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PubMed1983

A reproducible technique for breaking glass micropipettes over a wide range of tip diameters.

A new simple technique for the accurate modification of microelectrode and micropipette tips by breaking has been developed. The breaking is done by longitudinally inserting a micropipette into a larger previously broken pipette for stability and by applying a force on the micropipette to cause it to break. Tips will break cleanly at an easily predetermined diameter over a range of 3-200 micrometers.

Animals↗
PubMedDate not supplied

Frequency selectivity in the auditory periphery: similarities between damaged and developing ears.

Single fiber tuning curves (stimulus frequency versus neural threshold curves) were obtained from 198 auditory nerve fibers in 24 kittens between birth and the 16th postnatal day and from 74 auditory nerve fibers in adult cats. Three developmental stages during which adult-like frequency-resolving capacity was acquired were identified. During the early stage of postnatal development, all auditory nerve fibers were essentially untuned and responded to a narrow range of low to middle frequency tone bursts presented at intensities exceeding 110 dB sound pressure level (SPL) re 20 muPa. In the intermediate stage, which occurred during the second postnatal week, auditory nerve fibers tuned to low- and mid-range frequencies acquired adult-like frequency-resolving capacity. Fibers tuned to high frequencies, which were recorded later in development than those tuned to lower frequencies, were as sharply tuned as their adult counterparts, but exhibited a low contrast between thresholds at characteristic frequency (tip) and lower (tail) frequencies (ie, low tip-to-tail ratios). Adult-like tuning curves were observed during the third stage, primarily as a consequence of the acquisition of adult-like tip-to-tail ratios. Our understanding of the cochlear mechanism(s) by which frequency selectivity is produced in adult animals has recently been enhanced by a combined anatomy and physiology investigation conducted by Liberman and Dodds, in which clear anatomic foci of cochlear damage were identified in cats with functionally characterized hearing loss. Similarly, descriptions of anatomic differentiation in the feline auditory end-organ correlate with functional measures of peripheral auditory system development. In this report, anatomic and physiologic similarities between developing and damaged ears are considered in an attempt to better characterized the process whereby normal frequency selectivities and thresholds are developed. Our findings support the notion that anatomic changes in the cochlea during development, primarily the development of adult-like anatomic relations between the tectorial membrane and sensory cells, underlie the acquisition of adult-like auditory nerve fiber tuning.

Age Factors↗
PubMed1982

Interaural crosstalk in the cat.

The physiologically effective interaural acoustic crosstalk in cat was measured by means of binaural threshold differences for single auditory-nerve fibers and for cochlear microphonics. There were generally two maxima, at about 800 Hz and 3 kHz, attaining values as high as -25 dB (transmission to cochlea via contralateral ear re transmission via ipsilateral ear) in some cats. This figure could be reduced to -50 dB by mechanically isolating the acoustic drivers from each other and from the stereotaxic head frame.

Animals↗
PubMed1982

Efferent neural control of cochlear mechanics? Olivocochlear bundle stimulation affects cochlear biomechanical nonlinearity.

We confirm the report of Mountain (Mountain, D.C. (1980): Science 210, 77-72) that stimulating the crossed olivocochlear bundle (COCB) can change the magnitude of the distortion product (f2-f1) in the ear-canal sound pressure. Our results are extended to include (2f1-f2) as well as (f2-f1) from anesthetized chinchillas with both middle-ear muscles sectioned. In contrast to Mountain's report, the polarity of the change can be either positive, negative or absent, depending on the choice of two-tone stimulus frequencies. The influence of two-tone stimulus level is also complex, but we have not yet seen the polarity of the COCB effect change with stimulus level. The magnitude and polarity of the change in (2f1-f2) are not simply related to those for (f2-f1). The effect of COCB stimulation is abolished when scala tympani is perfused with artificial perilymph containing 10(-5) M d-tubocurarine. These results demonstrate that the COCB effect is postsynaptic, probably mediated by outer hair cells. We suggest that the normal cochlea contains an active biomechanical mechanism which reduces the damping of the cochlear-partition motion and is modulated by activating the efferents. It is thus possible that the central nervous system may be able to control the dynamics of the motion of the cochlear partition.

Acoustic Stimulation↗
PubMed1986

Spontaneous, click-, and toneburst-evoked otoacoustic emissions from normal ears.

Evoked and spontaneous otoacoustic emissions were recorded bilaterally in a group of normal subjects (n = 14) using clicks and tonebursts at four frequencies (0.5, 1, 1.5, and 3 kHz). All ears (n = 28) demonstrated evoked emissions, but not to every stimulus type. The 0.5-kHz toneburst evoked emissions in only 10 (36%) ears, the 1.5-kHz toneburst in all ears, and the remaining stimuli in at least 80% of ears. Two distinct patterns of evoked emissions were identified. Five (18%) ears showed short, broadband click-evoked emissions lasting less than 20 ms after stimulus onset. In these ears, toneburst-evoked emissions were often more prominent than click-evoked emissions and no spontaneous emissions were detected. Twenty-three (82%) ears showed click-evoked emissions lasting longer than 20 ms poststimulus onset. Spectral analysis of these emissions demonstrated several (2-10) narrow frequency peaks. Highly similar peaks were present in the spectra of toneburst-evoked emissions within the range of toneburst spectra. Spontaneous emissions were recorded in 12 of the 23 ears. In these ears, at the frequencies of spontaneous emissions, prominent peaks in both click- and toneburst-evoked emission spectra were always present. Otoacoustic emission characteristics correlated significantly between the ears of individual subjects inferring that a symmetrical cochlear mechanism generates otoacoustic emissions.

Acoustic Stimulation↗
PubMed1990

Mutant golden hamsters with an abnormal outer hair cell stereociliary arrangement.

A new malformation of the inner ear was found in golden hamster reared at our institute. It was studied using electron microscope and auditory electrophysiological measurements including auditory brainstem response (ABR), whole nerve action potential (AP) cochlear microphonic (CM) potential, and the summating potential (SP). The stereocilia on individual first row of outer hair cells in the hamsters with malformed inner ears (F-K hamsters) were arranged in a triple W form, but the entire bundle of stereocilia was irregular in orientation. These anomalies were seen in approximately 70 to 85% of sensory hairs, in all rotations, with no difference between the right and left sides. The cuticles of the first row of outer hair cells were displaced, but lower portions did not appear to be affected. ABR and SP revealed no differences from normal hamsters and it is believed that the F-K hamsters' hearing ability was normal. The CM potential and the amplitude of AP in the F-K hamsters were significantly lower, at 50 to 80 dB sound pressure level (SPL). The linear portions of the CM input-output relation curve were separated by 4 to 6 dBSPL and the saturating voltage levels differed by 2.5 to 3.0 microV. Based on these results, the actually-measured CM potentials were shown to represent a summation of the reaction of the three individual rows of outer hair cells.

Action Potentials↗
PubMed1990

Evoked otoacoustic emissions in guinea pig: basic characteristics.

Different types of evoked otoacoustic emissions (EOAEs) such as stimulus frequency emissions, tone burst and click EOAEs, were investigated in the guinea pig. Their correlates on cochlear microphonic potential were also recorded. Although it was confirmed that click EOAEs are difficult to detect in the guinea pig, partly because their delay (2 to 3 ms, measured on tone burst EOAEs) is much shorter than in man, other types of OAE were found in the interval (1.5-5 kHz) for almost every normal animal. Many of their properties were quite different from man, for instance their small number, low level, and the wide frequency range of some of them (up to 500 Hz), suggesting that they represent a sort of continuum. It is proposed that these particularities may not arise from different generating mechanisms but should be correlated with the well-known differences in hair cells patterns.

Acoustic Stimulation↗
PubMed2005

Auditory nerve representation of naturally-produced vowels with variable acoustics.

This investigation compared the encoding of naturally-produced, whispered and normally-voiced vowels by auditory nerve fibers. Speech syllables containing the vowels /open o/ and /ae/ were produced by two female speakers and presented at three intensities to ketamine-anesthetized chinchillas. Six different representations of the spectral components in the vowels in the responses of the auditory nerve fibers were evaluated. For both normal and whispered vowels over a 30 dB range, the formant peaks in the vowel were best displayed using rate-place representations. The spectral detail in the vowel was revealed by average localized synchronized rates (ALSR) and autocorrelations of individual peristimulus time histograms. The average localized interval rates (ALIR), autocorrelations of ensemble responses, and autocorrelations of individual spike trains demonstrated poor representations of vowel spectra, although the frequency components of normally-voiced vowels had better representations than those of whispered vowels. These analyses suggest that rate-based and synchronization-based measures yields two very different pieces of information, but only a normalized rate-based measure consistently identified the formants of both the whispered and normally-voiced vowels.

Acoustic Stimulation↗
PubMed2006

Effect of intracochlear perfusion of vanilloids on cochlear neural activity in the guinea pig.

Recent findings show that the vanilloid receptor subtype 1 (TRPV1) is expressed by cochlear outer hair cells and spiral ganglion cells, and that its expression is up-regulated in ganglion cells after aminoglycoside treatment. This study tested the hypothesis that agents that act on TRPV1 receptors affect the spectrum of ensemble background activity (EBA). Consecutive intracochlear perfusions of the TRPV1 agonist, capsaicin (CAP 0.1, 1, and 10 parts per million), as well as its antagonist capsazepine (CZP), were used to test effects of TRPV1 activation on EBA recorded from the cochlear base. Perfusion with CAP alone produced a dose-dependent increase of the 900-Hz peak ratio (power normalized re the overall spectrum) of the EBA. The CAP effect was attenuated during concurrent perfusion with CZP. These findings are consistent with the hypothesis that TRPV1 activation increases background activity of spiral ganglion cells and support a role of TRPV1 in gating spontaneous and evoked auditory nerve excitability.

Animals↗
PubMed2006

Bromate-induced ototoxicity.

For decades, it has been known that ingested potassium bromate and sodium bromate can induce hearing loss. Hearing loss onset, following high-dose ingestion, is generally rapid occurring within 4-16 h and of a severe to profound degree. Unlike the sensorineural hearing loss which is generally irreversible, bromate-induced tinnitus, which is less well-studied, may reportedly be permanent or temporary. It is not clear whether actual bromate-induced vestibulotoxicity occurs in clinical populations. The primary sites of lesion for bromate-induced ototoxicity appear to be in the cochlea. However, possible effects on the VIIIth nerve and central auditory system have not been fully investigated. Based on animal studies, in the cochlea, bromate damages the stria vascularis, Reissner's membrane, inner and outer hair cells, Claudius cells and inner sulcus cells. Physiologically, bromate reduces the endocochlear potential, cochlear microphonics, and electrophysiologic auditory thresholds. Possible mechanisms are discussed. The effects of long-term low-dose bromate exposure on hearing have not been studied. These effects, if they occur, may not be readily detected in many clinical populations, because idiopathic hearing loss occurs commonly in the population as a whole. Further it is unknown whether or not chronic bromate ingestion may exacerbate noise-induced hearing loss. Further study to determine the maximum safe exposure level for long-term administration and to develop possible antidotes is warranted.

Animals↗
PubMed1997

Auditory nerve neurophonic tuning curves produced by masking of round window responses.

In response to low-intensity, low-frequency, phase-locked tonal stimuli with non-alternating polarity, the time-average round window (RW) response of the gerbil is a mixture of the auditory nerve neurophonic (ANN) and cochlear microphonic (CM), with the former often being of equal or greater magnitude than the latter. Forward masking (using a conservative 25% amplitude reduction criterion) can be used to generate ANN tuning curves (TC). Most of these TCs are sharply tuned V-shaped functions. Harmonic distortion is often present in the ANN, especially in response to the lower-frequency (< or = 1 kz) or higher-intensity (> or = 50 dB) stimuli. The TCs created by forward masking of the harmonics are similar in appearance to those generated by masking the fundamental frequency of the ANN. When lower-frequency probe stimuli (< or = approximately equal to 1 kHz) are used, the frequency of the TC tip tends to be higher than that of the probe; with higher probe frequencies, the tip tends to be lower. Regardless of the frequency of the probe, the TC tip threshold occurs at an intensity level lower than that of the probe. The sharpness of these TCs generally increases as a function of the frequency of the probe stimulus and the values of Q10dB are comparable to those of FTCs of cochlear nerve fibers of the gerbil. The amplitude of the ANN is often enhanced in response to a limited intensity range of forward maskers over a restricted range of frequencies that are outside the high-frequency boundary of the forward masker TC. By alternating the polarity of the probe stimulus, the CM can be canceled, allowing the effects of simultaneous maskers to be evaluated.

Acoustic Stimulation↗
PubMed2000

Low-frequency acoustic modulations generated by the high-frequency portion of the cochlea, noninvasively recorded from the scalp of mice (Mus musculus).

Vocalizations often contain low-frequency modulations of the envelope of a high-frequency sound. The high-frequency portion of the cochlear nerve of mice (Mus musculus) generates a robust phase-locked response to these low-frequency modulations, and it can be easily recorded from the surface of the scalp. The cochlea is most sensitive to envelope modulation frequencies of approximately 500 to 2000 Hz. These responses have detection thresholds that are approximately 10 dB more sensitive than auditory brainstem responses, and they are very sharply tuned. These measurements may provide a nontraumatic means of repeatedly assessing cochlear functions involved in sound localization and perception of vocalizations.

Animals↗
PubMed1992

[Evoked otoacoustic emissions and their modification by contralateral acoustic stimulation].

The active vibration of the basilar membrane as well as evoked otoacoustic emissions (EOAE) are probably based on the motile properties of cochlear outer hair cells (OHC). In the present study we examined the effects of contralateral acoustic stimulation on ipsilateral EOAE and thereby the active cochlear micromechanics. Contralateral white noise with intensities below 30 dB HL enhanced the EOAE amplitude, whereas higher sound levels reduced the evoked acoustic emissions. Similar effects of contralateral acoustic stimuli on ipsilateral EOAE were observed in patients with a conductive hearing loss. However, the required sound levels were higher compared to probands with normal hearing. In controls with unilateral deaf patients white noise up to 60 dB HL did not alter the EOAE amplitude. We concluded, that in patients with normal hearing or unilateral conductive hearing loss, effects of contralateral acoustic stimulation on evoked ipsilateral sound emissions may be due to the activation of crossed olivo-cochlear efferents reaching the OHCs.

Acoustic Stimulation↗
PubMed1992

[Evoked otoacoustic emissions in diagnosis of cochlear hearing disorders].

The authors consider the possibility of routine use of evoked otoacoustic emissions (EOE) in diagnosis of sensory hearing loss by comparison of EOE curves with relative curves obtained by pure tone audiometry. 180 ears with sensory hearing loss of different aetiologies were examined. EOE were obtained by application of Bray and Kemp's Evoked Otoacustic Measurement Package (ILO88). The results obtained show a close correlation between presence of EOE and real hearing losses of different frequencies obtained by pure tone audiometric evaluation. We could detect no EOE with hearing losses over 50 dB HL at 500 Hz, 40 dB HL at 1000 Hz, 50 dB HL at 2000 Hz and 85 dB HL at 4000 Hz. With a rate of middle hearing loss over 45 dB HL we also did not find EOE for the whole frequency range. On the base of this study, the authors conclude that EOE explore the functional integrity of those parts of the cochlea that correspond to the middle frequencies of hearing range. If EOE are not detectable, statements on the nature and extent of hearing loss on the base of this examination are not valid.

Adolescent↗
PubMed1989

[Prognostic indications within the scope of the selection of cochlear implant patients].

The common selection criteria for cochlear implant patients do not allow any prognostic indication on the final result. On the other hand, some postoperative data (threshold, TDL, dynamic range, duration of deafness) corresponds clearly with the results, some of them also correspond with the preoperative data. Preoperative TDL, dynamic range as well as duration of deafness can therefore be used as suitable prognostic indicators.

Auditory Threshold↗
PubMed1992

Influence of spontaneous otoacoustic emissions (SOAE) on acoustic distortion product input/output functions: does the medial efferent system act differently in the vicinity of an SOAE?

Otoacoustic emission (OAE) generation mechanisms reside in the active micromechanical properties of the organ of Corti, and especially in the outer hair cells (OHCs). OHCs are strongly innervated by medial efferent olivo-cochlear fibres. Decrease of the intensity of transiently evoked otoacoustic emissions (TOAEs) and modification of spontaneous otoacoustic emissions (SOAEs) during acoustic stimulation of the contralateral ear have already been shown in humans. Similar results were obtained in guinea pigs with a decrease of 2F1-F2 acoustic distortion products (DPOAEs) and a suppression of the effect with sectioning of the floor of the fourth ventricle. The present study sought to investigate the influence of contralateral auditory stimulation on DPOAEs recorded in humans. It shows a decrease in DPOAE intensity for all frequencies, at levels above 45 dB SPL of contralateral broad band noise. This effect was found at levels of contralateral BBN well below the acoustic reflex threshold, and in subjects without acoustic reflex. Moreover, the influence of transcranial transmission could be ruled out since no effect was found when contralateral BBN applied to the altered ear of totally unilaterally deaf patients. Thus, the contralateral acoustic stimulation effect on DPOAEs provides a new means of functional exploration of the medial efferent system in humans. The effect obtained is more ample at low primary frequency levels. Moreover, as DPOAEs are known to be stronger and to show more irregular input/output function patterns in the vicinity of an SOAE, the influence of contralateral auditory stimulation was studied for DPOAEs recorded at 10 Hz, 50 Hz and 150 Hz from an SOAE frequency.

Acoustic Stimulation↗
PubMed1992

Cochlear microphonics and recruitment.

In this study, bilateral cochlear microphonics (CM) were evoked by tone burst simultaneously. A speaker was put in head-food axis 2 m from the mid-point of a given line connecting the bilateral external meatus. Five normal persons and 68 cases (34 cases of Meniere's disease, 27 cases of sudden hearing loss, and 7 cases of low-tone sensory hearing loss without vertigo) with unilateral sensory hearing loss and recruitment, in addition to 2 cases of bilateral Meniere's disease with recruitment were examined. CM shifted in normal and hearing loss ears and was absent in profound and totally deaf ears. When recruitment was present, CM at corresponding frequencies were enlarged and prolongated in 60 cases. Some of the enlarged and prolongated CM decayed slowly, others quickly. Meanwhile the CM of the opposite normal ear decreased obviously. The presence of enlarged and prolongated CM may indicate an increase of abnormal excitability of the hair cells caused by some pathological stimulations. This would cause excitability of the hair cells in the opposite cochlea to be inhibited by the effect of the efferent system. In such a condition, the patients complained that the stimulating sound was heard louder in the disordered ear than that in the opposite normal ear. CM was slightly enlarged during sleep.

Adult↗
PubMed1999

Clinical findings for a group of infants and young children with auditory neuropathy.

OBJECTIVE: To examine the prevalence of auditory neuropathy in a group of infants at risk for hearing impairment and to present an overview of the clinical findings for affected children. DESIGN: Results for 20 subjects who showed repeatable cochlear microphonic potentials in the absence of click-evoked auditory brain stem responses are included in this study. Behavioral and steady state evoked potential thresholds were established in each case. Where possible, otoacoustic emission and speech perception results (unaided and aided) also were obtained. RESULTS: One in 433 (0.23%) of the children in our series had evidence of auditory neuropathy. The audiometric findings for these subjects varied significantly, with behavioral thresholds ranging from normal to profound levels. Discrimination skills were also variable. Approximately half of the subjects showed little understanding, or even awareness, of speech inputs in both the unaided and aided conditions. There were, however, a number of children who could score at significant levels on speech discrimination tasks and who benefited from the provision of amplification. CONCLUSION: The results suggest that auditory neuropathy is more common in the infant population than previously suspected. The effects of neuropathy on auditory function appear to be idiosyncratic, producing significant variations in both the detection and discrimination of auditory signals. As such, the management of children with this disorder must allow for individual differences.

Audiometry, Evoked Response↗