and neuropsychological examinations are necessary.
Audiometry↗
Comparison of acoustically coupled and mechanically coupled speech.
Phonetically balanced work lists were mechanically coupled onto the ossicular chain of anesthetized guinea pigs by piezoelectric-type drivers and the resulting cochlear microphonic (CM) recorded on magnetic tape. Similar recordings of the CM resulting from free field tympanic membrane stimulation by hi-fi speakers were also obtained. The recordings were compared by conventional discrimination testing. In discrimination testing of all the raw recordings, listeners achieved essentially perfect scores. Addition of masking noise sufficient to reduce mean discrimination scores to 65-70% revealed no significant discrimination differences. When piezoelectrically initiated, CM-derived lists were compared with similar lists passed through hearing aids in an anechoic chamber, the preference of a panel of listeners for the quality of mechanically coupled speech was significantly higher. Mechanical-acoustical displacement equivalency at normal physiological levels and freedom from mechanical-electrical artifact were demonstrated by measurement of ossicular chain displacement by a fiber optic lever displacement transducer.
Animals↗
The Q10 of auditory brain stem responses in rats under hypothermia.
Auditory brain stem responses (ABRs) were recorded from normal Sprague-Dawley rats ranging in age from 15 to 120 days. Increased latencies for all four waves of the ABR were noted for animals of all ages as their body temperatures were reduced from 38 to 28 degrees C. The Q10S of the latency changes were highly variable but were still significantly higher for the first three waves of the ABR in animals less than 20 days of age compared with older animals. The Q10S for the fourth wave in both groups were alike. Wave heights tended to decrease during cooling, but this effect was inconsistent. The cochlear microphonic was recorded in some animals and tended to decrease in size with cooling. As seen in this study, the significant changes in wave latencies due to small temperature differences underscore the need to carefully control this variable when taking evoked responses from animal preparations and humans subject to variations in body temperature. The interanimal variability of the Q10 precludes any simple 'correction' of latency differences due to temperature for research or clinical purposes.
Animals↗
Nonlinear phenomena in click- and tone-burst-evoked otoacoustic emissions from human ears.
Otoacoustic emissions have been recorded from normally hearing subjects in response to clicks and 1-kHz tone bursts. Input-output relationships for response magnitudes and wave delays are presented. For the response magnitudes, two main effects are seen: (i) nonlinearities are maximal at moderate to high intensity levels (saturation), while deviations from linearity are minimal at the lowest levels (around the psychoacoustic threshold); (ii) the nonlinear behaviour is different at different time intervals (after stimulation): deviations from linearity are maximal for the latest parts of the response. Level- and time-dependent phenomena are also observed in the delay of identifiable response waves.
Acoustic Stimulation↗
Variability in the depression of cochlear microphonic responses after noise exposure.
20 guinea pigs were exposed to a broad band noise (120-140 dB SPL) for short durations. The conditions of stimulation were strictly identical for all animals. Cochlear microphonic responses (CM) were recorded with conventional differential electrodes after each exposure, from the first turn of the cochlea. Variations were observed in the degree of CM depression and also in the alteration of the CM transfer function. The origin of this variability is discussed.
Animals↗