Perinatal maturation of the auditory brain stem response: changes in path length and conduction velocity

Newborn Auditory Brainstem Responses in Children with Developmental Disabilities

We integrated data from a newborn hearing screening database and a preschool disability database to examine the relationship between newborn click evoked auditory brainstem responses (ABRs) and developmental disabilities. This sample included children with developmental delay (n = 2992), speech impairment (SI, n = 905), language impairment (n = 566), autism spectrum disorder (ASD, n = 370), and comparison children (n = 128,181). We compared the phase of the ABR waveform, a measure of sound processing latency, across groups. Children with SI and children with ASD had greater newborn ABR phase values than both the comparison group and the developmental delay group. Newborns later diagnosed with SI or ASD have slower neurological responses to auditory stimuli, suggesting sensory differences at birth.

Electrically Evoked Auditory Brainstem Responses in Children Fitted with Hearing Aids Prior to Cochlear Implantation

This study investigates the effect of hearing aid use on the peripheral auditory pathways in children with sensorineural hearing loss prior to cochlear implantation, as revealed by the electrically evoked auditory brainstem response (EABR). Forty children with hearing aids were recruited. Half of them had normal inner ear structures and the other half had inner ear malformations (IEMs). The EABR was evoked by electrically stimulating the round window niche (RWN) and round window membrane (RWM) during the cochlear implantation operation. The onset age of hearing aid use was significantly correlated with the peak latencies, but not amplitudes, of the wave III (eIII) and wave V (eV). Higher EABR thresholds were found for RWN stimulation than for RWM stimulation and in the children with IEMs than in those without IEMs. Our study provides neurophysiological evidence that earlier use of hearing aids may ameliorate physiological functions of the peripheral auditory pathway in children with and without IEMs. The EABR evoked by the electrical stimulation at RWM is more sensitive compared with that at RWN for evaluating functions of the auditory conduction pathway.

Delayed Auditory Brainstem Responses (ABR) in children after sight-recovery

Studies in non-human animal models have revealed that in early development, the onset of visual input gates the critical period closure of some auditory functions. The study of rare individuals whose sight was restored after a period of congenital blindness offers the rare opportunity to assess whether early visual input is a prerequisite for the full development of auditory functions in humans as well. Here, we investigated whether a few months of delayed visual onset would affect the development of Auditory Brainstem Responses (ABRs). ABRs are widely used in the clinical practice to assess both functionality and development of the subcortical auditory pathway and, provide reliable data at the individual level. We collected Auditory Brainstem Responses from two case studies, young children (both having less than 5 years of age) who experienced a transient visual deprivation since birth due to congenital bilateral dense cataracts (BC), and who acquired sight at about two months of age. As controls, we tested 41 children (sighted controls, SC) with typical development, as well as two children who were treated (at about two months of age) for congenital monocular cataracts (MC). The SC group data served to predict, at the individual level, wave latencies of each BC and MC participant. Statistics were performed both at the single subject as well as at the group levels on latencies of main ABR waves (I, III, V and SN10). Results revealed delayed response latencies for both BC children compared with the SC group starting from the wave III. Conversely, no difference emerged between MC children and the SC group. These findings suggest that in case the onset of patterned visual input is delayed, the functional development of the subcortical auditory pathway lags behind typical developmental trajectories. Ultimately results are in favor of the presence of a crossmodal sensitive period in the human subcortical auditory system.

Prenatal Exposure to Tobacco and Alcohol Alters Development of the Neonatal Auditory System

Prenatal exposures to alcohol (PAE) and tobacco (PTE) are known to produce adverse neonatal and childhood outcomes including damage to the developing auditory system. Knowledge of the timing, extent, and combinations of these exposures on effects on the developing system is limited. As part of the physiological measurements from the Safe Passage Study, Auditory Brainstem Responses (ABRs) and Transient Otoacoustic Emissions (TEOAEs) were acquired on infants at birth and one-month of age. Research sites were in South Africa and the Northern Plains of the U.S. Prenatal information on alcohol and tobacco exposure was gathered prospectively on mother/infant dyads. Cluster analysis was used to characterize three levels of PAE and three levels of PTE. Repeated-measures ANOVAs were conducted for newborn and one-month-old infants for ABR peak latencies and amplitudes and TEOAE levels and signal-to-noise ratios. Analyses controlled for hours of life at test, gestational age at birth, sex, site, and other exposure. Significant main effects of PTE included reduced newborn ABR latencies from both ears. PTE also resulted in a significant reduction of ABR peak amplitudes elicited in infants at 1-month of age. PAE led to a reduction of TEOAE amplitude for 1-month-old infants but only in the left ear. Results indicate that PAE and PTE lead to early disruption of peripheral, brainstem, and cortical development and neuronal pathways of the auditory system, including the olivocochlear pathway.

Continued development of auditory ability in autism spectrum disorder children: A clinical study on click-evoked auditory brainstem response

OBJECTIVES

The study aimed to analyze the developmental mode of auditory at the level of brainstem in preschool autistic children using click-evoked auditory brainstem response (click-ABR).

METHODS

Twenty children with autism spectrum disorder (ASD) and 20 age matched typical development children (TD) were recruited. The detail data recorded from click-ABR were collected at two time periods (T1 and T2).

RESULTS

There was no significant change in TD group at two time periods. In ASD group, wave V latency was significantly shortened at T2 compared to that recorded at T1. The interpeak latency of I-V was short at T2 versus at T1 in the autistic children. Compared to the TD group, ASD was associated with longer latencies for waves V and longer interpeak latencies of I-III, I-V at T1. In addition, ASD group also indicated longer latencies of wave III and wave V, longer interpeak latencies of I-III and I-V at T2 compared to the TD group.

CONCLUSIONS

ASD group had immature and dysfunction developmental mode in auditory stimuli perception at the level of brainstem. The performance of auditory ability in children with ASD improved gradually with ages. However, there are still differences compared with TD children.

Review article: Structural brain alterations in prelingually deaf

Functional studies show that our brain has a remarkable ability to reorganize itself in the absence of one or more sensory modalities. In this review, we gathered all the available articles investigating structural alterations in congenitally deaf subjects. Some concentrated only on specific regions of interest (e.g., auditory areas), while others examined the whole brain. The majority of structural alterations were observed in the auditory white matter and were more pronounced in the right hemisphere. A decreased white matter volume or fractional anisotropy in the auditory areas were the most common findings in congenitally deaf subjects. Only a few studies observed alterations in the auditory grey matter. Preservation of the grey matter might be due to the cross-modal plasticity as well as due to the lack of sensitivity of methods used for microstructural alterations of grey matter. Structural alterations were also observed in the frontal, visual, and other cerebral regions as well as in the cerebellum. The observed structural brain alterations in the deaf can probably be attributed mainly to the cross-modal plasticity in the absence of sound input and use of sign instead of spoken language.

Auditory brainstem response

The auditory brainstem response (ABR), consisting of five to six vertex-positive peaks with separation of about 0.8ms, is very sensitive to factors that affect conduction velocity and hence ABR wave latencies in the brainstem auditory pathways. In addition, disorders causing dissynchronization of neural activity result in an amplitude decrease or disappearance of ABR peaks. The opposite effects occur in the maturation process, which takes about 2 years postterm; here conduction velocity increases quickly to its adult value, but synaptic delays being sensitive to synchronous release of transmitter substance take considerably longer. In neurological disorders, those that cause dissynchrony, such as auditory neuropathy and vestibular schwannoma, Gaucher disease, and Krabbe disease, the (longer latency) ABR peaks are reduced or absent. Effects on neural conduction, resulting in increased ABR interwave latencies, are found in vestibular schwannomas, Bell's palsy, Duane retraction syndrome, Marcus Gunn ptosis, and various encephalomyopathies. These measures allow an assessment of the parts of the brainstem that are involved.

Auditory maturation and psychological risk in the first year of life

PURPOSE

To assess the potential association between psychological risk and limited auditory pathway maturation.

METHODS

In this longitudinal cohort study, 54 infants (31 non-risk and 23 at-risk) were assessed from age 1 to 12 months. All had normal hearing and underwent assessment of auditory maturation through cortical auditory evoked potentials testing. Psychological risk was assessed with the Child Development Risk Indicators (CDRIs) and PREAUT signs. A variety of statistical methods were used for analysis of results.

RESULTS

Analysis of P1 and N1 latencies showed that responses were similar in the both groups. Statistically significant differences between-groups were observed only for the variables N1 latency and amplitude at 1 month. Significant maturation occurred in both groups (p<0.05). There was moderate correlation between P1 latency and Phase II CDRIs, which demonstrates that children with longer latencies at age 12 months were more likely to exhibit absence of these indicators in Phase II and, therefore, were at greater psychological risk. The Phase II CDRIs also correlated moderately with P1 and N1 latencies at 6 months and N1 latencies at 1 month; again, children with longer latency were at increased risk.

CONCLUSION

Less auditory pathway maturation correlated with presence of psychological risk. Problems in the mother-infant relationship during the first 6 months of life are detrimental not only to cognitive development, but also to hearing. A fragile relationship may reflect decreased auditory and linguistic stimulation.

Initial Results of a Safety and Feasibility Study of Auditory Brainstem Implantation in Congenitally Deaf Children

OBJECTIVE

To determine the safety and feasibility of the auditory brainstem implant (ABI) in congenitally deaf children with cochlear aplasia and/or cochlear nerve deficiency.

STUDY DESIGN

Phase I feasibility clinical trial of surgery in 10 children, ages 2 to 5 years, over a 3-year period.

SETTING

Tertiary children's hospital and university-based pediatric speech/language/hearing center.

INTERVENTION(S)

ABI implantation and postsurgical programming.

MAIN OUTCOME MEASURE(S)

The primary outcome measure is the number and type of adverse events during ABI surgery and postsurgical follow-up, including behavioral mapping of the device. The secondary outcome measure is access to and early integration of sound.

RESULTS

To date, nine children are enrolled. Five children have successfully undergone ABI surgery and postoperative behavioral programming. Three children were screen failures, and one child is currently undergoing candidacy evaluation. Expected adverse events have been documented in three of the five children who received the ABI. One child experienced a cerebral spinal fluid leak, which resolved with lumbar drainage. One child demonstrated vestibular side effects during device programming, which resolved by deactivating one electrode. One child experienced postoperative vomiting resulting in an abdominal radiograph. Four children have completed their 1-year follow-up and have speech detection thresholds of 30 to 35 dB HL. Scores on the IT-MAIS/MAIS range from 8 to 31 (out of a total of 40), and the children are demonstrating some ability to discriminate between closed-sets words that differ by number of syllables (pattern perception).

CONCLUSION

ABI surgery and device activation seem to be safe and feasible in this preliminary cohort.

Fetal Development: Voice Processing in Normotensive and Hypertensive Pregnancies

Recent observation of maternal voice recognition provides evidence of rudimentary memory and learning in healthy term fetuses. However, such higher order auditory processing has not been examined in the presence of maternal hypertension, which is associated with reduced and/or impaired uteroplacental blood flow. In this study, voice processing was examined in 40 fetuses (gestational ages of 33 to 41 weeks) of hypertensive and normotensive women. Fetuses received 2 min of no sound, 2 min of a tape-recorded story read by their mothers or by a female stranger, and 2 min of no sound while fetal heart rate was recorded. Results demonstrated that fetuses in the normotensive group had heart rate accelerations during the playing of their mother's voice, whereas the response occurred in the hypertensive group following maternal voice offset. Across all fetuses, a greater fetal heart rate change was observed when the amniotic fluid index was above compared to below the median (i.e., 150 mm), indicating that amniotic fluid volume may be an independent moderator of fetal auditory sensitivity. It was concluded that differential fetal responding to the mother's voice in pregnancies complicated by maternal hypertension may reflect functional elevation of sensorineural threshold or a delay in auditory system maturation, signifying functional differences during fetal life or subtle differences in the development of the central nervous system.

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

BACKGROUND

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.

PURPOSE

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.

RESEARCH DESIGN

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.

STUDY SAMPLE

A total of 71 preschoolers (ages 3.12-4.99 yr) participated in the study. All had normal peripheral auditory function and IQ.

DATA COLLECTION AND ANALYSIS

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.

RESULTS

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.

CONCLUSIONS

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.

Development of subcortical speech representation in human infants

Previous studies have evaluated representation of the fundamental frequency (F0) in the frequency following response (FFR) of infants, but the development of other aspects of the FFR, such as timing and harmonics, has not yet been examined. Here, FFRs were recorded to a speech syllable in 28 infants, ages three to ten months. The F0 amplitude of the response was variable among individuals but was strongly represented in some infants as young as three months of age. The harmonics, however, showed a systematic increase in amplitude with age. In the time domain, onset, offset, and inter-peak latencies decreased with age. These results are consistent with neurophysiological studies indicating that (1) phase locking to lower frequency sounds emerges earlier in life than phase locking to higher frequency sounds and (2) myelination continues to increase in the first year of life. Early representation of low frequencies may reflect greater exposure to low frequency stimulation in utero. The improvement in temporal precision likely parallels an increase in the efficiency of neural transmission accompanied by exposure to speech during the first year of life.

Assessment of functional development of the otolithic system in growing children: a review

OBJECTIVES

Although the caloric test, rotational test, and posturography have been used to investigate balance function conventionally, and they are older than tests of otolithic organs, yet it seems that most clinicians are less familiar with the development of otolithic (saccular and utricular) function in children. This study reviewed the electrophysiological testing used to assess the functional development of the otolithic system in growing children.

METHODS

Based on the literature, studies of cervical vestibular-evoked myogenic potential (cVEMP) and ocular VEMP (oVEMP) tests in children ranging from newborns, small children to adolescents were reviewed. Papers concerning foam posturography in children were also included.

RESULTS

The cVEMPs can be elicited in newborns at day 5, whereas the oVEMPs are absent in neonatal period. When children grow to 2 years old, the oVEMPs can be induced with eyes closed condition, while the oVEMPs with eyes up condition can be elicited in children aged >3 years old, with the characteristic parameters similar to adult levels. In contrast with cVEMPs, it is until the neck length >15.3cm (aldolesence), one need not account for neck length in evaluating cVEMP latency. Additionally, foam posturography indicated by the Romberg quotient of the sway velocity/area on foam pad is considered to reflect the otolithic function, which reached adult levels when the children at 12 years old.

CONCLUSIONS

For the functional development of the otolithic system in growing children to approach adult levels, the earliest occurrence is the oVEMP test, followed by the foam posturography, and cVEMP test.

Auditory pathway maturational study in small for gestational age preterm infants

PURPOSE

To follow up the maturation of the auditory pathway in preterm infants small for gestational age (SGA), through the study of absolute and interpeak latencies of auditory brainstem response (ABR) in the first six months of age.

METHODS

This multicentric prospective cross-sectional and longitudinal study assessed 76 newborn infants, 35 SGA and 41 appropriate for gestational age (AGA), born between 33 and 36 weeks in the first evaluation. The ABR was carried out in three moments (neonatal period, three months and six months). Twenty-nine SGA and 33 AGA (62 infants), between 51 and 54 weeks (corrected age), returned for the second evaluation. In the third evaluation, 49 infants (23 SGA and 26 AGA), with age range from 63 to 65 weeks (corrected age), were assessed. The bilateral presence of Transient Evoked Otoacoustic Emissions and normal tympanogram were inclusion criteria.

RESULTS

It was found interaural symmetry in both groups. The comparison between the two groups throughout the three periods studied showed no significant differences in the ABR parameters, except for the latencies of wave III in the period between three and six months. As for the maturation with tone burst 0.5 and 1 kHz, it was found that the groups did not differ.

CONCLUSION

The findings suggest that, in the premature infants, the maturational process of the auditory pathway occurs in a similar rate for SGA and AGA. These results also suggest that prematurity is a more relevant factor for the maturation of the auditory pathway than birth weight.

Development of myelination and cholinergic innervation in the central auditory system of a prosimian primate (Otolemur garnetti)

Change in the timeline of neurobiological growth is an important source of biological variation, and thus phenotypic evolution. However, no study has to date investigated sensory system development in any of the prosimian primates that are thought to most closely resemble our earliest primate ancestors. Acetylcholine (ACh) is a neurotransmitter critical to normal brain function by regulating synaptic plasticity associated with attention and learning. Myelination is an important structural component of the brain because it facilitates rapid neuronal communication. In this work we investigated the expression of acetylcholinesterase (AChE) and the density of myelinated axons throughout postnatal development in the inferior colliculus (IC), medial geniculate complex (MGC), and auditory cortex (auditory core, belt, and parabelt) in Garnett's greater galago (Otolemur garnetti). We found that the IC and MGC exhibit relatively high myelinated fiber length density (MFLD) values at birth and attain adult-like values by the species-typical age at weaning. In contrast, neocortical auditory fields are relatively unmyelinated at birth and only attain adult-like MFLD values by the species-typical age at puberty. Analysis of AChE expression indicated that, in contrast to evidence from rodent samples, the adult-like distribution of AChE in the core area of auditory cortex, dense bands in layers I, IIIb/IV, and Vb/VI, is present at birth. These data indicate the differential developmental trajectory of central auditory system structures and demonstrate the early onset of adult-like AChE expression in primary auditory cortex in O. garnetti, suggesting the auditory system is more developed at birth in primates compared to rodents.

Atypical fetal response to the mother's voice in diabetic compared with overweight pregnancies

OBJECTIVE

To characterize fetal spontaneous heart rate changes and movements and auditory-elicited heart rate changes in fetuses in diabetic pregnancies compared with those in uneventful, overweight pregnancies.

METHODS

Spontaneous heart rate and movements and maternal voice-elicited heart rate changes were observed in 46 mother-fetal pairs (n = 14 gestational diabetic and n = 32 overweight prepregnancy) at 36 (±1) weeks gestational age. Fetal heart rate changes, body movements, and breathing movements were observed for 20 minutes while the mother was at rest. Subsequently, each fetus was presented with a 2-minute audio recording of the mother's voice using the following 6-minute procedure: 2 minutes no-voice baseline, 2 minutes voice presentation, and 2 minutes no-voice postvoice period; heart rate was recorded continuously.

RESULTS

There were no differences in spontaneous heart rate changes, body movements, or breathing movements between the 2 groups. Fetuses in the overweight group showed an increase in the heart rate during the playing of their mother's voice, whereas fetuses in the diabetic group showed no response.

CONCLUSIONS

Fetuses in overweight pregnancies responded to the mother's voice with an increase in the heart rate as has been reported previously in uneventful pregnancies. The lack of response to the mother's voice in fetuses in diabetic pregnancies may represent immature neural or auditory system development, an increased sensorineural threshold, and thyroid or iron deficiency.

Modifications of auditory brainstem responses (ABR): observations in full-term and pre-term newborns

OBJECTIVE

In this study, we have evaluated by means of auditory brainstem responses (ABR), in a population derived from a newborn hearing screening protocol, some aspects of maturation of the auditory pathways in the first months after birth, and the possible repercussions on early treatment.

MATERIALS AND METHODS

In this retrospective study newborns were recruited through our hearing screening program, and an ABR evaluation was performed on 339 newborns, that had risk factors or had failed the screening, or both. Such population was divided in two groups for statistical analysis purposes: full-term and pre-term. The initial ABR was pathological in 70 infants.

RESULTS

We observed an improvement over time of the estimated hearing threshold in follow-up ABRs in 43 newborns (26 in the full-term group, mean improvement 27.9 dB SPL, and 17 in the pre-term group, mean improvement 34.6 dB SPL); such an improvement might be related to a maturation of the auditory pathways that was not complete at birth.

CONCLUSIONS

The auditory system might not be completely developed at birth, and might require some months to complete; hence any early clinical approach should consider the possibility of an overtreatment, and any therapeutic strategy should only be considered once the diagnosis is certain and definitive.

The maturational process of the auditory system in the first year of life characterized by brainstem auditory evoked potentials

The study of brainstem auditory evoked potentials (BAEP) allows obtaining the electrophysiological activity generated in the cochlear nerve to the inferior colliculus. In the first months of life, a period of greater neuronal plasticity, important changes are observed in the absolute latency and inter-peak intervals of BAEP, which occur up to the completion of the maturational process, around 18 months of life in full-term newborns, when the response is similar to that of adults.

OBJECTIVE

The goal of this study was to establish normal values of absolute latencies for waves I, III and V and inter-peak intervals I-III, III-V and I-V of the BAEP performed in full-term infants attending the Infant Hearing Health Program of the Speech-Language Pathology and Audiology Course at Bauru School of Dentistry, Brazil, with no risk history for hearing impairment.

MATERIAL AND METHODS

The stimulation parameters were: rarefaction click stimulus presented by the 3ª insertion phone, intensity of 80 dBnHL and a rate of 21.1 c/s, band-pass filter of 30 and 3,000 Hz and average of 2,000 stimuli. A sample of 86 infants was first divided according to their gestational age in preterm (n=12) and full-term (n=74), and then according to their chronological age in three periods: P1: 0 to 29 days (n=46), P2: 30 days to 5 months 29 days (n=28) and P3: above 6 months (n= 12).

RESULTS

The absolute latency of wave I was similar to that of adults, generally in the 1st month of life, demonstrating a complete process maturity of the auditory nerve. For waves III and V, there was a gradual decrease of absolute latencies with age, characterizing the maturation of axons and synaptic mechanisms in the brainstem level.

CONCLUSION

Age proved to be a determining factor in the absolute latency of the BAEP components, especially those generated in the brainstem, in the first year of life.

Electrically evoked auditory brainstem responses in children with sequential bilateral cochlear implants

OBJECTIVE

To examine the effect of sequential bilateral cochlear implantation on auditory brainstem maturation and the effect of age in receiving the second implant (CI2).

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary academic referral center.

PATIENTS

Thirty prelingually deaf children, who received their first implant (CI1) at a mean age of 1.8 year and their CI2 at a mean age of 5.3 years.

INTERVENTION

Sequential bilateral cochlear implantation.

MAIN OUTCOME MEASURE

Electrically evoked auditory brainstem responses on the 2 implant sides were measured intraoperatively and postoperatively after 6, 12, and 24 months of bilateral implant use.

RESULTS

Electrically evoked auditory brainstem response latencies on the 2 implants were compared within subjects over time. Wave III did not show any significant differences between the 2 sides, whereas Wave V was initially prolonged on the CI2 side compared with the CI1 side. Although still apparent, this interaural latency difference of Wave V was no longer significant after 12 and 24 months. Interwave interval III to V latencies remained significantly prolonged on the CI2 side. Age in receiving the CI2 did not account for the individual differences in latencies for all waveforms.

CONCLUSION

The present data suggest that auditory brainstem maturation will occur after a relatively long period of unilateral deafness irrespective of the age in receiving the CI2. Because some abnormalities were still seen at the upper part of the brainstem, our results indicate that the CI2 side has not caught up with the CI1 side. Nevertheless, within our follow-up time, interaural (interwave) latencies decrease significantly, and longer-term data might reveal that the CI2 eventually will catch up with the CI1 side.

Incidence and clinical value of prolonged I-V interval in NICU infants after failing neonatal hearing screening

Infants admitted to neonatal intensive care units (NICUs) have a higher incidence of perinatal complications and delayed maturational processes. Parameters of the auditory brainstem response (ABR) were analyzed to study the prevalence of delayed auditory maturation or neural pathology. The prevalence of prolonged I–V interval as a measure of delayed maturation and the correlation with ABR thresholds were investigated. All infants admitted to the NICU Sophia Children’s Hospital between 2004 and 2009 who had been referred for ABR measurement after failing neonatal hearing screening with automated auditory brainstem response (AABR) were included. The ABR parameters were retrospectively analyzed. Between 2004 and 2009, 103 infants were included: 46 girls and 57 boys. In 58.3% (60 infants) of our population, the I–V interval was recordable in at least one ear at first diagnostic ABR measurement. In 4.9%, the I–V interval was severely prolonged. The median ABR threshold of infants with a normal or mildly prolonged I–V interval was 50 dB. The median ABR threshold of infants with a severely prolonged I–V interval was 30 dB. In conclusion, in case both peak I and V were measurable, we found only a limited (4.9%) incidence of severely prolonged I–V interval (≥0.8 ms) in this high-risk NICU population. A mild delay in maturation is a more probable explanation than major audiologic or neural pathology, as ABR thresholds were near normal in these infants.

Fitting model of ABR age dependency in a clinical population of normal hearing children

The purpose of this study was to present a simple and powerful fitting model that describes age-dependent changes of auditory brainstem responses (ABR) in a clinical population of normal hearing children. A total of 175 children (younger than 200 weeks postconceptional age) were referred for audiologic assessment with normal ABR results. ABR parameters of normal hearing children between 2003 and 2008 were included. The results of the right ears recorded at 90 dB nHL were analyzed. A simple and accurate fitting model was formulated based on these data. A very similar age-dependent effect was found for peaks III and V, and I–III and I–V intervals; latencies decrease as postconceptional age increases. It shows that the total age-dependent effect will be completed after 1.5–2 years. The age-dependent effect can be modeled by a relatively simple and accurate exponential function. This fitting model can be easily implemented to analyze ABR results of infants in daily clinical practice. We speculate about the underlying physiological processes.

A Multicentre Database for Normative Brainstem Auditory Evoked Potentials (BAEPs) in Children: Methodology for Data Collection and Evaluation

Background:

The influence of physiological and methodological factors on recordings of brainstem auditory evoked potentials (BAEPs) is greater in children than in adults.

Objective:

To collect and evaluate BAEP data in normal children, and measure intra- and inter-laboratory variability.

Methods:

Seven hundred and fifty unselected BAEP recordings were collected and evaluated from children ranging from neonates to 14-year-olds by eight laboratories in Italy.

Results:

In newborns, three laboratories showed satisfactory concordance; wave I was more broadly distributed than wave V and IPL I-V. The evaluation of pooled BAEP data from the older children showed that laboratories with age-matched data gave overlapping results; those with unmatched-age data differed significantly. The sound intensities of the laboratories did not significantly affect absolute BAEP latencies or IPLs. Females had shorter latencies than males; the difference was not significant. A single exponential regression model was an adequate but not the best predictor of normal data.

Conclusions:

The pooled data were consistent with the physiological maturation of the brainstem acoustic pathway. The BAEPs was reliably normalised using the natural logarithm of age. The differences between Centres were related to sample size, measurement accuracy, and inclusion and selection criteria.

Significance:

The creation of multicentre common database from an unmatched data collection is feasible and reliable enough for clinical diagnosis and multicentre clinical research.

[Early hearing experience and sensitive developmental periods]

This article reviews the studies on functional deficits in the auditory cortex of congenitally deaf animals. It compares their results with psychophysical and imaging data obtained from prelingually deaf humans. The studies demonstrate that the development of the auditory cortex is affected by the absence of hearing experience. In humans, the restoration of hearing after congenital deafness shows a sensitive period of 4 years, whereas even within this sensitive period cortical plasticity is already decreasing with increasing age. The reasons for the sensitive period are developmental changes of synaptic plasticity, developmentally modified synaptogenesis and synaptic pruning as well as changes in connectivity of the auditory cortex. Absence of top-down interactions from higher order auditory areas is another cardinal reason for the sensitive period. All these mechanisms contribute to the decreasing capacity for cortical plasticity during postnatal development. From the developmental and neurophysiological point of view, an early identification of hearing loss is an important prerequisite for effective therapy.

Auditory steady-state responses to bone conduction stimuli in children with hearing loss

OBJECTIVE

The auditory steady-state response (ASSR) to air-conduction (AC) stimuli has been widely incorporated into audiological test-batteries for the pediatric population. The current understanding of ASSR to bone conduction (BC) stimuli, however, is more limited, especially in the case of infants and children. There are few reports on ASSR thresholds to BC stimuli in infants and young children, and none for infants or children with hearing loss. The objective of this study was to investigate BC ASSR thresholds in young children with normal hearing and various types and degrees of hearing loss.

METHODS

AC and BC ASSR thresholds are reported for 48 young children (mean age+/-SD=2.8+/-1.9 years; age range=0.25-11.5 years; 23 female). Hearing status was classified by assessing all children with a comprehensive test battery including tympanometry, diagnostic distortion-product otoacoustic emissions, click-evoked AC auditory brainstem response, AC and BC ASSR thresholds, and an otologic examination. The subjects were assigned to the categories normal hearing, conductive loss, and sensorineural loss (mild-to-moderate or severe-to-profound), for group analysis. AC and BC ASSR stimuli (carrier frequencies: 0.25-4 kHz; 67-95 Hz modulation rates; 100% amplitude and 10% frequency modulated) were presented using the GSI Audera system.

RESULTS

Minimum levels at which spurious BC ASSR occur were established in the group of children with severe-to-profound sensorineural hearing loss (25, 40, 60, 60 and 60 dB for 0.25, 0.5, 1, 2, and 4 kHz, respectively). Children with normal hearing presented mean (1 SD) BC ASSR thresholds of 19 (9), 18 (7), 16 (11), 24 (7), and 26 (8) dB HL at 0.25, 0.5, 1, 2, and 4 kHz, respectively. Significantly lower thresholds (p<0.0001) were obtained for 0.25, 0.5 and 1 kHz than for 2 and 4 kHz. At 0.25 kHz, 39% of thresholds were at the minimum level of spurious response occurrence. More than half (54%) of the BC thresholds in the group with mild-to-moderate sensorineural hearing loss were recorded at or above the minimum levels at which spurious response occurred. In children with conductive hearing loss, the average BC ASSR thresholds corresponded closely to those in the normal hearing group except at 1 kHz and revealed an air-bone gap.

CONCLUSIONS

Spurious bone conduction ASSR responses limit the intensity range for which the technique may be employed in infants and children, especially at lower frequencies. Consequently, the 0.25 kHz stimulus is not recommended for clinical use. In infants and young children, sensorineural hearing loss of a moderate or greater degree in the high frequencies (1-4 kHz), and of a mild or greater degree in the low frequencies (0.5 kHz), cannot be quantified using BC ASSR. This is due to the presence of the stimulus artifact. In cases of conductive hearing loss, BC ASSR can effectively quantify sensory hearing between 0.5 and 4 kHz, but interpretations must be made cautiously within the limitations of stimulus artifact occurrence across frequencies.

Effects of age at onset of deafness and electrical stimulation on the developing cochlear nucleus in cats

This study examined the effects of deafness and intracochlear electrical stimulation on the anatomy of the cochlear nucleus (CN) after a brief period of normal auditory development early in life. Kittens were deafened by systemic ototoxic drug injections either as neonates or starting at postnatal day 30. Total CN volume, individual CN subdivision volumes, and cross-sectional areas of spherical cell somata in the anteroventral CN (AVCN) were compared in neonatally deafened and 30-day deafened groups at 8 weeks of age and in young adults after approximately 6 months of electrical stimulation initiated at 8 weeks of age. Both neonatal and early acquired hearing loss resulted in a reduction in CN volume as compared to normal hearing cats. Comparison of 8- and 32-week old groups indicated that the CN continued to grow in both deafened groups despite the absence of auditory input. Preserving normal auditory input for 30 days resulted in a significant increase in both total CN volume and cross-sectional areas of spherical cell somata, as compared to neonatally deafened animals. Restoring auditory input in these developing animals by unilateral intracochlear electrical stimulation did not elicit any difference in CN volume between the two sides, but resulted in 7% larger spherical cell size on the stimulated side. Overall, the brief period of normal auditory development and subsequent electrical stimulation maintained CN volume at 80% of normal and spherical cell size at 86% of normal ipsilateral to the implant as compared to 67% and 74%, respectively, in the neonatally deafened group.

The temporal relationship between speech auditory brainstem responses and the acoustic pattern of the phoneme /ba/ in normal-hearing adults

OBJECTIVE

To investigate the temporal relationship between speech auditory brainstem responses and acoustic pattern of the phoneme /ba/.

METHODS

Speech elicited auditory brainstem responses (Speech ABR) to /ba/ were recorded in 23 normal-hearing subjects. Effect of stimulus intensity was assessed on Speech ABR components latencies in 11 subjects. The effect of different transducers on electromagnetic leakage was also measured.

RESULTS

Speech ABR showed a reproducible onset response (OR) 6ms after stimulus onset. The frequency following response (FFR) waveform mimicked the 500Hz low pass filtered temporal waveform of phoneme /ba/ with a latency shift of 14.6ms. In addition, the OR and FFR latencies decreased with increasing stimulus intensity, with a greater rate for FFR (-1.4ms/10dB) than for OR (-0.6ms/10dB).

CONCLUSIONS

A close relationship was found between the pattern of the acoustic stimulus and the FFR temporal structure. Furthermore, differences in latency behaviour suggest different generation mechanisms for FFR and OR.

SIGNIFICANCE

The results provided further insight into the temporal encoding of basic speech stimulus at the brainstem level in humans.

Electrophysiological Evaluation of Human Brain Development

The complex development of the human brain during infancy can only be understood by convergent structural, functional, and behavioral measurements. The evaluation of event-related potentials (ERPs) is the most effective current way to look at infant brain function. ERP paradigms can be used to examine the simple transmission of sensory information to the cortex and the discrimination of this information within the cortex. The main developmental changes involve localization of function as the brain becomes tuned to the experienced world (related to synaptic pruning) and a speeding up of transmission as pathways become efficient (related to myelination). ERPs that occur in relation to different temporal aspects of a stimulus (onset-responses, offset-responses, sustained potentials and steady-state responses) and ERPs recorded at different stimulus rates may help track perceptual development from a temporal perspective. Particularly important in human development are the ERP changes that occur in the processing of speech sounds and human faces. At present, ERP studies can show differences between groups of subjects that can demonstrate developmental disorders or elucidate mechanisms of development. However, because of their variability, ERPs are less helpful in determining whether an individual infant is developing abnormally. Where possible, ERP measurements should be used in conjunction with behavioral tests so as to relate performance to mechanism, and with anatomical brain measurements to relate mechanism to structure.

The pattern of auditory brainstem response wave V maturation in cochlear-implanted children

OBJECTIVE

Maturation of acoustically evoked brainstem responses (ABR) in hearing children is not complete at birth but rather continues over the first two years of life. In particular, it has been established that the decrease in ABR wave V latency can be modeled as the sum of two decaying exponential functions with respective time-constants of 4 and 50 weeks [Eggermont, J.J., Salamy, A., 1988a. Maturational time-course for the ABR in preterm and full term infants. Hear Res 33, 35-47; Eggermont, J.J., Salamy, A., 1988b. Development of ABR parameters in a preterm and a term born population. Ear Hear 9, 283-9]. Here, we investigated the maturation of electrically evoked auditory brainstem responses (EABR) in 55 deaf children who recovered hearing after cochlear implantation, and proposed a predictive model of EABR maturation depending on the onset of deafness. The pattern of EABR maturation over the first 2 years of cochlear implant use was compared with the normal pattern of ABR maturation in hearing children.

METHODS

Changes in EABR wave V latency over the 2 years following cochlear implant connection were analyzed in two groups of children. The first group (n=41) consisted of children with early-onset of deafness (mostly congenital), and the second (n=14) of children who had become profoundly deaf after 1 year of age. The modeling of changes in EABR wave V latency with time was based on the mean values from each of the two groups, allowing comparison of the rates of EABR maturation between groups. Differences between EABRs elicited at the basal and apical ends of the implant electrode array were also tested.

RESULTS

There was no influence of age at implantation on the rate of wave V latency change. The main factor for EABR changes was the time in sound. Indeed, significant maturation was observed over the first 2 years of implant use only in the group with early-onset deafness. In this group maturation of wave V progressed as in the ABR model of [Eggermont, J.J., Salamy, A., 1988a. Maturational time-course for the ABR in preterm and full term infants. Hear Res 33, 35-47; Eggermont, J.J., Salamy, A., 1988b. Development of ABR parameters in a preterm and a term born population. Ear Hear 9, 283-9] of normal hearing children: a sum of two decaying exponential functions, one showing an early rapid decrease in latency and the other a slower decrease. Remarkably, the time-constants fell well within the ranges described by Eggermont and Salamy (i.e., 3.9 and 68 weeks), consistent with the time-course of the neurophysiological mechanisms presumably involved in auditory pathway maturation during the first 2 years of life: i.e., myelination and increased synaptic efficacy. In contrast, relatively little change in wave V was evident in children with late-onset deafness. In agreement with the notion that EABR maturation follows an apex-to-base gradient as described for ABR, we observed that wave V latencies were longer for the basal than the apical end of the implant electrode array and remained so throughout the study period, whatever the time of onset of deafness.

CONCLUSIONS

The findings in the early-onset of deafness group support the theory that auditory pathways remain "frozen" during the period of sensory deprivation until cochlear implant rehabilitation restores the normal chronology of maturational processes. In children with late-onset deafness, however, some maturational processes may occur before the onset of deafness, and thus less additional maturation is required during the first two years of implant use resulting in no significant EABR latency changes being observed in this period. The results suggest that the rehabilitation-induced plasticity of the auditory pathways is, in case of late auditory deprivation, unlikely to result in neurophysiological outcomes similar to those observed in children with early auditory deprivation.

SIGNIFICANCE

Changes in EABR wave V latency over the first 2 years of cochlear implant use were found to be well fitted by the sum of two decaying exponential functions in children with early-onset deafness. This is in line with the maturation of ABR wave V latency in normal-hearing children over the first two years of life. Further studies are needed to assess whether the differences observed in terms of auditory pathways maturation are associated with consistent differences in terms of language development.

Auditory processing deficits in growth restricted fetuses affect later language development

An increased risk for language deficits in infants born growth restricted has been reported in follow-up studies for more than 20 years, suggesting a relation between fetal auditory system development and later language learning. Work with animal models indicate that there are at least two ways in which growth restriction could affect the development of auditory perception in human fetuses: a delay in myelination or conduction and an increase in sensorineural threshold. Systematic study of auditory function in growth restricted human fetuses has not been reported. However, results of studies employing low-risk fetuses delivering as healthy full-term infants demonstrate that, by late gestation, the fetus can hear, sound properties modulate behavior, and sensory information is available from both inside (e.g., maternal vascular) and outside (e.g., noise, voices, music) of the maternal body. These data provide substantive evidence that the auditory system is functioning and that environmental sounds are available for shaping neural networks and laying the foundation for language acquisition before birth. We hypothesize that fetal growth restriction affects auditory system development, resulting in atypical auditory information processing in growth restricted fetuses compared to healthy, appropriately-grown-for-gestational-age fetuses. Speech perception that lays the foundation for later language competence will differ in growth restricted compared to normally grown fetuses and be associated with later language abilities.

Multiple Auditory Steady-State Response Thresholds to Bone-Conduction Stimuli in Young Infants with Normal Hearing

OBJECTIVE

Multiple auditory steady-state responses (ASSRs) probably will be incorporated into the diagnostic test battery for estimating hearing thresholds in young infants in the near future. Limiting this, however, is the fact that there are no published bone-conduction ASSR threshold data for infants with normal or impaired hearing. The objective of this study was to investigate bone-conduction ASSR thresholds in infants from a Neonatal Intensive Care Unit (NICU) and in young infants with normal hearing and to compare these with adult ASSR thresholds.

DESIGN

ASSR thresholds to multiple bone-conduction stimuli (carrier frequencies: 500 to 4000 Hz; 77 to 101-Hz modulation rates; amplitude/frequency modulated; single-polarity stimulus) were obtained in two infant groups [N = 29 preterm (32 to 43 wk PCA), tested in NICU; N = 14 postterm (0 to 8 mo), tested in sound booth]. All infants had passed a hearing screening test. ASSR thresholds, amplitudes, and phase delays for preterm and postterm infants were compared with previously collected adult data.

RESULTS

Mean (+/-1 SD) ASSR thresholds were 16 (11), 16 (10), 37 (10), and 33 (13) dB HL for the preterm infants and 14 (13), 2 (7), 26 (6), and 22 (8) dB HL for the postterm infants at 500, 1000, 2000, and 4000 Hz, respectively. Both infant groups had significantly better thresholds for 500 and 1000 Hz compared with 2000 and 4000 Hz, in contrast to adults who have similar thresholds across frequency (22, 26, 18, and 18 dB HL). When 500- and 1000-Hz thresholds were pooled, pre- and postterm infants had better low-frequency thresholds than adults. When 2000- and 4000-Hz thresholds were pooled, pre- and postterm infants had poorer thresholds than adults. ASSR amplitudes were significantly larger for low frequencies compared with high frequencies for both infant groups, in contrast to adults, who show little difference across frequency. ASSR phase delays were later for lower frequencies compared with higher frequencies for infants and adults, except for 500 Hz in the preterm group. ASSR phase delays were later for infants compared with adults across frequency.

CONCLUSIONS

Infant bone-conduction ASSR thresholds are very different from those of adults. Overall, these results indicate that low-frequency bone-conduction thresholds worsen and high-frequency bone-conduction thresholds improve with maturation. Bone-conduction ASSR threshold differences between the postterm infants and adults probably are due to skull maturation. Differences between preterm and older infants may be explained both by skull changes and a masking effect of high ambient noise levels in the NICU (and possibly to other issues due to prematurity).

An evoked potential study of the developmental time course of the auditory nerve and brainstem in children using cochlear implants

Central auditory responses to electrical stimulation from a cochlear implant were studied in 75 pre-lingually deafened children and 11 adults. Electrically evoked auditory brainstem response (EABR) latencies significantly decreased with duration of cochlear implant use and were not significantly affected by the age at implant activation. Significant decreases in early latency waves and interwaves occurred within the first 1-2 months of implant use, whereas longer term changes (6-12 months) were found for eV and eIII-eV, which measure activity in the more rostral brainstem. Comparisons to acoustically evoked auditory brainstem response (ABR) in children with normal hearing suggested shorter interwave EABR latencies, reflecting either distinct neural generators or increased neural synchrony, but similar rates of change in the later latency eV and eIII-eV with time in sound. In sum, normal-like development of the rostral auditory brainstem is promoted by cochlear implant use in children of a wide range of ages.

Comparison of fetal behavior in low- and high-risk pregnancies

Meta-analyses were conducted on archival data of human fetal behavior to identify differential behavior among high-risk fetuses in pregnancies complicated by threatened preterm delivery, maternal hypertension or diabetes compared with low-risk fetuses in uneventful pregnancies, delivering as healthy, full-term infants. Data for a total of 493 fetuses (260 high risk, 233 low risk) from 23 weeks' gestation to term who participated in a study using a standardized protocol including observations of spontaneous and auditory-induced behavior were retrieved from our laboratory database. There were no differences in spontaneous behaviors when scored using clinical criteria for the nonstress test and biophysical profile; however, there were differences in the magnitude of the behaviors measured in the tests. Developmental differences were observed between those threatening to deliver early and the fetuses of hypertensive and diabetic mothers. The latter two groups differed little from one another but differed from low-risk fetuses in their response to auditory stimulation. We concluded that differences in behavior among high-risk groups suggest that atypical fetal behaviors may represent adaptation to condition specific insult rather than a generalized response to insult per se. The finding that high-risk fetuses showed atypical responses to auditory stimuli indicates a need to examine the relation between fetal auditory function and later language acquisition.

Maturation of fetal responses to music

Maturation of fetal response to music was characterized over the last trimester of pregnancy using a 5-minute piano recording of Brahms' Lullaby, played at an average of 95, 100, 105 or 110 dB (A). Within 30 seconds of the onset of the music, the youngest fetuses (28-32 weeks GA) showed a heart rate increase limited to the two highest dB levels; over gestation, the threshold level decreased and a response shift from acceleration to deceleration was observed for the lower dB levels, indicating attention to the stimulus. Over 5 minutes of music, fetuses older than 33 weeks GA showed a sustained increase in heart rate; body movement changes occurred at 35 weeks GA. These findings suggest a change in processing of complex sounds at around 33 weeks GA, with responding limited to the acoustic properties of the signal in younger fetuses but attention playing a role in older fetuses.

Interaural time coincidence detectors are present at birth: evidence from binaural interaction

Binaural processing of sounds in mammals is presumably initiated within the auditory nuclei of the caudal pons. The binaural difference waveform (BD) can be derived from the sum of the waveforms evoked by right monaural clicks plus left monaural clicks minus the waveform evoked by binaural clicks. In adults, the BD's first positive peak (beta) is large only for stimuli with interaural time differences (ITDs) that produce a fused acoustic percept. Humans at birth can localize and discriminate sound sources, but their head circumference is about two-thirds of an adult head. In order to test whether beta is related to head circumference, we recorded beta in human neonates as a function of ITD. Binaural clicks with ITDs ranging between 0 and 1000 micros were used to derive BD waveforms in 34 neonates. For ITD=0, beta was detectable in 56% of newborns. The incidence of beta detection then decreased as ITD increased. Only 9% of the babies had detectable beta for all ITDs. No correlation was found between the existence of beta and other properties of the monaural or binaural auditory brainstem response. The finding that for some infants beta was present for all ITDs up to 1.0 ms suggests that there is no recalibration of brainstem delay lines with head growth. Our data suggest that the brainstem auditory pathway for detecting interaural time differences in the adult is probably present at birth. Maturational factors such as increased myelination and greater firing synchrony probably improve the detectability of beta with age. The second peak in the BD waveform (delta) was highly correlated with the existence of wave VI in the binaural and monaural waveforms.

Autism and auditory brain stem responses

OBJECTIVE

To study a controversy that has been discussed for more than two decades: whether or not children with autism have abnormalities affecting the cochlear nerve or the auditory pathway in the brain stem and, if so, to describe these abnormalities.

DESIGN

A group of 153 children and adolescents with autistic disorder were included in an investigation of auditory brain stem responses (ABR). Two thirds of this group, 101 individuals (75 boys, 26 girls), had normal hearing and they were selected for an in-depth ABR study. The results from the study group were compared with those of an age-matched comparison group.

RESULTS

The III-V interpeak latency (IPL) was significantly prolonged in both boys and girls with autism, compared with the controls. The latencies of ABR waves I and V were also significantly lengthened in the study groups. The individual test results showed that more than half of this normal-hearing autistic disorder group (58%) had abnormalities of one or more of eight ABR parameters studied. The most common abnormalities were prolongation of wave V (38%), and of I-V IPL (28%). A lengthening of the I-V IPL was also recorded in 27% of 49 children who were difficult to test or who had hearing loss. Abnormal left-right differences of ABR latencies were found in 18% of autism cases with normal hearing.

CONCLUSIONS

Possible causes of the reported ABR abnormalities, observed here as well as in other studies, are discussed. Brain stem lesion, occult cochlear dysfunction, and involvement of the cochlear efferent system are probable factors that can explain the ABR findings

Auditory brain stem and midbrain development after cochlear implantation in children

Input to the central auditory system through a cochlear implant promotes psychophysical improvement of auditory skills. However, the developmental changes along the pathways have never been characterized in children with hearing loss who use implants. We aimed to measure auditory development in such children by using the electrically evoked auditory brain stem response (EABR). We made repeated measures of the EABR in 41 nonsedated children with implants before chronic stimulation and after 2, 6, and 12 months of consistent implant use. The results show that EABRs were present in all of the children even before chronic auditory stimulation, and that EABR wave latencies decreased from the time of initial activation throughout the first year of cochlear implant use. These findings reflect auditory development to the level of the midbrain as a result of the cochlear implant. The decreasing latencies likely reflect decreased neural conduction times at this level, in part because of increased synaptic efficacy.

Maturation of human auditory cortex: implications for speech perception

This project traced the maturation of the human auditory cortex from midgestation to young adulthood, using immunostaining of axonal neurofilaments to determine the time of onset of rapid conduction. The study identified 3 developmental periods, each characterized by maturation of a different axonal system. During the perinatal period (3rd trimester to 4th postnatal month), neurofilament expression occurs only in axons of the marginal layer. These axons drive the structural and functional development of cells in the deeper cortical layers, but do not relay external stimuli. In early childhood (6 months to 5 years), maturing thalamocortical afferents to the deeper cortical layers are the first source of input to the auditory cortex from lower levels of the auditory system. During later childhood (5 to 12 years), maturation of commissural and association axons in the superficial cortical layers allows communication between different subdivisions of the auditory cortex, thus forming a basis for more complex cortical processing of auditory stimuli.

Deficits in auditory brainstem pathway encoding of speech sounds in children with learning problems

Auditory brainstem responses were recorded in normal children (NL) and children clinically diagnosed with a learning problem (LP). These responses were recorded to both a click stimulus and the formant transition portion of a speech syllable /da/. While no latency differences between the NL and LP populations were seen in responses to the click stimuli, the syllable /da/ did elicit latency differences between these two groups. Deficits in cortical processing of signals in noise were seen for those LP subjects with delayed brainstem responses to the /da/, but not for LPs with normal brainstem measures. Preliminary findings indicate that training may be beneficial to LP subjects with brainstem processing delays.

Event-related potential features indexing central auditory discrimination by newborns

Behavioral research has produced little evidence on sound feature discrimination in neonates. Sensory processes underlying sound perception can be studied using the mismatch negativity (MMN) component of auditory event-related potentials (ERPs), which is not contingent on conscious perception and response. Thus, MMN is suitable for studying newborns, who are difficult to obtain behavioral responses from. The present study thus utilized spectrally rich sounds, known to elicit the most replicable MMN in adults, to investigate newborns' preattentive analysis of sound duration and frequency changes. An attempt was also made to control for the obligatory ERP effects on the MMN. Three-partial harmonic tones were presented in Duration and in Frequency oddball conditions to 55 newborns. In the other two, Equiprobable duration and Equiprobable frequency, conditions frequency and duration deviants of the oddball paradigms were presented with equal probabilities among sounds of other durations and frequencies. MMN was elicited in 81% of newborns in Frequency oddball condition and in 78% of newborns in Duration oddball condition. No significant amplitude differences between the duration and frequency MMNs were found, but MMN latency was delayed in Duration condition. The obligatory components seemed to contribute significantly to the deviant-standard difference in Duration but not in Frequency condition. The majority of neonates appear to possess effective sound frequency and duration discrimination mechanisms. Their preattentive sound discrimination is facilitated by spectrally rich sound content. The present findings support a change-detection nature of MMN in neonates; however, sound duration-related obligatory effects need to be taken into account in infant MMN studies.

Relationships between otoacoustic emissions and auditory brainstem responses in neonates and young children: a correlation and factor analytical study

OBJECTIVES

To establish relationships among transient evoked otoacoustic emission (TEOAE) and auditory brainstem response (ABR) variables in a sample of normal hearing neonates and young children, ranging in age from approximately 3 weeks to 4 years.

STUDY DESIGN

Retrospective, non-randomized, cross-sectional analysis of clinical data obtained at a tertiary care medical center.

METHODS

Pearson product moment and Spearman rank order correlation analyses to evaluate pairwise relationships between TEOAE variables, ABR variables and age; factor analysis, to identify the structural composition and dimensionality of these relationships.

RESULTS

Significant pairwise correlations were obtained between variables within each test paradigm (TEOAEs, ABRs) and between ABR absolute and interpeak latencies with age. However, the most striking effect was the absence of strong correlations between ABR and TEOAE variables, indicating that these test measures provide independent information about auditory system integrity and sensitivity. Two factors, accounting for over 55% of the variance, characterized this data set: 1) a frequency-dependent OAE factor, which showed an inverse relation between biologic noise and whole wave percent reproducibility and half-octave band TEOAE amplitudes; and 2) a central nervous system (CNS) maturational factor, which showed an inverse relationship between age and certain absolute and interpeak ABR latency components.

CONCLUSIONS

TEOAE and ABR test results provide unique and functionally independent information about normal auditory system integrity and sensitivity. Therefore, a combination of both tests is well suited for use within a pediatric test battery. These results confirm that biologic noise and age at test differentially affect OAE and ABR test measures, and both effects require consideration during data acquisition and interpretation.

Brainstem auditory evoked potentials (BAEPs) in the cynomolgus macaque monkey. Equivalence with human BAEPs and proposal of a new nomenclature

Several groups have studied brainstem auditory evoked potentials (BAEPs) in non-human primates. However, the nomenclature of the waves elicited and their correspondence with human waves I-V differ among authors. BAEPs were recorded from six anaesthetised young cynomolgus macaques (Macaca fascicularis), using different sound stimuli parameters. A constant pattern of four main waveforms was present in all the animals with stimulus intensities over 60 dB SPL, although up to four smaller waveforms were observed in some of the individuals. Latency values increased with decreasing stimulus intensities and with increasing repetition rates. These results were similar to the BAEPs observed in other species of macaques. Although an approximate equivalence between human and monkey BAEPs is possible, some discrepancies suggest that there may be generators which contribute to different waves in both species. This is the reason for our proposal of a new nomenclature for BAEP waveforms in monkeys, following a descriptive order with Arabic numerals preceded by the letter M.