Early Human Development, 23 (1990) 41-51 Elsevier Scientific Publishers Ireland Ltd.

41

EHD 01073

Early development of brainstem auditory evoked potentials in Down’s syndrome Ze Dong Jiangasb, Yun Ya Wu” and Xiang Yun Liu” 9epartment of Child Health, Children’s Hospital, Shanghai Medical University, Fenglin St., Shanghai, 2ooO32 (P.R.C.) and 9epartment of Perinatal Medicine, King George V Hospital, Missenden Road, Camperdown, Sydney, N.S. W. 2050 (Australia) (Received 6 December 1989; revision received 30 March 1990; accepted 17 April 1990)

Summary Early development of brainstem auditory pathway was studied in 14 children with Down’s syndrome (age range from 1 month to 3 years). The brainstem auditory evoked potentials (BAEP) during infancy was characterised by elevated threshold and poorly differentiated wave I. All children within 2 years had elevated threshold in one or both ears, suggesting a high incidence of peripheral hearing deficits. Follow-up tests showed that as age increased up to 3 years the elevated threshold gradually decreased and the differentiation of wave I improved. The I-V interpeak interval was slightly shorter and the amplitude of wave V was smaller than the normal controls, which existed continuously during follow-up studies. Our findings suggest that the development of peripheral hearing is delayed, although persistent hearing deficits cannot be excluded, and the functioning and development of the brainstem auditory pathway may also be abnormal in Down’s syndrome children. Down’s syndrome; hearing development; developmental delay; children.

brainstem auditory

evoked potentials;

Introduction Down’s syndrome is the most common autosomal chromosome abnormality liveborn infants. It is well known that the most serious defect in Down’s syndrome mental retardation. However, there is limited knowledge of early development auditory function in such patients. The reason is, in part, related to the difficulty

in is of in

Correspondence to: Ze Dong Jiang, Department of Perinatal Medicine, King George V Hospital, Missenden Road, Camperdown, Sydney, N.S.W. 2050, Australia. 0378-3782/90/$03.50 0 1990 Elsevier Scientific Publishers Ireland Ltd. Published and Printed in Ireland

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obtaining valid information by means of conventional audiometry from such severely or profoundly retarded infants and children who are unable to cooperate appropriately during tests. It has been reported that 80% of the profoundly retarded and 51% of the severely retarded are untestable by conventional audiometric techniques [ 11, although there are many behavioral evidences that the auditory system is more likely to show dysfunction than are other sensory systems [2-41. The brainstem auditory evoked potential (BAEP) testing has been widely proved to be an objective electrophysiological.technique for evaluation of functional integrity of the brainstem auditory pathway. The BAEP consists of a series of waves which represent, respectively, the bioelectrical activity of the auditory nerve (wave I) and the specific brainstem auditory relay nuclei (from wave II to wave V) despite some ambiguity as to the exact generator of later waves [5,6]. Since BAEP has a close relationship to the anatomy of brainstem pathways, it also offers a neurophysiological indicator of brainstem function. The major advantage of BAEP is that it is independent of attention [7] or the state of consciousness [8,9], and is resistant to drugs [ 10,111. Therefore, BAEP testing is a technique which is particularly applicable to the difficult-to-test patients who are too young or too impaired physically or mentally to cooperate appropriately. Over the past two decades, many investigators have studied evoked potentials in Down’s syndrome [ 12-241. Some studies have shown that the amplitudes of long latency evoked potentials were larger in such individuals than in normal controls [ 14 -171. Ellingson [ 181 recorded stroboscopic visual evoked potentials (SVEP) and photic driving responses in 7 infants with trisomy-21. Compared with 12 normal full term infants, P2 latency in the trisomy-21 group was significantly prolonged at 1 week of age only, and this difference disappeared by 6 months. The optimal photic driving frequencies were found to be consistently (but not significantly) lower than normal infants. This suggested that the electrophysiological differences between trisomyand normal infants were subtle and transient [ 181. The BAEP of Down’s syndrome have also been studied recently [ 12,13,21-241. Widen et al. [23] reported BAEP results in young adults with Down’s syndrome. BAEP detection levels were elevated, response amplitude was reduced, and latency-intensity functions were significantly steeper for the subjects with Down’s syndrome than for the control group. These findings were associated with a high frequency (8000 Hz) hearing loss prevalent in the otherwise normal-hearing experimental group [23]. Galbraith (1984) analysed the BAEP results of five Down’s syndrome individuals using latency compensation analysis (LCA) and came to the conclusion that certain forms of mental retardation may be characterised by reduced stability in a neural system which is thought to be dependent upon “synaptically secure” neurons [21]. The data of the BAEP in Down’s syndrome children are rare. Folsom et al. [22] recorded BAEP in Down’s syndrome infants at the ages of 3, 6 and 12 months. These infants showed, in general, shorter absolute wave V latency values and steeper latency functions across intensity, indicating that cochlear function in Down’s syndrome infants may differ from normal infants [22]. In the present study, BAEP was recorded and followed prospectively in 14 Down’s syndrome children aged from birth to 3 years. The results were compared

43

with those of 134 age-matched normal children. Our purpose was to investigate early functional development of the brainstem auditory pathway in Down’s syndrome and to provide valuable information for establishment of an early medical intervention program in Down’s syndrome children. Subjects and Methods Subjects The subjects studied were selected from the Department of Child Health, Children’s Hospital, Shanghai Medical University. All children were screened and excluded from participation in the study if there were major perinatal complications, such as asphyxia, periventricular haemorrhage, intrauterine infection, based on clinical signs and laboratory examinations. The Down’s syndrome group was composed of 14 children (8 males and 6 females) who were diagnosed as trisomy-21 by karyotype. They were born at 37 to 40 weeks gestation and enrolled in the study at 1 month after birth to 3 years of age. Among them, 8 children were followed up two to five times. Normal control group included 134 children, 64 males and 70 females. The gestational age ranged from 37 to 42 months. All these children had normal neuropsychological development and had no hearing disorder or neurological disease. The age at testing ranged from 1 month post term to 3 years. The children were divided into 6 age groups, each group consisting of 14 to 32 children. Normal hearing level (nHL) was referred to average click thresholds obtained from 21 healthy adults (age range 22 to 36 years) with normal hearing tested in the same environment. The hearing thresholds in all children were within normal range (20 dB nHL or less). BAEP recording The children were tested in the supine position during sleep, sedated with chloralhydrate by mouth to minimise muscle artefacts and get satisfactory recordings. This was approved by the Academic Committee of this institution and was carried out with the consent of the parents. The BAEP recording was undertaken in a soundproofed and electrically shielded room. The active silver-silver chloride electrode was placed on the forehead at midline just below the hairline. The reference electrode was placed on the mesial surface of the earlobe of the ear ipsilateral to the sound stimuli and the ground electrode on the corresponding position of the contralateral earlobe. Interelectrode impedance was kept below 5,000 R. Rarefaction clicks were generated monaurally by 0.10 ms rectangular pulses delivered to the matched earphones which were magnetically and electrically screened. The contralateral ear was masked with white noise. The stimulus intensity was started at 80 dB nHL and decreased by 5-10 dB steps until no identifiable wave V was obtained to assess the response threshold. The repetition rate of click was usually fixed at 10 Hz and was increased to 30, 50, 70 and 90 Hz if the threshold was normal or nearly normal. Evoked responses were preamplified and filtered through a bandpass of 100-2000 Hz. Each trial consisted of 1024 averaged responses and was repeated for two to four times to ensure reproducibility. Both ears were tested separately for each child.

44

The evoked potentials was obtained with a two channel averager (PC/XT). A MPC40 Printer/Plotter was used to record BAEP results. Analysis of BAEP results The BAEP parameters analysed included waveform, peak latency, interpeak interval, wave amplitude and response threshold. In addition, III-V/I-III interval ratio, which is a parameter we proposed to evaluate accurately the relative development of the I-III interval and the III-V interval [25], was also analysed. The peak latency of BAEP was measured by locating the cursor on the peak of waves displayed on the screen with a digital readout in the cursor position provided by the computer. Wave amplitude was obtained from the distance between the positive peak and the subsequent negative trough. The BAEP results of children with Down’s syndrome were compared individually with normal controls at comparable ages. Results The BAEP in normal children demonstrated a clear developmental change. All latencies of waves I to VII and all interpeak intervals of I-V, I-III and III-V were markedly prolonged at early infancy relative to the values of adults. As age increased, the wave latencies and interpeak intervals decreased with the greatest developmental change occurring at early infancy. No significant differences were found between 2-3 years group and adult group for I-V interpeak intervals. The III-V/I-III interval ratio increased slightly with advancing age. By 2 to 3 years of age, the interval ratio remained smaller than that of adults. The means and standard deviations of main BAEP parameters were shown in Table I. Waves I, III and V can be clearly recognised in all children. Only five infants of less than 3 months of age showed poorly differentiated wave I. The amplitudes of all waves were relatively smaller at early infancy and increased with advancing age. With increasing repetition rate, all wave latencies and interpeak intervals increased (the details have been published elsewhere [26]), and all wave amplitudes diminished. As repetition rate increased from 10 Hz to 90 Hz, the I-V interpeak interval increased by 15-16% and the amplitude of wave V diminished by 25-41% at different age groups. The response thresholds in all children were below 20 dB nHL. In children with Down’s syndrome, the main details of BAEP results were shown in Table II. Compared with normal children, the major abnormalities were significantly elevated response threshold and poorly differentiated wave I during early infancy (Figs. 1,2). Of three infants of less than 3 months of age, wave I could not be detected in two infants and was very poorly differentiated in one infant. The thresholds were markedly elevated (greater than 50 dB nHL) in all six ears of the three infants. In 8 children of 4 to 15 months of age, the response thresholds were elevated (greater than 20 dB nHL) in 12 ears (75%) and were normal (20 or less dB nHL) in only four ears (25%). The differentiation of wave I was also poor in most recordings and the waveform was difficult to recognise when response threshold was greater than 50 dB nHL. Two children of 18 and 27 months of age had well recognised wave

45 TABLE I Mean and standard deviation of main BAEP parameters in normal children (70 dB HL).

Age (months)

Ears (N)

l-2

42

3

27

6

23

9

34

12-18

58

24-36

63

Adult

35

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

Latency of wave I (ms)

Interpeak interval (ms)

111-v/1--111

l--III

III-V

I-V

1.94 0.17 1.90 0.16 1.85 0.14 1.78 0.09 1.84* 0.18 1.76 0.15 1.71 0.11

2.83 0.18 2.77*’ 0.17 2.62’; 0.14 2.43 0.19 2.38* 0.19 2.23 0.15 2.09 0.15

2.06 0.20 1.99 0.14 1.95 0.14 1.86 0.20 1.82 0.16 1.82 0.15 1.84 0.18

4.89 0.24 4.80** 0.24 4.56** 0.12 4.29 0.23 4.21* 0.21 4.04 0.20 3.94 0.18

0.73 0.09 0.72 0.08 0.74 0.11 0.77 0.11 0.78 0.11 0.82; 0.09 0.89 0.13

Comparison of statistical difference of one group from the following group: *P < 0.05, **P < 0.01and no mark representing P> 0.05.

I, slightly elevated threshold in three ears and normal threshold in one ear. Both the waveform of wave I and response threshold were normal in the remaining oldest child of 35 months of age. The latencies of waves I and V were usually slightly below the mean value of normal controls at the same dB sensation level (SL) clicks. The I-V interpeak interval in most children with Down’s syndrome was also slightly below the mean value of normal controls, and in three children was below two standard deviations of the mean value. The I-III and III-V interpeak intervals in all children with Down’s syndrome were within two standard deviations of the means of normal controls. The III-V/I-III interval ratio was also within the normal range (Table II). With the exception of wave I, other waves were usually recognisable unless the threshold was markedly elevated. The amplitude of wave V was slightly smaller in most Down’s syndrome children than in the normal controls at corresponding intensity above threshold. With increasing repetition rate, the increase in latencies was similar to that of normal children, while the amplitude of wave V diminished more significantly than that of normal children. As repetition rate increased from 10 Hz to 90 Hz the amplitude of wave V diminished by more than 50% in 6 of 8 children whose response thresholds were 40 or less dB nHL. Follow-up tests: The longitudinal BAEP tests in 8 children showed a clear developmental change (Table II, Fig. 2). In four children whose age ranged from 1 to 5 months at initial test (subjects 1 to 4), the response thresholds were markedly elevated and wave I was very poorly differentiated or even could not be detected

46 TABLE II Details of BABP in 14 childrenwithDown’s syndrome. Subject No.

1

2

3

4

Age (month)

1 6 12 18 24 2 6 12 18 4

Undetected Poor Poor Good Good Undetected Undetected Poor Good Poor

12 23 5 12

Poor Good Poor Poor Good Good Good Poor Good Good Poor Good

9

24 11 24 12 24 36 15 21 27 30 34 2

10 11 12 13 14

6 10 12 18 35

5 6

7 8

Morphology of wave I

Good Good Good Poor Good Poor Good Good Good

Threshold (dBnHL) Right

Left

50” 50” 40” 3W 3W 70’ 60” 45” 40” 50” 4@ 20 60” 45” 30” 20” 10 70” 5F 40” 20 10

50” 45’ 3p 20 10 60”

3p 10 5 5W 40” 50” 20 35’ 5

55’ 40” 30” 5@ 40” 35’ 40” 3W 15 40” 25’ 5W 30” 35’ 0 10 40” 10 5 5@ 20 60 30” 20 10

Interpeak interval (ms)

111-v/1-111

I-III

III-V

I-V

-

2.00 1.90 1.80 1.70 1.70 -

-

-

4.10 3.90 3.85 -

0.78 0.77 0.80 -

4.20 4.05 4.60 4.10 3.95 4.2@ 3.75” 3.70 4.25 3.95 -

0.79 0.80 0.80 0.82 0.84 0.83 0.83 0.85 0.70 0.72 -

4.20 3.95 4.10 4.10 4.00 3.85 3.75 -

0.67 0.68 0.78 0.72 0.78 0.79 0.79 -

4.25” -

0.70 -

3.70” 3.95 3.80

0.85 0.75 0.77

2.30 2.20 2.15 2.35 2.25 2.55 2.25 2.15 2.30 2.05 2.00 2.50 2.30 2.45 2.35 2.30 2.35 2.25 2.15 2.10 2.50 2.00 2.25 2.15

2.00 1.85 1.80 2.05 1.85 1.80 1.90 1.70 1.70 1.75 1.65 1.70 1.65 1.60 1.80 1.65 1.75 1.70 1.65 2.10 1.75 1.75 1.70 1.70 1.65

“Abnormal result.

during early infancy. As age increased, the raised thresholds gradually decreased, and wave I became detectable and improved in morphology. The interpeak intervals of I-III, III-V and III-V decreased with advancing age. The I-V interpeak interval in all of the four children was consistently below the mean value of normal children at comparable ages. In subject 4, the I-V interpeak interval was still below two standard deviations of the normal mean value at 12 months. The interpeak intervals of I-III and III-V, and the III-V/I-III interval ratio were within the normal range at the corresponding age. As age increased, the amplitudes of BAEP waves increased, but the amplitude of wave V was continuously slightly smaller than that of normal children at comparable intensity above threshold. In the other four

47

AGE (MONTH1

c

6

12

0.2

I

I

I

0

2

4

I

6 TIME

(MS)

I

I

8

10

12

uv

0.2 uv I

I

I

0

2

4

I 6 TIME

I

I

8

10

12

(MS1

Fig. 1. Comparison between the BAEP recordings of a four months Down’s syndrome infant (B) and a normal infant of the same age (A) at the intensity of 70 dB nHL. v represents wave I, v represents wave V. Fig. 2. Longitudinal BAEP tests in a Down’s syndrome infant from I month to 2 years to show the developmental change of BAEP. The intensity was fixed at 70 dB nHL. v represents wave I, v represents wave V.

children with age range of 11 to 27 months at initial test, the developmental change of BAEP was similar to that of the above four children. Discussion

Our study of normal children shows that the developmental changes in the BAEP are consistent with those reported by other investigators [27]. All wave latencies and the I-V, I-III and III-V interpeak intervals shorten as a function of increasing age, and reach adult values at 2 to 3 years of age. The amplitudes of all BAEP waves increase with advancing age. In addition, we found that the III-V/I-III interval ratio increased with advancing age, indicating that during early childhood, the developmental changes in the I-III and III-V intervals make an unequal contribution to the change in the I-V interval. The shortening of the I-III interpeak interval contributes more than that of the III-V interpeak interval to the shortening of the I-V interpeak interval. Since the III-V/I-III interval ratio could reflect the relative functioning and development of the lower (I-III interval) and upper (III-V interval) regions of the brainstem auditory pathway [25], this observation would be suggestive of slightly faster development of the lower brainstem auditory pathway relative to that of upper brainstem auditory pathway during early childhood.

48

In the early literature, the reported incidences of hearing deficit in Down’s syndrome differ greatly [28,29]. In the past two decades, several authors have observed very high incidence (50-76%) of middle ear dysfunction and of mixed hearing loss in their Down’s populations, regardless of the age studied. The majority of hearing losses are conductive or mixed, and the remainder are sensorineural loss [30-341. Our present data of BAEP study authenticate the very high incidence of peripheral hearing deficit in Down’s syndrome children. The BAEP of these children was characterised by elevated threshold and poorly differentiated wave I during infancy. All children within 2 years had elevated threshold in one or both ears. These results reflect that the deficit in peripheral hearing exist universally in Down’s syndrome children during infancy. However, we found an age difference in the frequency of hearing loss. The threshold of BAEP was higher in younger children than in older children. Follow-up tests showed that as age increased, the elevated threshold gradually decreased and the differentiation of wave I improved. These findings indicate that the deficits in peripheral hearing may improve with maturation during early childhood. This in turn suggests that there is a delayed development in peripheral hearing in Down’s syndrome. However, persistent hearing deficits can not be excluded because the thresholds of BAEP were still abnormal in 50% of the ears studied at the last tests during BAEP follow-up studies (subjects 1 to 8). Furthermore, progressive sensorineural hearing loss has been reported to be frequently seen in Down’s syndrome from middle childhood to adult life [35]. Folsom et al. reported shorter absolute wave V latency in Down’s syndrome infants [22]. Squires et al. also observed shorter BAEP latencies in Down’s syndrome adults when compared with normal controls and other retarded persons [ 121. In the present study, the observations of the latencies of waves I and V are in accord with the above reports. In addition, the I-V interpeak interval in most Down’s syndrome children was found to be slightly shortened and in three children was significantly shortened. This abnormality persisted during follow-up tests. The changes in interpeak intervals of BAEP with increasing age have been attributed to developmental changes in nerve conduction velocity which is associated with axonal diameter and myelination, and synaptic efficacy. The I-V interpeak interval, which is defined as the brainstem conduction time (BCT) or central conduction time (CCT), has been widely used to reflect central nervous system activity at the level of brainstem. The shortened I-V interpeak interval, therefore, reflects that the nerve conduction velocity at the level of the brainstem is abnormal, which in turn suggests that the functioning and development of central auditory pathway or, more widely, the brainstem could be abnormal in Down’s syndrome. The second possibility is that the shortened brainstem conduction time could be related to structural abnormality in the brainstem or central auditory pathway. It has been reported that the whole brain weight in Down’s syndrome patients is 76% of normal, whereas the brainstem and cerebellum are less than 66% of normal weight which may be consistent with the lack of development in these structures [35]. The third interpretation is that the shorter I-V interpeak interval could be brought about by high-frequency hearing loss. It has been observed that high-frequency hearing loss prolongs the latencies of the earlier BAEP waves (I-IV) to a greater extent than that of wave V, producing a

49

shortened I-V interpeak interval [36]. Thus, the exact mechanism of the shortened I-V interpeak interval in Down’s syndrome during maturation is open to speculation. The interpeak intervals of I-III and III-V in all Down’s syndrome children fall within normal range at every age. The reason for this may be that the I -V interpeak interval is only slightly shortened and this effect is insufficient to further partition into the I-III and III-V interpeak intervals. The III-V/I-III interval ratio was found to be within normal range in all our Down’s syndrome children, suggesting that the relative function and development of lower and upper regions of the brainstem auditory pathway may be comparable to those of normal children. It is believed by some authors that absolute amplitudes were too variable to be of any clinical use [37]. We have experienced, however, that under satisfactory and consistent experimental conditions, the amplitude of wave V can be employed as a useful parameter of BAEP to assess the brainstem function [38]. Wave V represents a far-field summation of neural activity of many elements. In a previous study of assessment of brainstem function in children recovered from purulent meningitis, we found that the most sensitive BAEP parameter is the amplitude of wave V in that it can reveal more abnormalities in the brainstem which may be detected by using IV IPL or V/I amplitude ratio [39]. In young adults with Down’s syndrome, wave V amplitude was shown to be reduced [23]. In the present study, wave V amplitude in children with Down’s syndrome was also noted to be slightly smaller than in normal children, which existed continuously during maturation. This finding supports the concept of abnormal functioning of the brainstem in Down’s syndrome children. We further observed that with increasing repetition rate, the amplitude of wave V in Down’s syndrome reduced more significantly than in normal children, suggesting that the inferior colliculus in Down’s syndrome may be more vulnerable to increasing stimulus stress. The neurophysiological basis of such stimulus stress effect in Down’s syndrome is unknown. Multiple factors, such as synaptic function, transmitters, axonal conduction and synchrony, have been postulated to be associated with this reversible processes of metabolic exhaustion and recovery following stimulus stress. Our results of this stress test in Down’s syndrome suggest that the shift of interpeak interval which is within normal range, on one hand, and the reduction of amplitude which is abnormal, on the other hand, may represent two different kinds of biological mechanisms probably independent of each other. In conclusion, our findings reveal that in Down’s syndrome, the development of peripheral hearing is delayed, and the functioning and development of the brainstem auditory pathway or, more widely, the brainstem are probably also abnormal. Since hearing deficit hinders the child in the development of ability to learn, to communicate and to socialise, it is essential to identify early and to treat hearing disorders. We proposed that early rehabilitation programs for the developmental delay of hearing should be undertaken in Down’s syndrome infants. Our results validate the use of BAEP testing as a measure of assessing the development and detecting the problems of hearing in children with Down’s syndrome. However, a normal BAEP result does not guarantee a normal hearing. The reason for this is that the BAEP

50

testing reliably measures the transmission of an auditory stimulus only as far as the midbrain, while the hearing dysfunction in Down’s syndrome may also occur at higher levels, which prevent perception or interpretation of the auditory stimuli. Acknowledgments

The authors wish to thank Dr. Xiu Qi Li of the Pathology Laboratory, and Dr. Ling Ying Feng and Ping Chao of the Department of Child Health, Children’s Hospital, for invaluable assistance in collection of data. We are indebted to Mr. Nian Qiang Chen, Mr. Qing Ning Zhang and Mr. Xin Hui Wang for technical advice.

References 1 2 3 4 5 6

7 8 9 10 11 12

13 14 15 16

17

Hogan, D.O. (1973): Errors in computation of hearing loss in studies of large populations. Ment. Retard., 11, U-17. Friedlander, B.Z. (1970): Receptive language development in infancy: issues and problems. MerrillPalmer Q., 16,7--51. Rohr, A. and Burr, D.B. (1978): Aetiological differences in patterns of psycholinguistic development of children of IQ 30-60. Am. J. Ment. Defic., 82,549-553. Burr, D.B. and Rohr, A. (1978): Patterns of psycholinguistic development in the severely mentally retarded: a hypothesis. Sot. Biol., 25, 15-22. Buchwald, J.S. and Huang, C.M. (1975): Far-field acoustic response: origins in the cat. Science, 189,382-384. Starr, A. and Hamilton, A.E. (1976): Correlation between confirmed sites of neurological lesions and abnormalities of far-field auditory brainstem responses. Electroencephalogr. Clin. Neurophysiol., 41,595-608. Picton, T.W. and Hillyard, S.A. (1974): Human auditory evoked potentials. II. Effects of attention. Electroencephalogr. Clin. Neurophysiol., 36,191-200. Sohmer, H., Gafni, M. and Chisin, R. (1978): Auditory nerve and brain stem responses. Comparisons in awake and unconscious subjects. Arch. Neurol., 35,228-230. Amadeo, M. and Shagass. C. (1973): Brief latency click-evoked potentials during waking and sleep in man. Psychophysiology, 10,244-260. Stockard, J.J., Stockard, J.E. and Sharbrough, F.W. (1978): Non-pathologic factors influencing brainstem auditory evoked potentials. Am. J. EEC Technol., 18,177-209. Sanders, R.A., Duncan, P.G. and McCulloch, D.W. (1979): Clinical experience with brainstem audiometry performed under general anesthesia. J. Otolaryngol., 8,24-32. Squires, N., Aine, C., Buchwald, J., Norman, R. and Galbraith, G. (1980): Auditory brain stem response abnormalities in severely and profoundly retarded adults. Electroencephalogr. Clin. Neurophysiol., 50, 172-185. Squires, N., 0110, C. and Jordan, R. (1986): Auditory brainstem responses in the mentally retarded: Audiometric correlates. Ear. Hear., 7, 83-92. Barnet, A.B. and Lodge, A. (1967): Click evoked EEG responses in normal and developmentally retarded infants. Nature (Loud.‘), 214,252-255. Bigum, H.B., Dustman, R.E.. and Beck, E.C. (1970): Visual and somato-sensory evoked responses from mongoloid and normal children. Electroencephalogr. Clin. Neurophysiol., 28,574-585. Gliddon, J.B., Galbraith, G.C. and Busk, J. (1975): Effect of duration of a preconditioning visual evoked responses in Down’s syndrome and nonretarded subjects. Am. J. Ment. Defic., 80, 186190. Gliddon, J.B., Busk, J. and Galbraith, G.C. (1975): Visual evoked responses as a function of light intensity in Down’s syndrome and nonretarded subjects. Psychophysiol., 12,416-422.

51 18 Elllingsion, R.J. (1986): Development of visual evoked potentials and photic driving responses in normal full term, low risk premature, and Trisomy-21 infants during the first year of life. Electroencephalogr. Clin. Neurophysiol., 63,309-316. 19 Squires, N.K., Galbraith, G.C. and Aine, C.J. (1979): Event-related potential assessment of sensory and cognitive deficits in the mentally retarded. In: Event-Related Potentials in Man: Application and Problems, pp. 397-413. Editors: E. Callaway and D. Lehmann. Plenum, New York. 20 Galbraith, G.C., Aine, C., Squires, N. and Buchwald, J. (1983): Binaural interaction in auditory brainstem responses of mentally retarded and nonretarded individuals. Am. J. Ment. Defic., 87,551 -557. 21 Galbraith, G.C. (1984): Latency compensation analysis of the auditory brain-stem evoked response. Electroencephalogr. Clin. Neurophysiol., 58,333-342. 22 Folsom, R.C., Widen, J.E. and Wilson, W.R. (1983): Auditory brain-stem responses in infants with Down’s syndrome. Arch. Otolaryngol., 109,607-610. 23 Widen, J.E., Folson, R.C., Thompson, G. and Wilson, W.R. (1987): Auditory brainstem response in young adult with Down syndrome. Am. J. Ment. Defic., 91,472-479. 24 Stein, L.K., Kraus, N., bzdamar, ij., Cartee, C., Jabaley, T., Jeantet, C. and Reed, N. (1987): Hearing loss in an institutionalized mentally retarded population: Identification by auditory brainstem response. Arch. Otolaryngol. Head Neck Surg., 113,32-35. 25 Bang, Z.D., Wu, Y.Y., Zheng, M.S., Sun, D.K, Feng, L.Y, Pong, Y.M. and Liu, X.Y. (1990): Development of early and late brainstem conduction time in normal and intrauterine growth retarded children. Acta Paediatr. Scand., (in press). 26 Jiang, Z.D., Wu, Y.Y., Zheng, M.S., Sun, D.K., Feng, L.Y and Liu, X.Y. (1990): The effect of click rate on latency and interpeak interval of the brainstem auditory evoked potentials in children from birth to six years. Electroencephalogr. Clin. Neurophysiol., (in press). 27 Mochizuki, Y., Co, T., Ohkubo, H., Tatara, T. and Motomura, T. (1982): Developmental changes of brainstem auditory evoked potentials (BAEPs) in normal human subjects from infants to young adults. Brain Dev., 4, 127-136. 28 McIntyre, M.S., Menolascino, F.J. and Wiley, J.H. (1965): Mongolism some clinical aspects. Am. J. Ment. Defic., 69,794. 29 Fulton, R.T. and Lloyd, L.L. (1968): Hearing impairment in a population of children with Down’s syndrome. Am. J. Ment. Defic., 85,467. 30 Brooks, D.N., Wooley, H. and Kanjial, G.C. (1972): Hearing loss and middle ear disorders in patients with Down’s syndrome. J. Ment. Defic., 16,21. 31 Schwartz, D.M. and Schwartz, R.H. (1978): Acoustic impedance and otoscopic findings in young children with Down’s syndrome. Arch. Otolaryngol., 104,652. 32 Nolan, M., McCartney, E., McArthur, K. and Rowson, V.R. (1980): A study of the hearing and receptive vocabulary of the trainees of an adult training center. J. Ment. Defic. Res., 24,271. 33 Keiser, H., Montague, J., Wold, D., Maune, S. and Pattison, D. (1981): Hearing loss of Down’s syndromeadults. Am. J. Ment. Defic. 85,467. 34 Davies, B. (1988): Auditory disorders in Down’s Syndrome. Scan. Audiol. Suppl. 30,65-68. 35 Crome, L., Cowie, W. and Slater, E. (1966): A statistical note on cerebellar and brainstem weight in mongolism. J. Ment. Defic. Res., 10,69-72. 36 Coats, A.C. and Martin, J.L. (1977): Human auditory nerve action potentials and brain stem evoked responses. Arch. Otolaryngol., 103,605-622. 31 Chiappa, K.H. (1983): Brainstem evoked potentials: Methodology. In: Evoked Potentials in Clinical Medicine, pp. 122. Editor: K.H. Chiappa. Raven Press, New York. 38 Jiang, Z.D. (1988):\Brainstem Auditory Evoked Potentials in Normal and Developmental Delayed Children. Doctoral dissertation, Shanghai Medical University. 39 Jiang, Z.D., Liu, X.Y., Wu, Y.Y., Zheng, M.S. and Liu, H.C. (1990): Longterm impairments of brain and auditory function in children recovered from purulent meningitis. Dev. Med. Child. Neurol., 32,473-480.

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

Early development of brainstem auditory pathway was studied in 14 children with Down's syndrome (age range from 1 month to 3 years). The brainstem aud...
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