Valores normativos para potencial evocado auditivo de tronco encefálico binaural em adultos

Binaural interaction component in adults with normal hearing.

Binaural interaction of bone-conducted auditory brainstem responses in children with congenital atresia of the external auditory canal

The binaural interaction component (BIC) of the auditory brainstem response (ABR) is obtained by subtracting the sum of the monaural right and left ear ABRs from the binaurally evoked ABR. The result is a small but prominent negative peak (herein called "DN1"), indicating a smaller binaural than summed ABR, which occurs around the latency of wave V or its roll-off slope. The BIC has been proposed to have diagnostic value as a biomarker of binaural processing abilities; however, there have been conflicting reports regarding the reliability of BIC measures in human subjects. The objectives of the current study were to: (1) examine prevalence of BIC across a large group of normal-hearing young adults; (2) determine effects of interaural time differences (ITDs) on BIC; and (3) examine any relationship between BIC and behavioral ITD discrimination acuity. Subjects were 40 normal-hearing adults (20 males and 20 females), aged 21 to 48 years, with no history of otologic or neurologic disorders. Midline ABRs were recorded from electrodes at high forehead (Fz) referenced to the nape of the neck (near the seventh cervical vertebra), with Fpz (low forehead) as the ground. ABRs were also recorded with a conventional earlobe reference for comparison to midline results. Stimuli were 90 dB peSPL biphasic clicks. For BIC measurements, stimuli were presented in a block as interleaved right monaural, left monaural, and binaural stimuli with 2000+ presentations per condition. Four measurements were averaged for a total of 8000+ stimuli per analyzed waveform. BIC was measured for ITD = 0 (simultaneous bilateral) and for ITDs of ±500 and ±750 µs. Subjects separately performed a lateralization task, using the same stimuli, to determine ITD discrimination thresholds. An identifiable BIC DN1 was obtained in 39 of 40 subjects at ITD = 0 µs in at least one of two measurement sessions, but was seen in lesser numbers of subjects in a single session or as ITD increased. BIC was most often seen when a subject was relaxed or sleeping, and less often when they fidgeted or reported neck tension, suggesting myogenic activity as a possible factor in disrupting BIC measurements. Mean BIC latencies systematically increased with increasing ITD, and mean BIC amplitudes tended to decrease. However, across subjects, there was no significant relationship between the amplitude or latency of the BIC and behavioral ITD thresholds. Consistent with previous studies, measurement of the BIC was time consuming and a BIC was sometimes difficult to obtain in awake normal-hearing subjects. The BIC will thus continue to be of limited clinical utility unless stimulus parameters and measurement techniques can be identified that produce a more robust response. Nonetheless, modulation of BIC characteristics by ITD supports the concept that the ABR BIC indexes aspects of binaural brainstem processing and thus may prove useful in selected research applications, e.g. in the examination of populations expected to have aberrant binaural signal processing ability.

The auditory brainstem response (ABR) is a sound-evoked noninvasively measured electrical potential representing the sum of neuronal activity in the auditory brainstem and midbrain. ABR peak amplitudes and latencies are widely used in human and animal auditory research and for clinical screening. The binaural interaction component (BIC) of the ABR stands for the difference between the sum of the monaural ABRs and the ABR obtained with binaural stimulation. The BIC comprises a series of distinct waves, the largest of which (DN1) has been used for evaluating binaural hearing in both normal hearing and hearing-impaired listeners. Based on data from animal and human studies, the authors discuss the possible anatomical and physiological bases of the BIC (DN1 in particular). The effects of electrode placement and stimulus characteristics on the binaurally evoked ABR are evaluated. The authors review how interaural time and intensity differences affect the BIC and, analyzing these dependencies, draw conclusion about the mechanism underlying the generation of the BIC. Finally, the utility of the BIC for clinical diagnoses are summarized.

Objective: Speech evoked auditory brainstem responses (spABRs) provide a window to understand the neurophysiological processing of speech in the brain. The temporal and spectral characteristics of speech sounds are faithfully represented in the subcortical responses; thus, these responses can be used to assess specific impairments in auditory processing. However, the spABRs are known to be affected by the acoustic properties of speech, language experience and training. Hence, the establishment of language specific speech stimuli is warranted for brainstem processing. The objective of the study was to develop Hindi speech stimuli for brainstem response recordings. Study design: The Hindi stop-voiced and voiceless phoneme of CV combination of 40 ms was synthesized. The behavioural identification score and discrimination ability of the selected stimuli were obtained from children (6–13 years) and adults (18–25 years) with normal hearing (NH) and moderate sensorineural hearing loss (HI). Brainstem evoked responses to stimulus |da| were gained from normal hearing and hearing impaired adults. Results: The identification and discrimination scores of stimuli between NH and HI children and adults were calculated. Statistically significant differences in the mean identification scores of synthesized speech stimuli were obtained. The mean, median, standard deviation, minimum, maximum and 95% confidence interval values of electrophysiological responses to speech stimulus were measured for the discrete peaks and V-A complex for both the groups. Conclusion: This article has delineated a comprehensive methodological approach for the development of Hindi speech stimuli and the recording of auditory brain stem responses to speech stimuli. The acoustic characteristic of the stimulus |da| was faithfully represented at brainstem level in normal hearing adults and found to be statistically different from HI individuals. This suggests that spABR offers an opportunity to segregate normal speech encoding from abnormal speech processing and implies that alterations in brainstem responses could have clinical significance for the identification of subjects with possible speech processing disorders.

Investigating the optimal stimulus to evoke the binaural interaction component of the auditory brainstem response

This study addresses the effect of early asymmetric hearing loss in children, owing to otitis media with effusion (OME), on binaural hearing. Five children who had suffered from predominantly unilateral OME between the ages of 2 and 4 years and who were not treated for OME at any time participated in this study when they were about 12 years of age. All children had normal hearing at the time of testing. Data were compared to normative values obtained previously from normal-hearing adults. We measured the auditory brainstem response (ABR), the binaural interaction component (BIC) in the ABR, the masking level difference (MLD) and the suppression of transient evoked otoacoustic emissions (OAEs) with contralateral noise stimulation. The results indicated that the children's ABRs and BICs were comparable to normative data, that there was evident suppression of transient evoked OAEs in 4 of the 5 children and that the children's MLD values were within the normal (adult) range. The present results therefore do not support the presence of long-term auditory processing deficits induced by early asymmetric OME in man.

Speech-evoked auditory brainstem responses (spABRs) provide considerable information of clinical relevance to describe auditory processing of complex stimuli at the sub cortical level. The substantial research data have suggested faithful representation of temporal and spectral characteristics of speech sounds. However, the spABR are known to be affected by acoustic properties of speech, language experiences and training. Hence, there exists indecisive literature with regards to brainstem speech processing. This warrants establishment of language specific speech stimulus to describe the brainstem processing in specific oral language user. The objective of current study is to develop Hindi speech stimuli for recording auditory brainstem responses. The Hindi stop speech of 40ms containing five formants was constructed. Brainstem evoked responses to speech sound |da| were gained from 25 normal hearing (NH) adults having mean age of 20.9years (SD=2.7) in the age range of 18-25years and ten subjects (HI) with mild SNHL of mean 21.3years (SD=3.2) in the age range of 18-25years. The statistically significant differences in the mean identification scores of synthesized for speech stimuli |da| and |ga| between NH and HI were obtained. The mean, median, standard deviation, minimum, maximum and 95% confidence interval for the discrete peaks and V-A complex values of electrophysiological responses to speech stimulus were measured and compared between NH and HI population. This paper delineates a comprehensive methodological approach for development of Hindi speech stimuli and recording of ABR to speech. The acoustic characteristic of stimulus |da| was faithfully represented at brainstem level in normal hearing adults. There was statistically significance difference between NH and HI individuals. This suggests that spABR offers an opportunity to segregate normal speech encoding from abnormal speech processing at sub cortical level, which implies that alterations in brainstem responses have clinical significance to identify the subjects with possible processing disorders.

Contralateral broadband noise (BBN) elevates ipsilateral auditory thresholds (central masking) and reduces the amplitude of ipsilateral brainstem auditory evoked potentials (BAEPs). Binaural interactions are complex psychophysical phenomena, but binaural interaction components are easily extracted from BAEPs to monaural versus binaural click stimulation. However, contralateral, or binaural, acoustical stimulation is known to activate simultaneously the crossed and uncrossed medial olivocochlear (MOC) efferent systems and decrease activity in both cochleas. Particularly, contralateral BBN stimulation suppresses in part ipsilateral peripheral activity. What is the role of such contralaterally induced peripheral suppression in the overall changes in central BAEPs observed during contralateral masking or binaural stimulation? Compound action potentials (CAPs) of the auditory nerve and BAEPs were recorded simultaneously in awake guinea pigs from electrodes chronically implanted on the round window of the cochlea and the surface of the brain. Peripheral and central measures of contralateral masking and binaural interactions were obtained from responses to monaural or binaural clicks, with or without contralateral BBN, recorded before, during, and after the reversible blockade of the MOC function following a single intramuscular injection of gentamicin. Contralateral BBN effectively reduced the amplitudes of CAP and of all BAEP peaks. CAP to ipsilateral click did not, however, change significantly from monaural to binaural click stimulation; still, normal binaural interaction components developed in the BAEPs. When the medial efferent function was blocked by gentamicin, the normal contralateral BBN suppression of CAP and of the earliest BAEP peak was lost; however, the later BAEP peaks were suppressed by contralateral BBN as before gentamicin, and the central binaural interaction components were unchanged. In these experimental conditions, the MOC efferent system seems to play little role in centrally recorded contralateral masking and binaural interactions.

The auditory brainstem response (ABR) is an evoked potential that reflects the responses to sound by brainstem neural centers. The binaural interaction component (BIC) is obtained by subtracting the sum of the monaural ABR responses from the binaural response. Its latency and amplitude change in response to variations in binaural cues. The BIC is thus thought to reflect the activity of binaural nuclei and is used to non-invasively test binaural processing. However, any conclusions are limited by a lack of knowledge of the relevant processes at the level of individual neurons. The aim of this study was to characterize the ABR and BIC in the barn owl, an animal where the ITD-processing neural circuits are known in great detail. We recorded ABR responses to chirps and to 1 and 4kHz tones from anesthetized barn owls. General characteristics of the barn owl ABR were similar to those observed in other bird species. The most prominent peak of the BIC was associated with nucleus laminaris and is thus likely to reflect the known processes of ITD computation in this nucleus. However, the properties of the BIC were very similar to previously published mammalian data and did not reveal any specific diagnostic features. For example, the polarity of the BIC was negative, which indicates a smaller response to binaural stimulation than predicted by the sum of monaural responses. This is contrary to previous predictions for an excitatory-excitatory system such as nucleus laminaris. Similarly, the change in BIC latency with varying ITD was not distinguishable from mammalian data. Contrary to previous predictions, this behavior appears unrelated to the known underlying neural delay-line circuitry. In conclusion, the generation of the BIC is currently inadequately understood and common assumptions about the BIC need to be reconsidered when interpreting such measurements.

The binaural interaction component (BIC) is discussed as a potential tool to objectively measure listeners’ binaural auditory processing abilities. It is obtained from auditory brainstem responses (ABRs) by subtracting the sum of the ABRs to monaural left and monaural right stimulation from the ABR recorded under binaural stimulation. The sources of the BIC, however, have not yet been agreed upon. Candidate source regions are the lateral and medial superior olives (LSO and MSO, respectively) in the superior olivary complex where excitatory and inhibitory inputs converge. Our study aims at identifying the source of the BIC. Simultaneously to ABRs, we recorded local-field potentials (LFPs) and single-unit (SU) responses from the LSO and MSO of ketamine/xylazine-anaesthetised Mongolian gerbils and derived LFP-related and SU-related BICs the same way as ABR-related BIC. We then compared the properties of LFP-related and SU-related BICs with the ABR-related BICs. LFP-related BICs recorded in the LSO did not mirror the characteristics of the ABR-related BIC while the SU-related BIC did. In the MSO, neither LFP-related nor SU-related BIC mirrored ABR-related BICs. This suggests that the output of LSO units but not MSO units contribute substantially to the generation of the ABR-related BIC.

The binaural interaction component (BIC) represents the mismatch between auditory brainstem responses (ABR) obtained with binaural stimulation and the sum of ABRs obtained with monaural left and right stimulation. It is generally assumed that the BIC reflects binaural integration. Its potential use as a diagnostic tool, however, is hampered by the lack of direct evidence about its origin. While an origin at the initial site of binaural integration seems likely, there is no general agreement on the contribution of the two primary candidate nuclei, the lateral and medial superior olives (LSO and MSO, respectively). Here, we recorded local field potentials (LFP) and responses of units in the LSO and MSO of Mongolian gerbils (Meriones unguiculatus), presenting clicks with an interaural time or level difference (ITD and ILD, respectively), while simultaneously recording ABR. We determined the BIC from the ABR and, importantly, from LFP and responses of units in the LSO and MSO. If stimulus-induced changes in the ABR-derived BIC have their source in the LSO and/or MSO, we expect coherent changes in the unit-derived and the ABR-derived BIC. We find that BIC obtained from LSO units exhibits the same ITD and ILD dependence as the ABR-derived BIC. Neither BIC obtained from MSO units nor LFP-derived BIC recorded in either LSO or MSO did. The data thus strongly suggest that it is the activity of LSO units in the gerbil that is decisive for the generation of the ABR-derived BIC, determining its properties.

The auditory steady-state evoked response (ASSR) is a scalp-recorded potential elicited by modulated sounds or repetitive transient sounds presented at a high rate. The binaural interaction component (BIC) of the ASSR equals the difference between the response to binaural stimuli and the sum of the responses to a monaural stimulus presented to the left ear and the right ear. This study examined the effect of the interaural time (ITD) and level (ILD) difference on the BIC of the 80 Hz ASSR. Sixteen human participants with normal hearing were tested. The ITD and ILD were varied from -1.6 to +1.6 msec and from 0 to +12 dB, respectively. The ITD function of the BIC showed a "V" shape, with a 0 value of BIC at ITD 0 msec and a positive BIC at ITD +0.8 to +1.6 msec. For ILD conditions, the BIC displayed negative values, and its amplitude became more negative as the ILD was increased. The results indicate that the ITD and ILD may be processed by different groups of binaural neurons in different pathways. It is suggested that the 80 Hz ASSR provides an objective means for evaluating binaural functions in patients such as those with central auditory processing disorders.

Although bilateral cochlear implants (BiCIs) have succeeded in improving the spatial hearing performance of bilateral CI users, the overall performance is still not comparable with normal hearing listeners. Limited success can be partially caused by an interaural mismatch of the place-of-stimulation in each cochlea. Pairing matched interaural CI electrodes and stimulating them with the same frequency band is expected to facilitate binaural functions such as binaural fusion, localization, or spatial release from masking. It has been shown in animal experiments that the magnitude of the binaural interaction component (BIC) derived from the wave-eV decreases for increasing interaural place of stimulation mismatch. This motivated the investigation of the suitability of an electroencephalography-based objective electrode-frequency fitting procedure based on the BIC for BiCI users. A 61 channel monaural and binaural electrically evoked auditory brainstem response (eABR) recording was performed in 7 MED-EL BiCI subjects so far. These BiCI subjects were directly stimulated at 60% dynamic range with 19.9 pulses per second via a research platform provided by the University of Innsbruck (RIB II). The BIC was derived for several interaural electrode pairs by subtracting the response from binaural stimulation from their summed monaural responses. The BIC based pairing results are compared with two psychoacoustic pairing methods: interaural pulse time difference sensitivity and interaural pitch matching. The results for all three methods analyzed as a function of probe electrode allow for determining a matched pair in more than half of the subjects, with a typical accuracy of ± 1 electrode. This includes evidence for statistically significant tuning of the BIC as a function of probe electrode in human subjects. However, results across the three conditions were sometimes not consistent. These discrepancies will be discussed in the light of pitch plasticity versus less plastic brainstem processing.

Background and ObjectivesThis study was performed to comprehensively examine the amplitudes of the binaural interaction components (BICs) elicited by chirps, clicks, and 500 Hz tone-burst stimuli in individuals with normal hearing. Electrophysiological evidence of BICs was obtained and assessed for correlations with interaural time difference (ITD) and interaural level difference (ILD).Subjects and MethodsSixteen adults (4 males and 12 females) with normal hearing participated in this study. Auditory brainstem responses (ABRs) to chirp, click, and 500 Hz tone-burst stimuli were recorded, and BICs were derived based on wave V. The behavioral thresholds of ITDs and ILDs across multiple frequencies were obtained and analyzed.ResultsBICs were found in most participants, regardless of stimulus type. The amplitudes of BICs elicited by chirps were the highest, followed by those elicited by clicks and 500 Hz tone-bursts. A significant correlation was found between the amplitudes of chirp-evoked BICs and the thresholds of 500 Hz ITDs and ILDs.ConclusionsThis study found that chirp stimuli may be effective in eliciting BIC and predicting behavioral binaural interaction processing at low frequencies.