Contralateral auditory stimulation alters acoustic distortion products in humans

It is now generally accepted that otoacoustic emissions (OAE) represent the only objective and non-intrusive means of functional exploration of the active micromechanical characteristics of the outer hair cells of the organ of Corti. Previous studies showed a decrease of the transiently evoked otoacoustic emissions and spontaneous otoacoustic emissions in humans, during acoustic stimulation of the contralateral ear, and attributed this effect to the medial efferent system. Such an effect has been shown on acoustic distortion product otoacoustic distortion emissions (DPOAE) in guinea pigs, but has not been investigated for DPOAEs recorded in humans, although DPOAEs represent the easiest means of exploring active micromechanical cochlear properties both in humans and in laboratory animals. The present study sought to investigate the existence and characteristics of a contralateral auditory stimulation effect on DPOAEs recorded in humans. This study shows that contralateral broad-band noise (BBN) has a suppressive effect on DPOAEs recorded from 0.5 kHz to 5 kHz. This effect is not due to air conduction, as no change in the noise floor occurred under increasing contralateral stimulation, and as no reduction in DPOAE amplitude was obtained in subjects whose contralateral ear was sealed with a plastic ear plug. Moreover, cross-over attenuation by bone transmission has been ruled out, as no change in DPOAE amplitude was recorded in the healthy ear of total unilaterally deaf patients during acoustic stimulation of the deaf ear. The effect seen was not entirely due to the acoustic reflex, as it was found and could indeed be even greater in subjects with no acoustic reflex. Results presented here show that the contralateral BBN effect is greater at low levels of ipsilateral stimulation, which leads us to discuss the involvement of both passive and active mechanisms in DPOAE generation at high stimulation levels. The contralateral BBN effect seems to be greater in mid frequency cochlear regions. There is strong evidence that the medial efferent system is involved and that afferent and efferent inputs are, at least partly, integrated at a brainstem level in order to ensure cochlear interaction. DPOAEs provide an interesting model for functional exploration of the efferent system, since they seem to be the only type of otoacoustic emission that can be recorded in both humans and in the majority of animals, and since results are obtained in the same way from both animals and humans, which allows experimental animal models very close to the human model.     

Suppression of otoacoustic emission is unchanged after several minutes of contralateral acoustic stimulation

The influence of variable durations of contralateral acoustic stimulation on the suppression of click-evoked otoacoustic emissions was investigated in order to determine whether olivocochlear efferent fibers are equally effective whatever the acoustical stimulation duration or if they show fatigue. The suppression effect was measured for contralateral stimulus durations ranging from 10 to 180 s prior to the onset of otoacoustic emission recording, and continuing throughout the recording time (60 s). No significant stimulus duration effect was found.     

Electrophysiologic changes in preterm neonates: auditory brain stem response and distortion product otoacoustic emissions

The purposes of this investigation were to determine 1) if auditory peripheral maturity is present in the newborn; 2) if not, at what age maturational changes occur in the peripheral auditory system from preterm to full-term; and 3) how results of tests used to identify auditory dysfunction in neonates, such as distortion product otoacoustic emissions (DPEs) and auditory brain stem responses (ABRs), change during this period. Longitudinal DPE amplitude and ABR wave I latency measurements were obtained from a single ear of 18 preterm neonates. The DPEs were evoked at f2s of 2, 3, 4, and 5 kHz. The longitudinal data revealed that in general, DPE amplitude increased and ABR wave I latency decreased as a function of postconceptional age. These findings suggest that 1) the peripheral auditory system has not reached maturity in the preterm neonate; 2) maturational changes continue from preterm to full-term; and 3) these changes are reflected in ABR and DPE measurements.     

Otoacoustic emissions in the human

Otoacoustic emissions are sounds emitted by the cochlea, basically deriving from the active micromechanical properties of the outer hair cells of the organ of Corti. As they can be recorded painlessly and non-intrusively, they provide a good means of studying human cochlear functioning. In this report, the main types of otoacoustic emission are described, with their characteristics and relation to cochlear functioning. The contribution of otoacoustic emission studies to the physiology of the medial olivocochlear system is discussed, this being the only sensitive and non-intrusive way of studying this system, the function of which remains uncertain.     

An uncrossed tectopontine pathway mediates ipsiversive circling

Otoacoustic emissions have great promise for use in clinical tests of the functional status of outer hair cells, which represent cochlear structures that make a major contribution to the hearing process. A substantial literature is available concerning the evaluation of outer hair cell function by transiently evoked otoacoustic emissions. However, relatively little attention has been focused on the benefits of testing with distortion-product otoacoustic emissions. The purpose of this presentation is to provide knowledge of the principal advantages offered by distortion-product emissions testing.     

Time course of the medial olivocochlear efferent effect on otoacoustic emissions in humans

The time course of the medial olivocochlear efferent system has been studied in humans, using the suppressive effect of a contralateral broad-band noise (CBBN) on 2f1-f2 distortion product otoacoustic emissions (DPOAE) amplitude. DPOAE were recorded with F2 at 1.5 kHz, with a temporal resolution of 2.6 s, in the presence and absence of a 40 dB SL continuous CBBN, whose duration ranged between 30 s and 20 min. The CBBN suppressive effect on DPOAE amplitude was greatest from the first 2.6 s, and was sustained for 20 min. At the CBBN offset, when the CBBN duration was > or = 2 min, DPOAE amplitude continued to increase for > 1 min, showing an efferent effect outlasting CBBN stimulation.     

Contralateral frequency-modulated tones suppress transient-evoked otoacoustic emissions in humans

In order to test the sensitivity of the human medial olivocochlear bundle (MOCB) to stimulus frequency fluctuations, changes in transient-evoked otoacoustic emission (TEOAE) amplitude induced by frequency modulated (FM) tones were measured in 18 normal-hearing subjects. The results revealed that TEOAE amplitude was reduced by contralateral FM tones at 40 dB above pure-tone threshold, with significant influences of both modulation rate (MR) and modulation depth (MD). This finding is discussed in the light of other recent results indicating amplitude fluctuation and frequency bandwidth effects in MOCB activation in humans.     

Contralateral suppression of transiently evoked otoacoustic emissions by harmonic complex tones in humans

Variations in the amplitude of transiently evoked otoacoustic emissions (TEOAEs) produced by a contralateral complex tone were measured in 26 normal-hearing human subjects. TEOAEs were evoked using a 1-kHz tone pip at 60 dB SPL. The contralateral complex consisted of harmonic components with frequencies between 400 and 2000 Hz; it was presented at levels ranging from 40 to 50 dB SL and its fundamental frequency (F0) was varied. In experiment 1, the dependence of TEOAE amplitude variations on the F0 of the contralateral complex was measured by varying the F0 from 50 to 400 Hz in octave steps. The results revealed a nonmonotonic dependence of TEOAE amplitude variations on contralateral F0, with significantly larger TEOAE suppression for F0's of 100 and 200 Hz than for F0's of 50 and 400 Hz. Experiment 2, in which the harmonics were summed in alternating sine-cosine phase instead of constant sine phase, showed a shift of the function relating TEOAE attenuation to F0 towards lower F0's, indicating that the waveform repetition rate, rather than harmonic spacing, was the actual factor of the dependence of contralateral TEOAE attenuation on F0. Furthermore, significantly smaller suppression was observed with the alternating-phase complexes than with the sine-phase complexes, suggesting an influence of the waveform crest factor. Experiment 3 showed no difference between the contralateral TEOAE attenuation effects produced by positive and negative Schroeder-phase complexes. Overall, these results bring further arguments for the notion that contralaterally induced medial olivocochlear bundle (MOCB) activity, as measured through the contralateral suppression of TEOAEs in humans, is sensitive to the rate of temporal envelope fluctuations of the contralateral stimulus, with preferential rates around 100-200 Hz.     

The amino-terminal sequence of MUC5B contains conserved multifunctional D domains: implications for tissue-specific mucin functions

Otoacoustic emissions have historically been measured with an acoustical probe assembly hermetically sealed in the ear canal, imposing in most cases a limited stimulus bandwidth. A physically open recording system should afford the possibility of a greater stimulus bandwidth but the change in acoustical load may affect the magnitude of otoacoustic emissions obtained. Here it is reported that the authors have measured in the guinea pig transient-evoked otoacoustic emissions extending in frequency to 20 kHz and cubic distortion tone otoacoustic emissions for f2 = 4737 and 8096 Hz with a physically open sound system. To address the effect of acoustical load provided by a physically open versus hermetically sealed system, the authors compared the amplitude of electrically evoked otoacoustic emissions recorded from a guinea pig in each case. The change in acoustical load in the ear canal introduced by the change in recording setup did not appear to make a substantial difference to the magnitude of otoacoustic emissions measured. A physically open recording system provides a good alternative to traditional acoustical probe assemblies sealed in the ear canal for the laboratory measurement of acoustically evoked otoacoustic emissions, with the advantage of permitting a greater stimulus bandwidth.     

Spontaneous otoacoustic emissions in preterm neonates: prevalence and gender effects

A number of lines of evidence indicate that the human cochlea is fully functional as a mature sound transducer by 6 months of age. However, information about the development of the active cochlear mechanisms and notably the development of outer hair cell (OHC) activity is yet incomplete. Recording and analysis of otoacoustic emissions (OAEs), probably generated by the OHCs of the organ of Corti, have led to a better understanding, in humans, of how sounds are analysed in the cochlea by means of active mechanisms. Evoked OAEs (EOAEs) and spontaneous OAEs (SOAEs), when they can be recorded in full-term and preterm neonates, show different characteristics from those in adults, suggesting that maturation of the peripheral auditory system is incomplete at birth. To learn more about this maturation, using the best-established facts concerning SOAEs in adults, such as their greater prevalence in females and also in right ears, SOAEs were studied in more detail in 81 preterm neonates, from 30 to 40 weeks of conceptional age, all presenting bilateral EOAEs according to objective criteria. The first finding of this study was that SOAEs existed and could be recorded as of 30 weeks of conceptional age in humans. Some SOAE characteristics in preterm neonates, such as prevalence, peak number and acoustic frequencies, showed similarity with full-term neonates. Comparison of other criteria between the two populations, such as greater SOAE prevalence in right ears and higher SOAE peak number in females, suggested that these developmental factors emerge around term in humans. Comparison of SOAE characteristics between male and female preterms suggested that male preterms were less advanced in peripheral auditory development than were female preterms.     

Subjective assessment of allergy relief following group hypnosis and self-hypnosis: a preliminary study

Distortion Product Otoacoustic Emissions (DPOEs) are otoacoustic emissions evoked by two pure equilevel tones (f1, f2) called primaries and are believed to provide frequency-specific information regarding cochlear function. We recorded DPOEs at 2f1-f2 frequency with a constant frequency ration (f2/f1 = 1.22) in 8 normal hearing subjects (16 ears, mean age 28 +/- 1.5) to establish the characteristics of these emissions in the adult population. DPOEs were measured at the following F2 frequencies and respective fp geometric mean frequencies: 696/632, 1001/904, 1501/1360, 2002/1809, 3003/2714, 4004/3626, 5005/4531 e 6006/5435 Hz. Detailed testing included the recording of DPOE "audiograms" and input-output functions depicting the relationship of the amplitudes of DPOE to primary-tone levels ranging from 25 to 70 dB SPL in 5 dB steps. The present findings are in good agreement with investigations based on evoked otoacoustic emissions published by other researchers. The average DPOE "audiograms" demonstrated a low-frequency maximum at 1501 Hz (f2)/1360 (fp) and a high-frequency peak at 5005 Hz (f2)/4531 (fp). The two maximum regions were separated by a minimum around 3003 Hz (f2)/2714 (fp). This study confirms the feasibility of DPOE measurements among adults and provide a normal baseline for this age group. DPOEs could be useful, in association with evoked otoacoustic emissions and with auditory brainstem responses, in obtaining a precise evaluation of the peripheral auditory system.     

The role of removable prostheses and implants in the restoration of the worn dentition

Newborns are often discharged from hospital at the age of about 48 hours. At this age, transient evoked otoacoustic emissions (TEOAEs) are not necessarily recordable in all healthy newborns. In order to determine the factors which would enable the successful recording of TEOAEs before discharge to facilitate screening for hearing, 65 fullterm newborns under 48 hours of age were tested, the youngest being 10 hours old. The ears of those neonates in whom TEOAEs could not be obtained (N = 7 neonates bilaterally, 6 unilaterally) were examined otoscopically, cleaned of vernix and retested for TEOAEs. We were thus able to record in at least one ear in all neonates tested, if the ears were clean, if they were asleep and if the testing room was quiet.     

Clinical application of transiently evoked otoacoustic emissions in screening for auditory dysfunction

Transiently evoked otoacoustic emissions (TEOAE) should be used clinically as an objective and noninvasive screening test for auditory dysfunction in children. The features of TEOAE measured by "ILO88" with non linear click stimuli are discussed. The following results were obtained: 1) The normal range of a power spectrum was determined using 42 adults with normal hearing and compared with data for sensorineural hearing disturbance. The power spectrum of TEOAE in adults with normal hearing sloped downward at high frequency and was the same for right and left ears in both males and females. For comparison with sensorineural hearing disturbance, a significant correlation between the audiogram and power spectrum of TEOAE was sought. 2) Patients with otitis media with effusion (109 ears in 67 children) were examined by audiometry, tympanometry and TEOAE. The hearing disturbance threshold of 45 cases with TEOAE was lower than that in cases with no TEOAE. In tympanometry, low intratympanic pressure was noted in the absence of TEOAE. 3) TEOAE and spontaneous otoacoustic emission were examined in 42 adults with normal hearing and 27 neonates using the same probe and level of stimuli to clarify differences in TEOAE according to age. The amplitude of TEOAE and the highest peak of the frequency component at 4kHz in neonates exceeded those of adults. The peak stimuli recorded with the intracanal probe in neonates was also larger than that of adults. Three out of 15 neonates had spontaneous otoacoustic emission and essentially the same proportion was noted in young adults.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of crossed olivocochlear bundle section on transient evoked otoacoustic emissions

The purpose of this study was to investigate the effect of sectioning the crossed olivocochlear bundle (COCB) on transient evoked otoacoustic emissions (TEOAEs) in anesthetized adult chinchillas. Of particular interest is the role of cochlear efferents to the outer haircells (OHCs) and how they control mechanisms responsible for otoacoustic emissions. Specifically the experiment addressed whether a tonic level of inhibitory control is reduced by COCB section. The nonlinear component of TEOAEs was measured before and after COCB section. Analysis was made of the 1, 2, 3, 4, and 5 kHz frequency components and of the total emission, as quantified by fast Fourier transform (FFT) of the raw (time domain) response. After COCB section, the amplitude of the total response and of the 2, 3, 4, and 5 kHz components increased whereas the amplitude of the 1 kHz component decreased. The results indicate that COCB section reduces inhibitory control of the OHC mechanisms responsible for nonlinear TEOAE generation. It is not clear whether the nerve section eliminates a spontaneous level of activity in COCB efferents, or whether it results in the interruption of a stimulus-evoked feedback loop.     

Contralateral suppression of transiently evoked otoacoustic emissions and neuro-otology

Transiently evoked otoacoustic emissions can be suppressed with simultaneous contralateral sound stimulation. This is considered to be effected via the efferent pathway from the superior olivary complex (SOC) to the contralateral cochlea. This study examined this effect in patients with extrinsic and intrinsic lesions of the brainstem which may affect the efferent pathway either within the vestibular nerve which carries the efferent bundle to the cochlea or within the brainstem at the level of the SOC. Suppression is reduced or absent in these patients and the site and size of the lesion determines whether the suppression is affected unilaterally or bilaterally. Lesions affecting the auditory afferent pathway without significant alteration in hearing appear to affect the efferent pathway too.     

Transitory evoked and distortion products of otoacoustic emissions in absent auditory evoked potentials

Transient click-evoked otoacoustic emissions (TEOAE) and distortion-product otoacoustic emissions (DPOAE) are produced by an active biomechanical process in the cochlea, presumably related to outer hair-cell activity. Although it is generally accepted that in most cases of hearing loss with absent auditory evoked potentials neither TEOAE nor DPOAE can be found, some cases with such a constellation have been described. Here we report another four cases of children with severe to profound hearing loss where we discovered reproducible TEOAE and DPAOE, whereas auditory evoked potentials were missing. TEOAE and DPOAE recordings in these cases indicate substantially preserved outer hair-cell function independent of profound pre-sensineural hearing loss. Since the incidence of children with preserved otoacoustic emissions together with impairment of synaptic or postsynaptic function of the first neuron is not known, the unconditioned use of TEOAE nor DPOAE as a screening instrument must be seriously questioned. Secondly, in conjunction with subjective audiometry and brain-stem-evoked potentials, emission recordings is an indispensable measurement prior to cochlear implantation and use of high-power hearing aids.     

Relationships between left hemisphere predominance and disturbances of lipid metabolism in different ethnic groups

In neonates and infants, hearing impairment leads to impaired language and cognitive development. For that reason, early detection of this sensory deficit is of outstanding importance, particularly in pre-term neonates, who constitute a high risk population in regard to very early acquired hearing loss. Evoked (EOAE) and spontaneous otoacoustic emission (SOAE) recording in 93 pre-term and full-term neonates revealed that this technique is potentially useful for auditory screening in neonatology units. EOAEs and SOAEs can be recorded successfully from 30 weeks of conceptional age. SOAEs were found to be prevalent in females and presented higher peak numbers in right than in left ears. Furthermore, SOAE incidence in pre-term and full-term neonates was found to be high in EOAE positive ears, associated with strong and robust EOAEs.     

Influence of contralateral noise on distortion product latency in humans: is the medial olivocochlear efferent system involved?

To test the hypothesis of temporal modifications of cochlear responses when medial efferents are activated, otoacoustic emission latencies were estimated in 16 normal human subjects, in the presence and absence of a contralateral broadband noise, using measurements of the phase of the 2f1-f2 distortion product (group latency method). Significant decrease in the latency of lower frequency (0.8-2.7 kHz) emissions was found in the presence of increasing levels of contralateral sound, and this effect disappeared when the primary-tone levels increased to 60 dB SPL. To ensure that effects were not attributable to mechanisms involving middle ear structures, susceptible to activation by contralateral sound, latency measures were performed in seven subjects whose efferents were severed during a vestibular neurotomy and in two subjects with paralyzed stapedial muscle. Results in patients were compared to those obtained in three surgical control patients with intact efferent bundle, and in eight other normal subjects. All the subject groups exhibited a decrease in latency under contralateral sound except the patients with the severed efferent system who showed increased latencies.     

Effect of temperature on the transient evoked and distortion product otoacoustic emissions in rats

In order to study the energy dependence of the cochlear amplifier, transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) were recorded in rats during gradual cooling to 27 degrees C and heating to 40 degrees C. In the range 33-39 degrees C, the TEOAEs and DPOAEs were maximal in amplitude and almost insensitive to temperature. However, they were significantly depressed (reversibly) at higher and lower temperatures. Intensity functions were plotted at 37, 27 and 40 degrees C for both types of oto-acoustic emissions. At 37 degrees C intensity functions were nonlinear, with a notch at mid-intensity regions. At 27 degrees C, the magnitudes were depressed more at the lower intensities and threshold elevations were observed. As a result, the intensity functions were more linear and the notch was no longer seen. This result provides further evidence for a more active, energy-dependent component of the otoacoustic emissions at lower intensities for both TEOAEs and DPOAEs. The cooling probably affects the lower intensity otoacoustic emissions by inducing a depression in the endocochlear potential, by reducing the motility of the outer hair cells and by introducing a small conductive hearing loss.     

Transient evoked otoacoustic emissions in infants: effects of gender, ear asymmetry and activity status

This study examined the effects of gender, ear asymmetry and activity status of infants on various measures of transient evoked otoacoustic emission (TEOAE), including signal-to-noise ratio (SNR) and reproducibility of emissions, using TEOAE as a mass screening procedure in a community health setting. Five hundred and sixty-eight infants were screened for hearing at two months of age, before immunization. The ILO88 Otodynamic Analyzer Quickscreen program was used for all testing with pass/fail criteria similar to those used in the Rhode Island hearing assessment project. The results indicated a significant difference in SNR across sex, with females showing a higher mean SNR. The right ear was found to have higher values in 'reproducibility' and 'response level' than the left ear. A significant difference in SNR across activity states was also evident. Implications from these findings, as applied to community-based screening programs, are discussed.