Brainstem Auditory Evoked Potentials Threshold Research Articles

Transient evoked otoacoustic emissions and cochlear dysfunction

Amplitude measurement and reproducibility of Transient-otoacoustic emissions (T-EOAE) depend on synchronicity and functional integrity of cochlear outer hair cells, thus, the main objective of this study was to determine the usefulness of amplitude measurement and reproducibility in five selective frequencies of T-EOAE in patients with Sensorineural hearing loss (SNHL). We studied 44 subjects with SNHL by means of T-EOAE and Brainstem auditory evoked potentials (BAEP), and compared the results with those of a six control-normal-hearing subject group. We observed significant differences in the reproducibility of T-EOAE and in amplitudes of 0.7, 1.5, 2.2, 3.0 and 3.7kHz. In addition, we observed negative significant correlations between BAEP threshold and T-EOAE reproducibility and with all specific amplitude measurement frequency values. These results confirm the clinical usefulness of reproducibility and selective amplitude measurement of frequency of T-EOAE for SNHL identification.

Analysis of auditory function using brainstem auditory evoked potentials and auditory steady state responses in infants with perinatal brain injury

Approximately 2–4 % of newborns with perinatal risk factors present hearing loss. The aim of this study was to analyse the auditory function in infants with perinatal brain injury (PBI). Brainstem auditory evoked potentials (BAEPs), auditory steady state responses (ASSRs), and tympanometry studies were carried out in 294 infants with PBI (586 ears, two infants had unilateral microtia-atresia). BAEPs were abnormal in 158 (27%) ears, ASSRs in 227 (39%), and tympanometry anomalies were present in 131 (22%) ears. When ASSR thresholds were compared with BAEPs, the assessment yielded 92% sensitivity and 68% specificity. When ASSR thresholds were compared with tympanometry results as an indicator of middle-ear pathology, the assessment gave 96% sensitivity and 77% specificity. When BAEP thresholds were compared with tympanometry results, sensitivity was 35% and specificity 95%. In conclusion, BAEPs are useful test for neonatal auditory screening; they identify with more accuracy sensorineural hearing losses. ASSRs are more pertinent for identifying conductive hearing loss associated with middle-ear pathology. The consistency and accuracy of these results could be considered in additional studies.SumarioAproximadamente 2-4% de neonatos con factores de riesgo perinatales presentan pérdida auditiva. El objetivo de este estudio fue analizar la función auditiva de niños con daño cerebral perinatal (PBI). Se realizaron potenciales evocados auditivos de tallo cerebral (BAEPs) respuestas auditivas de estado estable (ASSRs) y timpanometrías en 294 niños con BPI (586 oídos; dos tenían microatresia unilateral). Los BAEPs fueron anormales en 158 (27%) de los oídos, las ASSRs en 227 (39%) y hubieron anomalías timpanométricas en 131 (22%) oídos. Cuando se compararon los umbrales de ASSR con BAEPs, la evaluación condujo a 92% de sensibilidad y 68% de especificidad. Al comparar umbrales de ASSR con timpanometrías como un indicador de patología del oído medio, la evaluación dio 96% de sensibilidad y 77% de especificidad. Cuando los umbrales BAEP se compararon con timpanometrías, la sensibilidad fue del 35% y la especificidad del 95%. En conclusión, los BAEPs son una prueba útil para el tamiz auditivo neonatal porque identifican con mayor precisión las pérdidas auditivas sensorineurales. Las ASSR son más pertinentes para identificar pérdidas conductivas asociadas con patología del oído medio. La consistencia y precisión de estos resultados podrá ser considerada para estudios adicionales.

Neurobehavioral Effects in Relation to Endocrine Alterations Caused by Exposure to Brominated Flame Retardants in Rats—Comparison to Polychlorinated Biphenyls

ABSTRACT The widespread use of brominated flame retardants (BFRs) has led to increasing concentrations in environmental samples. Previous reports suggested endocrine activity of these compounds. Because thyroid hormones and sex steroids are known to regulate the development of the nervous system, we examined neurobehavioral and endocrine effects of gestational exposure to 2,2′4,4′,5-pentabrominated diphenyl ether (PBDE99) and lifetime exposure to tetrabromobisphenol A (TBBPA) or hexabromocyclododecane (HBCD) in rats. Treatment with PBDE99 (0, 1, or 10 mg/kg bw) reduced serum testosterone and estradiol in male offspring and affected sexual development in both sexes. Exposed males exhibited increased sweet preference, indicating feminization of this sexually dimorphic behavior. In TBBPA and HBCD experiments, a benchmark design was used with dose ranges of 0-3000 mg/kg bw/day and 0–100 mg/kg bw/day, respectively. Because thyroid hormones are critical for auditory development, brainstem auditory evoked potentials (BAEPs) were recorded in young adult offspring. TBBPA exposure elevated BAEP thresholds in females and prolonged latencies in both sexes. Benchmark doses were comparable for auditory effects and decreased plasma T4. HBCD increased BAEP thresholds and delayed BAEP waves only in males, but the relation to thyroid hormones remains to be determined. HBCD also reduced latencies in haloperidol-induced catalepsy, suggesting effects on the dopaminergic system.

Effects of the brominated flame retardant hexabromocyclododecane (HBCD) on dopamine-dependent behavior and brainstem auditory evoked potentials in a one-generation reproduction study in Wistar rats

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant which has been recently detected in many environmental matrices. Data from a subacute toxicity study indicated dose-related effects particularly on the pituitary thyroid-axis and retinoids in female rats. Brominated and chlorinated aromatic hydrocarbons are also reported to exert effects on the nervous system. Several investigations revealed a pronounced sensitivity of the dopaminergic system and auditory functions to polychlorinated biphenyls. Therefore, the present experiment should examine, whether or not HBCD affects these targets. Rats were exposed to 0, 0.1, 0.3, 1, 3, 10, 30 or 100 mg HBCD/kg body weight via the diet. Exposure started before mating and was continued during mating, gestation, lactation, and after weaning in offspring. Haloperidol-induced catalepsy and brainstem auditory evoked potentials (BAEPs) were used to assess dopamine-dependent behavior and hearing function in adult male and female offspring. On the catalepsy test, reduced latencies to movement onset were observed mainly in female offspring, indicating influences on dopamine-dependent behavior. The overall pattern of BAEP alterations, with increased thresholds and prolonged latencies of early waves, suggested a predominant cochlear effect. Effects were dose-dependent with lower bounds of benchmark doses (BMDL) between ≤1 and 10 mg/kg body weight for both catalepsy and BAEP thresholds. Tissue concentrations at the BMDL values obtained in this study were 3–4 orders of magnitude higher than current exposure levels in humans.

Functional changes on ascending auditory pathway in rats caused by germanium dioxide exposure: An electrophysiological study

The semiconductor element, germanium (Ge), is essential for the manufacture of modern integrated circuits. Because of its anti-tumor and immunomodulative effects, Ge-containing compounds are also used as health-promoting ingredients in food. However, some histological studies have shown the toxic effects of Ge-containing compounds on various organs, including the central nervous system. Even now, the effect of germanium on auditory system function is not completely clear. To clarify this question, brainstem auditory evoked potentials (BAEPs) were applied to examine the effect of germanium dioxide (GeO 2) on the ascending auditory pathway. Since the voltage-gated sodium channel is important to neuron activation and nerve conduction, the effect of GeO 2 on voltage-gated sodium channels was also examined. The result revealed GeO 2 elevated the BAEPs threshold dose-dependently. GeO 2 also prolonged latencies and interpeak latencies (IPLs) of BAEPs, but the amplitudes of suprathreshold intensities (90 dB) did not show any obvious change. In addition, the results of whole cell patch clamp studies indicated GeO 2 reduced inward sodium current. These results suggest the toxic effect of GeO 2 on the conduction of the auditory system, and that inhibitory effect of GeO 2 on the voltage-gated sodium channels might play a role in GeO 2-induced abnormal hearing loss.

Exposure to tetrabromobisphenol A (TBBPA) in Wistar rats: Neurobehavioral effects in offspring from a one-generation reproduction study

Within the framework of an EU project on risk assessment of brominated flame retardants, TBBPA was studied for neurobehavioral effects in rats. To permit benchmark dose analysis, eight dose levels were chosen ranging from 0 to 3000 mg/kg body weight. Exposure of parental rats started 10 and 2 weeks before mating in males and females, respectively, and was continued throughout mating, gestation and lactation. After weaning, exposure was continued in the offspring throughout life. Previous studies had indicated TBBPA-induced effects on thyroid hormones. Because of the known implication of thyroid hormones in neurodevelopment, the present experiments tested if TBBPA exposure affects thyroid-dependent neurobehavioral functions in offspring, such as auditory responses and conditioned fear. Sweet preference was included because of sex-specific effects in littermates. No statistically significant effects were found on context or cue conditioned fear or sweet preference. Auditory responses were examined with brainstem auditory evoked potentials (BAEPs) at approximately 50–110 days of age. BAEP thresholds and wave IV latency were increased in exposed female rats in the low frequency range. In male rats, thresholds were unaffected, but absolute latency of wave IV and interpeak latencies II–IV showed exposure-related increases at low frequencies. The outcome pattern suggests a predominant cochlear effect of TBBPA in females while in males neural effects are more apparent. According to benchmark analysis, the critical effect doses (CED) for prolongations of wave IV latency at 0.5 kHz were in the range of 35–70 mg/kg body weight with lower bounds (BMDL) of approximately 8 mg/kg in males and females. The BMDL values for elevation of hearing thresholds in females were in the range of 1–40 mg/kg body weight, depending on frequency. The benchmark doses for effects on the BAEP were similar to values for decreases in circulating thyroid hormones. The comparison of the exposure level at which the most sensitive effect was found with current human exposure levels yielded a margin of exposure of about 5, according to a recent risk assessment. Further investigations are needed to examine exposure pathways, fate in the body and effects of TBBPA.

Acute and chronic effects of carbamazepine, phenytoin, valproate and vinpocetine on BAEP parameters and threshold in the guinea pig

ObjectiveTo characterize the acute and chronic effects of the antiepileptic drugs (AEDs): carbamazepine (CBZ), phenytoin (PHT), valproic acid (VPA) and vinpocetine (VPC), at doses 20, 6, 30 and 2mg/kg, respectively, on the latencies and amplitudes of the waves of brainstem auditory evoked potentials (BAEPs) elicited by a supra-threshold stimulus alongside BAEP threshold. MethodsBAEPs elicited by a stimulus of high (100dB nHL) intensity and BAEP thresholds were obtained at 4 and 8kHz: before, after the start of treatment, and following 28 days of a daily injection of the AEDs. ResultsAfter the start of treatment BAEPs were unchanged. After the long term treatment, CBZ and PHT increased P3 and P4 wave peak latencies and reduced P4 amplitude. Chronic VPA did not modify BAEP waves, and chronic VPC reduced P3 and P4 latencies. P1 and P2 were unchanged. BAEP thresholds at 4 and 8kHz were increased by CBZ, PHT and VPA, and decreased by VPC. ConclusionsThe chronic administration of several AEDs modifies BAEP waves of retro-cochlear origin. SignificanceAlterations in the generators of the later waves of BAEPs underlie, in most cases, the changes in hearing sensitivity produced by the long term treatment with AEDs at therapeutic relevant doses.

Vinpocetine inhibits the epileptic cortical activity and auditory alterations induced by pentylenetetrazole in the guinea pig in vivo

Here we investigate the effect of the neuroprotective drug, vinpocetine on the epileptic cortical activity, on the alterations of the later waves of brainstem auditory evoked potentials (BAEPs) and on the hearing decline induced by the convulsing agent, pentylenetetrazole (PTZ). Vinpocetine at doses from 2 to 10 mg/kg inhibits the tonic–clonic convulsions induced by PTZ (100 mg/kg). Vinpocetine injected at a dose of 2 mg/kg 4 h before PTZ completely prevents the characteristic electroencephalogram (EEG) changes induced by PTZ for the ictal and post-ictal periods. Vinpocetine also abolished the PTZ-induced changes in the amplitude and latency of the later waves of the BAEPs in response to pure tone burst monoaural stimuli (frequency 8 or 4 kHz intensity 100 dB), and the PTZ-induced increase in the BAEP threshold. These results show the antiepileptic potential of vinpocetine and indicate the capability of vinpocetine to prevent the changes in the BAEP waves associated with the hearing loss observed during generalized epilepsy.

Specialization of the auditory processing in harbor porpoise, characterized by brain-stem potentials

Brain-stem auditory evoked potentials (BAEPs) were recorded from the head surface of the three awaked harbor porpoises (Phocoena phocoena). Silver disk placed on the skin surface above the vertex bone was used as an active electrode. The experiments were performed at the Karadag biological station (the Crimea peninsula). Clicks and tone bursts were used as stimuli. The temporal and frequency selectivity of the auditory system was estimated using the methods of simultaneous and forward masking. An evident minimum of the BAEPs thresholds was observed in the range of 125–135 kHz, where the main spectral component of species-specific echolocation signal is located. In this frequency range the tonal forward masking demonstrated a strong frequency selectivity. Off-response to such tone bursts was a typical observation. An evident BAEP could be recorded up to the frequencies 190–200 kHz, however, outside the acoustical fovea the frequency selectivity was rather poor. Temporal resolution was estimated by measuring BAER recovery functions for double clicks, double tone bursts, and double noise bursts. The half-time of BAERs recovery was in the range of 0.1–0.2 ms. The data indicate that the porpoise auditory system is strongly adapted to detect ultrasonic closely spaced sounds like species-specific locating signals and echoes.

Age-related changes in the brainstem auditory evoked potentials of the marmoset

Changes in brain-stem auditory evoked potentials (BAEPs) with age were recorded in common marmosets ( Callithrix jacchus) at the age of 1–2, 6–8 and 10–12 years. The auditory function was assessed by thresholds, latencies and amplitudes of BAEPs evoked by use of tone burst stimulations with audible frequencies ranging from 1 to 99 kHz. Prolongation of the latencies of later waves was observed in the animals at the age of 6–8 and 10–12 years at high frequencies, suggesting that aging in marmosets, as reported previously in humans and other animals, may cause earlier hearing loss at high frequency than at low frequency within the hearing range. At 10–12 years of age, the elevations of BAEP thresholds and the declines of BAEP amplitudes in older animals were also observed. As the differences in the parameters are small, it was suggested that only a moderate hearing loss occurred with onset late in life in common marmoset similar to that in CBA/Ca mice. Based on the results obtained in this study, BAEP latencies appear to be more sensitive indicators than BAEP thresholds and amplitudes for the early detection of hearing impairment.

Sensitivity and specificity of the neonatal brain-stem auditory evoked potential for hearing and language deficits in survivors of extracorporeal membrane oxygenation

Objective: We determined the sensitivity and specificity of neonatal brain-stem auditory evoked potentials (BAEP) as markers for subsequent hearing impairment and for developmental problems found later in infancy and childhood. Methods: BAEP studies were performed before discharge in infants treated with extracorporeal membrane oxygenation (ECMO), and two specific abnormalities were analyzed: elevated threshold and delayed central auditory conduction. Behavioral audiometry was repeated during periodic follow-up until reliable responses were obtained for all frequencies, and standardized developmental testing was also conducted. The sensitivity and specificity of an elevated threshold on the neonatal BAEP for detecting subsequent hearing loss, and the relationship of any neonatal BAEP abnormality to language or developmental disorders in infancy, were calculated. Results: Test results for 46 ECMO-treated infants (57.5%) were normal, and those for 34 infants (42.5%) were abnormal, with either elevated wave V threshold, prolonged wave I-V interval, or both on neonatal BAEP recordings. Most significantly, 7 (58%) of the 12 children with subsequent sensorineural hearing loss had left the hospital after showing normal results on threshold tests. There was no significant difference in the frequency of hearing loss between subjects with abnormal (5/21, or 24%) and those with normal BAEP thresholds (7/59, or 12%; Fisher Exact Test, p = 0.28). Therefore the sensitivity of neonatal BAEP testing for predicting subsequent hearing loss was only 42%. Neonatal BAEP specificity for excluding subsequent hearing loss was 76%. In contrast, on language development testing, 19 children demonstrated receptive language delay. Of these children, 12 (63%) had abnormal neonatal BAEP recordings and 7 (37%) had a normal BAEP threshold, normal central auditory conduction test results, or both ( p = 0.04). Conclusions: Neonatal BAEP threshold recordings were of limited value for predicting subsequent hearing loss common in ECMO-treated survivors. However, an abnormal neonatal BAEP significantly increased the probability of finding a receptive language delay during early childhood, even in those with subsequently normal audiometry findings. Because neonatal ECMO is associated with a high risk of hearing and receptive language disorders, parents should be counseled that audiologic and developmental follow-up evaluations in surviving children are essential regardless of the results of neonatal BAEP testing. (J Pediatr 1997;131:233-9)

Antagonistic effect of Poria Cocos on ototoxicity of kanamycin in guinea-pigs

In order to prevent ototoxicity of kanamycin (KM), the effects of Poria Cocos (PC) on the ototoxicity induced by KM in guinea-pigs was observed by giving the PC decoction to guinea-pigs with comparing the difference in the general intoxicating symptom, Prayer’s reflex (PR) threshold, brainstem auditory evoked potentials (BAEPs) and the absence rate of outer hair cells in the first turn of cochlea. The results suggested that the ototoxicity of KM was retarded by PC decoction. On the 7th day after KM was given, PR threshold of 4, 6, 8 kHz in the medicated group and control group were 4.7±1.5 dB, 5.7±2.4 dB, 2.7± 1.2 dB and 10.5 ± 3.2 dB, 12.1±3.7 dB, 8.5±2.7 dB respectively. BAEPs threshold on the 13th day after KM was given, raised 22.7 ± 9.7 dB in the PC group and 51.3 ± 14.4 dB in the control group. The absence rate of outer hair cells in the first turn of cochlea were 39.4% and 67.4% respectively. The results suggested that PC might be antagonistic to the ototoxicity of KM in guinea-pigs.

Influence of auditory experience on the development of brain stem auditory-evoked potentials in mallard duck embryos and hatchlings

The development of brain stem auditory-evoked potentials (BAEP) was studied in devocalized ducklings reared in auditory isolation and in vocal ducklings exposed to enhanced species-specific auditory stimulation with embryonic contact-contentment calls (CTs). Thresholds and latency of BAEP wave P1 in the mute ducklings indicated that even short-term auditory deprivation affected the development of auditory sensitivity, substantially reducing the rate of decline in BAEP thresholds and latencies of P1, especially in the low-frequency (500 and 750 Hz) and high-frequency (above 2.0 kHz) ranges. The ducklings exposed to enhanced stimulation, on the other hand, showed an accelerated decline in BAEP thresholds and latencies of P1 across all test frequencies, with the most marked influence on low (below 1.5 kHz) and high (above 2.5 kHz) frequencies. The influence of species-specific auditory experience had its most potent effect during the embryonic critical period for postnatal auditory perceptual (behavioral) development, at which time the embryo produces and hears a special low-frequency (1.5-2.5 kHz) version of its own contact-contentment vocalization.

The effect of sound level, temperature and dehydration on the brainstem auditory evoked potential in anuran amphibians

Brainstem auditory evoked potentials (BAEPs) were used to examine the effects of sound level, temperature, and dehydration on the auditory pathway of three species of anuran amphibians: Rana pipiens, Bufo americanus and B. terrestris. BAEP latency, amplitude and a measure of threshold were determined for all stimulus and test conditions. Threshold values obtained with this technique were similar to other neural measures of threshold in anurans, and were stable for repeated measures within 12 h and over three days. Transient changes in temperature caused non-linear changes in BAEP threshold and latency. Above 20°C small threshold shifts were elicited, while below 20°C we observed rapid deterioration of threshold. Animals acclimated to a cold temperature (14°C) were acoustically less sensitive than warm (21°C) animals, even when both groups were tested at colder temperatures. Because peripheral components of the BAEP were most affected by both transient and acclimation (longer term) cooling and warming, the sensory epithelium appears to be the most temperature-sensitive component of the auditory pathway. Dehydrated frogs showed no auditory dysfunction until a critical level of dehydration was reached. More dehydration-resistant species ( B. terrestris and B. americanus) were less susceptible to BAEP degradation near their critical dehydration level.

Are click-evoked BAEPs useful in case of neonate hyperbilirubinemia?

There is still controversy about the usefulness of click-evoked brainstem auditory evoked potentials (BAEPs) for the investigation of neonatal hyperbilirubinemia. The present work concerns the study of click-evoked BAEP responses in a population of 72 hyperbilirubinemic children (conceptional age between 33 and 42 weeks). Their bilirubinemia rates were between 219 and 600 μmol/l. The waves I, III and V were always present, and click BAEP thresholds were normal in all subjects. Latency anomalies were found only for 8 of the 72 subjects. The comparison of subjects having the higher (> 307 μmol/l) bilirubin levels with the group having the lower ones failed to show any significant differences for the I–III and I–V intervals. The influence of prematurity in BAEP alteration has not been demonstrated in this study. These data show, on the one hand, normal click-BAEP thresholds but, on the other hand, alterations of central conduction time in some hyperbilirubinemic newborns. It seems that other factors than hyperbilirubinemia might be operating.

The use of evoked potentials in the intensive care unit: [formula omitted] (Neurologische Klinik des Zentralkinikums, D-8900 Augsburg, F.R.G.)

The semiconductor element, germanium (Ge), is essential for the manufacture of modern integrated circuits. Because of its anti-tumor and immunomodulative effects, Ge-containing compounds are also used as health-promoting ingredients in food. However, some histological studies have shown the toxic effects of Ge-containing compounds on various organs, including the central nervous system. Even now, the effect of germanium on auditory system function is not completely clear. To clarify this question, brainstem auditory evoked potentials (BAEPs) were applied to examine the effect of germanium dioxide (GeO2) on the ascending auditory pathway. Since the voltage-gated sodium channel is important to neuron activation and nerve conduction, the effect of GeO2 on voltage-gated sodium channels was also examined. The result revealed GeO2 elevated the BAEPs threshold dose-dependently. GeO2 also prolonged latencies and interpeak latencies (IPLs) of BAEPs, but the amplitudes of suprathreshold intensities (90 dB) did not show any obvious change. In addition, the results of whole cell patch clamp studies indicated GeO2 reduced inward sodium current. These results suggest the toxic effect of GeO2 on the conduction of the auditory system, and that inhibitory effect of GeO2 on the voltage-gated sodium channels might play a role in GeO2-induced abnormal hearing loss.

Estimation of auditory threshold during sleep using brainstem auditory-evoked potentials.

The brainstem auditory-evoked potential (BAEP) is often employed to determine auditory threshold in subjects who are unable to complete traditional behavioural testing. These responses are usually recorded during natural or drug-induced sleep. The effects of sleep on the BAEP threshold have however not been determined. BAEPs were recorded in 8 young adults in wakefulness and during natural sleep. Click stimuli were presented through a hearing aid device at either 0, 5, 10, 20 or 30 dB above the behavioural threshold. The amplitude of wave V decreased and its latency increased with decreases in stimulus intensity. The BAEP waveform was invariant in sleep. The overall mean BAEP threshold was approximately 16 dB above that determined by behavioural methods. This did not significantly vary in the sleeping subject.

Age-related hearing loss in BDF1 mice as evidenced by the brainstem auditory evoked potential.

Age-related hearing loss was studied in unanesthetized female BDF1 mice using brainstem auditory evoked potential (BAEP) latency-intensity (L-I) profiles and BAEP thresholds. The mice were divided into 5 age-related groups: 3-4 months, 5.5-7 months, 9-10 months, 12 months and 18 months. Relative to the youngest group, BAEP threshold data indicated shifts in auditory sensitivity ranging from +6 dB for the 5.5- to 7-month-old group to +71 dB for the 18-month-old group. The BAEP L-I profiles of older mice were consistent with recruitment-type sensorineural (cochlear) hearing losses. No evidence of retrocochlear involvement was observed.

Brainstem auditory evoked responses to tone bursts in the echolocating bat,Rousettus

1. Brainstem auditory evoked potentials (BAEPs) from subcutaneous electrodes were obtained from the megachiropteran echolocating bat,Rousettus aegyptiacus. 2. BAEP amplitude was measured as a function of a stimulus frequency. The lowest thresholds (defined as a 1 μV averaged response) lay between 10 and 20 kHz, and responses could be obtained from 5 to 45 kHz in most individuals (Fig. 3). Threshold increased at a rate of 30 dB/octave below 10 kHz and 40 dB/octave above 17 kHz. 3. Electrode configuration affected some components of the BAEP waveform (Fig. 1), but not the frequency response of the BAEP (Fig. 3). Pentobarbital anesthesia raised BAEP thresholds at all frequencies tested (Fig. 4), when compared with the unanesthetized state. BAEP thresholds were not affected by changes in deep rectal temperature in the range of 29–30 °C (Fig. 4). 4. Comparison of the BAEP frequency response curve with the behavioral audiogram (Fig. 6) suggests that it is an accurate predictor of the region of greatest auditory sensitivity.