Auditory evoked potential development in early childhood: a longitudinal study

Functional and structural maturation of auditory cortex from 2 months to 2 years old

In school-age children, the myelination of the auditory radiation thalamocortical pathway is associated with the latency of auditory evoked responses, with the myelination of thalamocortical axons facilitating the rapid propagation of acoustic information. Little is known regarding this auditory system function-structure association in infants and toddlers. The present study tested the hypothesis that maturation of auditory radiation white-matter microstructure (e.g., fractional anisotropy (FA); measured using diffusion-weighted MRI) is associated with the latency of the infant auditory response (P2m measured using magnetoencephalography, MEG) in a cross-sectional (2 to 24 months) as well as longitudinal cohort (2 to 29 months) of typically developing infants and toddlers. In the cross-sectional sample, non-linear maturation of P2m latency and auditory radiation diffusion measures were observed. After removing the variance associated with age in both P2m latency and auditory radiation diffusion measures, auditory radiation still accounted for significant variance in P2m latency. In the longitudinal sample, latency and FA associations could be observed at the level of a single child. Findings provide strong support for a contribution of auditory radiation white matter to rapid cortical auditory encoding processes in infants.

Maturation of auditory cortex neural responses during infancy and toddlerhood

The infant auditory system rapidly matures across the first years of life, with a primary goal of obtaining ever-more-accurate real-time representations of the external world. Our understanding of how left and right auditory cortex neural processes develop during infancy, however, is meager, with few studies having the statistical power to detect potential hemisphere and sex differences in primary/secondary auditory cortex maturation. Using infant magnetoencephalography (MEG) and a cross-sectional study design, left and right auditory cortex P2m responses to pure tones were examined in 114 typically developing infants and toddlers (66 males, 2 to 24 months). Non-linear maturation of P2m latency was observed, with P2m latencies decreasing rapidly as a function of age during the first year of life, followed by slower changes between 12 and 24 months. Whereas in younger infants auditory tones were encoded more slowly in the left than right hemisphere, similar left and right P2m latencies were observed by ∼21 months of age due to faster maturation rate in the left than right hemisphere. No sex differences in the maturation of the P2m responses were observed. Finally, an earlier left than right hemisphere P2m latency predicted better language performance in older infants (12 to 24 months). Findings indicate the need to consider hemisphere when examining the maturation of auditory cortex neural activity in infants and toddlers and show that the pattern of left-right hemisphere P2m maturation is associated with language performance.

The maturation of the P1m component in response to voice from infancy to 3 years of age: A longitudinal study in young children

INTRODUCTION

In the early development of human infants and toddlers, remarkable changes in brain cortical function for auditory processing have been reported. Knowing the maturational trajectory of auditory cortex responses to human voice in typically developing young children is crucial for identifying voice processing abnormalities in children at risk for neurodevelopmental disorders and language impairment. An early prominent positive component in the cerebral auditory response in newborns has been reported in previous electroencephalography and magnetoencephalography (MEG) studies. However, it is not clear whether this prominent component in infants less than 1 year of age corresponds to the auditory P1m component that has been reported in young children over 2 years of age.

METHODS

To test the hypothesis that the early prominent positive component in infants aged 0 years is an immature manifestation of P1m that we previously reported in children over 2 years of age, we performed a longitudinal MEG study that focused on this early component and examined the maturational changes over three years starting from age 0. Five infants participated in this 3-year longitudinal study.

RESULTS

This research revealed that the early prominent component in infants aged 3 month corresponded to the auditory P1m component in young children over 2 years old, which we had previously reported to be related to language development and/or autism spectrum disorders.

CONCLUSION

Our data revealed the development of the auditory-evoked field in the left and right hemispheres from 0- to 3-year-old children. These results contribute to the elucidation of the development of brain functions in infants.

Maturation of Auditory Cortex Neural Activity in Children and Implications for Auditory Clinical Markers in Diagnosis

Functional brain markers that can inform research on brain abnormalities, and especially those ready to facilitate clinical work on such abnormalities, will need to show not only considerable sensitivity and specificity but enough consistency with respect to developmental course that their validity in individual cases can be trusted. A challenge to establishing such markers may be individual differences in developmental course. The present study examined auditory cortex activity in children at an age when developmental changes to the auditory cortex 50 ms (M50) and 100 ms (M100) components are prominent to better understand the use of auditory markers in pediatric clinical research. MEG auditory encoding measures (auditory evoked fields in response to pure tone stimuli) were obtained from 15 typically developing children 6-8 years old, with measures repeated 18 and 36 months after the initial exam. MEG analyses were conducted in source space (i.e., brain location), with M50 and M100 sources identified in left and right primary/secondary auditory cortex (Heschl's gyrus). A left and right M50 response was observed at all times (Time 1, Time 2, Time 3), with M50 latency (collapsing across hemisphere) at Time 3 (77 ms) 10 ms earlier than Time 1 (87 ms; p < 0.001) and with M50 responses on average (collapsing across time) 5 ms earlier in the right (80 ms) than left hemisphere (85 ms; p < 0.05). In the majority of children, however, M50 latency changes were not constant across the three-year period; for example, whereas in some children a ~10 ms latency reduction was observed from Time 1 to Time 2, in other children a ~10 ms latency reduction was observed from Time 2 to Time 3. M100 responses were defined by a significant "peak" of detected power with magnetic field topography opposite M50 and occurring 50-100 ms later than the M50. Although M100s were observed in a few children at Time 1 and Time 2 (and more often in the right than left hemisphere), M100s were not observed in the majority of children except in the right hemisphere at Time 3. In sum, longitudinal findings showed large between- and within-subject variability in rate of change as well as time to reach neural developmental milestones (e.g., presence of a detectable M100 response). Findings also demonstrated the need to examine whole-brain activity, given hemisphere differences in the rate of auditory cortex maturation. Pediatric research will need to take such normal variability into account when seeking clinical auditory markers.

Magnetoencephalography and the infant brain

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that provides whole-head measures of neural activity with millisecond temporal resolution. Over the last three decades, MEG has been used for assessing brain activity, most commonly in adults. MEG has been used less often to examine neural function during early development, in large part due to the fact that infant whole-head MEG systems have only recently been developed. In this review, an overview of infant MEG studies is provided, focusing on the period from birth to three years. The advantages of MEG for measuring neural activity in infants are highlighted (See Box 1), including the ability to assess activity in brain (source) space rather than sensor space, thus allowing direct assessment of neural generator activity. Recent advances in MEG hardware and source analysis are also discussed. As the review indicates, efforts in this area demonstrate that MEG is a promising technology for studying the infant brain. As a noninvasive technology, with emerging hardware providing the necessary sensitivity, an expected deliverable is the capability for longitudinal infant MEG studies evaluating the developmental trajectory (maturation) of neural activity. It is expected that departures from neuro-typical trajectories will offer early detection and prognosis insights in infants and toddlers at-risk for neurodevelopmental disorders, thus paving the way for early targeted interventions.

Development of Auditory Evoked Responses in Normally Developing Preschool Children and Children with Autism Spectrum Disorder

The cortical responses to auditory stimuli undergo rapid and dramatic changes during the first 3 years of life in normally developing (ND) children, with decreases in latency and changes in amplitude in the primary peaks. However, most previous studies have focused on children >3 years of age. The analysis of data from the early stages of development is challenging because the temporal pattern of the evoked responses changes with age (e.g., additional peaks emerge with increasing age) and peak latency decreases with age. This study used the topography of the auditory evoked magnetic field (AEF) to identify the auditory components in ND children between 6 and 68 months (n = 48). The latencies of the peaks in the AEF produced by a tone burst (ISI 2 ± 0.2 s) during sleep decreased with age, consistent with previous reports in awake children. The peak latencies of the AEFs in ND children and children with autism spectrum disorder (ASD) were compared. Previous studies indicate that the latencies of the initial components of the auditory evoked potential (AEP) and the AEF are delayed in children with ASD when compared to age-matched ND children >4 years of age. We speculated whether the AEF latencies decrease with age in children diagnosed with ASD as in ND children, but with uniformly longer latencies before the age of about 4 years. Contrary to this hypothesis, the peak latencies did not decrease with age in the ASD group (24-62 months, n = 16) during sleep (unlike in the age-matched controls), although the mean latencies were longer in the ASD group as in previous studies. These results are consistent with previous studies indicating delays in auditory latencies, and they indicate a different maturational pattern in ASD children and ND children. Longitudinal studies are needed to confirm whether the AEF latencies diverge with age, starting at around 3 years, in these 2 groups of children.

Brain Stem Auditory Evoked Response

Brain stem auditory evoked responses (BAER) elicited by bone-conducted click stimuli were studied in 37 subjects. This technique was plagued with problems such as: low amplitude, poor wave configuration, and calibration difficulties. The authors found the technique of limited value in differentiating conductive from neurosensory hearing disorders in all but severely affected subjects. It can, however, evaluate cochlear function in the presence of a known severe conductive hearing loss, ie, external ear atresia. If an abnormal bone-conducted BAER is obtained the etiology of this abnormality (cochlear vs. retrocochlear) cannot be ascertained because a wave I is rarely elicited in individuals with neurosensory hearing disorders. In subjects with a severe conductive hearing loss, air-conduction elicited markedly prolonged wave V latencies. Such a marked prolongation was not observed in individuals with peripheral neurosensory loss and when present signified that a subject had a major conductive component to his hearing disorder. The authors also believe that all control subjects should be established as normal with an audiogram and not by an otologic history or auditory (subjective) click thresholds.

Elicitation of the Acoustic Change Complex to Long-Duration Speech Stimuli in Four-Month-Old Infants

The acoustic change complex (ACC) is an auditory-evoked potential elicited to changes within an ongoing stimulus that indicates discrimination at the level of the auditory cortex. Only a few studies to date have attempted to record ACCs in young infants. The purpose of the present study was to investigate the elicitation of ACCs to long-duration speech stimuli in English-learning 4-month-old infants. ACCs were elicited to consonant contrasts made up of two concatenated speech tokens. The stimuli included native dental-dental /dada/ and dental-labial /daba/ contrasts and a nonnative Hindi dental-retroflex /daDa/ contrast. Each consonant-vowel speech token was 410 ms in duration. Slow cortical responses were recorded to the onset of the stimulus and to the acoustic change from /da/ to either /ba/ or /Da/ within the stimulus with significantly prolonged latencies compared with adults. ACCs were reliably elicited for all stimulus conditions with more robust morphology compared with our previous findings using stimuli that were shorter in duration. The P1 amplitudes elicited to the acoustic change in /daba/ and /daDa/ were significantly larger compared to /dada/ supporting that the brain discriminated between the speech tokens. These findings provide further evidence for the use of ACCs as an index of discrimination ability.

The maturation of auditory responses in infants and young children: a cross-sectional study from 6 to 59 months

Background: An understanding of the maturation of auditory cortex responses in typically developing infants and toddlers is needed to later identify auditory processing abnormalities in infants at risk for neurodevelopmental disorders. The availability of infant and young child magnetoencephalography (MEG) systems may now provide near optimal assessment of left and right hemisphere auditory neuromagnetic responses in young populations. To assess the performance of a novel whole-head infant MEG system, a cross-sectional study examined the maturation of left and right auditory cortex responses in children 6- to 59-months of age.

Methods: Blocks of 1000 Hz (1st and 3rd blocks) and 500 Hz tones (2nd block) were presented while MEG data were recorded using an infant/young child biomagnetometer (Artemis 123). Data were obtained from 29 children (11 males; 6- to 59-months). Latency measures were obtained for the first positive-to-negative evoked response waveform complex in each hemisphere. Latency and age associations as well as frequency and hemisphere latency differences were examined. For the 1000 Hz tone, measures of reliability were computed.

Results: For the first response—a response with a “P2m” topography—latencies decreased as a function of age. For the second response—a response with a “N2m” topography—no N2m latency and age relationships were observed. A main effect of tone frequency showed earlier P2m responses for 1st 1000 Hz (150 ms) and 2nd 1000 Hz (148 ms) vs. 500 Hz tones (162 ms). A significant main effect of hemisphere showed earlier N2m responses for 2nd 1000 Hz (226 ms) vs. 1st 1000 Hz (241 ms) vs. 500 Hz tones (265 ms). P2m and N2m interclass correlation coefficient latency findings were as follows: left P2m (0.72, p < 0.001), right P2m (0.84, p < 0.001), left N2m (0.77, p < 0.001), and right N2m (0.77,p < 0.01).

Conclusions: Findings of strong age and latency associations, sensitivity to tone frequency, and good test-retest reliability support the viability of longitudinal infant MEG studies that include younger as well as older participants as well as studies examining auditory processing abnormalities in infants at risk for neurodevelopmental disorders.

Objective measurement of high-level auditory cortical function in children

OBJECTIVE

This study examined whether the N2 latency of the cortical auditory evoked potential (CAEP) could be used as an objective indicator of temporal processing ability in normally hearing children.

METHODS

The N2 latency was evoked using three temporal processing paradigms: (1) differences in voice-onset-times (VOTs); (2) speech-in-noise using the CV/da/embedded in broadband noise (BBN) with varying signal-to-noise ratios (SNRs); and (3) 16Hz amplitude-modulated (AM) BBN presented (i) alone and (ii) following an unmodulated BBN, using four modulation depths. Thirty-four school-aged children with normal hearing, speech, language and reading were stratified into two groups: 5-7 years (n=13) and 8-12 years (n=21).

RESULTS

The N2 latency shifted significantly and systematically with differences in VOT and SNR, and was significantly different in the two AM-BBN conditions.

CONCLUSIONS

For children without an N1 peak in the cortical waveform, the N2 peak can be used as a sensitive measure of temporal processing for these stimuli.

SIGNIFICANCE

N2 latency of the CAEP can be used as an objective measure of temporal processing ability in a paediatric population with temporal processing disorder who are difficult to assess via behavioural response.

Maturation of cortical auditory evoked potentials (CAEPs) to speech recorded from frontocentral and temporal sites: three months to eight years of age

The goal of the current analysis was to examine the maturation of cortical auditory evoked potentials (CAEPs) from three months of age to eight years of age. The superior frontal positive-negative-positive sequence (P1, N2, P2) and the temporal site, negative-positive-negative sequence (possibly, Na, Ta, Tb of the T-complex) were examined. Event-related potentials were recorded from 63 scalp sites to a 250-ms vowel. Amplitude and latency of peaks were measured at left and right frontal sites (near Fz) and at left and right temporal sites (T7 and T8). In addition, the largest peak (typically corresponding to P1) was selected from global field power (GFP). The results revealed a large positive peak (P1) easily identified at frontal sites across all ages. The N2 emerged after 6 months of age and the following P2 between 8 and 30 months of age. The latencies of these peaks decreased exponentially with the most rapid decrease observed for P1. For amplitude, only P1 showed a clear relationship with age, becoming more positive in a somewhat linear fashion. At the temporal sites only a negative peak, which might be Na, was clearly observed at both left and right sites in children older than 14 months and peaking between 100 and 200 ms. P1 measures at frontal sites and Na peak latencies were moderately correlated. The temporal negative peak latency showed a different maturational timecourse (linear in nature) than the P1 peak, suggesting at least partial independence. Distinct Ta (positive) and Tb (negative) peaks, following Na and peaking between 120 and 220 ms were not consistently found in most age groups of children, except Ta which was present in 7 year olds. Future research, which includes manipulation of stimulus factors, and use of modeling techniques will be needed to explain the apparent, protracted maturation of the temporal site measures in the current study.

Dynamics of infant cortical auditory evoked potentials (CAEPs) for tone and speech tokens

OBJECTIVES

Cortical auditory evoked potentials (CAEPs) to tones and speech sounds were obtained in infants to: (1) further knowledge of auditory development above the level of the brainstem during the first year of life; (2) establish CAEP input-output functions for tonal and speech stimuli as a function of stimulus level and (3) elaborate the data-base that establishes CAEP in infants tested while awake using clinically relevant stimuli, thus providing methodology that would have translation to pediatric audiological assessment. Hypotheses concerning CAEP development were that the latency and amplitude input-output functions would reflect immaturity in encoding stimulus level. In a second experiment, infants were tested with the same stimuli used to evoke the CAEPs. Thresholds for these stimuli were determined using observer-based psychophysical techniques. The hypothesis was that the behavioral thresholds would be correlated with CAEP input-output functions because of shared cortical response areas known to be active in sound detection.

DESIGN

36 infants, between the ages of 4 and 12 months (mean=8 months, s.d.=1.8 months) and 9 young adults (mean age 21 years) with normal hearing were tested. First, CAEPs amplitude and latency input-output functions were obtained for 4 tone bursts and 7 speech tokens. The tone bursts stimuli were 50 ms tokens of pure tones at 0.5, 1.0, 2.0 and 4.0 kHz. The speech sound tokens, /a/, /i/, /o/, /u/, /m/, /s/, and /∫/, were created from natural speech samples and were also 50 ms in duration. CAEPs were obtained for tone burst and speech token stimuli at 10 dB level decrements in descending order from 70 dB SPL. All CAEP tests were completed while the infants were awake and engaged in quiet play. For the second experiment, observer-based psychophysical methods were used to establish perceptual threshold for the same speech sound and tone tokens.

RESULTS

Infant CAEP component latencies were prolonged by 100-150 ms in comparison to adults. CAEP latency-intensity input output functions were steeper in infants compared to adults. CAEP amplitude growth functions with respect to stimulus SPL are adult-like at this age, particularly for the earliest component, P1-N1. Infant perceptual thresholds were elevated with respect to those found in adults. Furthermore, perceptual thresholds were higher, on average, than levels at which CAEPs could be obtained. When CAEP amplitudes were plotted with respect to perceptual threshold (dB SL), the infant CAEP amplitude growth slopes were steeper than in adults.

CONCLUSIONS

Although CAEP latencies indicate immaturity in neural transmission at the level of the cortex, amplitude growth with respect to stimulus SPL is adult-like at this age, particularly for the earliest component, P1-N1. The latency and amplitude input-output functions may provide additional information as to how infants perceive stimulus level. The reasons for the discrepancy between electrophysiologic and perceptual threshold may be due to immaturity in perceptual temporal resolution abilities and the broad-band listening strategy employed by infants. The findings from the current study can be translated to the clinical setting. It is possible to use tonal or speech sound tokens to evoke CAEPs in an awake, passively alert infant, and thus determine whether these sounds activate the auditory cortex. This could be beneficial in the verification of hearing aid or cochlear implant benefit.

Potencial evocado auditivo de longa latência para estímulo de fala apresentado com diferentes transdutores em crianças ouvintes

Objetivo: analisar, de forma comparativa, a influência do transdutor no registro dos componentes P1, N1 e P2 eliciados por estímulo de fala, quanto à latência e à amplitude, em crianças ouvintes. Método: 30 crianças ouvintes de quatro a 12 anos de idade, de ambos os sexos. Os potenciais evocados auditivos de longa latência foram pesquisados por meio dos transdutores, fone de inserção e caixa acústica, eliciados por estímulo de fala /da/, sendo o intervalo interestímulos de 526ms, a intensidade de 70dBNA e a taxa de apresentação de 1,9 estímulos por segundo. Foram analisados os componentes P1, N1 e P2 quando presentes, quanto à latência e à amplitude. Resultados: constatou-se um nível de concordância forte entre a pesquisadora e o juiz. Não houve diferença estatisticamente significante ao comparar os valores de latência e amplitude dos componentes P1, N1 e P2, ao considerar sexo e orelha, assim como para a latência dos componentes quando analisado os tipos de transdutores. Entretanto, houve diferença estatisticamente significante para a amplitude dos componentes P1 e N1, com maior amplitude para o transdutor caixa acústica. Conclusão: os valores de latência dos componentes P1, N1 e P2 e amplitude de P2 obtidos com fone de inserção podem ser utilizados como referência de normalidade independente do transdutor utilizado para a pesquisa dos potenciais evocados auditivos de longa latência.

Maturation of auditory evoked potentials from 6 to 48 months: prediction to 3 and 4 year language and cognitive abilities

OBJECTIVE

To investigate the maturation of long-latency auditory evoked potentials (LLAEP) from 6 to 48 months in infants with a family history of language impairment (FH+) and control infants (FH-).

METHODS

LLAEPs of seventeen FH+ infants were compared to 28 FH- infants at 6, 9, 12, 16, 24, 36 and 48 months. Participants received a passive oddball paradigm using fast- and slow-rate non-linguistic auditory stimuli and at 36 and 48 months completed a battery of standardized language and cognitive tests.

RESULTS

Overall, the morphology of LLAEP responses differed for fast- versus slow-rate stimuli. Significant age-related changes in latency and amplitude were observed. Group differences, favoring FH- infants, in the rate of maturation of LLAEPs were found. Responses to fast-rate stimuli predicted language abilities at 36 and 48 months of age.

CONCLUSIONS

The development of LLAEP in FH+ children is modulated by differences in the rate of maturation as well as variations in temporal processing abilities.

SIGNIFICANCE

These findings provide evidence for the role of non-linguistic auditory processes in early language development and illustrate the utility of using a perceptual-processing skills model to further our understanding of the precursors of language development and impairment.

The human auditory system: A timeline of development

This review traces the structural maturation of the human auditory system, and compares the timeline of anatomical development with cotemporaneous physiological and behavioral events. During the embryonic period, there is formation of basic structure at all levels of the system, i.e. the inner ear, the brainstem pathway, and the cortex. The second trimester is a time of rapid growth and development, and by the end of this period, the cochlea has acquired a very adult-like configuration. During the perinatal period, the brainstem reaches a mature state, and brainstem activity is reflected in behavioral responses to sound, including phonetic discrimination, and in evoked brainstem and early middle latency responses. The perinatal period is also the time of peak development of brainstem input to the cortex through the marginal layer, and of the long latency cortical potentials, the N(2) and mismatch negativity. In early childhood, from the sixth post-natal month to age five, there is progressive maturation of the thalamic projections to the cortex and of the longer latency Pa and P(1) evoked potentials. Later childhood, from six to twelve years, is the time of maturation of the superficial cortical layers and their intracortical connections, accompanied by appearance of the N(1) potential and improved linguistic discriminative abilities. Some consideration is given to the potential negative effects of deafness-induced sound deprivation during the perinatal period and childhood.

P300- long-latency auditory evoked potential in normal hearing subjects: simultaneous recording value in Fz and Cz

The P300 is and auditory Evoked Potential, called endogenous potential because it reflects the functional use the individual makes of the auditory stimulus, being highly dependent on cognitive skills; among them we list attention and auditory discrimination. It is a procedure of objective evaluation; however, one that depends on the examiner's experience to detect wave peaks, and it is important to use recording methods that facilitate the response presence analysis and result interpretation.

Aim

to analyze the P300 Long Latency Auditory Evoked Potential obtained through the use of two active electrodes positioned on Fz and Cz.

Materials and Methods

330 individuals from both genders and age ranging between 7 and 34 years participated in this study, they all had normal hearing and did not have any risk factor for mental problems.

Results

Results show that there was no statistically significant difference for N2 and P3 latency and P3 amplitude as far as gender is concerned, nor correlation with the individual's age. There was a strong correlation of these measures with Fz and Cz electrode positioning.

Conclusion

Fz and Cz active electrodes positioning can be considered one more resource to help in the P300 clinical analysis.

The maturation of human evoked brain potentials to sounds presented at different stimulus rates

The current study assessed the normal development of cortical auditory evoked potentials (CAEPs) in humans presented with pure tone stimuli at relatively fast stimulus rates. Traditionally, maturation of sound processing indexed by CAEPs has been studied in paradigms using inter-stimulus intervals (ISIs) generally slower than 1 Hz. While long ISIs may enhance the amplitude of CAEP components, speech information generally occurs at more rapid rates. These slower rates of sound presentation may not accurately assess auditory cortical functions in more realistic sound environments. We examined the effect of temporal rate on the elicitation of the P1-N1-P2-N2 components to unattended sounds at four levels of stimulus onset asynchrony (SOA, onset to onset, 200, 400, 600, and 800 ms) in children grouped separately by year (ages 8, 9, 10, 11 years), in adolescents (age 16 years) and in one group of young adults (ages 22-40 years). We found that both age and stimulus rate produced profound changes in CAEP morphology. Between the ages of 8-11 years, the P1 and N2 components dominated the ERP waveform at all stimulus rates. N1, the dominant CAEP component in adults, appeared as a bifurcation in a broad positive peak at earlier ages, and did not emerge as a separate component until adolescence. While the P1-N1-P2 components are more "adult-like" than "child-like" in the adolescent subjects, the N2 component, a hallmark of the child obligatory response, was still present. Faster rates resulted in the suppression of discrete components such that by 200 ms, only P1 in the adults and adolescents, and both P1 and N2 in the youngest children were discernable. We conclude that both age and ISI are important variables in the assessment of auditory cortex function and maturation. The presence of N2 in adolescents indicates that auditory cortical maturation persists into teen years.

Effects of auditory pathway anatomy and deafness characteristics? Part 2: On electrically evoked late auditory responses

The purpose of this study was to distinguish the effects of different parameters on latencies of wave N1, wave P2, and inter-peak interval N1-P2 of electrical late auditory responses (ELARs). ELARs were recorded from four intra-cochlear electrodes in fourteen adult HiRes90K cochlear implant users who had at least three months of experience. The relationship between latencies and stimulation sites in the cochlea was characterized to assess the influence of the auditory pathway anatomy on ELARs, i.e., whether the speed of neural propagation varies according to the place that is activated in the cochlea. Audiograms before implantation, duration of deafness, and psychophysics at first fitting were used to describe the influence of deafness characteristics on latencies. The stimulation sites were found to have no effect on ELAR latency and, while there was no influence of psychophysics on latency, a strong relationship was shown with duration of deafness and the pre-implantation audiogram. Thus, ELAR latency was longer for poorer audiograms and longer durations of deafness and this relationship appeared to be independent of stimulation parameters such as stimulation site. Comparison between these findings and those from the equivalent study on EABR waves IIIe and Ve latency [Guiraud, J., Gallego, S., Arnold, L., Boyle, P., Truy, E., Collet, L., 2007. Effects of auditory pathway anatomy and deafness characteristics? (1): On electrically evoked auditory brainstem responses. Hear. Res. 223 (1-2), 48-60] shows that, while ELAR and EABR latencies are related with parameters that reflect the integrity of the auditory pathway, ELAR latency is less dependent on stimulation parameters than EABR latency.

Maturation of the cortical auditory evoked potential in infants and young children

The aim of this study was to evaluate the maturation of the cortical auditory evoked potential (CAEP) in humans. The participants in this experiment were 10 newborns (<7 days), 19 toddlers (13-41 months), 20 children (4-6 years) and 9 adults (18-45 years). CAEPs were obtained in response to low (400 Hz) and high (3000 Hz) tones and to the word token /baed/, all presented at 60 dB HL, at a rate of 0.22 Hz. Latency and amplitude measures were made for CAEP components P1, N1, P2 and N2 as a function of participant age, stimulus type and electrode montage. CAEP component latencies were relatively stable from birth to 6 years, but adults demonstrated significantly shorter latencies compared to infants and children. Components P1 and N2 decreased in amplitude, while components N1 and P2 increased in amplitude from birth to adulthood. Words evoked significantly larger CAEPs in newborns compared to responses evoked by tones, but in other age groups the effects of stimulus type on component amplitudes and latencies were less consistent. There was evidence of immature tonotopic organisation of the generators of N1 when responses from infants and young children were compared to those of adults. The scalp distribution of components N1 and P2 was clearly different in newborns and toddlers compared to children and adults. In the younger groups, both N1 and P2 were uniformly distributed across the scalp but in children and adults these components showed more focal distributions, with evidence of response laterality increasing with maturity. The results of the present study describe, for the first time, CAEPs recorded from multiple scalp electrodes, for tones and speech stimuli, in infants and children from birth to 6 years of age. Frequency-related differences in component amplitude were apparent at all ages reflecting development of tonotopic organisation of the CAEP neural generators.

Prenatal impairment of brain serotonergic transmission in infants

OBJECTIVE

To evaluate whether the free fraction of L-tryptophan (L-Trp) and the N1/P2 component of the auditory evoked potentials (AEPs) are associated with impaired brain serotonin neurotransmission in infants with intrauterine growth restriction (IUGR).

STUDY DESIGN

We measured free, bound, and total plasma L-Trp and recorded the N1/P2 component of AEP in a prospective, longitudinal, and comparative study comparing IUGR and control infants.

RESULTS

Plasma free L-Trp was increased and the amplitude of N1/P2 component was significantly decreased in IUGR relative to control infants. The free fraction of L-Trp and N1/P2 component had a negative association.

CONCLUSIONS

In newborns with IUGR, the changes in measured plasma free fraction of L-Trp and in the amplitude the N1/P2 component of the AEP suggest an inverse association between free L-Trp and components of the AEP. The changes observed in the free fraction of L-Trp and AEP may be causally associated with brain serotonergic activity in utero. In IUGR, epigenetic factors such as stress-induced disturbances in brain serotonin metabolism or serotonergic activity, identifiable by alterations in AEP, influence cerebral sensory cortex development and may be causally associated with serotonin-related disorders in adulthood.

Cortical auditory evoked potentials in autism: a review

The question of etiology in autism remains elusive primarily due to the fact that autism does not result from a single dysfunction but is multi-faceted in nature. Investigations into etiology have ranged from identifying abnormalities in the genome to describing structural/functional brain abnormalities. Bearing in mind the risk of over-simplification, there is still utility in isolating a specific deficit to examine its etiologic contribution. It is known that individuals with autism have difficulty processing auditory information at the cortical level but this is not consistently seen subcortically. In recent years, cortical auditory processing has been extensively researched using event-related potentials (ERPs); however, these results in relation to autism have not been reviewed. This paper will examine this literature and discuss implications for future research.

Maturational effects on newborn ERPs measured in the mismatch negativity paradigm

The mismatch negativity (MMN) component of event-related potentials (ERPs), a measure of passive change detection, is suggested to develop early in comparison to other ERP components, and an MMN-like response has been measured even from preterm infants. The MMN response in adults is negative in polarity at about 150-200 ms. However, the response measured in a typical MMN paradigm can also be markedly different in newborns, even opposite in polarity. This has been suggested to be related to maturational factors. To verify that suggestion, we measured ERPs of 21 newborns during quiet sleep to rarely occurring deviant tones of 1100 Hz (probability 12%) embedded among repeated standard tones of 1000 Hz in an oddball sequence. Gestational age (GA) and two cardiac measures, vagal tone (V) and heart period (HP), were used as measures of maturation. GA and HP explained between 36% and 42% of the total variance of the individual ERP peak amplitude (the largest deflection of the difference wave at a time window of 150-375 ms) at different scalp locations. In the discriminant function analyses, GA and HP as classifying variables differentiated infants in whom the peak of the difference wave had positive polarity from those with a negative polarity at an accuracy level ranging from 72% to 91%. These results demonstrate that during quiet sleep, maturational factors explain a significant portion of the ERP difference wave amplitude in terms of its polarity, indicating that the more mature the ERPs are, the more positive the amplitude. The present study suggests that maturational effects should be taken into account in ERP measurements using MMN paradigms with young infants.

Age and task parameters in continuous performance tests for preschoolers

66 children (M=56.2 mo., SD=10.9), recruited from preschool and daycare centers, were administered two continuous performance tests, one auditory and one visual. Both tests utilized a format with one target and one nontarget. Interstimulus interval was fixed at 1350 msec. for the visual test and 5000 msec. for the auditory test. The visual test produced greater rates of omission and commission errors than the auditory test. Age was significantly related to mean reaction time and response variability for both tests; however, the visual test produced an unexpected pattern of increasing response time across age groups. On both tests omission rates improved significantly with age, while commission rates were consistent across ages 3-6 years. When considering continuous performance test paradigms for preschoolers, 3-yr.-olds may need at least a 4000-msec. interstimulus interval to make a choice for the stimulus cue. Hits following an interstimulus interval shorter than 1400 msec. may reflect younger preschoolers' response to a previous stimulus.

Early postnatal development of sensory gating

Sensory gating represents the nervous system's ability to inhibit responding to irrelevant environmental stimuli. In order to characterize the early development of acoustic sensory gating, suppression of auditory evoked potential component P1 (i.e. P50) in response to paired clicks was measured during REM sleep in healthy infants (1-4 months) that were without genetic risk for disrupted sensory gating function (i.e. having a relative with schizophrenia). As a group, the subjects exhibited significant response suppression. A correlation between increasing age and stronger response suppression was uncovered, even within this restricted age range. Parallel changes in sleep physiology could not be ruled out as the explanation for this change. Nevertheless, these results demonstrate that the neural circuits underlying sensory gating are functional very early in postnatal development.

Maturation of the auditory event-related potentials during the first year of life

This study examined the maturation of cortical auditory event-related potentials (ERPs) from birth until 12 months of age. In the 15 infants studied, all ERP peaks observable at 12 months of age, the P150, N250, P350, and N450 were identifiable already at birth, As in previous studies, the amplitudes of the ERP peaks increased and latencies shortened with increasing age. In addition, the time courses of the amplitude growth of these peaks differed from each other. It was concluded, that the generators of all the infantile ERP peaks are functional already at birth, and that the maturational changes in the waveform morphology can mostly be accounted for by the changing relative strengths of the different generators.

Developmental changes in P1 and N1 central auditory responses elicited by consonant-vowel syllables

Normal maturation and functioning of the central auditory system affects the development of speech perception and oral language capabilities. This study examined maturation of central auditory pathways as reflected by age-related changes in the P1/N1 components of the auditory evoked potential (AEP). A synthesized consonant-vowel syllable (ba) was used to elicit cortical AEPs in 86 normal children ranging in age from 6 to 15 years and ten normal adults. Distinct age-related changes were observed in the morphology of the AEP waveform. The adult response consists of a prominent negativity (N1) at about 100 ms, preceded by a smaller P1 component at about 50 ms. In contrast, the child response is characterized by a large P1 response at about 100 ms. This wave decreases significantly in latency and amplitude up to about 20 years of age. In children, P1 is followed by a broad negativity at about 200 ms which we term N1b. Many subjects (especially older children) also show an earlier negativity (N1a). Both N1a and N1b latencies decrease significantly with age. Amplitudes of N1a and N1b do not show significant age-related changes. All children have the N1b; however, the frequency of occurrence of N1a increases with age. Data indicate that the child P1 develops systematically into the adult response; however, the relationship of N1a and N1b to the adult N1 is unclear. These results indicate that maturational changes in the central auditory system are complex and extend well into the second decade of life.

Maturation of human cortical auditory function: differences between normal-hearing children and children with cochlear implants

OBJECTIVE

We investigated maturation of cortical auditory function in normal-hearing children and in children who receive stimulation of their auditory system through a cochlear implant.

DESIGN

As a measure of cortical auditory function, auditory evoked responses (AERs) were recorded from normal-hearing children and adults as well as from children and adults fitted with a cochlear implant. Morphological and latency changes for evoked responses recorded at electrode Cz are reported.

RESULTS

For normal-hearing children, there is a gradual evolution of AER features that extends through adolescence, with P1 latency becoming adult-like in the late teens. Latency changes for P1 occur at the same rate for implanted children, but the overall maturation sequence is delayed. By extrapolation from the existing data, the age at which P1 latency becomes adult-like is delayed by approximately 5 yr for the implanted population. Other typical features of the AER, namely N1 and P2, are either delayed in developing or absent in the implanted children.

CONCLUSIONS

These preliminary findings suggest both similarities and differences in cortical auditory maturation for normal-hearing and implanted children. For implanted children, the 5 yr delay for maturation of P1 latency roughly corresponds to the average 4.5 yr interval between the onset of deafness and the time of implantation. These findings suggest that during the period of deafness, maturation of cortical auditory function does not progress. However, some, if not all, maturational processes resume after stimulation is reintroduced.

Topography of auditory evoked long-latency potentials in normal children, with particular reference to the N1 component

Topographic maps of late auditory evoked potentials were obtained with the Brain Atlas III system in 34 healthy, normal hearing children aged 8-16 years. The stimulus was a 100 msec, 500 Hz tone burst, presented separately to the left and right ears, at 75 dB HL. The resulting auditory evoked potentials showed a prominent N1, after about 100 msec, and a topographic map with a corresponding fronto-lateral focus designated as the focus of N1 (FN1). Foci with varying positions and amplitudes were identified in 33 of 34 subjects after left ear stimulation and in 29 of 32 subjects after right ear stimulation. The topography showed a high degree of stability in most subjects, with the position of the negative "peak" of FN1 in front of the interaural line and with a dominance contralateral to the ear stimulated. There was a significant decrease in the latency of N1 with increasing age. FN1 tended to change position with age and some differences from adults were also observed. In conclusion, a distinct topographic pattern of the N1 component of the late auditory evoked potentials was seen in the majority of children. It remains to be established to what extent this method may be clinically useful for disclosing functional disturbances in the central auditory pathways.

Evoked potentials in full-term and premature infants: a comparative study

In this study the maturation of the central nervous system of full-term and premature infants were investigated electrophysiologically. The subjects were 16 full-term and 15 premature infants. Neurologic examination, psychometric tests, and measurement of evoked potentials were carried out periodically in babies who had no birth trauma, metabolic disorder, or intrauterine infection. Neurophysiologic comparison of the results was evaluated. As the babies grew older, I-V interpeak latency became shorter according to the results of brainstem auditory evoked potentials; N1-P1 amplitude became higher and P1 latency shorter according to the results of visual evoked potentials. Central nervous system maturation of full-term babies and prematures appear to be alike at 6 months of age.

Hemispheric asymmetry of late auditory evoked response induced by pitch changes in infants: influence of sleep stages

Late auditory evoked potentials (LAEPs) have been recorded in response to a 1000 Hz standard (occurrence 80%) or a 2000 Hz deviant (occurrence 20%) tone on the left (T3) and right (T4) temporal scalp in 6-week-old full-term newborns during pure quiet or active sleep states. Sleep states were premanently controlled by polygraphic recording including EEG, EOG, EMG, EKG and respiratory movements. During quiet sleep LAEPs consisted of a clear polygraphic response: N1-P2-N2-P3. Mean latencies ranges on T3 and T4 were: N1 = 28-70 ms; P2 = 343-407 ms; N2 = 966-1178 ms; and P3 = 1461-1492 ms. During active sleep LAEPs consisted of a N1-P2-N2 response. Mean latency ranges on T3 and T4 were: N1 = 36-79 ms; P2 = 278-304 ms; N2 = 555-620 ms. N2 latency was significantly shorter in AS than in QS. Amplitude of the N1-P2-N2 complex was significantly lower during active sleep. In response to standard stimuli, mean amplitudes and latencies of the LAEP were similar on T3 and T4 during active or quiet sleep states. In response to deviant stimuli mean amplitude of the N1-P2-N2 complex was significantly higher and mean latencies of N1 and N2 were significantly shorter on T3 during quiet sleep. No significant difference was observed during active sleep. These results confirm that sleep stages have a considerable influence on cortical auditory pathways. The auditory message is amplified during quiet sleep and inhibited during active sleep. Therefore sleep states need to be controlled to analyze LAEPs in young children.(ABSTRACT TRUNCATED AT 250 WORDS)

Middle-latency somatosensory evoked potentials following median and posterior tibial nerve stimulation in Down's syndrome

Middle-latency somatosensory evoked potentials (SEPs) following median and posterior tibial nerve stimulation were studied in 40 patients with Down's syndrome and in age- and gender-matched healthy controls as well as in middle-aged and aged healthy subjects. In median nerve SEPs, latencies of the initial cortical potentials, N18 and P18, showed no significant difference, but the following potentials N22, P25, N32, P41 and P46 were relatively or significantly shorter in latency in Down's patients than in the controls. Amplitudes of all components in Down's patients were significantly larger than those of age- and gender-matched controls as well as of those of middle-aged healthy subjects, but there was only a small difference in their amplitudes from aged healthy subjects. Results of posterior tibial nerve SEPs were generally consistent with those of median nerve SEPs. Therefore, 'short latency with large amplitude' is the main characteristic of middle-latency SEPs in Down's syndrome, possibly related to accelerated physiological aging of the central nervous system.

Detectability of auditory evoked response components in preterm infants

In determining the detectability of brainstem, middle latency and cortical auditory evoked responses in preterm newborns, one has to deal with the ongoing maturation of the auditory system. In the preterm period the detectability of evoked responses is closely related to the appearance of the individual evoked response components. The detectability of the individual evoked response components in preterm infants is important, because low detectability rates make the absence of a particular evoked response component irrelevant with respect to the clinical-neurophysiological correlation. In a longitudinal study we determined the detectability and cumulative detectability, i.e. the presence of individual evoked response components in one or more recordings of evoked response components in 37 low risk preterm infants between 30 and 41 weeks conceptional age (CA). On the basis of their detectability it is concluded that evoked response components, determined between 30 and 34 weeks CA, are generally of limited use for clinical application, except for auditory brainstem response (ABR) components I, IIn, V and Vc and middle latency response (MLR) component Na. Our study made clear that improvement can be achieved by performing more than one examination within a period of approximately 4 weeks between the recording sessions. The cumulative detectability rates after two recordings showed improvement for all components involved in this study. The cumulative detectability rates of ABR components I, II, IIN, III, V, IIc, IIINc, Vc, MLR components Na and P0, and auditory cortical response (ACR) components PbP1 and N2p are sufficient to use as measures in the neurophysiological judgement of functional integrity of the central auditory pathway in preterm infants.

Electrophysiological effects of fenfluramine or combined vitamin B6 and magnesium on children with autistic behaviour

The authors compared the effects of fenfluramine or combined vitamin B6 and magnesium treatment on the evoked potential conditioning of 12 children whose autistic behaviour had improved clinically following treatment. The children who were clinically sensitive to combined vitamin B6 and magnesium developed a conditioning phenomenon and the fenfluramine-sensitive children showed an enhancement of the Cz evoked response amplitude. Results are discussed with reference to behaviour modifications observed during treatment.

Psychomotor and mental development during infancy. Relation to psychosocial conditions and health. Part IV of a longitudinal study of children in a new Stockholm suburb

This article presents the fourth substudy in a Swedish research project of a birth cohort of children in a newly-built Stockholm suburb. The aims are to follow and to describe their mental development by prospective methods. Here we present the results of the one-year follow-up. The children's mental development, measured with the Griffiths' Development Scales, and their behaviour in the test situation and during the home visit are described. These results are related to various psychosocial background factors (such as the parents' ages, number of siblings, form of custody), home environment factors (the parents' mental disease, addictions and criminality) and the children's physical health and development. Children with deviant behaviour during the home visits are described separately. Of 640 women who paid their first visit to the maternal welfare centers in a new Stockholm suburb during one prospective year, 532 (85%) were interviewed with regard to 41 stress factors forming a "Life stress score" (LSS). The interviews were supplemented with data from hospital, social welfare and police records concerning the expectant mother and the father. The 532 mothers were divided into three groups according to the degree of psychosocial stress (194 without psychosocial stress, 171 with severe psychosocial stress and 167 in an intermediate group). The pregnancies and deliveries of all mothers were evaluated. The physical health and development (using information from the child welfare clinics) and the mental health and development (using information from home visits and testings) were studied during infancy in 452 children (226 boys and 226 girls)--i.e. 77% of all children born in the suburb during the year. The children were tested with the Griffiths' Development Scales and their behaviour during the test was observed on home visits by the same psychologist (L.N.) at the age of 10 months (79 boys, 73 girls) or 14 months (92 boys, 107 girls), or about the age of 18 months (55 boys, 46 girls). The test results are mainly reported by descriptive methods. In summary, the results of the evaluation of the children's mental health during the first year of life, generally showed average developmental quotients. However, 20% of the children had values below the average. Thirty-two per cent of the children with low test results (less than -1 standard deviation on the total test) came from homes with serious psychosocial stress and 29% from homes with a mild degree of psychosocial stress. Of the nine children who had generally very low scores in the Griffiths' evaluation, seven came from homes with psychosocial stress.(ABSTRACT TRUNCATED AT 400 WORDS)

Short-latency somatosensory evoked potentials following median nerve stimulation in Down's syndrome

Short-latency somatosensory evoked potentials (SEPs) following median nerve stimulation were recorded in 42 patients with Down's syndrome and in 42 age- and sex-matched normal subjects. There were no significant differences between the 2 groups in the absolute peak latencies of N9, N11 and N13 components. However, interpeak latencies, N9-N11, N11-N13 and N9-N13, were prolonged significantly in Down's syndrome. These findings suggest impaired impulse conduction in the proximal part of the brachial plexus, posterior roots and/or posterior column-medial lemniscal pathway. Interpeak latency N13-N20, representing conduction time from cervical cord to sensory cortex, was not significantly different between the 2 groups. Cortical potentials N20 and P25 in the parietal area and P20 and N25 in the frontal area were of significantly larger amplitude in Down's syndrome. P25 had double peaks in 16 of 42 normal subjects, but these were not apparent in any of the patients.

The maturation of the central auditory conduction in preterm infants until three months post term. V. The auditory cortical response (ACR)

Auditory cortical evoked responses (ACRs) were recorded in 65 preterm infants, at least on 3 occasions in 48 of them. The infants were divided into 5 groups according to their gestational age (GA). The recording sessions were performed at 8 conceptional age (CA) levels, defined as the gestational age added to the chronological age. The last recordings were obtained at 50-52 weeks CA. The ACRs were analyzed for the primary complex containing middle latency components (MLR) and the secondary complex, containing the slow late components. The ACR records first appear at about 25 weeks CA, initiating the premature stage followed by a transitional stage around term date and the gradual development into the mature stage, achieved at 50-52 weeks CA. The detectability rate of the various components generally increased with increasing conceptional age, for some of the components, especially N2p and N2, this rate achieved a value of about 80%. The degree of prematurity did not influence appreciably the development of the ACR. The waveforms, and to a lesser extent the latency and amplitude values, are strongly age dependent. Remarkable topographic differences between the ACR parameter latency and more importantly amplitude values are found between the derivations from the vertex and the central temporal areas, supporting the theory of different generation sites for the ACR components. The premature and mature ACR appeared relatively insensitive to changes in the states of vigilance. The ACR in premature infants are useful in developmental studies with respect to the central audition in premature infants and might contribute in the clinical assessment on the quality of the premature central auditory system.

Differential maturation of cortical auditory evoked potentials to speech sounds in normal fullterm and very low-birthweight infants

Cortical auditory evoked potentials (AEP) to the consonant-vowel syllables/da/and/ta/and 800Hz tone were recorded at 40 weeks post-conceptional age and at one, two and three months after term in normal fullterm and very low-birthweight infants. As a group, the very low-birthweight infants exhibited significantly less mature AEPs to consonant-vowel syllables than the normal-birthweight infants at 40 weeks post-conceptional age. Consistent but statistically non-significant differences also were found for tones at 40 weeks post-conceptional age, and for all stimuli at one and two months after term. By three months, all the infants exhibited mature AEP morphology and topography.

Sources of variability in auditory brain stem evoked potential measures over time

Auditory brain stem EPs elicited in 10 normal adults by monaural clicks delivered at 72 dB HL, 20/sec showed no significant change in wave latencies or in the ratio of wave I to wave Y amplitude across 250 trial subsets, across 250 trial subsets, across 1500 trial blocks within a test session, or across two test sessions separated by several months. Sources of maximum variability were determined by using mean squared differences with all but one condition constant. 'Subjects' was shown to contribute the most variability followed by 'ears', 'sessions' and 'runs'; collapsing across conditions, wave III latencies were found to be the least variable, while wave II showed the most variability. Some EP morphologies showed extra peaks between waves II and IV, missing wave IV or wave IV fused with wave V. Such variations in wave form morphology were independent of EMG amplitude and were characteristic of certain individuals.

The seed and the soil: effect of dosage, personality and starting state on the response to delta 9 tetrahydrocannabinol in man

1 The effects of two doses of delta 9THC (2.5 and 10 mg), delivered by paced smoking of herbal cigarettes, on CNV magnitude, subjective mood ratings and heart rate were studied in 20 subjects. 2 There were highly significant interactions between drug dosage and Extraversion and Neuroticism scores, so that the direction and degree of response to the different doses of delta 9THC depended on the personality characteristics of the subjects. 3 The effects of 9 mg delta 9THC and placebo, delivered in herbal cigarettes smoked naturally, on smoking behaviour, subjective mood ratings, measures of autonomic activity and auditory and visual cortical evoked responses were compared in 12 subjects. 4 Smoking behaviour, subjective 'high' rating and elevation of heart rates were the most significant discriminators between drug and placebo. The latency of some of the components of the visual evoked responses was also increased by delta 9THC. 5 There was a significant correlation between the effects of delta 9THC on skin conductance reactivity and the basal (pre-drug) level, reactivity increasing after drug in subjects with low basal reactivity and decreasing in those with high basal levels. 6 Both experiments provided clear evidence of dose-dependent biphasic stimulant and depressant actions of delta 9THC on both subjective and objective measures, and these effects were influenced by the personality and the starting state of the subjects.

The evolution of visual and auditory evoked potentials in infants with perinatal disorder

The evolutionary changes of evoked potentials (EPs) were studied from the neonatal period up to 1 year of age in 41 infants with various perinatal disorders. Abnormal EPs in the first week of life recovered quickly. In infants with normal outcome, abnormal EPs became normal within a month. In infants with cerebral palsy (CP) or mental retardation (MR), EPs recovered within 2-3 months of age. Infants with more severe neurological damage showed abnormal EPs even beyond 6 months of age. Abnormal EPs beyond 2 weeks of age indicated poor prognosis. As for the wave form of EPs, absent responses or abnormal wave form reflected more severe brain dysfunction. AEPs tended to show more profound abnormalities than VEP. However, some infants with absent AEP in the first week of life had a favorable prognosis. AEPs seemed to be more easily affected by brain dysfunction.

Plasticity of the developing auditory system

Anatomical, physiological and behavioral data indicate that the auditory system matures from the periphery centrally, ie, centripetally. There is now information which shows that the developing auditory system can be modified by anatomical changes which have their greatest effect during early development. Anatomical, physiological and behavioral changes can also be brought about by the quality of the auditory stimuli which th auditory system experiences. Evidence for the plasticity of the developing auditory system has come from studies of a number of different species. The plasticity of the auditory system is of theoretical and clinical significance.

Brain stem auditory evoked response

A developing method for testing auditory function and detecting neurological disorders is the brain stem auditory evoked response (BAER) to sound stimuli. Elicitation of the BAER is noninvasive and produces an objective measurement of a subject's auditory function. Basic principles of this technique and normative data are presented in this paper. It was found that the BAER can detect asymptomatic high-frequency hearing losses. The sensitivity of this technique makes it an ideal method for evaluating functional hearing losses. Two illustrations of functional hearing losses are presented. Wave V's threshold, latency and amplitude, along with comparisons between the auditory (subjective) and BAER threshold, are useful parameters when testing for nonorganic hearing disorders. However, this sensitivity to minor hearing losses makes it imperative that all control subjects be established as normal by an audiogram. A mere negative history for hearing disorders is felt by the authors to be an inadequate screening of control subjects.