Auditory Brainstem Response Characteristics Research Articles

Newborn auditory brainstem response and sudden infant death syndrome.

Sudden infant death syndrome (SIDS)-the sudden and unexplained death of a seemingly healthy infant, <1 year old-may be associated with abnormalities in the brain regions that underlie breathing and arousal during sleep. While post-mortem studies suggest abnormalities in SIDS infants' brainstems, there are no studies of these infants' brainstem function before death. One way to assess the function of the brainstem is with auditory brainstem response (ABR), a routine hearing-screening method that noninvasively measures the brainstem's response to sound. We hypothesize that anomalies in newborns' ABR measures may predict SIDS. Indeed, previous studies identified abnormalities in ABR characteristics in small samples of near-miss SIDS infants hospitalized for infant apnea syndrome. However, there is a need to examine the ABRs of infants who died of SIDS. Therefore, in the current study, we propose integrating two secondary datasets to examine newborns' ABRs (N = 156,972), including those who later died of SIDS (n = ~42; .27 out of every 1000 infants), using existing archived records of neonatal ABR results from a sample of newborns born in Florida. We hypothesize that infants who die from SIDS are more likely than non-SIDS infants to have abnormal ABRs as newborns. Understanding the association between SIDS and ABR may facilitate more accurate identification of an infant's risk for SIDS at birth, enabling increased monitoring, which may facilitate interventions and improve survivorship.

Supra-Threshold LS CE-Chirp Auditory Brainstem Response in the Elderly

Introduction: Aging deteriorates peripheral and central auditory structures and functions. In elders, for an accurate audiological evaluation, it is important to explore beyond the cochlear receptor. Audiograms provide an estimation of hearing thresholds, while the amplitudes and latencies of supra-threshold auditory brainstem response (ABR) can offer noninvasive measures of the auditory pathways functioning. Regarding ABR, in young populations, level-specific chirp (LS CE-chirp) stimulus has been proposed as an alternative synchronizing method to obtain larger ABR responses than those evoked by clicks. However, the supra-threshold characteristics of chirp evoked ABR, and their association to hearing thresholds is relatively unknown in the elderly. The aim of this study was to evaluate supra-threshold LS CE-chirp ABRs in an aged population by comparing their features with click ABRs, and evaluating their relationship with audiometric hearing thresholds. Methods: We carried out a cross-sectional study to characterize the hearing of 125 adults aged over 65 years. We determined the audiometric hearing thresholds and supra-threshold ABRs elicited by LS CE-chirp and click stimuli at 80 dB nHL. We evaluated associations by means of partial correlations and covariate adjustment. We performed specific frequencies’ analysis and subgroup analysis per hearing level. Results: Wave V responses had significantly shorter latencies and larger amplitudes when elicited by LS CE-chirp as compared to click-evoked responses. Audiometric hearing thresholds correlated with age, but ABR characteristics did not. We found mild correlations between hearing thresholds and ABR characteristics, predominantly at higher frequencies and with chirp. We found scarce evidence of correlation between ABR characteristics and the average of behavioral hearing thresholds between 0.5 to 4 kHz (0.5–4 kHz PTA). After subgroup analysis according to the hearing level, no stronger or more significant correlations were found between ABR characteristics and 0.5–4 kHz PTA. Discussion: In this study, we found that supra-threshold LS CE-chirp ABR presented some of the previously described similitudes and differences with supra-threshold click ABR in younger populations. Although, the average amplitude and latency of wave V evoked by LS CE-chirp were larger and faster than those evoked by clicks, these results should be taken with caution at the individual level, and further studies are required to state that LS CE-chirp ABRs are better than click ABRs in elders for clinical evaluations. We did not find consistent associations between hearing thresholds and supra-threshold wave V features, suggesting that these measures should be considered independently in the elderly.

The human neuroprotective placental protein composition suppressing tinnitus and restoring auditory brainstem response in a rodent model of sodium salicylate-induced ototoxicity

The effect of neuroprotective placental protein composition (NPPC) on the suppression of tinnitus and the restoration of the auditory brainstem response (ABR) characteristics was explored in tinnitus-induced rats. The animals were placed into two groups: (1) the study group, rats received sodium salicylate (SS) at the dose of 200 mg/kg twice a day for two weeks, and then 0.4 mg of the NPPC per day, between the 14th and 28th days, (2) the placebo group, rats received saline for two weeks, and then the NPPC alone between the 14th and 28th days. The gap pre-pulse inhibition of the acoustic startle (GPIAS), the pre-pulse inhibition (PPI), and the ABR assessments were performed on animals in both groups three times (baseline, day 14, and 28). The GPIAS value declined after 14 consecutive days of the SS injection, while NPPC treatment augmented the GPIAS score in the study group on the 28th day. The PPI outcomes revealed no significant changes, indicating hearing preservation after the SS and NPPC administrations. Moreover, some changes in ABR characteristics were observed following SS injection, including (1) higher ABR thresholds, (2) lowered waves I and II amplitudes at the frequencies of 6, 12, and 24 kHz and wave III at the 12 kHz, (3) elevated amplitude ratios, and (4) prolongation in brainstem transmission time (BTT). All the mentioned variables returned to their normal values after applying the NPPC. The NPPC use could exert positive therapeutic effects on the tinnitus-induced rats and improve their ABR parameters.

Auditory Brain Stem Response Predictors of Hearing Outcomes after Middle Fossa Resection of Vestibular Schwannomas

Abstract Objectives To analyze the relationship between preoperative and intraoperative auditory brain stem response (ABR) characteristics and hearing outcomes in patients with vestibular schwannomas (VS) undergoing hearing preservation (HP) surgery via a middle cranial fossa (MCF) approach. Design Prospective study. Setting Academic tertiary skull base referral center. Methods Pre- and postoperative pure-tone average (PTA) and word recognition score (WRS) were examined. Intraoperative ABR wave III latency, wave V latency, and amplitude were recorded. HP was defined as postoperative WRS ≥50%. Participants Adult patients with VS and WRS ≥50% who underwent MCF tumor resection between November 2017 and September 2019. Main Outcome Measures Postoperative hearing outcomes. Results Sixty patients were included. Mean tumor size was 9.2 mm (range, 3–17). HP rates were 56.7% for the cohort and 69.7% for tumors &lt;10 mm. A complete loss of wave V was associated with an 82.9% increase in postoperative PTA (p &lt; 0.001) and 97.2% decrease in WRS (p &lt; 0.001), whereas a diminished wave V was correlated with 62.7% increase in PTA (p &lt; 0.001) and 55.7% decrease in WRS (p = 0.006). A diminished or absent wave V, but not increased wave III/V latency or decreased wave V amplitude, was correlated with a decline in postoperative hearing class (r = 0.735, p &lt; 0.001). Receiver-operating characteristic analysis demonstrated that a stable wave V has the highest accuracy in predicting HP (sensitivity of 82.6%, specificity of 84.8%). Conclusion Of the examined preoperative and intraoperative ABR characteristics, a stable wave V intraoperatively was the strongest predictor of HP after MCF resection of VS. Level of Evidence Level III.

Towards optimal selection of stimuli polarity method for effective evoking auditory brainstem responses.

Towards eliminating stimulus artifacts, alternating polarity stimuli have been widely adopted in eliciting the auditory brainstem response. However, considering the difference in the physiologic basis of the positive and negative polarity stimuli on the auditory system, it is unclear whether alternating polarity stimuli would adversely affect the auditory brainstem response characteristics. This research proposes a new polarity method for stimulus artifacts elimination, Sum polarity, that separately utilized the rarefaction and condensation stimuli and then summed the two evoked responses. We compared the waveform morphology and latencies of the auditory brainstem responses evoked by familiar stimuli (including click, tone-burst, and chirp) with different polarity methods in normal-hearing subjects to investigate the new method's effectiveness. The experimental results showed that alternating polarity of the click and chirp had little effect on the auditory brainstem response. In contrast, alternating polarity affected the waveform morphology and latencies of the auditory brainstem responses to the low-frequency tone-burst, with the effect decreasing as the stimulus frequency increased. These results demonstrated the performance of any polarity method is related to the characteristics of the stimulus signal itself, and no polarity method is optimal for all types of stimuli. Based on the analysis of experimental results, a fixed polarity and alternating polarity were recommended for the click and chirp auditory brainstem responses, respectively. Furthermore, considering the apparent latency differences between the responses to opposite polarity stimuli, the Sum polarity was suggested for the tone-burst auditory brainstem responses. Moreover, this work verified the feasibility of the Sum polarity, which offers another choice for eliminating stimulus artifacts in an evoked potential acquisition.

Electrophysiologic Characteristics of Various Degrees of Selective Outer Hair Cell Loss in Rats.

The characteristics of auditory brainstem response (ABR), electrocochleogram (ECochG), and distortion product otoacoustic emissions (DPOAE) of different degrees of selective outer hair cells (OHCs) loss may be helpful for clinicians to evaluate the pathogeny, diagnosis, and rehabilitation of individuals' hearing loss. How many OHCs are necessary to maintain cochlear amplifier function remains unknown. The electrophysiologic characteristics may indicate different degrees of OHCs loss. Electrophysiological characteristics were tested using 8-kHz pure-tone stimulus and OHCs counted specifically in the region of the cochlea corresponding to 8-kHz. Rat models of selective OHCs loss were established by injecting kanamycin (KM) at various dosages, and the region of 8-kHz was obtained by 8-kHz pure-tone exposure. The ABR thresholds were affected slightly with OHCs loss < 30%, and were increased dramatically with OHCs loss ranging from 30 to 70%, but the thresholds did not increase further when OHCs loss exceeded 70%. As OHCs loss increased, the compound action potential (CAP) amplitude decreased. The CAP amplitude and OHCs loss were negatively correlated. Moreover, the summating potential (SP)/action potential (AP) increased as OHCs loss increased. DPOAE and cochlear microphonics (CM) exhibited reduced amplitudes when OHCs loss < 30%. Electrophysiologic characteristics may indicate different degrees of OHCs loss. While OHCs loss > 70%, the cochlear amplification may lose completely, but it is difficult to detect OHCs loss < 30%, because the ABR or DPOAE may reveal "normal" at this level. Moreover, the decreased CAP amplitude or increased SP/AP may be indicators for OHCs loss.

Correlation between Auditory Brainstem Response Characteristics and Hearing Recovery in Sudden Deafness

Background and Objectives Auditory brainstem response (ABR) can be utilized to verify the hearing threshold and determine the existence of retrocochlear pathology in sudden deafness. However, little is known about the significance of ABR characteristics as a prognostic factor in sudden deafness. The purpose of this study is to evaluate which characteristics of ABR is associated with the prognosis of sudden deafness. Subjects and Method We studied patients who were diagnosed with unilateral sudden deafness from January 2017 to May 2018. ABR results of click stimuli at 90 dB nHL were analyzed by the latency of wave I, III, and V. Results A total of 113 patients (55 men and 58 women) participated in the study. Hearing recovery was observed in 94 cases (83.2%). The absolute latency of wave I, III, and V was prolonged in the affected ears when compared with the unaffected ears. Hearing improvement was only correlated to the interaural latency delay of wave I (Pearson’s r=-0.278, p＜0.05). Prolonged interaural latency delay was noted from complete toward slight hearing recovery group. When the hearing outcome was evaluated by the interaural latency delay of wave I at 0.2 ms, the result of under 0.2 ms was significantly better than that over 0.2 ms and no visible wave I. Conclusion Prolonged interaural delay of wave I over 0.2 ms and no visible wave I in ABR showed worse hearing outcome in sudden deafness. This finding may provide ABR as a potential prognostic indicator in sudden deafness. Key words: Auditory ㆍ Evoked potentials ㆍ Latency

Elderly listeners with low intelligibility scores under reverberation show degraded subcortical representation of reverberant speech

In order to elucidate why many elderly listeners have difficulty understanding speech under reverberation, we investigated the relationship between word intelligibility and auditory brainstem responses (ABRs) in 28 elderly listeners. We hypothesized that the elderly listeners with low word intelligibility scores under reverberation would show degraded subcortical encoding information of reverberant speech as expressed in their ABRs towards a reverberant /da/ syllable. The participants were divided into two groups (top and bottom performance groups) according to their word intelligibility scores for anechoic and reverberant words, and ABR characteristics between groups were compared. We found that correlation coefficients between responses to anechoic and reverberant /da/ were lower in the bottom performance group than in the top performance group. This result suggests that degraded neural representation toward information of reverberant speech may account for lower intelligibility of reverberant speech in elderly listeners.

Large-scale phenotyping of noise-induced hearing loss in 100 strains of mice

A cornerstone technique in the study of hearing is the Auditory Brainstem Response (ABR), an electrophysiologic technique that can be used as a quantitative measure of hearing function. Previous studies have published databases of baseline ABR thresholds for mouse strains, providing a valuable resource for the study of baseline hearing function and genetic mapping of hearing traits in mice. In this study, we further expand upon the existing literature by characterizing the baseline ABR characteristics of 100 inbred mouse strains, 47 of which are newly characterized for hearing function. We identify several distinct patterns of baseline hearing deficits and provide potential avenues for further investigation. Additionally, we characterize the sensitivity of the same 100 strains to noise exposure using permanent thresholds shifts, identifying several distinct patterns of noise-sensitivity. The resulting data provides a new resource for studying hearing loss and noise-sensitivity in mice.

Auditory Brainstem Responses in Senile Presbycusis Patients over 90 years

ObjectiveTo analyze the characteristics of auditory brainstem response (ABR) in presbycusis patients elder than 90 years. MethodsFourteen presbycusis patients elder than 90 years (presbycusis group, 91.1.4± 1.3 years, 26 ears) and 9 normal-hearing young adults (control group, 22.7±1.2 years, 18 ears) participated in the study. Alternative click-evoked ABRs were recorded in both groups. The peak latency (PL) of peak I, III, and V, and the inter-peak latency (IPI) of I-III, III-V, and I-V were compared between groups. ResultsIn elder presbycusis patients, the occurrence rate of peak I and III were both 76.9%, and that of peak V was 84.6%. In presbycusis group, the peak latencies of I, III, V were significantly longer than that of control group (P<0.001). There was no significant difference between groups in the IPI of peak I-I III (P=0.298, peak III-V (P=0.254) and peak I-V (P=0.364). ConclusionsAuditory brainstem responses in presbycusis patients elder than 90 years showed worse wave differentiation

Preoperative Characteristics of Auditory Brainstem Response in Acoustic Neuroma with Useful Hearing: Importance as a Preliminary Investigation for Intraoperative Monitoring

We classified the results of preoperative auditory brainstem response (ABR) in 121 patients with useful hearing and considered the utility of preoperative ABR as a preliminary assessment for intraoperative monitoring. Wave V was confirmed in 113 patients and was not confirmed in 8 patients. Intraoperative ABR could not detect wave V in these 8 patients. The 8 patients without wave V were classified into two groups (flat and wave I only), and the reason why wave V could not be detected may have differed between the groups. Because high-frequency hearing was impaired in flat patients, an alternative to click stimulation may be more effective. Monitoring cochlear nerve action potential (CNAP) may be useful because CNAP could be detected in 4 of 5 wave I only patients. Useful hearing was preserved after surgery in 1 patient in the flat group and 2 patients in wave I only group. Among patients with wave V, the mean interaural latency difference of wave V was 0.88 ms in Class A (n = 57) and 1.26 ms in Class B (n = 56). Because the latency of wave V is already prolonged before surgery, to estimate delay in wave V latency during surgery probably underestimates cochlear nerve damage. Recording intraoperative ABR is indispensable to avoid cochlear nerve damage and to provide information for surgical decisions. Confirming the condition of ABR before surgery helps to solve certain problems, such as choosing to monitor the interaural latency difference of wave V, CNAP, or alternative sound-evoked ABR.

Auditory Brainstem Responses to Level-Specific Chirps in Normal-Hearing Adults

Upward chirps are often designed to compensate for the cochlear traveling wave delay which is regarded as independent of stimulation level. A chirp based on a traveling wave model is therefore referred to as a level-independent chirp. Another compensation strategy, for instance based on frequency-specific auditory brainstem response (ABR) latencies, results in a chirp that changes with stimulation level and is therefore referred to as a level-dependent chirp. One such strategy, the direct approach, results in a chirp family that is called the level-specific chirp. The level dependence is in agreement with the findings that the chirp, which generates the largest ABR in normal-hearing adults, has a duration (sweeping rate) that changes with stimulus level. A direct comparison of ABRs to a fixed chirp and to a level-specific chirp has not been performed at higher levels of stimulation where the differences are thought to have the greatest effect on the ABR characteristics from normal-hearing adults. To make a direct comparison of the ABRs to two different chirp stimuli-a level-specific chirp (LS-Chirp) and a level-independent chirp (CE-Chirp)-and to evaluate the hypothesis that at higher levels of stimulation the LS-Chirp generates significantly higher response amplitudes, and produces higher resolution of the different peaks in the ABR than the CE-Chirp. ABRs are recorded in 10 normal-hearing adults (20 ears) in response to three stimuli at four presentation levels using ER-3A insert earphones. The three stimuli are (1) a level-specific chirp (LS-Chirp), (2) a level-independent chirp (CE-Chirp), and (3) a standard 100-μs click as a reference. The recorded ABRs are evaluated by the peak to trough amplitude (wave V), the peak latency (wave V), the frequency of appearance of wave I, III, and V, and the Grand Average waveforms. Amplitude and latency differences are evaluated statistically by the Wilcoxon matched-pair signed rank test. At higher levels (80 dB nHL), the amplitude and waveform resolution of the ABR to the LS-Chirp are significantly higher than to the CE-Chirp. At lower levels (20, 40, and 60 dB nHL), no significant differences are found between the amplitudes of the ABR to the two stimuli, but at 60 dB nHL the waveform resolution is better for the LS-Chirp than for the CE-Chirp. For all levels, the amplitude of the ABRs to the two chirps are significantly larger than to the Click, except at 80 dB nHL where the ABR to the CE-Chirp gets distorted and low in amplitude. The differences between the ABR latencies to the three stimuli are large at higher levels, but small at lower levels. At higher levels, the LS-Chirp and the Click generate similar resolutions of the main ABR peaks, but the ABRs to the LS-Chirp are significantly larger than to the Click. The study confirms the experimental hypothesis that at higher levels of stimulation the LS-Chirp generates significantly higher response amplitudes than both the CE-Chirp and the Click. It also generates a much better response resolution than the CE-Chirp, but the same response resolution as the Click.

Auditory brainstem response morphology and analysis in very preterm neonatal intensive care unit infants

Analysis of auditory brainstem response (ABR) in very preterm infants can be difficult owing to the poor detectability of the various components of the ABR. We evaluated the ABR morphology and tried to extend the current assessment system. Prospective cohort study. We included 28 preterm very low birth weight infants admitted to the neonatal intensive care unit of Sophia Children's Hospital. ABRs were measured between 26 and 34 weeks postconceptional age. The presence of the following ABR parameters was recorded: the ipsilateral peaks I, III and V, the contralateral peaks III and V, and the response threshold. In 82% of our population, a typical "bow tie" response pattern was present as a sign of early auditory development. This bow tie pattern is the narrowest part of the response wave and is predominantly characterized by the ipsilateral negative peak III. This effect may be emphasized by the contralateral peak III. The bow tie pattern is seen approximately 0.1 milliseconds before the ipsilateral peak III. From 30 weeks postconceptional age onward, a more extensive morphologic pattern is recorded in 90% of the infants. A flow chart was designed to analyze the ABR morphology of preterm infants in an unambiguous stepwise fashion. A typical bow tie pattern preceding peak III seems to be the earliest characteristic of the developing ABR morphology in preterm infants. As ABR characteristics will improve with increasing age, neonatal hearing screening should be postponed until after 34 weeks.

Auditory brainstem responses predict auditory nerve fiber thresholds and frequency selectivity in hearing impaired chinchillas

Noninvasive auditory brainstem responses (ABRs) are commonly used to assess cochlear pathology in both clinical and research environments. In the current study, we evaluated the relationship between ABR characteristics and more direct measures of cochlear function. We recorded ABRs and auditory nerve (AN) single-unit responses in seven chinchillas with noise-induced hearing loss. ABRs were recorded for 1–8 kHz tone burst stimuli both before and several weeks after 4 h of exposure to a 115 dB SPL, 50 Hz band of noise with a center frequency of 2 kHz. Shifts in ABR characteristics (threshold, wave I amplitude, and wave I latency) following hearing loss were compared to AN-fiber tuning curve properties (threshold and frequency selectivity) in the same animals. As expected, noise exposure generally resulted in an increase in ABR threshold and decrease in wave I amplitude at equal SPL. Wave I amplitude at equal sensation level (SL), however, was similar before and after noise exposure. In addition, noise exposure resulted in decreases in ABR wave I latency at equal SL and, to a lesser extent, at equal SPL. The shifts in ABR characteristics were significantly related to AN-fiber tuning curve properties in the same animal at the same frequency. Larger shifts in ABR thresholds and ABR wave I amplitude at equal SPL were associated with greater AN threshold elevation. Larger reductions in ABR wave I latency at equal SL, on the other hand, were associated with greater loss of AN frequency selectivity. This result is consistent with linear systems theory, which predicts shorter time delays for broader peripheral frequency tuning. Taken together with other studies, our results affirm that ABR thresholds and wave I amplitude provide useful estimates of cochlear sensitivity. Furthermore, comparisons of ABR wave I latency to normative data at the same SL may prove useful for detecting and characterizing loss of cochlear frequency selectivity.

Abnormal auditory forward masking pattern in the brainstem response of individuals with Asperger syndrome

Abnormal auditory information processing has been reported in individuals with autism spectrum disorders (ASD). In the present study auditory processing was investigated by recording auditory brainstem responses (ABRs) elicited by forward masking in adults diagnosed with Asperger syndrome (AS). Sixteen AS subjects were included in the forward masking experiment and compared to three control groups consisting of healthy individuals (n = 16), schizophrenic patients (n = 16) and attention deficit hyperactivity disorder patients (n = 16), respectively, of matching age and gender. The results showed that the AS subjects exhibited abnormally low activity in the early part of their ABRs that distinctly separated them from the three control groups. Specifically, wave III amplitudes were significantly lower in the AS group than for all the control groups in the forward masking condition (P < 0.005), which was not the case in the baseline condition. Thus, electrophysiological measurements of ABRs to complex sound stimuli (eg, forward masking) may lead to a better understanding of the underlying neurophysiology of AS. Future studies may further point to specific ABR characteristics in AS individuals that separate them from individuals diagnosed with other neurodevelopmental diseases.

Measurement and Response Characteristics of Auditory Brainstem Responses in Pinnipeds

The measurement of auditory evoked potentials (AEPs) has proven to be a useful tool for examining the auditory physiology of odontocete cetaceans and there is growing interest in applying this electrophysiological approach to study the hearing of other marine mammals. The aim of the current investigation was to examine some of the basic measurement and response characteristics of the auditory brainstem response (ABR) in pinnipeds. The subjects were California sea lions (Zalophus californianus), harbor seals (Phoca vitulina), and northern elephant seals (Mirounga angustirostris) that were awake, sedated, or anesthetized during in-air testing. Auditory stimuli were broadband clicks and Hanning-gated tone bursts that were presented binaurally in a direct field. The amplitude and waveform of the ABRs were evaluated as a function of subject state, electrode type and position, analog bandpass filtering, stimulus presentation rate, and stimulus bandwidth. Results indicate that the ABRs were of highest amplitude when measured from subdermal electrodes arranged in a common reference configuration, with the cephalic electrode placed 2 to 4 cm forward of the ears on the dorsal midline of the head. The ABR waveforms were generally similar among the species tested, although the amplitude of the elephant seal ABR was much smaller than that of the other two species at similar stimulus levels. Bandpass filtering of the ABR resulted in improved signal-tonoise ratios but also caused reduction in response amplitude and distortion of the ABR waveform at high-pass settings above 65 Hz. Five-cycle tone bursts provided the best tradeoff between response amplitude and frequency specificity. The amplitude of ABRs evoked by clicks and tone bursts as a function of stimulus level was approximately linear for California sea lions and harbor seals over a range of ~25 dB. Visually estimated thresholds for California sea lions were noise limited but were sensitive enough to show hearing loss in one older subject. These findings should inform future research efforts involving electrophysiological assessment of auditory function, hearing sensitivity, and noise impacts in pinnipeds.

Impact of conventional anesthesia on auditory brainstem responses in mice

Anesthesia is known to affect the auditory brainstem response (ABR) in animals often used in hearing research. This study describes the differences in ABRs between awake and anesthetized FVB/N mice. Intracranial electrodes connected to a head fixation pedestal were used for click-evoked ABR recordings. This pedestal served to immobilize mice, either awake or under anesthesia, in a `free' sound field. The presence of myogenic noise in the awake condition obviously increases recording time. However it is demonstrated that recording times can be significantly reduced by increasing the stimulus repetition rate from 23 up to 80 impulses per second. This causes only a small but significant increase in absolute peak latencies in the awake condition, but has no significant effect on the overall ABR-waveform, nor on the ABR-threshold, nor on the ABR interpeak latencies, nor on the absolute peak latencies in the anesthetized condition. Anesthesia with ketamine/xylazine caused a significant prolongation of ABR-peak latencies and interpeak latencies as well as a significant upward shift (8.0 ± 1.8 dB) of ABR-thresholds as compared to the awake condition. Under anesthesia the measurement accuracy of peak latencies, interpeak latencies and thresholds decreases. In conclusion, the awake condition is preferable for more accurate measurements of ABR characteristics, in spite of the myogenic noise concomitant with this condition.

Hearing-aid-processed Tone Pips: Electroacoustic and ABR Characteristics

The auditory brainstem response (ABR) recorded while wearing a hearing aid may supply supplemental information about the benefit and appropriateness of the hearing aid for certain infants. The purposes of this study were (1) to determine the effects of different output limiting circuits on the acoustics of tone-pip stimuli used for ABR recordings and (2) assess how changes in hearing-aid-processed stimuli affect ABR characteristics. Electroacoustic input/output functions to tone-pip stimuli were constructed for three different output limiting circuits (wide dynamic range compression, output compression, and linear with peak clipping) available in a programmable hearing aid. Wave V latency and amplitude functions were then measured to the same stimuli and hearing aid settings in five normal-hearing adults. Electroacoustic results showed that none of the output limiting circuits, including linear peak clipping, were effectively activated by tone pips compared to the hearing aid performance to continuous tones. Aided wave V latency and amplitude functions were asymptotic to high stimulus levels, suggesting that cochlear output was in saturation.

Auditory brain stem responses to air- and bone-conducted clicks in the audiological assessment of at-risk infants.

Auditory brain stem responses (ABRs) to air- and bone-conducted clicks were used to assess the auditory status of 170 at-risk neonates. During the perinatal period, 20.6% (35/170 cases) of the at-risk infants failed ABRs to air-conducted clicks at 30 dB nHL in at least one ear. Ear-specific results indicated an initial failure rate of 15.0% (51/340 ears). Approximately two-thirds (32/51 ears) of these initial failures showed purely conductive deficits, whereas the remaining one-third (19/51 ears) involved suspected sensorineural components. Follow-up audiological evaluations were performed for 87.1% (148 cases) of these at-risk infants at 4 mo and/or 1 yr corrected age. Based on the initial tests and follow-up assessments, the tentative operating characteristics of ABRs to both air- and bone-conducted clicks for identification of sensorineural deficits in at-risk neonates were calculated. It was found that the ABR to bone-conducted clicks yielded better specificity, predictive value of positive results, and overall efficiency. It is suggested that the ABR to bone-conducted stimuli should be viewed as a valuable addition in the assessment of cochlear reserve in infants who fail a newborn auditory screening to air-conducted stimuli.

Characteristics of auditory brainstem responses in ground squirrels.

Auditory brainstem responses (ABRs) were characterized at 37 degrees C in ground squirrels (Citellus lateralis) which were implanted with recording screws to record ABRs, and a thermistor to record brain temperature. After two weeks ground squirrels were reanesthetized and tone pips and clicks were delivered through a TDH-49 headphone. Recorded ABRs were found to vary in a predictable manner as a function of stimulus frequency and intensity. At intensities above 50 dB SPL, ABRs could be recorded over the range tested (2-32 kHz). An 8 kHz tone pip was the best frequency for recording ABRs at the lowest stimulus intensities. Latencies decreased as stimulus frequencies increased from 4 kHz to 32 kHz.