Click-evoked Auditory Brainstem Responses Research Articles

Using click-evoked auditory brainstem response thresholds in infants to estimate the corresponding pure-tone audiometry thresholds in children referred from UNHS

ObjectiveTo examine whether behavioral pure-tone audiometry (PTA) thresholds in children can be accurately estimated from the corresponding infants' click-evoked auditory brainstem response (ABR) thresholds through a retrospective review of data from a universal newborn hearing screening (UNHS) program in Taiwan. MethodAccording to medical records from Mackay Memorial Hospital, Taipei Hospital District, 45,450 newborns received hearing screening during January 1999–December 2011. Among these newborns, 104 (82, both ears; 22, one ear; total, 186 ears) received regular follow-up and were recruited as subjects. The relationship between infant click-evoked ABR thresholds and the corresponding child PTA thresholds was determined through Pearson correlation coefficient and linear regression analyses. ResultsThe correlation coefficient between click-evoked ABR thresholds and behavioral PTA thresholds at the average of frequencies of 1–4 and 2–4 kHz was 0.76 and 0.76, respectively. Linear regression analysis showed that behavioral audiometry thresholds at the average of frequencies of 1–4 and 2–4 kHz were accurately estimated from click-evoked ABR thresholds in 57% and 58% children, respectively. ConclusionClick-evoked ABR testing is a reliable tool to cautiously estimate behavioral PTA thresholds at the average of frequencies of 1–4 and 2–4 kHz. For accurately performing hearing aid fitting and auditory rehabilitation in congenitally deaf infants, a combination of frequency-specific tone-burst ABR and click-evoked ABR should be used.

Maturation of auditory brainstem responses in young children with congenital monaural atresia

ObjectiveTo date, the impact of conductive hearing loss on the auditory pathway at brainstem level has only been investigated in animal studies, which showed a species-specific delay of maturation. In this study, the functional maturation of auditory brainstem response (ABR) parameters in humans with unilateral atresia of the external auditory canal was investigated. Methods42 newborns and toddlers ranging in age from 13 days to 11 months were included. The click-evoked ABR interpeak latencies (IPL) of the atretic ears and the contralateral ears with normal hearing were evaluated. The children had no comorbidities and had never been fitted with any kind of hearing aid. The absolute latencies (AL) and IPL of a matched control group were compared to the contralateral normally hearing ears of the children with unilateral atresia. ResultsThe mean air-bone gap in the ears with atresia was 44 dB HL. Despite this partial acoustic deprivation, no significant difference between the IPLs of normal ears and ears with atresia could be detected. Both for AL and IPL, the differences between the normal ears and the control group were all within 1 standard deviation to the mean. ConclusionThe data showed that the monaural acoustic deprivation by a block of sound conduction does not produce any delay of functional maturation at brainstem level in this group of patients. With regard to the AL and IPL on brainstem level, no differences between the normal ears of children with unilateral atresia and children with bilateral normal hearing could be detected.

High-pass filtering obscures stimulus encoding characteristics of the auditory brainstem response: Evidence from click and tone stimuli

The auditory brainstem response (ABR) is an electrophysiological measure of early auditory processing. While previous work has examined ABRs to clicks, tones, speech, and music, it remains unclear how changes in acoustic properties (e.g., frequency) map onto specific changes in ABR components. This may be partly due to filtering during data processing. High-pass filtering can severely distort cortical and subcortical responses, potentially obfuscating how stimuli are encoded. To address this, we measured ABRs to a wide range of pure tones (250 to 8000 Hz) and examined how high-pass filtering affects tone- and click-evoked ABRs. In Experiment 1, various high-pass filter settings (0.1-300 Hz) were applied to click-evoked ABRs. In Experiment 2, ABRs to brief tones across a six-step frequency continuum were collected, and the same high-pass filter settings were applied. Results indicate that excessive high-pass filtering diminishes the amplitude of ABR components, consistent with previous findings. In addition, filtering can obscure true effects of stimulus frequency. With appropriate filters, we find that the amplitude of wave V tracks stimulus frequency log-linearly, demonstrating that tonotopic organization is preserved and easily detectable early in processing. Future ABR work should minimize the use of high-pass filters when studying the encoding of acoustic information.

Sub-clinical auditory neural deficits in patients with type 1 Diabetes Mellitus

Diabetes mellitus (DM) is associated with a variety of sensory complications. Very little attention has been given to auditory neuropathic complications in DM. The aim of this study was to determine whether type 1 DM affects neural coding of the rapid temporal fluctuations of sounds, and how any deficits may impact on real-world listening tasks. Participants were 30young normal-hearing type 1 DM patients, and 30 age-, sex-, and audiogram-matched healthy controls. Tests included non-invasive electrophysiological measures of auditory nerve and brainstem function using the click-evoked auditory brainstem response (ABR), and of brainstem neural temporal coding using the sustained frequency-following response (FFR), as well as behavioural tests of temporal coding (interaural phase difference, IPD, discrimination and the frequency difference limen, FDL) and tests of speech perception in noise. There were no significant differences between DM patients and controls in the ABR. However, the DM group showed significantly lower FFR responses, higher IPD and FDL thresholds, as well as worse speech-in-noise performance. The results suggest that type 1 DM is associated with degraded neural temporal coding in the brainstem in the absence of an elevation in audiometric threshold, and that this deficit may impact on real-world hearing ability.

Relating Click-Evoked Auditory Brainstem Response Waveforms to Hearing Loss in the Bottlenose Dolphin (Tursiops truncatus)

Hearing sensitivity in captive Atlantic bottlenose dolphins was assessed using a portable electrophysiologic data collection system, a transducer attached to the pan region of the mandible, and non-invasive recording electrodes. The auditory steady-state response (ASSR) was evoked using sinusoidal amplitude-modulated tones at half octave steps from 20–160 kHz and utilized to determine the upper frequency limit of hearing (i.e., the frequency at which threshold was ≤ 120 dB re 1 μPa). An auditory brainstem response (ABR) was then recorded to a moderate-amplitude click (peak-equivalent sound pressure level of 122 dB re 1 μPa) and examined to determine if relationships existed between the upper frequency limit of hearing and the waveform characteristics of the click-evoked ABR. The ASSR and click-evoked ABR were measured in 6 bottlenose dolphins with varying hearing sensitivity and frequency range of hearing. A significant relationship existed between click-evoked ABR wave amplitudes and the upper frequency limit of hearing. Test times for assessment using frequency-specific ASSR and click-evoked ABR were ∼45 minutes and 1 minute, respectively. With further definition of normative data, measurement of click-evoked ABRs could form the basis of an expedited electrophysiologic method for hearing screening in marine mammals.

The contribution of inferior colliculus activity to the auditory brainstem response (ABR) in mice

In mice, the auditory brainstem response (ABR) is frequently used to assess hearing status in transgenic hearing models. The diagnostic value of the ABR depends on knowledge about the anatomical sources of its characteristic waves. Here, we studied the contribution of the inferior colliculus (IC) to the click-evoked scalp ABR in mice. We demonstrate a non-invasive correlate of the IC response that can be measured in the scalp ABR as a slow positive wave P0 with peak latency 7–8 ms when recorded with adequate band-pass filtering. Wave P0 showed close correspondence in latency, magnitude and shape with the sustained part of evoked spiking activity and local field potentials (LFP) in the central nucleus of the IC. In addition, the onset peaks of the IC response were related temporally to ABR wave V and to some extent to wave IV. This relation was further supported by depth-dependent modulation of the shape of ABR wave IV and V within the IC suggesting generation within or in close vicinity to the IC. In conclusion, the slow ABR wave P0 in the scalp ABR may represent a complementary non-invasive marker for IC activity in the mouse. Further, the latency of synchronized click-evoked activity in the IC supports the view that IC contributes to ABR wave V, and possibly also to ABR wave IV.

Click-Evoked Auditory Brainstem Responses in an Australian Sea Lion (Neophoca cinerea)

Click-Evoked Auditory Brainstem Responses in an Australian Sea Lion (Neophoca cinerea)

The Role of Age-Related Declines in Subcortical Auditory Processing in Speech Perception in Noise.

Older adults, even those without hearing impairment, often experience increased difficulties understanding speech in the presence of background noise. This study examined the role of age-related declines in subcortical auditory processing in the perception of speech in different types of background noise. Participants included normal-hearing young (19 – 29 years) and older (60 – 72 years) adults. Normal hearing was defined as pure-tone thresholds of 25 dB HL or better at octave frequencies from 0.25 to 4 kHz in both ears and at 6 kHz in at least one ear. Speech reception thresholds (SRTs) to sentences were measured in steady-state (SS) and 10-Hz amplitude-modulated (AM) speech-shaped noise, as well as two-talker babble. In addition, click-evoked auditory brainstem responses (ABRs) and envelope following responses (EFRs) in response to the vowel /ɑ/ in quiet, SS, and AM noise were measured. Of primary interest was the relationship between the SRTs and EFRs. SRTs were significantly higher (i.e., worse) by about 1.5 dB for older adults in two-talker babble but not in AM and SS noise. In addition, the EFRs of the older adults were less robust compared to the younger participants in quiet, AM, and SS noise. Both young and older adults showed a “neural masking release,” indicated by a more robust EFR at the trough compared to the peak of the AM masker. The amount of neural masking release did not differ between the two age groups. Variability in SRTs was best accounted for by audiometric thresholds (pure-tone average across 0.5–4 kHz) and not by the EFR in quiet or noise. Aging is thus associated with a degradation of the EFR, both in quiet and noise. However, these declines in subcortical neural speech encoding are not necessarily associated with impaired perception of speech in noise, as measured by the SRT, in normal-hearing older adults.

Loss of glycine receptors containing the α3 subunit compromises auditory nerve activity, but not outer hair cell function

Inhibitory glycine receptors containing the α3 subunit (GlyRα3) regulate sensory information processing in the CNS and retina. In previous work, we demonstrated the presence of postsynaptic GlyRα3 immunoreactivity at efferent synapses of the medial and lateral olivocochlear bundle in the organ of Corti; however, the role of these α3-GlyRs in auditory signalling has remained elusive. The present study analyzes distortion-product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs) of knockout mice with a targeted inactivation of the Glra3 gene (Glra3−/−) and their wildtype littermates (Glra3+/+) before and seven days after acoustic trauma (AT; 4–16 kHz, 120 dB SPL, 1 h).Before AT, DPOAE thresholds were slightly, but significantly lower, and DPOAE amplitudes were slightly larger in Glra3−/− as compared to Glra3+/+ mice. While click- and f-ABR thresholds were similar in both genotypes before AT, threshold-normalized click-ABR wave I amplitudes were smaller in Glra3−/− mice as compared to their wildtype littermates. Following AT, both the decrement of ABR wave I amplitudes and the delay of wave I latencies were more pronounced in Glra3−/− than Glra3+/+ mice. Accordingly, correlation between early click-evoked ABR signals (0–2.5 ms from stimulus onset) before and after AT was significantly reduced for Glra3−/− as compared to Glra3+/+ mice. In summary, these results show that loss of α3-GlyRs compromises suprathreshold auditory nerve activity, but not outer hair cell function.

Study in air-conducted and bone-conducted auditory brainstem responses in children with congenital external auditory canal atresia

Objective To study the clinical value of air- and bone-conduction auditory brainstem responses(ABRs) in children with congenital aural atresia. Methods Air- and bone-conduction click-evoked ABRs in 38 children with congenital external auditory canal atresia were compared to those in 34 normal-hearing children. Results ABR threshold were (65.0±8.7) dBnHL for air conduction and (10.6±7.0) dBnHL for bone conduction in children with congenital external auditory canal atresia; and (25.6±1.7) dBnHL and (9.7±6.7) dBnHL respectively in normal hearing children.There was statistically difference between the two groups in air-conduction ABR threshold(t'=21.59, P 0.05). While the air-bone ABR threshold gap was greater in children with external auditory canal atresia than in normal hearing children(t'=13.78, P 0.05). Conclusion Bone conduction ABR is valuable in assessing function of cochlea, auditory nerve and brainstem in individuals with congenital external auditory canal atresia.It has important clinical value in objective differential diagnosis of conductive deafness with combined application of air- and bone-conduction ABRs. Key words: Ear, external; Congenital abnormalities; Auditory brainstem response

Slc26a4 expression prevents fluctuation of hearing in a mouse model of large vestibular aqueduct syndrome

SLC26A4 mutations cause fluctuating and progressive hearing loss associated with enlargement of the vestibular aqueduct (EVA). SLC26A4 encodes a transmembrane anion exchanger called pendrin expressed in nonsensory epithelial cells of the lateral wall of cochlea, vestibular organs and endolymphatic sac. We previously described a transgenic mouse model of EVA with doxycycline (dox)-inducible expression of Slc26a4 in which administration of dox from conception to embryonic day 17.5 (DE17.5) resulted in hearing fluctuation between 1 and 3months of age. In the present study, we hypothesized that Slc26a4 is required to stabilize hearing in DE17.5 ears between 1 and 3months of age. We tested our hypothesis by evaluating the effect of postnatal re-induction of Slc26a4 expression on hearing. Readministration of dox to DE17.5 mice at postnatal day 6 (P6), but not at 1month of age, resulted in reduced click-evoked auditory brainstem response (ABR) thresholds, less fluctuation of hearing and a higher surface density of pendrin expression in spindle-shaped cells of the stria vascularis. Pendrin expression in spindle-shaped cells was inversely correlated with ABR thresholds. These findings suggest that stabilization of hearing by readministration of dox at P6 is mediated by pendrin expression in spindle-shaped cells. We conclude that early re-induction of Slc26a4 expression can prevent fluctuation of hearing in our Slc26a4-insufficient mouse model. Restoration of SLC26A4 expression and function could reduce or prevent fluctuation of hearing in EVA patients.

Efficacy of the cat deafening method: Co-administration of ethacrynic acid and kanamycin

Objective: This study was designed to determine if hearing status monitoring during intravenous infusion of EA reduces individual variability and to evaluate the correlation between EA dose and Bwt.Materials and methods: Twenty-five cats with the mean age of 24 ± 3.7 weeks (range = 20.6–28.3) and a mean weight of 3.21 ± 0.84 kg (range = 1.9–5.1) were administered a subcutaneous injection of KM (300 mg/kg) followed by an intravenous infusion of EA (1 mg/min). Click-evoked auditory brainstem responses (ABRs) were recorded to monitor hearing during the infusion. When ABR thresholds exceeded a 90 dB sound pressure level, the infusion of EA was terminated. Histopathology forapex, middle, and base sections of the cochlea were examined after 6 months.Results: The dose of EA was optimized for deafening through simultaneous ABR measurements. Bwt was positively correlated with EA dose (mg) (p < 0.001, R2 = 0.548), which was different from a study previously reported. Cochlear histopathology assessments revealed an absence of organ of Corti in the majority of cochleae.Conclusion: Co-administration of kanamycin (KM) and ethacrynic acid (EA) was an easy and effective method for deafening procedures in adult animals. Body weight (Bwt) was positively correlated with EA dose (mg) and an optimal EA dose can be calculated.

Speech auditory brainstem response audiometry in children with specific language impairment

Objective: Children with specific language impairment (SLI) exhibit significantly delayed language development in the absence of any other abnormality. The aim of this study was to evaluate speech-evoked auditory brainstem responses (c-ABRs) in normal children and those with SLI assuming timing differences between these two populations.Study design: Forty children aged 3–7 years with bilateral normal peripheral hearing, normal developmental milestones and IQ were divided into two groups: a control group (20 children with normal language development) and a study group (20 children with SLI). The study used full history, otological examination, pure tone audiometry, speech audiometry and immittance measures. Click-evoked auditory brainstem response (ABR) was recorded first followed by recording of speech-evoked ABR (c-ABR) using CV speech syllable /da/.Results: There were significantly delayed latencies and reduced amplitudes of waves A, C, D, E, F and O components of c-ABR in the study group compared with the controls.Conclusion: Children with specific language impairment had abnormal encoding for speech.

Cisplatin‐Induced Ototoxicity and the Effects of Intratympanic Diltiazem in a Mouse Model

To evaluate whether the calcium-channel blocker diltiazem has protective effects against cisplatin-induced ototoxicity in a mouse model. Original basic science in vivo investigation. Academic setting: Otolaryngology-Head and Neck Surgery laboratory at University of Connecticut Health Center. Thirty-nine female CBA/J mice. Pure tone- or click-evoked auditory brainstem responses (ABRs) were recorded in CBA/J mice to determine auditory thresholds. All mice had baseline ABRs recorded. They were then given a single cisplatin bolus (14 mg/kg), followed by 5 consecutive days of intratympanic diltiazem or saline control. Follow-up thresholds were recorded on days 7, 14, and 21 postcisplatin. Tone-evoked ABRs evaluated the otoprotective effect of 2-mg/kg diltiazem in 9 mice, and dose effect was examined in response to click-evoked ABR with 2- or 4-mg/kg diltiazem in 2 groups of 15 mice. Saline-treated ears had significantly elevated tone-evoked auditory thresholds when compared with diltiazem-treated ears (P = .038) on day 7 postcisplatin only. Click-evoked ABR thresholds were significantly elevated in saline-treated ears versus diltiazem-treated ears for the 2-mg/kg group (P = .001) and 4-mg/kg group (P = .011) on days 7, 14, and 21 postcisplatin. Intratympanic diltiazem has significant protective effects against cisplatin ototoxicity at 2 and 4 mg/kg. This is the first in vivo study to demonstrate that diltiazem offers a potentially novel therapy for cisplatin-induced ototoxicity.

Relating click-evoked auditory brainstem response waveforms to hearing loss in the bottlenose dolphin (Tursiops truncatus)

Hearing sensitivity in captive Atlantic bottlenose dolphins was assessed using a portable electrophysiologic data collection system, a transducer attached to the pan region of the mandible, and non-invasive recording electrodes. The auditory steady-state response (ASSR) was evoked using sinusoidal amplitude-modulated tones at half octave steps from 20–160 kHz and utilized to determine the upper frequency limit of hearing (i.e., the frequency at which threshold was ≤ 120 dB re 1 μPa). An auditory brainstem response (ABR) was then recorded to a moderate-amplitude click (peak-equivalent sound pressure level of 122 dB re 1 μPa) and examined to determine if relationships existed between the upper frequency limit of hearing and the waveform characteristics of the click-evoked ABR. The ASSR and click-evoked ABR were measured in 6 bottlenose dolphins with varying hearing sensitivity and frequency range of hearing. A significant relationship existed between click-evoked ABR wave amplitudes and the upper frequency limit of hearing. Test times for assessment using frequency-specific ASSR and click-evoked ABR were ∼45 minutes and 1 minute, respectively. With further definition of normative data, measurement of click-evoked ABRs could form the basis of an expedited electrophysiologic method for hearing screening in marine mammals.

Neuronal erythropoietin overexpression protects mice against age-related hearing loss (presbycusis)

So far, typical causes of presbycusis such as degeneration of hair cells and/or primary auditory (spiral ganglion) neurons cannot be treated. Because erythropoietin's (Epo) neuroprotective potential has been shown previously, we determined hearing thresholds of juvenile and aged mice overexpressing Epo in neuronal tissues. Behavioral audiometry revealed in contrast to 5 months of age, that 11-month-old Epo-transgenic mice had up to 35 dB lower hearing thresholds between 1.4 and 32 kHz, and at the highest frequencies (50–80 kHz), thresholds could be obtained in aged Epo-transgenic only but not anymore in old C57BL6 control mice. Click-evoked auditory brainstem response showed similar results. Numbers of spiral ganglion neurons in aged C57BL6 but not Epo-transgenic mice were dramatically reduced mainly in the basal turn, the location of high frequencies. In addition, there was a tendency to better preservation of inner and outer hair cells in Epo-transgenic mice. Hence, Epo's known neuroprotective action effectively suppresses the loss of spiral ganglion cells and probably also hair cells and, thus, development of presbycusis in mice.

Rapid Increase in Neural Conduction Time in the Adult Human Auditory Brainstem Following Sudden Unilateral Deafness.

Individuals with sudden unilateral deafness offer a unique opportunity to study plasticity of the binaural auditory system in adult humans. Stimulation of the intact ear results in increased activity in the auditory cortex. However, there are no reports of changes at sub-cortical levels in humans. Therefore, the aim of the present study was to investigate changes in sub-cortical activity immediately before and after the onset of surgically induced unilateral deafness in adult humans. Click-evoked auditory brainstem responses (ABRs) to stimulation of the healthy ear were recorded from ten adults during the course of translabyrinthine surgery for the removal of a unilateral acoustic neuroma. This surgical technique always results in abrupt deafferentation of the affected ear. The results revealed a rapid (within minutes) reduction in latency of wave V (mean pre = 6.55ms; mean post = 6.15ms; p < 0.001). A latency reduction was also observed for wave III (mean pre = 4.40ms; mean post = 4.13ms; p < 0.001). These reductions in response latency are consistent with functional changes including disinhibition or/and more rapid intra-cellular signalling affecting binaurally sensitive neurons in the central auditory system. The results are highly relevant for improved understanding of putative physiological mechanisms underlying perceptual disorders such as tinnitus and hyperacusis.

Zucker diabetic fatty rats, a model for type 2 diabetes, develop an inner ear dysfunction that can be attenuated by losartan treatment.

Hearing loss secondary to diabetes remains under debate. In our study, we used Zucker Diabetic Fatty (ZDF) rats as an animal model of type 2 diabetes to investigate whether (1) hearing ability impairment and structural alterations of the inner ear occur in diabetes and (2) an angiotensin II receptor blocker (losartan) can protect rats from diabetic damage. Homozygous mutants were treated with a placebo or losartan and heterozygous animals served as non-diabetic controls. All animals underwent immunohistochemical and electronmicroscopical analysis. Functional testing of hearing ability was performed by click-evoked auditory brainstem responses. The present study showed significant sensorineural hearing impairment in placebo-treated diabetic rats (hearing threshold, 45.0 ± 2.1dB SPL) compared to both non-diabetic controls (34.7 ± 4dB SPL) and losartan-treated diabetic rats (36.1 ± 7.4dB SPL). Concurrently, the functional decline in the placebo-treated rats was associated with significant morphological abnormalities, particularly in the intermediate cells of the stria vascularis and with strial dysfunction. These degenerative changes were indicated by the down-regulation of several pumps, ionic and cellular channels, which are involved in the cycling of K(+) and the maintenance of the endocochlear potential essential for the hearing process. Thus, the inner ear can be regarded as a target organ during hyperglycemic disorders and a metabolically induced "diabetic otopathy" may be added to angiopathy, nephropathy and neuropathy as a specific complication of diabetes mellitus. Blockade of the angiotensin II receptor can prevent this "diabetic otopathy" despite hyperglycemic serum levels.

Auditory Processing of Speech and Non-Speech Stimuli in Children who Stutter: Electrophysiological Evidences

Objectives: Current scientific evidence supports the hypothesis that people who stutter have anomalous connections in auditory regions of the left hemisphere. Thus, it is reasonable to suppose that abnormal results in auditory evoked potentials may be related to this type of disorder. In the present study, Auditory Brainstem Responses (ABR) using stimuli of different complexities were recorded in order to investigate possible neural synchrony deficits in children who stutter (CWS). Methods: Ten CWS aged between seven and 11 years and their non-stuttering peers (CWNS) underwent electrophysiological (speech- and click-evoked ABR) assessment. Results: CWS showed greater variability in latency values, as well as a statistical trend towards significance regarding differences between right and left ears for the interpeak I-III in the click-evoked ABR. In the speech-evoked ABR, the latency values of wave C and the amplitude of VA complex were significantly higher in CWS. Conclusions: The results suggest that CWS present differences in neural processes related to the processing of acoustic information, when compared to typically developing children, especially when more complex stimuli, such as speech, are considered.

Continued maturation of the click-evoked auditory brainstem response in preschoolers.

Click-evoked auditory brainstem responses (ABRs) are a valuable tool for probing auditory system function and development. Although it has long been thought that the human auditory brainstem is fully mature by age 2 yr, recent evidence indicates a prolonged developmental trajectory. The purpose of this study was to determine the time course of ABR maturation in a preschool population and fill a gap in the knowledge of development. Using a cross-sectional design, we investigated the effect of age on absolute latencies, interwave latencies, and amplitudes (waves I, III, V) of the click-evoked ABR. A total of 71 preschoolers (ages 3.12-4.99 yr) participated in the study. All had normal peripheral auditory function and IQ. ABRs to a rarefaction click stimulus presented at 31/sec and 80 dB SPL (73 dB nHL) were recorded monaurally using clinically-standard recording and filtering procedures while the participant sat watching a movie. Absolute latencies, interwave latencies, and amplitudes were then correlated to age. Developmental changes were restricted to absolute latencies. Wave V latency decreased significantly with age, whereas wave I and III latencies remained stable, even in this restricted age range. The ABR does not remain static after age 2 yr, as seen by a systematic decrease in wave V latency between ages 3 and 5 yr. This finding suggests that the human brainstem has a continued developmental time course during the preschool years. Latency changes in the age 3-5 yr range should be considered when using ABRs as a metric of hearing health.