Auditory brain-stem evoked potentials to clicks at different presentation rates: estimating maturation of pre-term and full-term neonates

Short-term outcome of functional integrity of the auditory brainstem in term infants who suffer perinatal asphyxia

OBJECTIVES

To assess short-term outcome of impaired functional integrity of the auditory brainstem in term infants who suffer perinatal asphyxia.

METHODS

Maximum length sequence brainstem auditory evoked response (MLS BAER) was recorded and analyzed at a mean age of 3months in term infants after perinatal asphyxia. The data were compared with age-matched normal term infants.

RESULTS

The infants after asphyxia showed an increase in the latency of MLS BAER wave III at 91, 455 and 910/s, and wave V at all click rates of 91-910/s. The interpeak intervals in the infants after asphyxia were increased at almost all click rates. The IV and I-III intervals were increased at all click rates, and the III-V interval was increased at 455 and 910/s. These increases were generally more significant at higher than at lower click rates. The amplitudes of waves I, III and V in the infants after asphyxia were reduced at all click rates. The V/I amplitude ratio was increased at 91-455/s clicks. The slope of III-V interval-rate function was abnormally increased. 17.1% of the infants after asphyxia had an abnormal increase in IV intervals.

CONCLUSIONS

MLS BAER was moderately abnormal at 3months of age in term infants after perinatal asphyxia, suggesting moderate impairment in the functional integrity of the auditory brainstem. The impairment occurs in 17.1% of the infants. Compared with that found at term, the impairment has improved, but not completely recovered.

Reading ability reflects individual differences in auditory brainstem function, even into adulthood

Research with developmental populations suggests that the maturational state of auditory brainstem encoding is linked to reading ability. Specifically, children with poor reading skills resemble biologically younger children with respect to their auditory brainstem responses (ABRs) to speech stimulation. Because ABR development continues into adolescence, it is possible that the link between ABRs and reading ability changes or resolves as the brainstem matures. To examine these possibilities, ABRs were recorded at varying presentation rates in adults with diverse, yet unimpaired reading levels. We found that reading ability in adulthood related to ABR Wave V latency, with more juvenile response morphology linked to less proficient reading ability, as has been observed for children. These data add to the evidence indicating that auditory brainstem responses serve as an index of the sound-based skills that underlie reading, even into adulthood.

Brainstem auditory response findings in late preterm infants in neonatal intensive care unit

AIM

To examine brainstem auditory function at term in late preterm infants admitted to neonatal intensive care unit (NICU).

METHODS

Fifty-two preterm infants, born at 33-36 week gestation, were recruited in an NICU and were studied at term using brainstem auditory evoked response (BAER).

RESULTS

Compared with normal term infants, BAER wave V latency in the NICU preterm infants was increased at 51 and 91/sec (p<0.05, 0.05). Intervals of III-V and I-V were increased at all 21, 51 and 91/sec clicks (p<0.05-0.01), which was more significant at higher than lower rates. Interval ratio of III-V/I-III was increased significantly at 51 and 91/sec (p<0.05 and 0.01). Wave I and III latencies and I-III interval did not differ significantly from normal controls at any click rates. All amplitudes of waves I, III and V amplitude tended to be reduced at higher rates, while wave I amplitude was reduced significantly at 91/sec clicks.

CONCLUSION

There were BAER abnormalities in the NICU late preterm infants, suggesting compromised brainstem auditory function. Compared with a basically normal BAER in low-risk late preterm infants previously reported, the abnormalities suggest that perinatal problems or complications adversely affect the late preterm auditory brainstem.

Maximum length sequence brainstem auditory evoked response in low-risk late preterm babies

OBJECTIVES

Recent research indicates that there is delayed development in the more central part of the auditory brainstem in very preterm babies. We aimed to study whether this is also the case for late preterm babies.

METHODS

The maximum length sequence brainstem auditory evoked response (MLS BAER) was used to study functional status of the auditory brainstem. Babies born at 33-36 week gestation and without any major perinatal complications were recruited. MLS BAER was recorded and analyzed at term age.

RESULTS

No significant correlation was found between most MLS BAER variables and physiological factors (gender, postconceptional age, bodyweight, and head circumference obtained at time of testing). Wave latencies and amplitudes, and I-V and I-III intervals in the preterm babies were essentially similar to those in the term controls at all click rates. However, III-V interval increased significantly at 227-910/s clicks (p<0.05-0.01). All latencies, amplitudes and intervals correlated significantly with click rates (all p<0.001). No differences were found in the slopes of MLS BAER variables-rate functions between the later preterm babies and term controls.

CONCLUSIONS

Babies born at 33-36 weeks gestation without major complications had an increased III-V interval at high-rate stimulation. This suggests that late preterm babies have a mild delay in neural conduction in the more central part of the auditory brainstem.

Impairment of perinatal hypoxia-ischemia to the preterm brainstem

Hypoxia-ischemia is a major perinatal problem that results in severe damage to the newborn brain. This study assessed functional integrity of the brainstem at term in preterm infants after perinatal hypoxia-ischemia to shed light on the influence of hypoxia-ischemia on the preterm brainstem. We recruited sixty-eight preterm infants after perinatal hypoxia-ischemia, ranging in gestation 28-35 weeks. Brainstem evoked response was studied at term age (37-42 weeks postconceptional age) with 91-910/s clicks using the maximum length sequence technique. Compared with healthy preterm infants, the preterm infants after perinatal hypoxia-ischemia showed a significant increase in I-V interval at very high rates 455 and 910/s of clicks (P<0.05, 0.05). III-V interval and III-V/I-III interval ratio also increased significantly at 455 and 910/s (P<0.05-0.01). The slope of III-V interval-rate function was significantly steeper than in the healthy preterm infants (P<0.05). Compared with normal term controls, the preterm infants after hypoxia-ischemia showed similar, but slightly more significant, abnormalities. The differences between the preterm infants after hypoxia-ischemia and the healthy preterm and term infants generally increased with increasing click rate. These results demonstrated that central components of brainstem auditory evoked response were abnormal at very high click rates in the preterm infants after perinatal hypoxia-ischemia. Click rate-dependent change in the more central part of the brainstem is also abnormal. Apparently, functional integrity of the brainstem, mainly in the more central part, is impaired. Hypoxic-ischemic damage to the preterm brainstem is unlikely to completely recover within a relatively short period after the insult, which is of clinical importance.

Age-related changes in BAER at different click rates from neonates to adults

AIM

To characterize age-related changes in brainstem auditory evoked response (BAER) at different click rates from neonates to adults.

METHODS

BAER was studied at repetition rates 11-91/sec of clicks in 165 normal neonates and children of various ages and 29 young adults.

RESULTS

BAER wave latencies and inter-peak intervals increased linearly with increasing click rate at all ages. The younger was the age, the greater were BAER click rate-dependent changes. At 9 months and younger, the slopes of latency- and interval-rate functions were all significantly greater than in the adults (all p < 0.01). The slopes of wave I latency- and I-III interval-rate functions at 1-2 years and older were similar to those in adults. The slopes of wave III and V latency-rate functions and I-V and III-V interval-rate function at 3-4 years and older did not differ significantly from those in adults.

CONCLUSION

BAER is affected by stimulus rate more in younger children than in the older. Adult-like rate-dependent changes are reached at 1-2 years for wave I latency and I-III interval, and 3-4 years for wave III and V latencies and I-V and III-V intervals. Our BAER data at different click rates provide normal references for subjects of various ages.

Normal brainstem responses in moderately preterm infants

AIM

The aim of this study was to detect any differences in brainstem auditory evoked responses (BAERs) to different click rates between moderately preterm and term infants.

METHODS

BAER was recorded with 21-91/s clicks at term age (37-42 weeks postconceptional age) in 39 moderately preterm infants (gestation 33-36 weeks). The results were compared with 37 healthy term infants.

RESULTS

The latencies of waves I, III and V, and I-V interval in preterm infants were all similar to term infants at all click rates. The I-III interval decreased slightly and differed from term infants at 91/s (ANOVA, p < 0.05), while the III-V interval increased slightly. The III-V/I-III interval ratio increased slightly and differed from term infants at 91/s (p < 0.05). Wave amplitudes were similar in the two groups of infants, except an increase in wave V amplitude at 91/s in preterm infants (p < 0.05). No significant differences were found in BAER click rate-dependent changes between the two groups.

CONCLUSION

No marked differences were found in BAER at any click rates at term age between moderately preterm and term infants, suggesting that moderately preterm birth does not have a marked effect on neonatal BAER. BAER normal data and criteria from term infants can generally be used for moderately preterm infants.

Tone-evoked ABR in full-term and preterm neonates with normal hearing

This study was designed to investigate the feasibility of applying tone-ABRs in the nursery and neonatal intensive care unit (NICU), and to provide normative tone-ABR data from neonates. Normative tone-ABR latency data were determined. The study obtained intensity series of tone-ABRs from thirty preterm neonates and twenty full-term neonates who had confirmed normal peripheral auditory function after passing both an OAE and ABR screening examination. ABRs were collected in response to 500, 1500, and 4000 Hz tone bursts at 70, 50, 30, and 20 dB nHL. Mean wave V latencies were compared between groups, ears, and by gender. Responses to tone bursts of 20 and 30 dB nHL were detected in 97% and 100% of all ears respectively, in addition to responses to the higher-intensity stimuli. Preterm neonates' ABRs showed significantly longer latencies than those of the full-term infants. Tone-ABR evaluation was found to be both feasible and reliable as a measure of auditory function in neonates.

Functional impairment of the brainstem in infants with bronchopulmonary dysplasia

OBJECTIVES

To gain new insights into the influence of bronchopulmonary dysplasia on the immature brain and to detect abnormalities, we studied the functional integrity of the brainstem in infants with bronchopulmonary dysplasia.

METHODS

Forty-one very preterm infants with bronchopulmonary dysplasia were studied at postconceptional ages of 37 to 42 weeks. Brainstem auditory evoked responses were recorded and analyzed by using the maximal length sequence technique.

RESULTS

Compared with term control subjects, wave V latency in the maximal length sequence brainstem auditory evoked response of the infants with bronchopulmonary dysplasia increased significantly at all 91 to 910 clicks per second rates. Similarly, I-V and particularly III-V interpeak intervals increased significantly. The III-V/I-III interval ratio also increased significantly at all click rates. All of these abnormalities became more significant as the click rate was increased. Compared with healthy, very preterm control subjects, all of these maximal length sequence brainstem auditory evoked response variables increased significantly at all click rates, although the differences between the 2 groups were slightly smaller than those between the infants with bronchopulmonary dysplasia and the term control subjects. The wave I and III latencies and I-III interval in the infants with bronchopulmonary dysplasia did not show any abnormalities. The slopes of the wave V latency-rate function and I-V and particularly III-V interval-rate functions for the infants with bronchopulmonary dysplasia were significantly steeper than those for both term and healthy, very preterm control subjects. The slope of the III-V/I-III interval ratio-rate function for the infants with bronchopulmonary dysplasia was also significantly steeper than those for the 2 control groups.

CONCLUSIONS

The results suggest poor myelination and synaptic function of the brainstem in infants with bronchopulmonary dysplasia, resulting in impaired functional integrity. In comparison, peripheral neural function was relatively intact.

Sub-optimal function of the auditory brainstem in term infants with transient low Apgar scores

OBJECTIVES

To assess functional integrity of the auditory brainstem in neonates with transient low Apgar scores.

METHODS

Forty-two term infants were studied with brainstem auditory evoked response (BAER) using the maximum length sequence during the first month of life. All had transient low Apgar scores but no clinical signs of hypoxic-ischaemic encephalopathy (HIE).

RESULTS

The latencies of BAER waves I and III in these infants were similar to those of age-matched normal controls at all click rates (91/s, 227/s, 455/s and 910/s) during the period studied. Wave V latency was increased at 910/s on day 1 (P<0.01), but did not differ from that in the controls on any other days. I-V interval was increased significantly at 455/s and 910/s on day 1 (P<0.01 and 0.001) and day 3 (P<0.05 and 0.01). On days 5 and 7, BAER wave latencies and intervals were similar to those in the controls. On day 30, all latencies and intervals reached the values in the controls. No abnormalities were seen in BAER wave amplitude variables on any days.

CONCLUSIONS

Neonates with transient low Apgar scores but without HIE had a significant increase in I-V interval at very high click rates on the first three days of life.

SIGNIFICANCE

Brainstem auditory function is sub-optimal during the first few days in neonates with transient low Apgar scores.

Maximum length sequence BAER at term in low-risk babies born at 30-32 week gestation

Thirty babies born at 30-32 week gestation without any major perinatal problems were studied at term with brainstem auditory evoked response (BAER) to detect any abnormalities in central auditory function in low-risk very preterm babies. The BAER was recorded and analyzed at 37-42 week postconceptional age using maximum length sequence technique (MLS). The data obtained were compared with those of 38 normal term controls. Wave I and III latencies in the very preterm babies did not show any significant differences from the controls at all repetition rates of click stimuli used (91-910 s(-1)). Wave V latency and I-V interpeak interval tended to increase at all click rates, and differed significantly from the controls at the highest rate 910 s(-1) (P < 0.05). Both III-V interval and III-V/I-III interval ratio increased significantly at all click rates, particularly at 455 and 910 s(-1) (P < 0.05-0.001). On the other hand, I-III interval tended to decrease. None of wave I, III and V amplitudes showed any abnormalities. Neither did V/I nor V/III amplitude ratios. These results suggest that development of the central auditory system is slightly delayed, which can be shown by MLS BAER at very high rate-stimulation, in low-risk very preterm babies.

Assessment of gestational age and neuromaturation

Neuromaturation is the functional development of the central nervous system (CNS). It is by its very nature a dynamic process, a continuous interaction between the genome and first the intrauterine environment, then the extrauterine environment. Understanding neuromaturation and being able to measure it is fundamental to infant neurodevelopmental assessment. Fetal and preterm neuromaturation has become easier to observe with the advent of prenatal ultrasonography and neonatal intensive care units. A number of measures of degree of fetal maturation have been developed and used to estimate gestational age (GA) at birth. The most reliable measures of GA are prenatal measures, especially from the first trimester. Postnatal GA measurements tend to be least accurate at the extremes of gestation, that is, in extremely preterm and post-term infants. Observations of measures of neuromaturation in infants born to mothers with pregnancy complications, including intrauterine growth restriction, multiple gestation, and chronic hypertension, have led to the discovery that stressed pregnancies may accelerate fetal pulmonary and CNS maturation. This acceleration of neuromaturation does not occur before 30 weeks' gestation and has a cost with respect to cognitive limitations manifested in childhood. The ability to measure fetal and preterm neuromaturation provides an assessment of neurodevelopmental progress that can be used to reassure parents or identify at risk infants who would benefit from limited comprehensive follow-up and early intervention services. In addition, measures of neuromaturation have the potential to provide insight into mechanisms of CNS injury and recovery, much-needed early feedback in intervention or treatment trials and a measure of early CNS function for research into the relationships between CNS structure and function.

Brain-stem auditory impairment during the neonatal period in term infants after asphyxia: dynamic changes in brain-stem auditory evoked response to clicks of different rates

OBJECTIVE

To explore dynamic changes in brain-stem auditory electrophysiology during the neonatal period in term infants after perinatal asphyxia.

METHODS

Sixty-eight term newborn infants who suffered asphyxia were studied on days 1, 3, 5, 7, 14 and 30 after birth. Brain-stem auditory evoked response (BAER) was recorded with clicks, delivered at 21, 51 and 91 s(-1) and > or =40 dB above BAER threshold of each subject.

RESULTS

During the neonatal period wave I latency in the infants after asphyxia increased slightly while later BAER components changed more significantly. On the first day after birth wave III and V latencies and I-V and III-V intervals increased significantly at all rates of clicks (ANOVA P<0.01-0.001). On day 3, the latencies and intervals increased further. III-V/I-III interval ratio increased at 51 and 91 s(-1), suggesting a relatively more significant increase in III-V interval than in I-III interval at higher rates. Thereafter, wave III and V latencies and all intervals decreased progressively, although these BAER variables were still significantly longer than in normal controls on days 5 and 7 (P<0.05-0.001) On day 30, all latencies and intervals approached near normal values, with a slight increase in wave V latency and I-V and III-V intervals at 51 and 91 s(-1).

CONCLUSIONS

Perinatal asphyxia has a major effect on central auditory function, resulting in acute impairment. The impairment progresses during the first 3 days and then tends towards recovery. By 1 month the impaired auditory function has largely returned to normal. Significant increase in click rates can moderately improve the detection of auditory impairment.

SIGNIFICANCE

After perinatal asphyxia early detection of hypoxic-ischaemic damage to the central auditory system and initialisation of neuroprotective and therapeutic measures during the first hours after birth are critical to prevent or reduce deterioration of central impairment.

The combined effects of forward masking by noise and high click rate on monaural and binaural human auditory nerve and brainstem potentials

OBJECTIVE

To study effects of forward masking and rapid stimulation on human monaurally- and binaurally-evoked brainstem potentials and suggest their relation to synaptic fatigue and recovery and to neuronal action potential refractoriness.

METHODS

Auditory brainstem evoked potentials (ABEPs) were recorded from 12 normally- and symmetrically hearing adults, in response to each click (50 dB nHL, condensation and rarefaction) in a train of nine, with an inter-click interval of 11 ms, that followed a white noise burst of 100 ms duration (50 dB nHL). Sequences of white noise and click train were repeated at a rate of 2.89 s(-1). The interval between noise and first click in the train was 2, 11, 22, 44, 66 or 88 ms in different runs. ABEPs were averaged (8000 repetitions) using a dwell time of 25 micros/address/channel. The binaural interaction components (BICs) of ABEPs were derived and the single, centrally located equivalent dipoles of ABEP waves I and V and of the BIC major wave were estimated.

RESULTS

The latencies of dipoles I and V of ABEP, their inter-dipole interval and the dipole magnitude of component V were significantly affected by the interval between noise and clicks and by the serial position of the click in the train. The latency and dipole magnitude of the major BIC component were significantly affected by the interval between noise and clicks. Interval from noise and the click's serial position in the train interacted to affect dipole V latency, dipole V magnitude, BIC latencies and the V-I inter-dipole latency difference. Most of the effects were fully apparent by the first few clicks in the train, and the trend (increase or decrease) was affected by the interval between noise and clicks.

CONCLUSIONS

The changes in latency and magnitude of ABEP and BIC components with advancing position in the click train and the interactions of click position in the train with the intervals from noise indicate an interaction of fatigue and recovery, compatible with synaptic depletion and replenishing, respectively. With the 2 ms interval between noise and the first click in the train, neuronal action potential refractoriness may also be involved.

Brainstem auditory evoked response in normal term neonates

Brainstem auditory evoked response (BAER) is a reliable test for neonatal auditory and neurological dysfunction and it permits early diagnosis and rehabilitation. The purpose of this study is to demonstrate latencies of BAER in normal term neonates in order to obtain reference values in a university hospital. BAER was performed in the second day of life in 47 normal newborns (25 male, 22 female) which gestational ages were higher than 37 and lower than or equal to 40 weeks that did not present familial history of deafness. The exam was performed with 80 dBHL alternating polarity 10/sec clicks presented monaurally. Two thousand stimulus trials were averaged and duplicated for each ear. Mean wave latencies in msec was: I, 1.79 (SD 0.20); II, 2.88 (SD 0.28); III, 4.54 (SD 0.31); IV, 5.86 (SD 0.36); V, 6.75 (SD 0.38); inter-peak latencies (IPL) I-III, 2.75 (SD 0.36); IPL III-V, 2.22 (SD 0.22); and IPL I-V, 4.97 (SD 0.43).

The cumulative effect of high click rate on monaural and binaural processing in the human auditory brainstem

OBJECTIVE

The objective of the present study was to compare the effects of high stimulus rate and click position in the train on monaurally and binaurally evoked activities in the human auditory brainstem and suggest their possible physiological mechanism.

METHODS

Auditory brainstem evoked potentials (ABEPs) were recorded from 15 normally and symmetrically hearing adults from 3 channels, in response to 50dB nHL, alternating polarity clicks, presented at a rate of 21/s as well as separately to each click in a train of 10 with an interstimulus interval of 11ms. Click trains were presented at a rate of 5.13/s. The binaural interaction components (BICs) of ABEPs were derived by subtracting the response to binaural clicks from the algebraic sum of monaural responses. Single, centrally located equivalent dipoles were estimated as concise measures of the surface-summated activity of ABEPs and BICs generators.

RESULTS

A significant effect of click position in the train on equivalent dipole latency of ABEP component V and on equivalent dipole magnitude of III were found. Latency was prolonged and amplitude was increased the later the click's position in the train. A significant effect of click position in the train on equivalent dipole latencies of all components of BICs was found. Latencies were prolonged if the click's position occurred later in the train, with most of the latency shift achieved by the third click in the train for the first major BIC and by the seventh click for other BIC components. No significant effects on equivalent dipole magnitudes of BICs were found. No significant effect of click position in the train on orientation of any of the equivalent dipoles of ABEP or BIC was found.

CONCLUSIONS

The progressive prolongation of latency of ABEP and BIC components with advancing position in the train may be attributed to cumulatively decreased synaptic efficacy at high stimulus rates, resulting in prolonged synaptic delays along the auditory pathway. The paradoxic enhancement of ABEP dipole III magnitude with advancing click position in the train may reflect higher sensitivity of inhibitory brainstem neurons to increased stimulus rate, resulting in disinhibition. The absence of significant effects on BIC dipole magnitudes may reflect the amplifying effect of divergence in the ascending auditory pathway, as has been observed for the monaurally evoked ABEP components from the upper pons.

Auditory neural responses to click stimuli of different rates in the brainstem of very preterm babies at term

Auditory neural responses to acoustic stimuli of different rates were studied by analyzing changes in brainstem auditory evoked responses (BAER) with increasing repetition rate of clicks, or rate-dependent changes, in 62 very preterm babies (gestation 24-32 wk). None had perinatal asphyxia or major complications at the time of testing (37-42 wk postconceptional age) to exclude their possible effects on the recorded BAER. As the rate of clicks was increased from 21/s to 51/s and 91/s, I-V interpeak interval in these babies increased similarly to that in normal term neonates. The rate-dependent change decreased significantly in I-III interval, but increased significantly in III-V intervals and III-V/I-III interval ratio (all p < 0.01). At all three rates of clicks, the I-V interval, the most commonly used BAER variable, tended to increase slightly but did not differ significantly from the term neonates. The I-III interval decreased significantly at higher click rates (ANOVA p < 0.05 at 51/s and < 0.001 at 91/s), whereas the III-V interval and III-V/I-III interval ratio increased significantly at all 21/s, 51/s, and particularly 91/s (p < 0.01-0.001). No abnormalities were found in wave V amplitude at any rates. These results suggest that very preterm babies have an advanced peripheral development of the brainstem auditory pathway but a retarded central development or central impairment. A nearly normal I-V interval does not exclude a possible abnormality in its subcomponents (I-III and III-V intervals). In babies who have a normal BAER at a conventionally used low rate of clicks, we cannot exclude an abnormal BAER at higher rates.

Maximum length sequence brainstem auditory evoked responses in term neonates who have perinatal hypoxia-ischemia

Maximum length sequence brainstem auditory evoked response (BAER) was studied within the first week after birth in 28 term neonates who had perinatal hypoxia-ischemia, or asphyxia. In the BAER recorded using conventional averaging techniques (click rate 21/s), the only abnormality was a slight increase in III-V interval, in addition to an increase in wave latencies when including those who had an elevated threshold (t test, all p<0.05). In the maximum length sequence BAER, however, both the III-V and I-V intervals in the asphyxiated infants were significantly increased at all the 91/s, 227/s, 455/s, and particularly 910/s click rates (p<0.05-0.001). The I-III interval was also increased significantly at 455/s and 910/s click rates (both p< 0.05). Wave V amplitude was significantly reduced at all the click rates used (ANOVA, p<0.05-0.001), particularly at 910/s, which sometimes was the only abnormality indicative of brain damage. Both the amplitude ratios V/I and V/III were significantly decreased at 455/s and 910/s click rates (p<0.01 or 0.001). A general trend was that BAER abnormalities after hypoxia-ischemia became more prominent as click rate was increased. Significant abnormalities occurred mainly at very high click rates (455/s and 910/s), which can be achieved using the maximum length sequence technique but not by using conventional averaging techniques. Thus, this technique, which can be used at the cribside, appears to be a better method for the early detection of brain damage after hypoxia-ischemia than using conventional averaging techniques, enhancing the diagnostic value of the BAER.

Morphological changes in serial auditory brain stem responses in 24 to 32 weeks' gestational age infants during the first week of life

OBJECTIVE

The purpose of this investigation was to describe and quantify the sequential morphological changes in the auditory brain stem response (ABR) during the first postnatal week of life in very premature infants < or = 32 wk gestational age. These normative data could be useful in predicting neurological outcome in infants with perinatal risk factors.

DESIGN

Sequential ABRs were recorded on a total of 135 infants on 5 out of the first 7 days of life. For analysis, data were grouped by gestational age in 2 wk intervals. In addition, a unique system was devised to categorize waveform response types in premature infants: type 1, a response with normal morphology and replicable waves III and V; type 2, a replicable response with either a wave III or wave V; type 3, a replicable response with neither a wave III or wave V; type 4, a response with no replicable waveform.

RESULTS

The frequency of detection of waves improves over the first week of life with the detectability of waves III and V being more frequent than wave I at all gestational ages. There was a gradual improvement in response types in infants > 26 wk with the greatest improvement occurring during the 28 to 29 wk gestation. ABRs were predominantly types 3 and 4 at 24 to 25 wk, type 3 at 26 to 27 wk, type 2 at 28 to 29 wk, and types 1 and 2 at 30 to 31 wk. Absolute wave latencies and interwave latencies also progressively decreased during the first postnatal week. In some infants there was a transient increase in latencies or worsening of response type on the second to third test day.

CONCLUSIONS

There is progressive improvement in frequency of detection of waves I, III, and V with increasing gestational age. Response types gradually mature over the first postnatal week, particularly in premature infants 28 to 32 wk gestational age.

Early neurological and neuropsychological development of the preterm infant and polyunsaturated fatty acids supply

OBJECTIVES

To compare the early neurological maturation of premature newborns (PT) fed breast milk (BM) or a formula containing only 18-carbon polyunsaturated fatty acids (PUFA) (A) or enriched with long chain (LC) PUFA (B).

METHODS

PT enrolled the 2nd day of enteral feeding (D0) were fed BM (n = 15; 4 dropped out) or randomly assigned to A (n = 11; 2) or B (n = 14; 1) for at least 30 days (D30). Auditory and visual evoked potentials (EPs) and nerve conduction velocity (NCV) and plasma and red blood cell (RBC) phospholipid composition were determined at D0 and D30. No difference was found between groups for the D0-D30 changes in EP parameters. The maturation of motor NCV was slower in the B group than in the two other groups. In plasma, the changes were higher in B than in the BM and A groups for linoleic acid (P < 0.05), in BM versus B group for arachidonic acid (P < 0.02). In RBC, formula groups displayed higher linoleic acid level than the BM group (P < 0.05). No difference was found between groups for the changes in arachidonic and docosahexaenoic acids.

CONCLUSIONS

A balanced supply of n-6 and n-3 PUFA without addition of LC-PUFA allowed an adequate early maturation of the central nerve system. The effects of LC-PUFA on the maturation of NCV remain to be confirmed.

Immaturity of electrophysiological response of the neonatal auditory brainstem to high repetition rates of click stimulation

Changes in brainstem auditory evoked response (BAER) with varying stimulus repetition primarily represent neural processes concerning the efficacy of synaptic transmission in the brainstem auditory pathway. In this study the BAER to different rates of clicks was recorded from 16 term neonates. The results were compared with those from 16 adults to examine whether the degree of maturation of synaptic transmission of the neonatal brainstem auditory pathway parallels that of general function of the pathway. All BAER wave latencies and interpeak intervals increased linearly and wave amplitudes reduced with increasing click rate. The absolute rate-dependent changes in BAER measures were much greater in the neonates than in the adults, reflecting a significant immaturity in the efficacy of synaptic transmission in the neonatal auditory brainstem and in the ability of the neonatal brainstem to process rapid acoustic stimulation. When the data obtained at higher click rates at various age groups were analyzed as percentages, using the BAER measurements at conventionally used slow rate (21/s) of clicks as the denominators, the changing rates (%), or relative changes, of most BAER measures at higher rates in the neonates were still greater than those in the adults. Therefore, the rate-dependent BAER changes in the neonates are relatively less mature than general aspects of the BAER, reflected by the BAER elicited with conventionally used slow rates of clicks. These findings suggest that synaptic efficacy in the neonatal brainstem auditory pathway is relatively less mature than general function of the pathway and thus may be more susceptible to unfavourable perinatal conditions.

The development of auditory behavior (or what the anatomists and physiologists have to explain)

OBJECTIVE

Infants' and children's performance in detecting and discriminating between sounds is often poorer than that of adults. Behavioral immaturity often coexists with mature-looking morphology and physiological responses from the peripheral and brain stem structures that limit performance among adults. One interpretation of this pattern of results is that "hearing" is mature but some unnamed central process is immature.

DESIGN

The approach to the problem taken here is to view auditory behavior as the process to be explained and physiological or anatomical measurements as giving us clues about the underlying processes. The development of four aspects of hearing-frequency resolution, detection, temporal resolution, and intensity resolution-is reviewed in this paper, and new data addressing these topics are presented.

RESULTS

Frequency resolution, detection, temporal resolution, and intensity resolution all undergo development during infancy and childhood, although the mechanisms underlying development vary across capacity and developmental period.

CONCLUSIONS

A coherent argument can be made that both primary auditory pathway maturation and maturation of specific central processes are involved in development. Both types of maturation continue into childhood, and both types of maturation can influence hearing directly.

Visual evoked potentials and dietary long chain polyunsaturated fatty acids in preterm infants

The influence of dietary long chain polyunsaturated fatty acid (LCP) supply, and especially of docosahexaenoic acid (DHA), on evoked potential maturation, was studied in 58 healthy preterm infants using flash visual evoked potentials (VEPs), flash electroretinography (ERG), and brainstem acoustic evoked potentials (BAEPs) at 52 weeks of postconceptional age. At the same time, the fatty acid composition of red blood cell membranes was examined. The infants were fed on breast milk (n = 12), a preterm formula supplemented with LCP (PF-LCP) (n = 21), or a traditional preterm formula (PF) (n = 25). In the breast milk and PF-LCP groups the morphology and latencies of the waves that reflect the visual projecting system were similar; in the PF group the morphology was quite different and the wave latencies were significantly longer. This could mean that the maturation pattern of VEPs in preterm infants who did not receive LCP was slower. Moreover, a higher level of erythrocyte LCP, especially DHA, was found in breast milk and PF-LCP groups compared with the PF group. ERG and BAEP recordings were the same in all three groups. These results suggest that a well balanced LCP supplement in preterm formulas can positively influence the maturation of visual evoked potentials in preterm infants when breast milk is not available.

Functional auditory development in preterm and full term infants

Bilateral ABRs were recorded from 452 infants 32-45 weeks conceptional age. Differences in laterality, gender and appropriateness for gestational age were investigated in order to increase our understanding of developmental processes in early life. Rate effects were also studied in a subsample of infants (145 ears). All subjects were free of conditions known to affect ABR parameters. Left/right differences were evident for all ABR measures except the amplitude of wave I. Shorter interwave intervals and larger amplitudes were consistently observed on the right. Females exhibited shorter absolute latencies for waves III and V and larger wave I amplitudes than males. Small for gestational age (SGA) infants displayed shorter wave V latencies and interwave intervals relative to AGA infants. These differences, however, disappeared by term age whereas the contrasts in laterality persisted. Increasing the rate of stimulation reduced wave I amplitude irrespective of conceptional age and increased wave V amplitude prior to term. An increase in wave V latency was more pronounced at the higher rate on the left than the right. There was no interaction between rate and appropriateness for gestational age, although SGA infants had shorter wave V and interwave latencies. Our data indicate a slight but significant right ear advantage in the processing of auditory signals. Gender differences were apparent as well. While research on adults and older children have reported similar findings, no other studies to date have observed these results in neonates. The present work also lends support to the view that accelerated neurological development occurs in growth-retarded infants.

Intra- and extra-uterine development of neonatal 3-channel Lissajous' trajectory of auditory brainstem evoked potentials

This study compared intra- and extra-uterine maturation of the auditory pathway, using auditory brainstem evoked potentials (ABEPs), recorded with three orthogonal differential electrode configurations. From the three records of each subject, 3-channel Lissajous' trajectories (3CLTs) were derived and analyzed. 107 newborns were compared at the same gestational and post-conceptional (gestational+postnatal) age, from 29 weeks (wks) up to 43 wks. In addition, we explored the effects and neurophysiological consequences of early exposure to extra-uterine life, on the peripheral and central portions of the auditory pathway. Our findings indicate that exposure of premature infants to the extra-uterine environment is associated with advanced peripheral development, but slower central conduction compared to intra-uterine development.

Effects of Maternal Cocaine Abuse on Neonatal Auditory Brainstem Responses

Auditory brainstem responses (ABRs) were recorded from 18 neonates born to mothers who used cocaine during pregnancy, and from 18 control infants matched to the cocaine group on the basis of birthweight and conceptional age. ABRs were elicited using click signals presented at 40, 60, and 80 dB nHL at a rate of 33 clicks/sec and also at 11 and 89 clicks/sec at 80 dB nHL. The absolute latencies for ABR components I, III, and V and wave I-V interpeak latencies (IPLs) were measured for each signal condition.ABR absolute and IPLs for the infants who had been exposed to cocaine were prolonged relative to their age- and weight-matched controls. Neurodevelopmental compromise of the auditory system appears to result from gestational exposure to cocaine.

Maturation and effect of stimulus rate on brainstem auditory evoked potentials

Brainstem auditory evoked potentials (BAEPs) at three stimulus rates (20, 41.3 and 61.3 c/s) were recorded in 104 normal preterm infants, distributed in four age groups between 32 and 39 weeks (conceptional age), and in 20 normal adults. The latency shifts between 61.3 c/s and 20 c/s, and between 41.3 c/s and 20 c/s, were calculated for each wave, and studied as a function of age. A significant effect of conceptional age was shown on the '61.3-20 c/s' and the '41.3-20 c/s' wave V latency shifts, and a significant difference between adults and newborns was noted for the wave V and wave III latency shifts. No significant difference was obtained for the wave I latency shifts. This suggests that the changes of auditory adaptation with maturation may be predominantly at a central level, i.e. on central synapses.

Critical ages in brainstem development revealed by neonatal 3-channel Lissajous' trajectory of auditory brainstem evoked potentials

Auditory brainstem evoked potentials (ABEPs) were recorded from 91 newborns from 7 age groups between 26 to 43 weeks of gestation. In addition to the widely used vertex-mastoid derivation, potentials were recorded from three orthogonal electrode configurations, and represented in 3 dimensional voltage-space as three-channel Lissajous' trajectories (3CLTs). ABEPs were evoked by alternating polarity, monaural 75 dBnHL clicks presented at rates of 10/s, 55/s and 80/s. Potentials were also recorded to 45 dBnHL and 15 dBnHL clicks presented at 10/s. 3CLT point by point (apex latencies, amplitudes and orientation) as well as planar segment (planar segment position and duration) descriptors, along with peak latencies of the vertex-mastoid peaks, were followed for effects of age, stimulus intensity and rate. ABEPs began to appear consistently at 29 weeks of gestation to high stimulus intensities, with a rapid decrease of ABEP thresholds up to 34 weeks. At 35 weeks, thresholds stabilized approximately at adult values. The results indicate a significant effect of stimulus rate and intensity as well as of gestational age group on apex latencies. The findings also showed changes in apex orientations associated with stimulus rate and intensity interacting with gestational age. 3CLT descriptors enhanced the understanding of these results in relation to developmental and maturational aspects of the auditory system. The results may be explained by maturational change in relative contributions of constituents of the complex ABEP generators.

Normal auditory brain stem evoked responses in infants of diabetic mothers

Auditory brain stem responses potentials were recorded from 71 newborns within the first 2 weeks after birth; conceptional age ranged from 37 to 41 weeks. Thirty-nine newborns were infants of diabetic mothers (IDMs) (17 White A, 22 White B-D) and 32 healthy term newborns served as control group. IDMs with additional high risk for cochlear or brain stem integrity were excluded. Birthweight for gestational age was significantly higher for IDMs. No differences in auditory brain stem responses wave latencies or amplitudes were observed between healthy infants of the control group and IDMs.

Brainstem auditory evoked responses in infants and children with AIDS

Brainstem auditory evoked responses were measured in 16 infants and children with acquired immunodeficiency syndrome (AIDS) and in 9 normal infants and children. Two stimulation rates were used: a conventional rate of 10 Hz and a high rate of 50 Hz. Latencies of waves III, IV, and V on the left were significantly longer in the AIDS group when a stimulation rate of 10 Hz was used. With a higher stimulation rate of 50 Hz, significant differences between the two groups occurred in the latencies of waves I, III, and V bilaterally, but there were no significant differences in the interpeak latencies. A measure of the differential effect of the increasing stimulus rate on the two groups was significant for wave I latency and for I-III and I-V interpeak latencies on the left, revealing that increasing stimulation rate prolongs these measures more in the AIDS group. Increased brainstem auditory evoked response stimulation rate may unmask abnormalities in infants and children with AIDS that are not observed when the lower stimulation rate is used.

Developmental course of brain-stem auditory evoked potentials in the first days of full term infants

Modifications of brain-stem acoustic evoked potentials (BAEPs) in the first 5 days of life of normal full-term infants are reported. BAEPs were recorded using rarefaction clicks at 70, 60, 40, 20 dB HL. Multiple linear regression analysis was performed to evaluate chronological and gestational age differences for all positive and negative peaks, interpeak latencies, amplitudes and amplitude ratios. The percentage of newborn infants with auditory threshold of 20 dB HL increased with the number of days. At all intensities the latency of PIII and PV decreased significantly between the 2nd and 3rd day, while the latency of PI decreased significantly between the 3rd and the 4th day; PIII and PV latencies decreased also between the 4th and the 5th day. The longer the period of gestation the longer was the PI latency recorded between the 2nd and 5th day after birth. The anatomical and physiological changes developing shortly after birth are probably responsible for the above findings. These changes most probably appear firstly in the cochlear and trapezoid nuclei and later on in the organ of Corti.

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 auditory brainstem evoked potentials in newborn infants: a three-channel Lissajous' trajectory study

Auditory brainstem evoked potentials (ABEP) were recorded from 50 newborns (35-43 weeks gestational age), using three orthogonal differential electrode pairs, in addition to the widely used vertex-mastoid derivation. Potentials were evoked by alternating polarity, 75 dBnHL clicks presented monaurally at a rate of 10/s. From the records of the three orthogonal electrode pairs (nasion-inion; vertex-spinous cervical process VII; left-right mastoids), Three-channel Lissajous' trajectories (3CLT) were derived and analyzed. 3CLT point-by-point, as well as segmental descriptors were compared with peak latencies of the vertex-mastoid derivation. Point-by-point 3CLT descriptors included apex amplitude, latency and orientation. Segmental descriptors included planar segment beginning latencies, duration and orientation. The interpretation of these results in relation to developmental aspects of the auditory system, as well as to the question of ABEP generators, is enhanced by using 3CLT descriptors of ABEP, which are more comprehensive than their single-channel counterparts. 3CLT apices correlated well with the Vertex-Mastoid defined peaks. Both peak and apex latency changes indicate that at the developmental stages surveyed in this study, development takes place in the more central portions of the pathway, whereas the peripheral portion is already relatively mature. The results also indicate a maturational change in the relative contributions of constituent generators of ABEP components.

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.

The effect of click rate on latency and interpeak interval of the brain-stem auditory evoked potentials in children from birth to 6 years

Latency and interpeak interval of the brain-stem auditory evoked potentials at different click rates were measured in 80 healthy children from birth to 6 years, and 21 adults. Clicks were presented at 10, 30, 50, 70 and 90/sec, and 70, 40 and 20 dB HL. At high stimulus intensity (70 dB SL), all latencies of waves I, III and V and the I-V, I-III and III-V intervals showed a progressive prolongation with increasing repetition rate. The latency- and the interval-rate functions were similar for all age groups but their slopes were slightly steeper in younger than in older. As click rate increased from 10/sec to 90/sec, the latencies of waves I, III and V at different age groups were prolonged by 4-10%, 9-13% and 12-15% respectively, and the intervals of I-V, I-III and III-V were prolonged by 15-16%, 8-16% and 14-24% respectively. The mean increments of wave V latency and I-V interval in different age groups were 0.404-0.575 and 0.332-0.526 msec respectively with increasing click rate from 10 to 50/sec, and 0.697-1.009 and 0.629-0.776 msec respectively with increasing click rate from 10 to 90/sec. The younger the age the larger the absolute increments for all these BAEP parameters, but the increasing rates for a BAEP measure were similar among different age groups, exhibiting no age-dependent differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory brainstem of the ferret: maturation of the brainstem auditory evoked response

A longitudinal study of developmental changes in the brainstem auditory evoked response (BAER) was made on 19 ferrets between postnatal days 25 (P25) and 50. Responses to free-field click stimuli were recorded from anaesthetized animals, and compared with data obtained from 8 adult ferrets. A reproducible BAER was first recordable on P27, although the response onset was generally later in smaller animals. BAER onset preceded eye opening, which started on P32. Adult-like thresholds were observed in all animals by P40, but the age at which they were attained was also dependent on size. The BAER in the adult ferret consists of 4 main vertex-positive peaks occurring in the first 5 ms following transient acoustic stimulation. In the youngest animals the presence of an additional peak (between II and III) and the slurring of peaks III and IV were consistent features. The individual peaks undergo an asymmetrical pattern of development, with mean peak I latency attaining an adult value at P40, while mean peak IV latency is still 115% of the mean adult value at that age. BAERs could routinely be recorded using high stimulus presentation rates (greater than 40/s), though an increase in absolute and interpeak latencies occurred, the extent of which decreased with age. The pattern of BAER development in the ferret is compared with that in other species, and the concept of the 'silent period' (period between conception and onset of hearing) as a standard unit of auditory development is introduced.

Brain-stem auditory evoked responses as indicators of early brain insult

The relationship between cranial ultrasonograms (SONOs) and brain-stem auditory evoked responses (BAERs) was evaluated in 2 independent samples of newborn infants at risk for brain injury (n = 113 and 203). Features of the BAER wave forms subjected to stepwise linear discriminant analysis formed the basis of an algorithm used to detect and follow early brain injury. Using this algorithm, information derived from BAERs reliably predicted SONO abnormalities at least 82.3% of the time in the initial study which was replicated with the second sample (77.3%). The wave I component latency (CL) and the wave III-V inter-peak latency interval (IPL) were independent of each other, and both contributed to a prediction of SONO abnormality. Possible mechanisms for these BAER results include compromise to the cochlear membrane or to the auditory nerve itself as well as prolongation of transmission in the brain-stem due to brain-stem hemorrhage, edema, or compression. Normative BAER values and non-linear regression functions for the wave I, III and V CLs, and the I-III, III-V, and I-V IPLs were calculated across age using data from 109 infants who demonstrated normal BAER patterns and had no history of SONO abnormalities. Our analyses indicate BAER techniques, where a single higher intensity is used to produce the BAER wave form, are both valid and efficient for use in the evaluation of early brain injury.