Development of human cochlear active mechanism asymmetry: involvement of the medial olivocochlear system?

The Magnitude of Contralateral Suppression of Otoacoustic Emissions Is Ear- and Age-Dependent

The maturation of the uncrossed medial olivocochlear (UMOC) efferent remains poorly documented to date. The UMOC efferent system allows listeners to not only detect but also to process, recognize, and discriminate auditory stimuli. Its fibers can be explored non-invasively by recording the effect of contralateral acoustic stimulation (CAS), resulting in a decrease in the amplitude of transient evoked otoacoustic emissions (TEOAE). The objective of the present cross-sectional study was to investigate how the effectiveness of this system varies with age in healthy subjects aged 8 years to adulthood. For this purpose, 120 right-handed native French-speaking subjects (57 females and 63 males) were divided into five age groups of 24 subjects each: 8y-10y, 10y-11y6m, 11y6m-13y, 13y-17y, and ≥18y. TEOAE amplitudes with and without CAS were recorded. The equivalent attenuation (EA) was calculated, corresponding to the change in TEOAE amplitude equivalent to the effect generated by CAS. General linear models were performed to control for the effect of ear, sex, and age on EA. No sex effect was found. A stronger EA was consistently found regardless of age group in the right ear compared to the left. In contrast to the right ear, for which, on average, EA remained constant across age groups, an increasingly weaker TEOAE suppression effect with age was found in the left ear, reinforcing the asymmetrical functioning of the UMOC efferent system in favor of the right ear in adulthood. Further studies are needed to investigate the lateralization of the UMOC efferent system and its changes over time in cases of atypical or reversed cortical asymmetries, especially in subjects with specific learning disorders.

Inhibitory effect of contralateral noise on transient otoacoustic emissions in infants with congenital syphilis

OBJECTIVES

Analyze the inhibitory effect of contralateral noise on transient otoacoustic emissions in infants with congenital syphilis (CS).

METHODS

Cross-sectional study, approved by the Research Ethics Committee n° 3.360.991. Infants with treated CS at birth and infants without risk indicators for hearing impairment were selected. Both groups had the waves I, III and V presence at 80 dB nHL with click BAEP and the presence of response in the nonlinear TEOAEs at 80 dB NPS bilaterally. For suppression, TEOAE were analyzed without the contralateral noise, with the linear stimulus at 60 dB SPL. The neonates who presented a response in three frequencies per ear performed the second TEOAE collection with the contralateral white noise at an intensity of 60 dB SPL. Inferential analysis were performed using the Mann-Whitney and Wilcoxon test, adopting a significance level p < 0.05.

RESULTS

The sample consisted of 30 subjects divided into two groups, the Study Group (SG), consisting of 16 infants, and the Control Group (CG), consisting of 14 infants with no risk indicators for hearing loss. No differences were observed between the groups and the inhibition values, in the SG 30.8% presented inhibition and 25% for the CG in the right ear, in the left ear it was 46.7% in the SG and 38.5% in the CG. The SG demonstrated greater inhibition in the RE for the frequency bands from 1.5 to 4 KHz.

CONCLUSIONS

The analyses adopted in this study point out that the inhibitory effect of contralateral noise on TEOAEs in infants with CS does not differ from infants without risk indicators for hearing loss.

Contralateral suppression of otoacoustic emissions in pre-school children

BACKGROUND

Contralateral suppression of otoacoustic emissions (OAEs) may serve as an index of the medial olivocochlear (MOC) reflex. To date, this index has been studied in various populations but never in pre-school children. The purpose of this study was to fill this gap and describe how the MOC reflex affects the properties of transiently evoked OAEs (TEOAEs) in this age group. In addition, the influence of the presence of spontaneous OAEs (SOAEs) in the studied ear on the suppression of TEOAEs was also investigated.

METHODS

TEOAEs with and without contralateral acoustic stimulation (CAS) by white noise were measured in 126 normally hearing pre-school children aged 3-6 years. The values of response levels, suppression by CAS, and signal-to-noise ratios (SNRs) of TEOAEs were investigated for the whole signal (global) and for half-octave frequency bands from 1 to 4 kHz. Only ears with SNR >6 dB were used in the analyses. SOAEs were acquired using the so-called synchronized SOAEs (SSOAEs) technique.

RESULTS

Ears with SSOAEs had higher response levels and SNRs than ears without SSOAEs, and suppression was lower (0.58 dB compared to 0.85 dB). Only 22% of all studied ears had an SNR >20 dB, a level recommended in some studies for measuring suppression. There were no significant effects of age or gender on TEOAE suppression.

CONCLUSIONS

Suppression levels for pre-school children did not differ appreciably from those of adults measured under similar conditions in other studies. Taken together with no effect of age in the data studied here, it seems that there is no effect of age on TEOAE suppression. However, we did find that the presence of SSOAEs had an effect on TEOAE suppression, a finding which has not been reported in earlier studies on different populations. We suggest that the presence of SSOAEs might be a crucial factor related to MOC function.

Does Contralateral Inhibition of Transient Evoked Otoacoustic Emissions Suggest Sex or Ear Laterality Effects?

PURPOSE

The purpose of this study was to examine contralateral inhibition of transient evoked otoacoustic emissions (TEOAEs) in young adults with normal hearing as a function of ear and sex.

METHOD

Young female (n = 50) and male (n = 50) adults with normal hearing participated. TEOAEs were measured bilaterally with 80 dB peSPL nonlinear clicks and 60 dB peSPL linear clicks with and without a contralateral broadband noise elicitor at 65 dB SPL. Absolute TEOAE inhibition and normalized TEOAE inhibition (i.e., percentage of inhibition) were examined.

RESULTS

With both 80 and 60 dB peSPL evoking stimuli, there were significant main effects of ear and sex (p < .05). TEOAE levels were larger in women and in the right ear. There were no statistically significant main effects of ear and sex on absolute TEOAE inhibition (p > .05). Significant main effects of ear and sex were, however, found with normalized TEOAE inhibition (p < .05; greater in men and in the left ear). Statistically significant negative correlations and significant linear predictive relations were found between TEOAE levels and normalized TEOAE inhibitions in both ears (p < .001). There is no evidence of the same with absolute inhibition of TEOAEs (p > .05).

CONCLUSIONS

If one considers that efferent inhibition of TEOAEs is an absolute quantity, the significant effect of ear and sex on normalized inhibition and the negative association and linear predictive relationship between TEOAE level and inhibition can be viewed as spurious effects. As such, contralateral inhibition of TEOAEs does not suggest sex or ear laterality effects.

Acoustic Reflex Testing in Neonatal Hearing Screening and Subsequent Audiological Evaluation

PURPOSE

The aims of the study were to examine the acoustic reflex screening and threshold in healthy neonates and those at risk of hearing loss and to determine the effect of birth weight and gestational age on acoustic stapedial reflex (ASR).

METHOD

We assessed 18 healthy neonates (Group I) and 16 with at least 1 risk factor for hearing loss (Group II); all of them passed the transient evoked otoacoustic emission test that assessed neonatal hearing. The test battery included an acoustic reflex screening with activators of 0.5, 1, 2, and 4 kHz and broadband noise and an acoustic reflex threshold test with all of them, except for the broadband noise activator.

RESULTS

In the evaluated neonates, the main risk factors were the gestational age at birth and a low birth weight; hence, these were further analyzed. The lower the gestational age at birth and birth weight, the less likely that an acoustic reflex would be elicited by pure-tone activators. This effect was significant at the frequencies of 0.5, 1, and 2 kHz for gestational age at birth and at the frequencies of 1 and 2 kHz for birth weight. When the broadband noise stimulus was used, a response was elicited in all neonates in both groups. When the pure-tone stimulus was used, the Group II showed the highest acoustic reflex thresholds and the highest percentage of cases with an absent ASR. The ASR threshold varied from 50 to 100 dB HL in both groups. Group II presented higher mean ASR thresholds than Group I, this difference being significant at frequencies of 1, 2, and 4 kHz.

CONCLUSIONS

Birth weight and gestational age at birth were related to the elicitation of the acoustic reflex. Neonates with these risk factors for hearing impairment were less likely to exhibit the acoustic reflex and had higher thresholds.

Early uneven ear input induces long-lasting differences in left-right motor function

How asymmetries in motor behavior become established normally or atypically in mammals remains unclear. An established model for motor asymmetry that is conserved across mammals can be obtained by experimentally inducing asymmetric striatal dopamine activity. However, the factors that can cause motor asymmetries in the absence of experimental manipulations to the brain remain unknown. Here, we show that mice with inner ear dysfunction display a robust left or right rotational preference, and this motor preference reflects an atypical asymmetry in cortico-striatal neurotransmission. By unilaterally targeting striatal activity with an antagonist of extracellular signal-regulated kinase (ERK), a downstream integrator of striatal neurotransmitter signaling, we can reverse or exaggerate rotational preference in these mice. By surgically biasing vestibular failure to one ear, we can dictate the direction of motor preference, illustrating the influence of uneven vestibular failure in establishing the outward asymmetries in motor preference. The inner ear–induced striatal asymmetries identified here intersect with non–ear-induced asymmetries previously linked to lateralized motor behavior across species and suggest that aspects of left–right brain function in mammals can be ontogenetically influenced by inner ear input. Consistent with inner ear input contributing to motor asymmetry, we also show that, in humans with normal ear function, the motor-dominant hemisphere, measured as handedness, is ipsilateral to the ear with weaker vestibular input.

Despite a long-standing fascination with asymmetries in left–right brain function, very little is known about the causes of functional brain asymmetry in mammals, which appear independent of the mechanisms that create anatomical asymmetries during development. Asymmetries in motor function are a common example and include preferred turning direction, handedness, and footedness. In this study, using mouse models, we establish a causal link between transient imbalances in degenerating inner ear function and the establishment of stable asymmetries in neural pathways that regulate motor activity and in motor behavior. Our study also suggests that shared mechanisms may underlie lateralized motor behaviors across mammalian species. For example, we show that in humans with normal ear function, the strength of the vestibular response from each ear in the forebrain correlates with asymmetric motor behavior, measured as handedness. In a broader sense, our study reveals a conceptually novel role for sensory input in shaping the asymmetric distribution of brain function, a process for which there is otherwise no clear mechanism.

Efeito de supressão das emissões otoacústicas em lactentes termo e pré-termo

RESUMO Objetivo Verificar a ocorrência e a magnitude do efeito de supressão das emissões otoacústicas evocadas por estímulo transiente, em lactentes a termo e pré-termo, estabelecendo-se níveis de referência para utilização clínica. Método A amostra foi composta por 40 lactentes, de 5 dias a 4 meses de idade, sem risco para alteração neurológica e auditiva e com emissões otoacústicas presentes ao nascimento, sendo 20 nascidos a termo e 20 nascidos pré-termo que permaneceram mais de cinco dias em Unidade de Terapia Intensiva Neonatal. O clique linear foi apresentado a 65 decibels Nível de Pressão Sonora, em blocos de 15 segundos sem ruído e com ruído contralateral, a 60 decibels Nível de Pressão Sonora. Considerou-se presença de supressão quando houve redução da resposta na presença de ruído. Os valores médios de supressão foram estabelecidos e a comparação entre os grupos foi analisada estatisticamente. Resultados A supressão ocorreu em 100% das crianças e não variou em função do lado da orelha e entre os grupos. Conclusão Todas as crianças apresentaram supressão, independente do grupo. A supressão média obtida na população total foi de 0,85 decibel. O critério de referência mínimo recomendado para utilização clínica foi a redução de 0,20 decibel na resposta geral.

Maturation of the human medial efferent reflex revisited

Past work applying otoacoustic emissions to gauge maturational status of the medial olivocochlear (MOC) reflex in human newborns has produced mixed results. The present study revisits the question while considering the dual nature of the 2f(1) - f(2) distortion product otoacoustic emission (DPOAE) and expanding measures of medial efferent function. Subjects included premature and term-born neonates, 6-month-old infants and young adults. The MOC reflex was elicited with contralateral acoustic stimulation (CAS) while shifts in amplitude and phase of the DPOAE, and its distortion and reflection components, were monitored. Overall, CAS-elicited reductions in DPOAE level did not differ among age groups. For all ages, the MOC reflex was strongest at frequencies below 1.5 kHz, and the reflection component of the DPOAE was most affected, showing maximally reduced amplitude and shallower phase slope when contralateral noise was presented. Results suggest that the MOC reflex likely reaches maturation prior to full-term birth. However, prematurely born neonates show markedly more episodes of CAS-induced DPOAE level enhancement. This may be due to more intrusive component mixing in this age group or disruptions in the formation of the MOC pathway or synapse in the most premature neonates.

Listening difficulties in children: bottom-up and top-down contributions

The brain mechanisms of hearing include large regions of the anterior temporal, prefrontal, and inferior parietal cortex, and an extensive network of descending connections between the cortex and sub-cortical components of what is presently known as the auditory system. One important function of these additional ('top-down') mechanisms for hearing is to modulate the ascending, sensory ('bottom-up') auditory information from the ear. In children, normal, immature hearing during the first decade of life is more strongly influenced by top-down mechanisms than in adulthood. In some children, impaired top-down function presents a significant challenge to their auditory perception, often associated with a range of language and learning difficulties and sometimes called auditory processing disorder.

The MOC reflex during active listening to speech

PURPOSE

The purpose of this study was to test the hypothesis that active listening to speech would increase medial olivocochlear (MOC) efferent activity for the right vs. the left ear.

METHOD

Click-evoked otoacoustic emissions (CEOAEs) were evoked by 60-dB p.e. SPL clicks in 13 normally hearing adults in 4 test conditions for each ear: (a) in quiet; (b) with 60-dB SPL contralateral broadband noise; (c) with words embedded (at -3-dB signal-to-noise ratio [SNR]) in 60-dB SPL contralateral noise during which listeners directed attention to the words; and (d) for the same SNR as in the 3rd condition, with words played backwards.

RESULTS

There was greater suppression during active listening compared with passive listening that was apparent in the latency range of 6- to 18-ms poststimulus onset. Ear differences in CEOAE amplitude were observed in all conditions, with right-ear amplitudes larger than those for the left. The absolute difference between CEOAE amplitude in quiet and with contralateral noise, a metric of suppression, was equivalent for right and left ears. When the amplitude differences were normalized, suppression was greater for noise presented to the right and the effect measured for a probe in the left ear.

CONCLUSION

The findings support the theory that cortical mechanisms involved in listening to speech affect cochlear function through the MOC efferent system.

Auditory efferents facilitate sound localization in noise in humans

The mammalian auditory system contains descending neural pathways, some of which project onto the cochlea via the medial olivocochlear (MOC) system. The function of this efferent auditory system is not entirely clear. Behavioral studies in animals with olivocochlear (OC) lesions suggest that the MOC serves to facilitate sound localization in noise. In the current work, noise-induced OC activity (the OC reflex) and sound-localization performance in noise were measured in normal-hearing humans. Consistent with earlier studies, both measures were found to vary substantially across individuals. Importantly, significant correlations were observed between OC-reflex strength and the effect of noise on sound-localization performance; the stronger the OC reflex, the less marked the effect of noise. These results suggest that MOC activation by noise helps to counteract the detrimental effects of background noise on neural representations of direction-dependent spectral features, which are especially important for accurate localization in the up/down and front/back dimensions.

Auditory measures in clinically depressed individuals. I. Basic measures and transient otoacoustic emissions

This is the first paper in a series of two papers addressing possible differences in auditory function between individuals with and without clinical depression. Clinical depression is a common yet serious medical condition diagnosed based on the patient's symptoms. Selective serotonin reuptake inhibitors (SSRIs) are widely prescribed if the symptoms are determined to be consistent with low serotonin levels. Three groups of individuals were tested: the control group consisted of subjects with no depression; the medicated group consisted of subjects with depression who were on SSRIs for at least a month: the unmedicated group consisted of subjects with depression who were unmedicated for at least a month. The results indicated no significant differences between the groups in pure-tone threshold, uncomfortable loudness levels, dynamic range of hearing, and acoustic reflex thresholds However, the unmedicated group exhibited higher amplitudes of transient otoacoustic emissions compared to the control group, especially in the right ear.

Maturation of the auditory system: 1. Transient otoacoustic emissions as an index of inner ear maturation

The transiently evoked otoacoustic emission amplitude of 42 preterm babies (84 ears; post-conceptional age [PCA] 30-36 weeks) was compared with the TEOAE amplitude of 39 full-term babies (78 ears; PCA 37-45 weeks) in order to trace the inner ear maturation characteristics. An ILO-92 otoacoustic emission recording system was used with linear clicks of 70 dB peak equivalent SPL. The results obtained indicated: (1) There was no statistically significant difference between preterm and full-term ears; (2) There was no significant difference between males and females; (3) There was a significant difference between left and right ear TEOAE amplitude; (4) The interaction of ear with age in relation to TEOAE amplitude was statistically significant; (5) Noise and stimulus parameters did not reveal any significant differences between right and left ears; (6) A positive correlation existed between birthweight and TEOAE amplitude; and (7) A negative correlation existed between aminoglycoside treatment and TEOAE amplitude. The results indicate subtle changes in TEOAE amplitude over time, showing a natural development of the inner ear function during the process of maturation.

Maturation of the auditory system: 2. Transient otoacoustic emission suppression as an index of the medial olivocochlear bundle maturation

Contralateral suppression of transient otoacoustic emissions in 42 premature babies (84 ears; post-conceptional age [PCA] 30-36 weeks) was compared to that of 39 full-term babies (78 ears; PCA: 37-45 weeks). Eighteen healthy adults and ten young children (5-14 years old) were studied as controls. Risk factors for hearing loss were registered in both preterm and full-term groups. An ILO-92 otoacoustic emission recording system was used to deliver linear clicks to the ear examined and broadband noise to the contralateral ear in an alternating on and off mode. Suppression in full-term babies was statistically higher than in preterms, whereas no differences existed between children and adults and children and full-terms. Peripheral auditory lateralization was evident in adults but was observed only as a trend in newborns. Only prematurity at the time of examination and aminoglycoside treatment for more than seven days had a negative impact on suppression. The results support the conclusion that maturation of the efferent system takes place from 30 to 45 weeks PCA. The exact age at which this maturation is accomplished has not yet been clearly determined.

Tone burst evoked otoacoustic emissions in neonates

Aim

Materials and Methods

Study

Results

Conclusion

TEOAE suppression in adults with learning disabilities

The presentation of contralateral noise during the recording of transient evoked otoacoustic emissions (TEOAEs) reduces the amplitude of the TEOAE in normally-hearing adults. This is known as TEOAE suppression. The present study investigated TEOAE suppression in 18 adults with learning disabilities (LDs) compared to 18 adults without LDs. TEOAEs were elicited by 60 dB p.e. SPL clicks and were suppressed by the presentation of 60 dB SPL contralateral broadband noise. Suppression was measured as a change in the overall TEOAE response amplitude, and also analysed in 2-ms epochs representing different TEOAE frequency-response bands. A significant interaction was evident between group type and ear tested. Participants in the control group had right ear dominance for the suppression effect, whereas the left ear was found to be dominant for the LD group. These findings suggest a mechanism of the medial olivary cochlear bundle and efferent auditory pathway that differs in those with LD compared to those with typical learning abilities.

Contralateral suppression of linear and nonlinear transient evoked otoacoustic emissions in neonates at risk for hearing loss

To investigate the transient evoked otoacoustic emissions (TEOAE) contralateral suppression in neonates at risk for hearing loss, 55 neonates at risk for hearing loss (risk group) and 72 full-term neonates not at such risk (control group) were bilaterally tested. In all neonates, the TEOAE were recorded in two stimulation modes (linear and nonlinear clicks), with and without contralateral acoustic stimulation. Findings revealed significant contralateral suppression of otoacoustic emissions in both groups, but the amount of TEOAE contralateral suppression was reduced for at risk group (p=0.001), supporting the hypothesis that medial olivocochlear bundle function is reduced in neonates at risk for hearing loss. The combination of contralateral acoustic stimulation and TEOAE enables easy and noninvasive study of auditory efferent function. However it should be emphasized that the reduction in TEOAE contralateral suppression in the risk group, statistically identified as a group effect, might not be detectable in individual cases. Further studies are needed in order to determine whether the lower amount of TEOAE contralateral suppression in neonates at risk for hearing loss represents a risk for developing auditory processing disorders.

LEARNING OUTCOMES

The reader will be introduced to the study using auditory efferent pathway activation by contralateral acoustic stimulation (CAS), resulting in the TEOAE suppression effect. The characteristics of TEOAE suppression in the neonatal population, in which it provides evidence of the reduced medial olivocochlear system function in those at risk for hearing loss, will also be addressed.

Balance in healthy individuals assessed with Equitest: maturation and normative data for children and young adults

OBJECTIVE

The purpose of the present prospective study was to obtain normative data for Equitest computerized dynamic posturography (CDP) in children and young adults and to observe the balance maturation process.

METHODS

Equilibrium pattern and SOT of 195 healthy children aged from 6 to 14 years were compared to those of 64 young adults aged 20 years, using Equitest.

RESULTS

The mean stability scores for children progressively improve with age and are significantly lower than those of young adults. Furthermore, sensory organization scores were lower in children compared to young adults, whereas visual preference scores were similar for the whole studied groups.

CONCLUSIONS

According to previous literature, it may be stressed that due to a presumed incomplete development of vestibular system and central nervous system integration, children unlike young adults have lower equilibrium scores, especially when visual information was not available or was incorrect. Our results confirm previous ones obtained in children and young adults with Equitest CDP. This study also provides Equitest data for these age groups, which complete those that have been previously reported.

Olivocochlear efferents: anatomy, physiology, function, and the measurement of efferent effects in humans

This review covers the basic anatomy and physiology of the olivocochlear reflexes and the use of otoacoustic emissions (OAEs) in humans to monitor the effects of one group, the medial olivocochlear (MOC) efferents. MOC fibers synapse on outer hair cells (OHCs), and activation of these fibers inhibits basilar membrane responses to low-level sounds. This MOC-induced decrease in the gain of the cochlear amplifier is reflected in changes in OAEs. Any OAE can be used to monitor MOC effects on the cochlear amplifier. Each OAE type has its own advantages and disadvantages. The most straightforward technique for monitoring MOC effects is to elicit MOC activity with an elicitor sound contralateral to the OAE test ear. MOC effects can also be monitored using an ipsilateral elicitor of MOC activity, but the ipsilateral elicitor brings additional problems caused by suppression and cochlear slow intrinsic effects. To measure MOC effects accurately, one must ensure that there are no middle-ear-muscle contractions. Although standard clinical middle-ear-muscle tests are not adequate for this, adequate tests can usually be done with OAE-measuring instruments. An additional complication is that most probe sounds also elicit MOC activity, although this does not prevent the probe from showing MOC effects elicited by contralateral sound. A variety of data indicate that MOC efferents help to reduce acoustic trauma and lessen the masking of transients by background noise; for instance, they aid in speech comprehension in noise. However, much remains to be learned about the role of efferents in auditory function. Monitoring MOC effects in humans using OAEs should continue to provide valuable insights into the role of MOC efferents and may also provide clinical benefits.

[Characteristics of transient evoked otoacoustic emissions in newborn hearing screening program]

BACKGROUND

Otoacoustic emissions (OAE) are considered the main instrument of the Newborn Hearing Screening Program (NHSP).

AIM

To analyze the OAE of newborns evaluated in the NHSP.

METHOD

Transient evoked OAE recordings were captured in 1000 infants. The data were analyzed using the analysis of multivaried variance (Manova).

RESULTS

Reference tables were calculated for the over all OAE levels and for frequency bands, according to gender and ear. The duration of the exam in the nursery was shorter than in the clinic.

CONCLUSION

The level of the OAE was influenced by gender and ear, except for 0,7kHz. However, there were no observed differences between neonates without and with auditory risk.

Transient otoacoustic emissions in the detection of olivocochlear bundle maturation

OBJECTIVE

The medial olivocochlear bundle, forms a neural pathway connecting the superior olivary complex to the outer hair cells of mainly the contralateral cochlea. Although the biological significance of the bundle remains ambiguous, it is clear that activation of medial olivocochlear fibers alters cochlear output and this can be experimentally evident through a series of changes on otoacoustic emissions, called otoacoustic emission suppression. The aim of this study is to observe the maturation of the medial olivocochlear bundle by measuring the suppression effects on transient otoacoustic emissions.

METHODS

The study population consisted of 27 premature babies (53 ears) from the P&A Kyriakou Neonatal Intensive Care Unit (conceptional age: 31-36 weeks) and 43 fullterm babies (61 ears) (conceptional age: 37-42 weeks) from the same unit. The ILO-92 system is used to deliver both the linear clicks to the ear examined (producing the emissions) and the white noise to the contralateral ear. The mode used is based on the alternating on and off presence of the white noise in the contralateral ear.

RESULTS

12/53 (22%) ears of preterm babies presented suppression > or =1 dB. 32/61 (52.4%) ears of fullterm babies presented suppression > or =1 dB. The mean suppression for the ears of premature infants was 0.52 dB, (+/-0.1 S.E.M.). The mean suppression for the ears of fullterm infants was 0.90 dB, (+/-0.09 S.E.M.). At the second half of the time window, suppression of fullterms rises above 1 dB (a pattern similar to that of adults), whereas it remains below 1 dB for preterms.

CONCLUSIONS

Suppression of otoacoustic emissions helps us to study the function of the medial olivocochlear bundle in different populations. It appears in premature babies but becomes stronger as the postconceptional age advances.

Contralateral Suppression of Otoacoustic Emissions in Children with Specific Language Impairment

OBJECTIVE

The purpose of the investigation was to determine whether a group of children with specific language impairments (SLI) have reduced peripheral auditory processes thought to be associated with speech-in-noise intelligibility.

DESIGN

Transient evoked otoacoustic emissions (TEOAE) and their suppression by the efferent activity of the medial olivocochlear system (MOCS) in response to contralateral acoustic stimulation were used to compare these processes in 18 children with SLI and 21 controls.

RESULTS

The results revealed no group difference in TEOAE suppression effect or left/right asymmetry of TEOAE suppression effect.

CONCLUSIONS

These results suggest that children with SLI do not have auditory processing problems at this peripheral level casting doubt on a hypothesized relationship between strength of MOCS activity and language impairment.

Lateral asymmetry in the ABR of neonates: Evidence and mechanisms

Lateralized processing of auditory stimuli occurs at the level of the auditory cortex but differences in function between the left and right sides are not clear at lower levels of the auditory system. The current study is designed to (1) investigate asymmetric auditory function at the ear and brainstem in human infants and (2) investigate possible mechanisms for asymmetry at these levels. Study 1 evaluated auditory brainstem responses (ABRs) in response to high and low-level clicks presented to the right and left ears of neonates. Wave V was significantly larger in amplitude and waves III and V were shorter in latency when the ABR was generated in the right ear. Study 2 investigated two possible mechanisms of such asymmetry by (a) using contralateral white noise masking to activate the medial olivocochlear system and (b) increasing stimulus rate to reveal neural conduction and synaptic mechanisms. ABR wave V, evoked by clicks to the left ear, showed a greater reduction in amplitude with contralateral noise than the response evoked from the right ear. No systematic asymmetries in ABR latencies or amplitudes were found with increased stimulus rate. We conclude that (1) the click-evoked ABR in neonates demonstrates asymmetric auditory function with a small but significant right ear advantage and (2) asymmetric activation of the medial olivocochlear system, specifically greater contralateral suppression of ABR produced by the left ear, is a possible mechanism for asymmetry.

Mudanças das emissões otoacústicas por transientes na supressão contralateral em lactentes

TEMA: tem sido sugerido que a função do sistema olivo coclear medial (SOCM) pode ser avaliada pelo efeito de supressão das emissões otoacústicas por transientes (EOAT). O ruído competitivo tem um efeito inibitório no funcionamento das células ciliadas externas reduzindo o nível das emissões otoacústicas. Apesar de não haver crescimento pós natal da cóclea, o crescimento da orelha média e o desenvolvimento do processamento auditivo continuam após o nascimento. OBJETIVO: analisar as mudanças no SOCM relacionadas à idade por meio da supressão das EOAT em lactentes saudáveis. MÉTODO: 25 lactentes a termo sem indicadores de risco auditivo foram avaliados em dois momentos: ao nascimento e no sexto mês de vida. Nas duas idades as EOAT foram captadas no modo "Quickscreen", estímulo clique não linear a 78dB peNPS, nas duas orelhas, com e sem ruído contralateral apresentado a 60dB NPS. RESULTADOS: a análise dos dados por meio da ANOVA revelou significante supressão contralateral das EOAT em ambos grupos, porém tanto os níveis das EOAT quanto a magnitude da supressão contralateral das EOAT foram menores no sexto mês de vida quando comparados com a fase neonatal (p<0,01). O efeito de supressão das EOAT no período neonatal foi 2,81dB (± 0,19dB) e no sexto mês de vida foi 1,41dB (± 0,29dB). CONCLUSÃO: a magnitude da supressão das EOAT diminuiu do nascimento ao sexto mês de idade. A associação entre a estimulação acústica contralateral e um sistema, disponível comercialmente, rápido na medida das EOAT possibilita o monitoramento não invasivo dos mecanismos eferentes auditivos e parece ser clinicamente promissor na avaliação do estado coclear e do desenvolvimento da função eferente auditiva de lactentes de risco.

Hemispheric Specialization for Processing Auditory Nonspeech Stimuli

The left hemisphere specialization for speech perception might arise from asymmetries at more basic levels of auditory processing. In particular, it has been suggested that differences in "temporal" and "spectral" processing exist between the hemispheres. Here we used functional magnetic resonance imaging to test this hypothesis further. Fourteen healthy volunteers listened to sequences of alternating pure tones that varied in the temporal and spectral domains. Increased temporal variation was associated with activation in Heschl's gyrus (HG) bilaterally, whereas increased spectral variation activated the superior temporal gyrus (STG) bilaterally and right posterior superior temporal sulcus (STS). Responses to increased temporal variation were lateralized to the left hemisphere; this left lateralization was greater in posteromedial HG, which is presumed to correspond to the primary auditory cortex. Responses to increased spectral variation were lateralized to the right hemisphere specifically in the anterior STG and posterior STS. These findings are consistent with the notion that the hemispheres are differentially specialized for processing auditory stimuli even in the absence of linguistic information.

Selective serotonin reuptake inhibitors treatment effects on auditory measures in depressed female subjects

The purpose of this study was to evaluate the auditory effects of selective serotonin reuptake inhibitors (SSRI), known to enhance serotonin (5-HT) transmission in the brain. The experimental group consisted of 14 clinically depressed female subjects, and the control group consisted of 11 non-depressed females. A battery of tests was administered to the experimental group while on and off of SSRI medication. The control group was also administered the test battery twice. Results indicated no significant differences in the control group between sessions. The experimental group showed significantly smaller transient evoked emissions, higher SCAN-A (auditory processing test) composite scores, and smaller amplitude growth functions for Auditory brainstem response peak V and Auditory late response peak N(1)P(2) while on SSRI medication. The increased 5-HT levels in the presence of SSRI (due to reduced reuptake of 5-HT) may be contributing to the significant changes seen in auditory measures with the experimental group.

Cochlear maturation and otoacoustic emissions in preterm infants: a time–frequency approach

Click-evoked otoacoustic emissions (CEOAEs) from preterm infants were analyzed to characterize developmental changes of cochlear active mechanisms. Due to their strong time-varying properties, CEOAEs were studied with a time-frequency approach--the wavelet transform (WT). By means of the WT, CEOAEs were decomposed into 12 frequency bands, spanning the 0.25-6.25 kHz range. For each band, the root-mean-square (RMS) level and latency were studied as functions of both frequency and age. Because CEOAEs were averaged using the non-linear mode of acquisition, the developmental changes in observed in this study are related to the non-linear component (which is actually the most predominant component of the active cochlear response) of CEOAEs, the linear one being mostly canceled out by non-linear averaging. In our study, there was evidence that properties of CEOAE non-linear components are related to the post-conception age (PCA) in that the levels and latency of CEOAE frequency components changed until the age of about 38 weeks post-conception, whereas after 38 weeks, CEOAE features were very similar to those of term newborns. In particular, the CEOAE levels increased and latency decreased with age. The observed changes in CEOAE properties seem to reveal a development of cochlear active mechanisms, although contributions from outer and middle ear development cannot be excluded. Also, in agreement with previous physiological and behavioral findings, our results revealed that the development of CEOAE properties was not the same for all the frequencies, being greater for frequencies 4 kHz, and resembled the development of the cochlear partition, which proceeds from base to apex.

Loss of Peripheral Right-Ear Advantage in Age-Related Hearing Loss

In young adults with normal hearing, the right ear is more sensitive than the left to simple sounds (peripheral right-ear advantage) and to processing complex sounds such as speech (central right-ear advantage). In the present investigation, the effects of hearing loss and aging on this auditory asymmetry were examined at both peripheral and central levels. Audiograms and transient evoked otoacoustic emission (TEOAE) and distortion product otoacoustic emission amplitudes were used to assess cochlear function. The contralateral suppression of TEOAEs was measured to assess the medial olivocochlear efferent system. The Hearing in Noise Test (HINT; binaural speech) was conducted to assess higher central auditory function. A group of aged subjects with normal hearing (flat audiograms) were compared to a group of aged subjects with sloping audiograms (presbycusis). At the cochlear (peripheral) level, the normal hearing group showed significantly higher otoacoustic emission amplitudes for the right ear compared to the left ear, which is consistent with the right-ear dominance normally seen in young adults. However, this finding was reversed in the presbycusic group that showed higher left-ear emission amplitudes. At the brainstem level, the amplitudes of TEOAE contralateral suppression were small and no significant difference was found between the right and left ears in both groups. On the contrary, HINT results showed a continuous dominance of the right ear (left hemisphere) in both groups, which was consistent with previous reports showing that the right hemisphere is more affected by age than the left hemisphere.

Reduced auditory efferent activity in childhood selective mutism

BACKGROUND

Selective mutism is a psychiatric disorder of childhood characterized by consistent inability to speak in specific situations despite the ability to speak normally in others. The objective of this study was to test whether reduced auditory efferent activity, which may have direct bearings on speaking behavior, is compromised in selectively mute children.

METHODS

Participants were 16 children with selective mutism and 16 normally developing control children matched for age and gender. All children were tested for pure-tone audiometry, speech reception thresholds, speech discrimination, middle-ear acoustic reflex thresholds and decay function, transient evoked otoacoustic emission, suppression of transient evoked otoacoustic emission, and auditory brainstem response.

RESULTS

Compared with control children, selectively mute children displayed specific deficiencies in auditory efferent activity. These aberrations in efferent activity appear along with normal pure-tone and speech audiometry and normal brainstem transmission as indicated by auditory brainstem response latencies.

CONCLUSIONS

The diminished auditory efferent activity detected in some children with SM may result in desensitization of their auditory pathways by self-vocalization and in reduced control of masking and distortion of incoming speech sounds. These children may gradually learn to restrict vocalization to the minimal amount possible in contexts that require complex auditory processing.

Development of f2/f1 ratio functions in humans

Otoacoustic emissions (OAEs) presumably represent active processes within the cochlea fundamental to frequency-selectivity in peripheral auditory function. Maturation of the cochlear amplifier, vis-a-vis frequency encoding or selectivity, has yet to be fully characterized in humans. The purpose of this study was to further investigate the maturation of features of the f2/f1 frequency ratio (Distortion Product OAE amplitude X f2/f1 ratio) presumed to reflect cochlear frequency selectivity. A cross-sectional, multivariate study was completed comparing three age groups: pre-term infants, term infants and young adult subjects. Frequency ratio functions were analyzed at three f2 frequencies--2000, 4000 and 6000 Hz. An analysis included an estimation of the optimal ratio (OR) and a bandwidth-like measure (Q3). Analysis revealed significant interactions of age x frequency x gender for optimal ratio and a significant interaction of age x frequency for Q3. Consistent and statistically significant differences for both OR and Q3 were found in female subjects and when f2 = 2 or 6 kHz. This supports research by others [Abdala, J. Acoust. Soc. Am. 114, 3239-3250 (2003)] suggesting that the development of cochlear active mechanisms may still be somewhat in flux at least through term birth. Furthermore, OAEs appear to demonstrate gender differences in the course of such maturational changes.

Assessment of medial olivocochlear system function in pre-term and full-term newborns using a rapid test of transient otoacoustic emissions

This study was conducted to investigate maturation of the medial olivocochlear efferent system (MOCS) in pre- and full-term neonates using Quickscreen (Otodynamics Ltd) and to confirm previous findings on transient otoacoustic emission (TEOAE) suppression in neonates. MOCS maturation was investigated in 46 neonates born at the Chaim Sheba Medical Center, Tel Hashomer, Israel, using Quickscreen. All neonates were normal with no family history of general or auditory disease and no risk factors for hearing impairment. MOCS function appears gradually in human pre-term neonates and is considered to reach maturity shortly after term birth. The clinical value of MOCS testing in specific populations of newborns at risk for hearing and/or brainstem function can be legitimately raised as activation of the MOCS clearly alters cochlear output. The present results can be interpreted to support the testing of infants at risk of developing abnormal MOCS function using a commercially available rapid TEOAE measurement system.

Contralateral suppression of otoacoustic emissions in neonates

The effect of contralateral acoustic stimulation on transient evoked otoacoustic emissions (TEOAEs) was used to investigate the activity of the medial olivocochlear bundle in neonates. TEOAEs were bilaterally recorded, with and without contralateral noise, in 120 full-term neonates without risk for hearing loss. Otoacoustic emission recordings were carried out using the Otodynamic ILO88 system quickscreener non-linear mode, and the contralateral stimulation was presented at 60 dB SPL delivered by CD player. The results revealed a significant (p<0.01) contralateral suppression of TEOAE response amplitude: 2.32 dB in females and 3.28 dB in males. This study shows that the suppression effect is present in 88.5% of neonates, with a gender difference (greater suppression in males) and frequency effect, suggesting a functional maturation of the medial olivocochlear bundle in the studied population.