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PubMed1986

Follow-up of auditory-evoked potentials and temporary threshold shift in subjects developing noise-induced permanent hearing loss.

The effects of auditory fatigue, using a temporary threshold shift (TTS) paradigm, on cochlear microphonics (CM) and on auditory brainstem-evoked potentials (ABEP), were studied in normal-hearing subjects during the development of permanent threshold shift (PTS). Behavioral threshold shifts were accompanied by different effects on CM and on ABEP, as PTS was gradually induced by occupational noise. Measures of the effect of increasing stimulus rate (ISR) on ABEP revealed decreased latency shifts during auditory fatigue. ABEP proved useful in early detection of changes in the auditory system, resulting from exposure to noise. In addition, this study further supports the suggestion that TTS acts as a peripheral attenuator of the effect of ISR on the central auditory pathway.

Adolescent↗
PubMed1996

Frequency specificity of 80-Hz amplitude-modulation following response.

The usefulness of 80-Hz amplitude-modulation following response (AMFR) detected by phase coherence to predict the hearing threshold during sleep was evaluated in 90 ears of 53 children with hearing impairment. The threshold of 80-Hz AMFR at carrier frequency of 1,000 Hz and the threshold of auditory brainstem response (ABR) elicited by 1,000 Hz tone pips in children during sleep were compared with behavioral hearing threshold, which was determined by standard pure-tone audiometry or play audiometry. In 12 ears of 12 children with various patterns of hearing impairment, 80-Hz AMFR at different carrier frequencies were examined, and the threshold pattern was compared with the pure-tone audiogram to investigate the frequency specificity of 80-Hz AMFR detected by phase coherence. The mean and standard deviation of the difference between 80-Hz AMFR and pure-tone thresholds was 4.3 and 12.1 dB, respectively, and that between ABR and pure-tone thresholds was 6.6 and 14.2 dB, respectively. The threshold patterns of 80-Hz AMFR very closely resembled the corresponding audiogram patterns in all types of hearing impairment. The measurement of 80-Hz AMFR in children during sleep thus appeared to be more accurate in hearing prediction than that by ABR elicited with tone pips and to have a good frequency specificity.

Adolescent↗
PubMed2003

Auditory steady-state response thresholds of adults with sensorineural hearing impairments.

This study evaluated the use of multiple auditory steady-state responses (ASSRs) to estimate the degree and configuration of behavioral audiograms of subjects with sensorineural hearing impairments. Place specificity of the multiple-ASSR method was also assessed. Multiple amplitude-modulated (77-105 Hz) tones (500, 1000, 2000 and 4000 Hz) were simultaneously presented to one ear. The results showed that, on average, multiple-ASSR thresholds were 14 +/- 13, 8 +/- 9, 10 +/- 10 and 3 +/- 10 dB above behavioral thresholds for 500, 1000, 2000 and 4000 Hz, respectively. Behavioral and multiple-ASSR thresholds were significantly correlated (r = 0.75-0.89). There were no significant differences between behavioral and multiple-ASSR measures of the audiogram configuration. In subjects with steep-sloping > or = 30 dB/ octave) hearing losses, multiple-ASSR thresholds did not underestimate behavioral thresholds revealing good place specificity. These results indicate that the multiple-ASSR method provides good estimates of the degree and configuration of hearing in individuals with sensorineural hearing impairments.

Adult↗
PubMed2003

[The effects of Streptolysin-O and sodium hyaluronate on the permeability of the round window membrane in guinea pigs--an electrophysiologic study].

BACKGROUND: The round window membrane (RWM) acts like a barrier for topically applied substances into the middle ear preventing diffusion into the perilymphatic fluid compartment. MATERIAL AND METHOD: In an animal model, modulation of the permeability of the RWM was attempted using Streptolysin-O (SLO) in various concentrations and sodium hyaluronate. Thereafter, the effect of intratympanically applied Lidocain 2 % on hearing threshold measured by auditory brainstem response was tested for Lidocain 2 % and Lidocain 2 % in combination with SLO or sodium hyaluronate. RESULTS: The results show that both, SLO and sodium hyaluronate, influence the effect of Lidocain 2 % on hearing thresholds as an indirect sign for changes of the permeability of the RWM. However SLO by itself in low concentrations decreased auditory thresholds in some animals while this was never observed with sodium hyaluronate. CONCLUSIONS: Our findings preclude SLO and favor sodium hyaluronate as a modulator of RWM permeability in therapeutic trials.

Animals↗
PubMed2006

Multiple auditory steady-state response thresholds to bone-conduction stimuli in young infants with normal hearing.

OBJECTIVE: Multiple auditory steady-state responses (ASSRs) probably will be incorporated into the diagnostic test battery for estimating hearing thresholds in young infants in the near future. Limiting this, however, is the fact that there are no published bone-conduction ASSR threshold data for infants with normal or impaired hearing. The objective of this study was to investigate bone-conduction ASSR thresholds in infants from a Neonatal Intensive Care Unit (NICU) and in young infants with normal hearing and to compare these with adult ASSR thresholds. DESIGN: ASSR thresholds to multiple bone-conduction stimuli (carrier frequencies: 500 to 4000 Hz; 77 to 101-Hz modulation rates; amplitude/frequency modulated; single-polarity stimulus) were obtained in two infant groups [N = 29 preterm (32 to 43 wk PCA), tested in NICU; N = 14 postterm (0 to 8 mo), tested in sound booth]. All infants had passed a hearing screening test. ASSR thresholds, amplitudes, and phase delays for preterm and postterm infants were compared with previously collected adult data. RESULTS: Mean (+/-1 SD) ASSR thresholds were 16 (11), 16 (10), 37 (10), and 33 (13) dB HL for the preterm infants and 14 (13), 2 (7), 26 (6), and 22 (8) dB HL for the postterm infants at 500, 1000, 2000, and 4000 Hz, respectively. Both infant groups had significantly better thresholds for 500 and 1000 Hz compared with 2000 and 4000 Hz, in contrast to adults who have similar thresholds across frequency (22, 26, 18, and 18 dB HL). When 500- and 1000-Hz thresholds were pooled, pre- and postterm infants had better low-frequency thresholds than adults. When 2000- and 4000-Hz thresholds were pooled, pre- and postterm infants had poorer thresholds than adults. ASSR amplitudes were significantly larger for low frequencies compared with high frequencies for both infant groups, in contrast to adults, who show little difference across frequency. ASSR phase delays were later for lower frequencies compared with higher frequencies for infants and adults, except for 500 Hz in the preterm group. ASSR phase delays were later for infants compared with adults across frequency. CONCLUSIONS: Infant bone-conduction ASSR thresholds are very different from those of adults. Overall, these results indicate that low-frequency bone-conduction thresholds worsen and high-frequency bone-conduction thresholds improve with maturation. Bone-conduction ASSR threshold differences between the postterm infants and adults probably are due to skull maturation. Differences between preterm and older infants may be explained both by skull changes and a masking effect of high ambient noise levels in the NICU (and possibly to other issues due to prematurity).

Acoustic Stimulation↗
PubMed1993

A model of cochlear mechanics with outer hair cell motility.

The outer hair cell (OHC) is known to have the ability to change its length in response to voltage changes across its membrane. The apparent function of this OHC motility is to enhance the tuning of the basilar membrane. The model presented in this paper represents the displacement-to-voltage and voltage-to-displacement transducers of the OHC explicitly, each as low-pass filter functions. The model results show that this OHC representation is sufficient to provide a model of cochlear mechanics with mechanical tuning at the inner hair cell which is comparable to the threshold tuning curves observed in single auditory nerve fibers. The enhancement of tuning provided by OHC motility can be interpreted as the combined action of a cochlear amplifier and a second filter. This model demonstrates that realistic cochlear tuning does not require intrinsic resonance in any cochlear structure other than the basilar membrane.

Acoustic Stimulation↗
PubMed1994

Lateral suppression and inhibition in the cochlear nucleus of the cat.

1. The ability of cells in the cochlear nucleus (CN) to encode frequency information in the presence of background noise on the basis of "place/rate" information was investigated by measuring the threshold, magnitude, and extent of lateral suppression in the ventral and dorsal CN of the anesthesized cat. The suppression regions were delineated through the use of "masked" response areas (MRAs). The MRA is a family of isointensity curves derived from the average discharge rate in response to a tone of variable frequency and sound pressure level in the presence of a concurrently presented broadband, quasi-flat-spectrum noise. Tonal stimuli of sufficient intensity are often effective in significantly reducing the average discharge rate of CN neurons over a wide frequency range. 2. Most units in the CN exhibit prominent lateral suppressive sidebands, but the variability in threshold, magnitude, and extent of suppression is large. Primary-like and onset units of the ventral CN manifest the least suppression and have the highest suppression thresholds. Pauser/buildup units in the dorsal division and choppers distributed throughout the CN show the largest amount of suppression and have the lowest suppression thresholds. 3. Auditory nerve fibers manifest some degree of lateral suppression, particularly fibers of low and medium spontaneous rate. However, in few instances are the threshold, magnitude, and extent comparable with that observed among the majority of chopper and pauser/buildup units. For this reason the lateral suppression observed among the latter unit types is unlikely to originate entirely from cochlear processes, but rather is likely to reflect largely neural mechanisms intrinsic to the CN. In contrast, the MRAs of most primary-like and onset units suggest that the suppression behavior of most of these cells originates mostly, if not entirely, in the cochlea and auditory nerve. 4. A primary consequence of lateral suppression is to preserve the sharp frequency selectivity of CN neurons at moderate to high sound pressure levels, particularly in background noise. In this fashion lateral suppressive mechanisms potentially enhance the representation of spectral information on the basis of place/rate information relative to that in the auditory nerve under noisy background conditions. 5. Lateral suppressive mechanisms probably underlie the dynamic range shift seen in the presence of a simultaneously presented noise. This mechanism may be crucial for preserving the ability to perceive signals in a noisy background.

Animals↗
PubMed2002

Decreased arousals in infants who sleep with the face covered by bedclothes.

OBJECTIVE: The risk of becoming a victim of sudden infant death syndrome is increased in infants who sleep with their face under bedding items. The present study was designed to evaluate auditory arousal thresholds of infants who sleep with their face covered by bedclothes. METHODS: Twenty healthy infants with a median age of 11.5 weeks (range: 4-22 weeks) were recorded polygraphically for 1 night. Although they slept in their usual supine position, a bed sheet was placed over their face for 60 minutes. Fifteen of the 20 infants were chosen at random and were exposed to white noises of increasing intensities to determine their auditory arousal thresholds. All infants were challenged with the face covered and with the face free during both rapid eye movement (REM) and non-REM (NREM) sleep. Seven infants were first challenged with the face covered, and 8 were challenged with the face free. The following variables were recorded simultaneously: electroencephalogram, breathing and heart rates, and rectal and pericephalic temperatures. In 5 infants who were not exposed to the auditory challenges, end tidal CO2 was recorded for 30 minutes while sleeping with the face covered. RESULTS: During REM sleep, arousals occurred for significantly more intense auditory stimuli when the infant's face was covered than when free. No significant difference was seen in NREM sleep. Compared with the face-free periods, the face-covered sleep periods were characterized by greater rectal and pericephalic temperatures, a greater density of body movements, and a decrease in NREM sleep. Respiratory frequency was increased during the face-covered periods in both REM and NREM sleep. No differences were seen in the frequency or duration of apnea. There was a tendency for heart rate to increase during both sleep stages when the face was covered, compared with the face-free periods, but the changes were not statistically significant. A positive correlation was found between pericephalic temperatures and arousal thresholds (r = 0.60) during REM sleep. End tidal CO2 values increased when the face was covered, reaching a maximum value during the first 5 minutes of the experiment. No fall in oxygen saturation was seen. CONCLUSIONS: Covering the infant's face with a bed sheet was associated with a significant increase in auditory arousal threshold. The finding could be related to an elevation in temperatures within the infant's microenvironment.

Bedding and Linens↗
PubMed1990

Transient elevation of threshold of the neonatal auditory brain stem response.

Auditory brain stem responses (ABRs) of 33 high risk, full term or near term newborns with transient elevation of ABR threshold (transient group) were compared with those of normal infants (normal group) and high-risk infants with known conductive (conductive group) and known sensorineural hearing loss (sensorineural group). ABRs of infants in the transient group initially were not significantly different from those of the conductive group in terms of wave I latency, wave V latency, and the slope of the latency-intensity (L-l) function of wave V. In infants with transient unilateral threshold elevation, significantly shorter interpeak latencies were recorded in the affected ear than in the ear that passed. This finding has been previously described in infants with conductive disorders. On follow-up, ABRs in the transient group closely resembled those of the normal group with respect to the same measures. Otologic histories in the transient group were unremarkable in the majority of cases. Increased slope of the L-l function in infants with confirmed conductive disorders was an unexpected finding. Previous studies of patients with conductive loss had not revealed a significant deviation from normal for this measure. An age interaction for the effect might explain the discrepancy between this and previous studies.

Age Factors↗
PubMed2001

[Synergetic protective effects of glial cell line-derived neurotrophic factor combined with neurotrophin-3 in F-actin on hair cell after noise trauma].

OBJECTIVE: To investigate if glial cell line-derived neurotrophic factor (GDNF) combined with neurotrophin-3 (NT-3) provides synergetic protection in filamentous actin (F-actin) on hair cell (HC) from acoustic trauma. METHODS: Guinea pigs were exposed to 4 kHz narrow band noise at 115 dB SPL for 4 h. Test group (n = 12) with a mixture of GDNF (100 ng/ml) and NT-3(2.5 micrograms/ml) or control group (n = 9) with artificial perilymph (AP) was delivered to the scala tympani via a mini-osmotic pump (0.5 microliter/h) for a total of 14 days. Auditory function was assessed by measuring thresholds of auditory brainstem responses (ABRs) elicited by clicks prior to surgery, 3 days after surgery (1 day before noise exposure) and 10 days following noise exposure (before animals were sacrificed), respectively. F-actin, labeled by rhodamine-phalloidin, was examined in the guinea pig cochlea using fluorescence microscopy for quantitative assessment of hair cell damage. RESULTS: There was a statistically significant increase the survival of out hair cell(P < 0.001, P < 0.01) and inner hair cell(P < 0.01, P < 0.01) and decrease in ABR threshold (P < 0.05, P < 0.01) in both the GDNF and NT-3 treated and untreated ear of animals. CONCLUSION: Our findings indicate that GDNF combined with NT-3 may effectively protect the inner ear from noise--induced hearing loss.

Actins↗
PubMed1997

Distortion product otoacoustic emissions in the C57BL/6J mouse model of age-related hearing loss.

One of the earliest histopathological changes associated with age-related hearing loss appears to be the disruption of outer hair cells (OHCs). To evaluate age-related changes in OHC function, distortion product otoacoustic emissions (DPOAEs) were recorded in the young and aging C57BL/6J mouse. Starting in young adulthood, the C57 mouse displays age-related elevation of auditory brainstem response thresholds, beginning in the high frequencies and progressing toward lower frequencies. The 2f1-f2 DPOAEs of mice between 2 and 20 months of age were examined for f2s between 8 and 16 kHz. In this octave region, the features of 2f1-f2 DPOAEs in the 2-month-old C57 mouse were comparable to those described for non-murine rodents in the literature in terms of optimum f2/f1 ratio, optimum primary level difference, input/output (I/O) function features and microstructure. It was determined that f2/f1 = 1.2 and L1-L2 = 20 dB were optimal stimulus parameters for investigation of the effects of age on C57 DPOAEs. Age-related changes in DPOAE I/O functions consisted of a right shift (i.e. increased DPOAE detection thresholds), disappearance of 'notches' and shallowing of the slopes after 8 months of age. As DPOAE I/O functions continued to shift to the right and DPOAE levels decreased with age, the appearance of I/O functions became complex to include regions of steep or shallow slopes and plateaus. The present results suggest that the age-related elevation of auditory thresholds in the C57 mice is associated with substantial progressive changes in OHC function.

Acoustic Stimulation↗
PubMed2002

Bilateral superior cervical sympathectomy and noise-induced, permanent threshold shift in guinea pigs.

The rich sympathetic innervation to the cochlea suggests its potential control of cochlear blood flow and activity during noise exposure, as part of the general and local stress sympathetic reaction evoked by noise. In a previous study, superior cervical sympathectomy prior to sound exposure in guinea pigs in an awake state, resulted in reduced temporary threshold shift. The present study was conducted to explore whether this potential protection would also be manifested in conditions producing permanent threshold shift (PTS). Thirty-six guinea pigs, divided into four groups of nine guinea pigs each, were sound exposed for 2 h in an awake state. Eighteen guinea pigs underwent superior cervical sympathectomy prior to sound exposure. Auditory brainstem thresholds were recorded prior to sound exposure, and then at 24 h, 1 and 6 weeks post-exposure. Results indicated a reduced PTS at 122 dB sound pressure level (SPL) exposure, suggesting a protective effect of the sympathectomy. However, at 125 dB SPL exposure, the protective effect was reduced.

Animals↗
PubMed1985

Effects of d-methamphetamine on auditory and visual reaction times and detection thresholds in the baboon.

Baboons were trained in both auditory and visual reaction time procedures to release a response lever in the presence of low-intensity stimuli. By varying the stimulus intensity from trial to trial, functions relating reaction time (elapsed time from stimulus onset to lever release) to stimulus intensity were established, and detection thresholds were measured. The effects of acute, IM injections of d-methamphetamine (0.001-1.0 mg/kg) were examined on these psychophysical performance baselines. Reaction times for acoustic stimuli generally were faster for higher drug doses, whereas reaction times for visual stimuli either lengthened or shortened, depending on both drug dose and individual differences among animals. Auditory thresholds were unaffected at all drug doses studied, whereas visual thresholds were generally elevated at doses of 0.1 mg/kg and above.

Acoustic Stimulation↗
PubMedDate not supplied

Combined effects of noise and gentamicin on hearing in the guinea pig.

The last ten years, the use of gentamicin has increased due to antibiotic resistance among bacterial pathogens. One of the side effects of gentamicin is its toxicity on hearing. Several authors had even pointed out synergistic effects of gentamicin and noise on hearing. It was therefore reasonable to think that the damaging effects of noise could be emphasized by a gentamicin treatment of the subjects. In order to test the applicability of the Leq8h for estimating the hazard of noise on animals treated with a non-ototoxic dose of gentamicin (40 mg/kg for 8 days), two experiments were carried out with guinea pigs. The animals were exposed to octave band noises centred at 8 kHz and treated with gentamicin either simultaneously or sequentially with regard to the noise exposure. Two noise exposures having different acoustic energy, respectively Leq8h = 85 dB and 98.8 dB SPL, were tested. The auditory function of the guinea pigs was tested by recording auditory-evoked potentials. The electrophysiological findings were completed by histological data. The gentamicin treatment tested in the current studies did not cause any auditory permanent threshold shift neither cochlear disruptions, although the treatment could be considered as approximately ten times the therapeutic dose used in human. The auditory deficit induced by the mixed exposures to noise and gentamicin did not worsen the noise effect alone in our experimental conditions. As a result, the European value recommended for noise exposure (Leq8h=85 dB) seems to be robust enough to protect gentamicin-treated workers.

Animals↗
PubMed1983

Suppression of auditory nerve responses. II. Suppression threshold and growth, iso-suppression contours.

Two-tone "synchrony suppression" was studied in responses of single auditory nerve fibers recorded from anesthetized cats. Suppression thresholds for suppressor tones set to a fiber's characteristic frequency (CF) were approximately equal to discharge rate thresholds for CF tones. Suppression thresholds above and below CF were usually lower than the corresponding discharge rate thresholds. However, at all frequencies studied (including CF), suppression thresholds were higher than the corresponding thresholds for discharge synchronization. Across fibers, rates of suppression growth for suppressors at CF were greatest in low-CF fibers and least in high-CF fibers, and there was a systematic decrease in suppression growth rate at CF as CF increased. Within fibers, rates of suppression growth above CF were typically less than at CF, and slopes were monotonically decreasing functions of frequency. Within-fiber rates of suppression growth below CF were variable, but they usually were greater than rates of growth at CF. Iso-suppression contours (frequencies and intensities producing criterion amounts of suppression) indicated that tones near CF are the most potent suppressors at near-threshold intensities, and that the frequency producing the most suppression usually shifts downward as the amount of suppression increases. These data support the notion that synchrony suppression arises primarily as a passive consequence of hair cell activation.

Acoustic Stimulation↗
PubMed1992

Sound perception induced by extracranial magnetic stimulation in deaf patients.

Two profoundly hard-of-hearing and deaf patients were examined by non-invasive extracranial magnetic stimulation (EMS) in an effort to determine whether EMS could evoke auditory sensations. The patients were fitted with standard earplugs and were stimulated at the auricle, the mastoid and the temporal lobe area. The threshold of auditory sensation (TAS) was determined at each stimulus position and found to be approximately 20-40% of the maximum EMS level (2.0 Tesla). The TAS was generally lowest in mastoid stimulation, but was variable, and dependent on the angle and position of the stimulating coil relative to the skull. Middle-ear muscle reflex (MEMR) tests performed by EMS of the auricle, mastoid and temporal lobe area contralateral to the probe ear were negative. It was concluded that EMS of the auditory system, particularly the mastoid area, can evoke auditory sensations in cochlea-deaf ears, and that this technique deserves further study as a non-invasive procedure for evaluating potential cochlear implant patients in conjunction with electrostimulation.

Acoustic Impedance Tests↗