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PubMedDate not supplied

Some comparisons between auditory brain stem response thresholds, latencies, and the pure-tone audiogram.

Aspects of auditory brain stem responses (ABR) and pure-tone behavioral audiograms were compared in patients with cochlear hearing loss. Click-evoked ABR thresholds appeared to be related most closely to the audiometric thresholds at 2000 and 4000 Hz, with relatively poor agreement at either 1000 or 8000 Hz. These results were related to the amplitude spectrum of the eliciting stimulus. The slope of the wave V latency-intensity function appeared to be related to the configuration of the hearing loss. Patients with high-frequency sensorineural losses had steeper slopes than normal subjects, whereas patients with flat sensorineural losses had shallower slopes. These results were related to the principle that response latency is determined by the cochlear region that predominates the ABR for different stimulus intensities.

Acoustic Stimulation↗
PubMed2002

Expression of Klotho protein in the inner ear.

The Klotho mouse is a recently developed model that exhibits phenotypes resembling human aging. We used this model to investigate sensorineural hearing loss from the point of view that it may be considered an issue of aging. Using reverse transcription-polymerase chain reaction, Western blotting and immunohistochemical staining, we were able to confirm klotho gene transcription and protein synthesis in the kidney and inner ear. Klotho protein was mainly expressed in the stria vascularis and spiral ligament of the inner ear and in the distal convoluted tubule of the kidney, likely serving a common function in the two organs, i.e., modulating ion transport. The threshold for the auditory brainstem response was significantly higher in Klotho mice than in wild-type mice, and wave I latencies were prolonged. On the other hand, Klotho mice exhibited a normal distribution of I-IV interpeak intervals. No obvious morphological abnormalities were detected in Klotho mice, although no expression of Klotho protein was detected, and there was an apparent hearing disorder. Taken together, these findings suggest that by contributing to the maintenance ion homeostasis in the endolymph, Klotho protein serves as a key mediator of auditory function.

Aging↗
PubMedDate not supplied

Threshold prediction from the auditory 40-Hz evoked potential.

This is an investigation of the accuracy with which the 40-Hz evoked potential (EP) threshold can be used to predict low frequency behavioral audiometric thresholds. The EP thresholds for 500 and 1000 Hz tone bursts were compared with behavioral thresholds obtained from 40 hearing-impaired ears. Correlation coefficients (between EP and behavioral thresholds) of 0.79 and 0.87 were obtained for the 500 and 1000 Hz signals, respectively. Confidence intervals for EP estimates of behavioral thresholds were -10 to +30 dB for 500 Hz signals and -20 to +20 for 1000 Hz. Problems associated with the use of the EP for predicting behavioral thresholds are discussed.

Adolescent↗
PubMed2001

Roles of the glutamate receptor epsilon2 and delta2 subunits in the potentiation and prepulse inhibition of the acoustic startle reflex.

We examined the regulation of the acoustic startle response in mutant mice of the N-methyl-D-aspartate (NMDA)- and delta-subtypes of the glutamate receptor (GluR) channel, which play important roles in neural plasticity in the forebrain and the cerebellum, respectively. Heterozygous mutant mice with reduced GluRepsilon2 subunits of the NMDA receptor showed strongly enhanced startle responses to acoustic stimuli. On the other hand, heterozygous and homozygous mutation of the other NMDA receptor GluRepsilon subunits exerted no, or only small effects on acoustic startle responses. The threshold of the auditory brainstem response of the GluRepsilon2-mutant mice was comparable to that of the wild-type littermates. The primary circuit of the acoustic startle response is a relatively simple oligosynaptic pathway located in the lower brainstem, whilst the expression of GluRepsilon2 is restricted to the forebrain. We thus suggest that the NMDA receptor GluRepsilon2 subunit plays a role in the regulation of the startle reflex. Ablation of the cerebellar Purkinje cell-specific delta2 subunit of the GluR channel exerted little effect on the acoustic startle response but resulted in the enhancement of prepulse inhibition of the reflex. Because inhibition of the acoustic startle response by a weak prepulse is a measure of sensorimotor gating, the process by which an organism filters sensory information, these observations indicate the involvement of the cerebellum in the modulation of sensorimotor gating.

Acoustic Stimulation↗
PubMed2000

Study of mechanical motions in the basal region of the chinchilla cochlea.

Measurements from the 1-4-mm basal region of the chinchilla cochlea indicate the basilar membrane in the hook region (12-18 kHz) vibrates essentially as it does more apically, in the 5-9-kHz region. That is, a compressive nonlinearity in the region of the characteristic frequency, amplitude-dependent phase changes, and a gain relative to stapes motion that can attain nearly 10,000 at low levels. The displacement at threshold for auditory-nerve fibers in this region (20 dB SPL) was approximately 2 nm. Measurements were made at several locations in individual animals in the longitudinal and radial directions. The results indicate that there is little variability in the phase of motion radially and no indication of higher-order modes of vibration. The data from the longitudinal studies indicate that there is a shift in the location of the maximum with increasing stimulus levels toward the base. The cochlear amplifier extends over a 2-3-mm region around the location of the characteristic frequency.

Animals↗
PubMed1992

Dynamic range of neural rate responses in the ventral cochlear nucleus of awake cats.

1. Response thresholds and dynamic range properties of neurons in the ventral cochlear nucleus (VCN) of awake cats were measured by fitting a computational model to rate-level functions for best frequency (BF) tone bursts and for bursts of broad-band noise. Dynamic range measurements were performed in quiet and in the presence of continuous background noise. 2. The sample of neurons obtained in the VCN of awake cats exhibited a variety of peristimulus histograms (PSTHs) and thresholds. All PSTH response types previously described in the VCN of anesthetized cats were found in awake cats. The lowest thresholds for neural responses were observed at sound pressure levels that were equivalent to behavioral thresholds of absolute auditory sensitivity. 3. When responses to BF tones or bursts of broad-band noise were recorded in quiet backgrounds, the dynamic range properties of most units in the VCN of awake cats were not significantly different from dynamic range properties of auditory nerve fibers (ANFs) in anesthetized cats or VCN units in decerebrate cats. All auditory units showed a larger dynamic range for noise bursts than for tone bursts, but VCN units with primary-like and onset PSTHs showed larger dynamic ranges for responses to noise bursts than that of ANFs and VCN chopper units. 4. When tests were performed in the presence of continuous noise, rate-level functions for BF tone bursts shifted to higher tone levels and showed a more compressed range of driven rates in comparison with data obtained in quiet. Compression of the rate-level function in noise resulted from an increase in driven rate at low tone levels and a decrease in rate at high tone levels. These changes in the rate-level function suggest that noise may reduce the range of BF tone levels that are potentially encoded by a unit's rate responses. By exhibiting larger shifts and less compression in background noise, VCN units in awake cats better preserved the dynamic range of their rate responses to BF tones than ANFs in anesthetized cats or VCN units in decerebrate cats. 5. Rate-level functions were obtained from a small sample of VCN units not only with the cat performing the behavioral task but also with the cat awake and sitting quietly in the testing apparatus. No differences in noise-induced shift or compression were noted between the two testing conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1991

Influence of noise spectra on auditory frequencies & degree of temporary threshold shift.

Influence of noise spectra on auditory frequencies of 131 audiometrically normal human volunteers was assessed. Each subject was exposed to four different types of noise on different days for a period of 30 min. Noises utilized in this study were broadband noise (100 dBA), broadband noise (BBN) mixed independently with tones of 0.5, 1.2 and 4 kHz at three intensity levels (85, 95 and 105 dBA) and noises of different bandwidths (100 dBA) around the above tones as centre frequencies. BBN produced maximum TTS2 at 4 kHz (21.42 +/- 0.61 to 26.15 +/- 1.00 dB), while concentration of sound energy around these tones, affected hearing at one-half octave above the point of concentration of sound energy. TTS2 produced by 4 kHz tonal component of 95 and 105 dBA and 2 kHz of 105 dBA were significantly higher than the one produced by BBN at 4 kHz. The single tones of 2 and 4 kHz and noise of 1/3rd octave bandwidth (cf 4 kHz) produced TTS2s which were significantly higher as compared to that of BBN at 4 kHz. At the same centre frequency, noise concentrated in thinner bands was more injurious than that in the thicker bands. Lower frequencies of hearing appears to be more resistant to noise as for the same sound pressure level the TTS2 observed in low frequencies was less as compared to higher frequencies.

Acoustic Stimulation↗
PubMed1993

A comparison of auditory brain stem response thresholds and latencies elicited by air- and bone-conducted stimuli.

Auditory brain stem responses (ABRs) were measured for stimuli presented both by air conduction and by bone conduction. Stimuli included clicks and tone bursts at octave frequencies from 250 to 4000 Hz. ABR thresholds were comparable for air- and bone-conducted stimuli. Wave V latencies were longer for bone-conducted stimuli compared to similar responses for air conduction. This effect was evident for both clicks and tone bursts. The fact that these latency differences were largely independent of stimulus spectrum suggests that they are not due to differences between the frequency responses of air and bone conduction transducers. This finding is expected when one considers the interaction between output, threshold, and frequency for both transducer types. These data also suggest that there are inherent differences in transmission by air and bone conduction that affect response latency but are unrelated to the amplitude spectrum in the signal.

Acoustic Stimulation↗
PubMedDate not supplied

Threshold and suprathreshold temporal integration function in normal and cochlear-impaired subjects.

Auditory and acoustic reflex threshold temporal integration slopes were obtained for 20 normally hearing and 20 cochlear-impaired subjects. For both groups, the results at auditory threshold are similar to findings reported by other investigators. For the normally hearing subjects, suprathreshold slopes approximated those obtained at auditory threshold. The sensorineural group, however, demonstrated steeper slopes at suprathreshold levels than at auditory threshold. Therefore, at suprathreshold levels there were no significant differences between the slopes of the two groups. The implications of these findings are discussed.

Acoustic Stimulation↗
PubMed2005

Assessment of auditory temporal-order thresholds - a comparison of different measurement procedures and the influences of age and gender.

PURPOSE: The relationship between auditory temporal-order perception and phoneme discrimination has been discussed for several years, based on findings, showing that patients with cerebral damage in the left hemisphere and aphasia, as well as children with specific language impairments, show deficits in temporal-processing and phoneme discrimination. Over the last years several temporal-order measurement procedures and training batteries have been developed. However, there exists no standard diagnostic tool for adults that could be applied to patients with aphasia. Therefore, our study aimed at identifying a feasible, reliable and efficient measurement procedure to test for auditory-temporal processing in healthy young and elderly adults, which in a further step can be applied to patients with aphasia. METHODS: The tasks varied according to adaptive procedures (staircase vs. maximum-likelihood), stimuli (tones vs. clicks) and stimulation modes (binaural- vs. alternating monaural) respectively. A phoneme-discrimination task was also employed to assess the relationship between temporal and language processing. RESULTS: The results show that auditory temporal-order thresholds are stimulus dependent, age related, and influenced by gender. Furthermore, the cited relationship between temporal-order threshold and phoneme discrimination can only be confirmed for measurements with pairs of tones. CONCLUSION: Our results indicate, that different norms have to be established for different gender and age groups. Furthermore, temporal-order measurements with tones seem to be more suitable for clinical intervention studies than measurements with clicks, as they show higher re-test reliabilities, and only for measurements with tones an association with phoneme-discrimination abilities was found.

Acoustic Stimulation↗