Early development of brainstem auditory evoked potentials in Down's syndrome

Auditory Neural Responses and Communicative Functioning in Children With Microcephaly Related to Congenital Zika Syndrome

OBJECTIVES

Children with microcephaly exhibit neurodevelopmental delays and compromised communicative functioning, yielding challenges for clinical assessment and informed intervention. This study characterized auditory neural function and communication abilities in children with microcephaly due to congenital Zika syndrome (CZS).

DESIGN

Click-evoked auditory brainstem responses (ABR) at fast and slow stimulation rates and natural speech-evoked cortical auditory evoked potentials (CAEP) were recorded in 25 Brazilian children with microcephaly related to CZS ( M age: 5.93 ± 0.62 years) and a comparison group of 25 healthy children ( M age: 5.59 ± 0.80 years) matched on age, sex, ethnicity, and socioeconomic status. Communication abilities in daily life were evaluated using caregiver reports on Vineland Adaptive Behavior Scales-3.

RESULTS

Caregivers of children with microcephaly reported significantly lower than typical adaptive functioning in the communication and socialization domains. ABR wave I latency did not differ significantly between the groups, suggesting comparable peripheral auditory function. ABR wave V absolute latency and waves I-V interwave latency were significantly shorter in the microcephaly group for both ears and rates. CAEP analyses identified reduced N2 amplitudes in children with microcephaly as well as limited evidence of speech sound differentiation, evidenced mainly by the N2 response latency. Conversely, in the comparison group, speech sound differences were observed for both the P1 and N2 latencies. Exploratory analyses in the microcephaly group indicated that more adaptive communication was associated with greater speech sound differences in the P1 and N2 amplitudes. The trimester of virus exposure did not have an effect on the ABRs or CAEPs.

CONCLUSIONS

Microcephaly related to CZS is associated with alterations in subcortical and cortical auditory neural function. Reduced ABR latencies differ from previous reports, possibly due to the older age of this cohort and careful assessment of peripheral auditory function. Cortical speech sound detection and differentiation are present but reduced in children with microcephaly. Associations between communication performance in daily life and CAEPs highlight the value of auditory evoked potentials in assessing clinical populations with significant neurodevelopmental disabilities.

The challenge of a mature final diagnosis of hearing loss severity and early cochlear implantation

PURPOSE

Despite the recent trend of cochlear implantation (CI) at the age of six or even four months is prevalent in many centers around the world, clinicians should be cautious because perinatal risk factors of auditory neuropathy and/or delayed maturation carry the possibility of reversible hearing loss, yielding better auditory performance at the age of one year. The purpose of this study is to raise awareness that early CI may not be universal for all patients. In addition, we specify the factors to be considered in the pre-operative evaluation of CI in infants younger than one year.

METHODS AND RESULTS

This study describes four cases provisionally diagnosed with severe to profound sensorineural hearing loss that were presented to the CI clinic to determine candidacy for implantation. Two cases had histories of prematurity, one had Down syndrome, and one had a family history of hearing loss. None of the study cases were candidates for CI, as they had varying degrees of hearing improvement.

CONCLUSION

Although early CI may yield better auditory performance, the final diagnosis should be made only after repeated subjective and objective measurements as well as family feedback on the child's auditory performance, especially in preterm children. Early auditory brainstem response (ABR) prior to the age of one year in children with cognitive, neurologic, or developmental comorbidities should be interpreted with caution, as ABR "alone" could not accurately represent the child's true hearing ability in this patient population.

The Effects of Different Exteroceptive Experiences on the Early Motor Repertoire in Infants With Down Syndrome

OBJECTIVE

Down syndrome is a chromosomal abnormality in which muscle tone, motor development, and sensory systems are affected. The objectives of this study were to examine the changes in movements and postures of 3- to 5-month-old infants with Down syndrome and infants who were neurotypical controls during exposure to a rough-textured surface and to compare the differences occurring before and during an exteroceptive condition that was different between the 2 groups.

METHODS

In this quasi-experimental study, participants were 20 infants with Down syndrome (8 female infants; age range = 10-18 weeks, mean [SD] = 12 weeks 2 days [2 weeks 2 days]) and 20 age-matched infants with typical development (8 female infants; age range = 9-17 weeks, mean (SD) = 12 weeks 6 days [1 week 5 days]). The movements and postures of the infants, including fidgety movements, were assessed according to the General Movements Assessment, which determines the Motor Optimality Score (MOS), on 2 surfaces.

RESULTS

The MOS outcomes of the infants with Down syndrome (median = 21.5, range = 6-28) were significantly lower than those of the infants who were neurotypical (median = 28, range = 23-28) on a standard mattress. The postures were found to be significantly better in infants with Down syndrome during exposure to a rough-textured surface. The MOS did not change due to the different exteroceptive experiences in infants with Down syndrome and infants who were neurotypical.

CONCLUSION

The different exteroceptive experiences caused only postural alterations, which might play a crucial role in early intervention programs for infants with Down syndrome.

IMPACT

This is the first study, to our knowledge, on the effects of different exteroceptive conditions, such as a coco coir mattress covered with muslin fabric, on the early motor repertoire in infants with Down syndrome. The findings showed that infants with Down syndrome had heterogeneity in their fidgety movements and large variability of the MOS, and the MOS results from infants with Down syndrome were lower than those of infants who were neurotypical. Fidgety movements and the MOS did not change due to the different exteroceptive experiences in either group. Significant improvements in posture were observed during exposure to a rough-textured surface. The improvement of posture is essential; clinicians might consider the positive effect of putting an infant with Down syndrome on a rough-textured surface and include this strategy in early intervention programs.

Auditory brainstem evoked responses in newborns with Down syndrome

Auditory brainstem evoked responses (ABRs) were compared in 15 newborns with Down syndrome and 15 sex-, age-, and weight-matched control newborns. Participants had normal ABRs based upon values specific to 32- to 42-weeks postconceptional age. Although Wave III and Wave V component latencies and the Wave I-III interpeak latency (IPL) were shorter in ABRs of infants with Down syndrome, the Wave III-V IPL was not, pointing to anomalies in the lower rather than upper brainstem auditory pathways. Shorter Down syndrome ABR latencies have been reported at many ages. Extending these findings to newborns suggests that the underlying basis for this develops prenatally. ABR patterns in infants with Down syndrome were similar to reports for intrauterine growth restricted newborns.

Education and children with Down syndrome: neuroscience, development, and intervention

Of the recent advances in education-related research in Down syndrome, the characterization of the Down syndrome behavioral phenotype has become a potentially critical tool for shaping education and intervention in this population. This article briefly reviews the literature on brain-behavior connections in Down syndrome and identifies aspects of the Down syndrome behavioral phenotype that are potentially relevant to educators. Potential challenges to etiologically informed educational planning are discussed.

Sensory evoked potentials in infants with Down syndrome

AIM

To investigate the sensory functions of the peripheral to central pathways in infants with Down syndrome (DS) by sensory evoked potentials.

METHODS

Fifty-five infants, 30 DS infants and 25 controls, were examined by multimodal evoked potentials, including brainstem auditory evoked potentials (BAEP), visual evoked potentials (VEP) and short-latency somatosensory evoked potentials (SSEP).

RESULTS

No obvious difference was found in the peak latencies between the two groups for BAEP. Nine children with DS showed abnormal BAEP; six had hearing loss and three had prolonged wave I latencies. For VEP, the peak latencies of P(2) and N(2) were significantly longer and the amplitudes were smaller in the DS group than in the control group. Of the 30 infants with DS, five had significantly prolonged P(2) latencies and two had lower amplitudes. In SSEP, the mean latencies of N(20) and the interpeak latencies of N(13)-N(20) of the infants with DS showed apparent prolongation compared to the controls. Seven of 30 (23.3%) DS patients had prolonged N(20) latencies.

CONCLUSION

Our results indicate that various sensory deficits occur in patients with DS during the first year of life.

Brain auditory evoked potentials in children with Down syndrome

Researchers have been examining the condition of the auditory organ in people with Down syndrome for many years. The aim of this work was an objective evaluation of the hearing threshold and a functional evaluation of the hearing pathway in children with Down syndrome without any disturbances in the middle ear.

MATERIAL

Seventy children with Down syndrome, aged from 2 months to 17 years. Brain auditory evoked potentials (BAEP) were performed. The peak latencies in children who had a normal BAEP pattern at 70 dB sHL were analysed. Peaks I-III and interpeak latencies I-III were significantly shortened in Down syndrome children up to the age of 1 year, as compared to older children with Down syndrome and to the control group. Peak III and interpeak latencies I-III were significantly longer in older children with Down syndrome in comparison to the control group.

CONCLUSIONS

Hearing loss in children with Down syndrome is more frequent than in healthy children. The average latency values of BAEP established for healthy children should not be used as a reference for children with Down syndrome. The shortening of the latency values in BAEP results of children with Down syndrome under 1 year of age may be connected with accelerated maturation of the nervous system or anatomical and/or functional disturbances of the central nervous system. BAEP is a valuable method that allows for the objective evaluation of the hearing threshold and functional condition of the hearing pathway in subjects who do not cooperate during testing.

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

Down's syndrome: a genetic disorder in biobehavioral perspective

Down's syndrome is a genetic disorder that can lead to mental retardation of varying degrees. How this chromosomal abnormality causes mental retardation remains an open question. This paper reviews what is currently known about the neural and cognitive features of Down's syndrome, noting the growing evidence of disproportionate impairment of specific systems such as the hippocampal formation, the prefrontal cortex and the cerebellum. The development of animal models of these defects offers a way of ultimately connecting the genetic disorder to its cognitive consequences.

Maturation of peripheral and brainstem auditory function in the first year following perinatal asphyxia: a longitudinal study

Maturation of peripheral hearing and auditory brainstem following perinatal asphyxia was investigated by longitudinal recording of brainstem auditory evoked potentials (BAEP) during the first year of life in affected infants. The general maturational course of the BAEP following asphyxia was similar to that in a control group of infants with normal births, although there were some abnormalities in the BAEP Response threshold elevation seen in a few asphyxiated infants improved significantly during the first 3 months. The interpeak intervals in the asphyxiated infants did not differ significantly from that of the control-group infants except in the first month, when the I-V and III-V intervals were significantly prolonged in the severe asphyxia group. In contrast, wave V amplitude and V/I ratio were always smaller when compared to that of the control-group infants. Amplitude reduction of wave V was more sustained than the prolonged I-V interval. Persistent hearing loss and brainstem auditory impairment were seen in 6.8% and 14.6% of the asphyxiated infants, respectively. These findings suggest that asphyxia does not interfere significantly with the maturation of the auditory system in most asphyxiated infants and that sustained peripheral hearing loss and brainstem impairment occur only in a small proportion of affected infants.

Auditory evoked potentials in young patients with Down syndrome. Event-related potentials (P3) and histaminergic system

Subjects with Down syndrome exhibit various types of cognitive impairment. Besides abnormalities in a number of neurotransmitter systems (e.g. cholinergic), histaminergic deficits have recently been identified. Brainstem auditory evoked potentials (BAEPs) and auditory event-related potentials (ERPs), were recorded from 10 children (aged 11-20 years) with Down syndrome and from 10 age- and sex-matched healthy control subjects. In Down subjects, BAEPs revealed shortened latencies for peaks III and V with shortened interpeak latencies I-III and I-V. ERPs showed a delay of components N1, P2, N2 and P3. In addition, subjects with Down syndrome failed to show P3 amplitude reduction during repeated stimulation. To evaluate the cognitive effects of histaminergic dysfunction, ERPs were recorded from 12 healthy adults (aged 20-28 years) before and after antihistaminergic intervention (pheniramine) compared to placebo. Whereas components N1, P2, N2 remained unchanged after H1-receptor antagonism, P3 latency increased and P3 amplitude showed no habituation in response to repeated stimulation. The results suggest that the characteristic neurofunctional abnormalities present in children with Down syndrome must be the consequence of a combination of structural and neurochemical aberrations. The second finding was that antihistaminergic treatment affects information processing tested by ERPs similar to that seen with anticholinergic treatment.

Preliminary observations on the development of auditory sensitivity in infants with Down syndrome

OBJECTIVE

Hearing loss commonly is associated with Down syndrome, but little is known about the development of auditory sensitivity in individuals with Down syndrome. This study had two objectives: 1) to determine whether an observer-based procedure can be used to assess the behavioral sensitivity of infants with Down syndrome, and 2) to provide preliminary information about the early course of hearing development among infants with Down syndrome.

DESIGN

Behavioral measures of sensitivity were made in 16 infants with Down syndrome using an observer-based procedure. Ten of the infants were followed longitudinally between 2 and 12 mo of age. All infants passed a screening auditory brain stem response at 20 dB nHL during the study and completed screening tympanometry at each test session. The infants detected a 4000 Hz tone at levels ranging from 25 to 50 dB SPL; psychometric functions and thresholds for the tone were obtained.

RESULTS

Infants with Down syndrome completed 80% of the test sessions they began, a rate similar to that seen in normally developing infants in the same type of study. Performance improved with increasing stimulus level, as one would expect, and thresholds were obtained from 15 of 16 infants for at least one age. The performance of infants with Down syndrome generally improved with age. The sensitivity of 2- to 3-mo-olds was poorer than that of older infants, but little if any improvement in sensitivity occurred between 4 and 12 mo. This pattern is similar to that seen in normally developing infants. Thresholds of infants with Down syndrome were 10 to 25 dB higher than those reported for normally developing infants. The psychometric functions of infants with Down syndrome were shallower than the psychometric functions of normally developing infants, and the slope of the psychometric functions did not change with age. Infants with Down syndrome achieved only 75 to 80% correct at any of the levels tested, 5 to 10% poorer than reported for other infants. These characteristics of the psychometric functions of the infants with Down syndrome suggest that they are inattentive during testing more often than are normally developing infants.

CONCLUSIONS

An observer-based procedure can be used to obtain reasonable thresholds from infants with Down syndrome who are as young as 2 mo of age. Both sensory and nonsensory factors could contribute to the threshold elevation seen in infants with Down syndrome. At least on preliminary examination, the course of auditory sensitivity development of infants with Down syndrome is qualitatively similar to that seen in normally developing infants.

Auditory evoked potentials in Down's syndrome

Short-, middle- and long-latency auditory evoked potentials (SAEPs, MAEPs and LAEPs) were examined in 12 subjects with Down's syndrome and in 12 age-matched normal subjects. In comparison with the normal subjects, Down subjects showed shorter latencies for SAEP peaks II, III, IV and V (and correspondingly shorter interpeak intervals I-II and I-III) so long as stimulus intensity was at least 45 dB SL. The MAEP peak Na had a longer latency in Down subjects than in normal subjects, but not the Pa latency. In passive oddball experiments for LAEPs, the latencies of all components from N1 to P3 were progressively longer in Down subjects, and the N2-P3 amplitude increased slightly between the first and fourth blocks of stimuli (whereas in the normal subjects it decreased). These alterations in auditory evoked potentials, which may correlate with cerebral alterations in organization and responsiveness responsible for deficient information processing, may constitute an electrophysiological pattern that is characteristic of Down's syndrome.

Long-term effect of perinatal and postnatal asphyxia on developing human auditory brainstem responses: peripheral hearing loss

Peripheral hearing was assessed by examining brainstem auditory evoked responses (BAER) in children who suffered perinatal or postnatal asphyxia, particularly in those with residual neurodevelopmental deficits, to investigate the long-term effect of asphyxia on the developing auditory sensitivity. The BAER data were collected at least 6 months after the episode of asphyxia. Of the children who suffered perinatal asphyxia, hearing loss was found more frequently in those who exhibited residual neurodevelopmental deficits (17.1%) than in those who did not (6.3%), but this difference did not reach statistical significance. This implied that the long-term effect of perinatal asphyxia on the peripheral auditory system and its effect on the central nervous system may be relatively discrete or not closely correlated. The occurrence of hearing loss did not appear to be closely related to the degree of perinatal asphyxia, although hearing loss occurred more frequently in the children after severe asphyxia compared to those after mild asphyxia. There was no evidence for permanent hearing loss in the children who survived severe, prolonged postnatal asphyxia and exhibited residual neurodevelopmental deficits. These findings suggest that a critical period of particular sensitivity to the effect of hypoxia may exist during the development of the human peripheral auditory system. This period may range from some time prenatally to some time shortly after birth, probably the third postnatal month. After that, hypoxia is unlikely to lead to permanent hearing loss.

Maturation of the auditory brainstem in low risk-preterm infants: a comparison with age-matched full term infants up to 6 years

Whether preterm birth has a significant effect on the maturation of the human brain remains an equivocal issue. Since experience plays a crucial role in the development of the brain, it is conceivable that extra-uterine preterm exposure could exert some effects on the maturation of the developing human brain. The present study compared the post-term maturation of the central components of brainstem auditory evoked response (BAER) in low risk preterm infants with that of age-matched full term infants up to 6 years. The preterm infants demonstrated similar maturational profiles to those of the term infants in both interpeak intervals and amplitude measures. No systematic, statistically significant differences were found between the preterm and term infants in any of the BAER variables although the I-V interval tended to be slightly shortened in the prematurely born infants. These results suggest that preterm birth or earlier exposure to sound environment extra utero is unlikely to lead to significant neurophysiological consequence in the developing auditory brainstem of low risk infants.

Auditory brainstem responses of children with developmental language disorders

Brainstem auditory evoked potentials (BAEPs) were recorded from 48 children with language disorders (aged four to nine years old, IQs normal to borderline, normal audiometric thresholds and attending special school) and 20 healthy children (four to eight years old, with normal IQs, audiometry and school-level). The language-disabled group showed significantly lower absolute latency values of the BAEPs than controls. There were no significant differences in the central conduction time of the auditory pathway (I-V interval). Therefore, the only significant difference corresponded to a minor value for the first wave (auditory nerve discharge) of the BAEP. A reduction in the control mechanisms of the sensory inputs at the peripheral level, or a disturbance in the inhibitory mechanisms of cortico-subcortical modulation, might explain these findings.

Brainstem auditory evoked responses from birth to adulthood: development of wave amplitude

Brainstem auditory evoked response (BAER) was recorded in children from birth to 6 years and adults to study the development of wave amplitude. The amplitudes of all BAER waves increased with age, the greatest changes occurring during early infancy. Adult values were reached at 6 months of age for wave I and 2 years for wave V. The two waves continued to increase above the adult values until the highest amplitude value was reached at 3 years for wave I and 5 years for wave V. Subsequently, the amplitudes decreased towards the values in adults. The V/I amplitude ratio, which was slightly than the adult value shortly after birth, decreased during the first year of life and reached the minimum value between 1 and 4 years. Thereafter, it increased towards the adult value. Throughout the maturational stages the ratio was smaller than in adults. The amplitude of wave V was relatively stable and its variation was much smaller than those of wave I and V/I amplitude ratio. Lower normative limits of these amplitude measures were given to provide a reference baseline for further study under the similar experimental conditions. We suggest that, in light of age-related differences of the V/I ratio, the normative criteria for the amplitude ratio should be established in relation to age. The amplitude of wave V is recommended to be useful in some clinical situations.

Development of the brainstem auditory pathway in low birthweight and perinatally asphyxiated children with neurological sequelae

Low birthweight (LBW) and perinatal asphyxia are known to be high-risk factors for a number of neurodevelopmental deficits. In this study, we analyzed brainstem auditory evoked response (BAER) in 18 LBW and 36 perinatally asphyxiated children with non-progressive neurological sequelae after the age of 6 months to inspect and compare the long-term influence of LBW and perinatal asphyxia on the brainstem auditory pathway. The typical changes in the BAER of children born with LBW were slightly shorter III-V interpeak interval and smaller III-V/I-III interval ratio than normal controls. On the contrary, the abnormalities in the BAER of 36 children surviving perinatal asphyxia were characterized by a reduction of the amplitude of wave V with normal intervals. This discrepancy in the BAER between the children born with LBW and those with perinatal asphyxia implies that the two high-risk factors exert different long-term influences on the development of the brainstem auditory pathway. It is hypothesized that these characteristic changes may be indicative of a major influence of LBW on the generators contributing to wave III and that of asphyxia on the generators contributing to wave V. An increase in response threshold with abnormal latency-intensity function was found in 11% of the LBW children and 19% of the asphyxiated children, suggesting that sensorineural hearing impairment occurred more frequently in children surviving perinatal asphyxia than in those born with LBW. Follow-up study demonstrates that the abnormalities in the brainstem auditory pathway of LBW and asphyxiated children after the age of 6 months is likely to be persistent.

Brainstem auditory evoked responses from birth to adulthood: normative data of latency and interval

Development of wave latency and interpeak interval (IPI) in brainstem auditory evoked responses (BAER) from birth to adulthood was examined. Adult equivalence was reached for most wave latencies and IPIs between the ages of 9 months and 3 years. The observation of the III-V/I-III interval ratio suggests that after term data the I-III IPI decreases more than the III-V IPI. I-III, III-V and I-V IPIs shortened from the l-month old group to the 4-6 year old group by 22%, 15% and 19% respectively. The III-V/I-III interval ration may be a useful BAER measure. Normative data of various BAER measures at different ages are presented. The slope of the L-I function for wave V was slightly steeper in younger groups than in older groups (40 microseconds/dB in the 1-month old group 32 microseconds/dB in the adult group). This change which was accompanied by an age-related difference in the absolute wave latency. It is suggested that age-dependent norms should be used in evaluation of the L-I function.

Development of early and late brainstem conduction time in normal and intrauterine growth retarded children

Development of early (I-III) and late (III-V) brainstem conduction time (BCT) in the brainstem auditory evoked responses was examined and compared in 178 appropriate-for-gestational-age (AGA) and 24 small-for-gestational-age (SGA) children from birth to 6 years of age. In AGA children, the III-V/I-III interval ratio increased with age from birth to 2 years and remained relatively steady. This indicates that the development of the early and late BCT, or probably the lower and upper brainstem is not synchronous during early childhood, with a slightly faster development of the early BCT relative to the late BCT. In SGA children, the I-V, I-III and III-V intervals showed similar developmental trends to those in AGA children. However, the III-V/I-III ratio followed a developmental course which differed remarkably from that in AGA children. The ratio decreased slightly with age up to 2 years and was consistently smaller than in normal children after 1 year, indicating that the relative development of early and late BCT deviates from normal. This finding suggests that prenatal factors responsible for intrauterine growth retardation could alter the late or long-term development of the nervous system, resulting in sub-optimal outcome.

Intensity effect on amplitude of auditory brainstem responses in human

Click intensity effect (90 to 0 dB HL) on amplitude of the auditory brainstem responses (ABAR) was studied in 152 normal children from birth to 6 years and 16 adults. All age groups showed similar amplitude-intensity functions for waves I and V. Wave I amplitude exhibited a 'transitional' response at 60 dB HL intensity, whereas wave V exhibited a more gradual change. As the clicks were decreased from 90 to 60 dB HL, amplitude reduction was much more dramatic for wave I (mean 57%) than for wave V (mean 30%), and the V/I amplitude ratio more than doubled (mean 70%). At moderate intensity range, the reduction in amplitude with the decrease in intensity is only slightly more for wave I than for wave V, and the V/I ratio continued to increase, but more slowly. Wave V amplitude changed linearly with click intensity at the rate of 0.024-0.042 microV/dB for different age groups. The older the children, the larger the decrement of wave V amplitude with decreasing intensity, which was accompanied by an age-related difference in the absolute amplitude at equal click intensities. The V/I amplitude ratio increased with decreasing intensity at a rate of about 0.01/dB, showing no apparent age-related difference.

Amplitude change with click rate in human brainstem auditory-evoked responses

The effect of click rate on wave amplitude of human brainstem auditory-evoked response (BAER) was examined at repetition rates of 10, 30, 50, 70 and 90 Hz in 80 healthy children aged 1 month to 6 years and in 21 adults. As repetition rate was increased from 10 to 90 Hz at 70 dB HL, the amplitudes in different age groups decreased by 33-45% (0.109-179 microV) for wave I and 25-41% (0.055-0.145 microV) for wave V. The older the children, the larger the absolute decrements of wave amplitudes with increasing repetition rate, but the relative decrements or reduction rates of wave amplitudes exhibited no systematically age-related differences. The V/I amplitude ratio tended to increase with increasing repetition rate in most age groups, suggesting that the amplitude of wave I is affected by the repetition rate slightly more than that of wave V. The patterns of the changes in wave amplitudes with repetition rate at lower intensity levels were essentially similar.

Intensity effect on latency and interval of human BAER

Intensity effect on wave latency and interval (IPI) in brainstem auditory evoked responses (BAER) from birth to adulthood was investigated. The L-I functions were slightly steeper in younger groups than in older groups, which was associated with age-related difference in the absolute latencies. Wave I latency in most age groups exhibited two "transitional" responses: one at 70 dB HL or, sometimes, at 60 dB HL and the other mostly at 20 dB HL. As click intensity decreased, the I-III IPI tended to decrease slightly while the III-V IPI tended to increase slightly in most age groups. Since the I-V IPI was constant at various intensities which could be attributed to a slight change in the morphology of wave III with altering intensity.