Maturation of Cochlea, Auditory Nerve and Brainstem as Observed by Auditory Brainstem Evoked Potentials in Human Infants and children R. C. DEKA, D. DEKA 8- S. K. KACKER
M y e l i n a t i o n of t h e 8th nerve and M a t u r a t i o n of t h e brainstem have a direct relationship t o t h e function of hearing and speech development. If disease conditions a f f e c t t h e p a t h w a y d~ring early childhood, damage results in deficit of a u d i t o r y Qnd speech skills. W e have studied this by employing auditory brainstem evoked potentials in 11 children (1 m o n t h to 2 years). From 1 month to 6 months, there is no evidence of significant myelination at ABER testing. It becomes clearly evident soon a f t e r and it is completed a t 2 years of age.which is comparable to adult values. The cochlea fully develops at birth as evidenced by w a v e I latency w h i c h ,s comparable to adult values. Since Hec~ : and Galambos (1974) published their work on auditory brainstem evoked potentials in human infants, a number of publications has appeared in the literature during the last decade (Sohrher and Feinmesser, 1973, Starr et. al. 1977, Mokotoff et. al. 1977 ; Smith and Simmons 1982 ; Chiappa, 1983). This technique is used now a days routinely in most of the audiologic and rehabilitation clinics for assessing nearing function in at risk patients such as perinatal jaundice, congenital rubella, menirrgitis, consanguinity etc. Numbers of other conditions in pediatric practice also attracted this technique. These include (a) (a) perinatal asphyxia (b) prematurity (c) mental retardation (d) sudden infant death syndrome and Apnea as well ~s "'nearmiss'" SI DS, (e) metabolic disorders such as nonkitotic hyperglycaemia with intractable seizures (f)~Leigh'sdisease (g) brainstem glioma, and ( h ) h y drocephalus.
In children, speech and language-skills alongwith mental development mostly depend on the effective auditory function. Early detection of any hearing deficit in infants and children is the key to successful rehabilitation programme. In this paper, our aim is to establish normative data in infants upto 2 years of age and also to know the pattern of maturation o f the auditory pathways as the age advances during perinatal and postnatal periods. Although we are using this technique for evaluation of auditory function in at-risk children and in in those already handicappe~l in speech-language and au~litory skills, it would be communicated in a separate article (Deka and Kacker 1985).
Auditory brain stem evoked potentials can ,provide the status of neural elements within the auditory pathways. It includes, the cochlea, eighth nerve, with its segments in the petrous bone and From : Evoked Potentials Laboratory, Department of E.N.T. All India Institute subarachnoid space and its entry into the brainstem at the postof Medical Sciencs, New Delhi. medullary border ; the cochlear This work was partly supported by a Instinucleus in the upper part of the tute's Research Research Grant and also lower third of the pons, the lateral by the N.E.S. India. leminiscus-tracts and nuclei in ths Reprint request to : Dr. R. C. Deka, Assistant Professor, mid to upper pons, the inferior Incharge of Evoked Potential Laboratory, colliculus in the midbrain and the medial geniculate body. in the Department of Otolaryngo~ogy. All India Institute of Medical Sciences, thalamus. Ponrine auditory strucNew Delhi. --10029 tures are situated in the most Indian Journal of Otolaryngology, Volume 38, No. 2, June, 1986
posterior and lateral regions of the tegmentum. Both ipsilaterally and contralaterally the auditory input ascends and there are crossing fibres at each level of w a v e generations in the brainstem upto ¢he inferior colliculus. These structures are packed into a relatively small area. The distance between the entry of the eighth nerve into the brainstem and the inferior collicules is 2.5 to 4.0 cm (Chiappa, 1983) and the sites of wave generations are therefore ~s follows : W a v e I at the distal end of eighth nerve, wave II, cochlear nucleus, wave III superior olivary nucleus, wave IV lateral leminiscus, wave V, the inferior colliculus, waves VI and VII are poorly understood.
Materials and M e t h o d s Materials included 11 infants/children(6 males/5 females) with varying ages from 1 month to 2. years. They were otherwise normal babies at ENT Examination before subjectirrg-~nem to the auditory brainstem evoked potentials. The conventional far-field scalp electrode-averaging technique employing "ERA-2250' electrical averaging system (Madsen Electronics) was used in the study. The technique of recording was as follows : The reference electrode was placed on the mastoid of the test 56 ak.
MATURATION OF COCHLEA, AUDITORY NERVE AND BRAINSTEM AS OBSERVED BYAUDITORY BRAINSTEM EVOKED POTENTIALS IN H U M A N INFANTS AND CHILDREN--DEKA e t a l side, the active electrode over the forehead (vertex positive up) and the ground on the opposite mastoid. The electrode resistance was kept, at 4-6 Kohms in the preamplifier. The T D H w 3 9 headphones were employed. It was however, held by the side of the test ear as it could not be applied tightly as in the case of adult. This factor might allow some leakage of the stimulus. The laboratory is a sound proof room. The intensity used was considered to be equivalent to 80 dB SL as used in the: case of normal adults in the same laboratory. The stimulus employed was a 4 KHz monoaural filtered clicks delivered at the rate of 29 per sec and a total of 2048 clicks were averaged to obtain a response. The stimulus was given in three polarities such as negative (Rarefaction) positive (condensation) and alternately -~ve and --ve, and a number of readings were taken both from right and/or left ears until two consistent and identical tracings were obtained. Selected tracings were copied with the help of x-y plotter for record as well as final analysis. However, latency values were calculated from the built-in-computer in the machine for all the waves (I through V) and the inter peak latency, for I-Ill, III-V and I-V with the help of cursors in the machine. Amplitudes were considered for wave dentification. They were variable ;and it was therefore not calculated for analysis. Results
Results are shown in table No. I and II for infants from 1 month age to 6 months and in table ill and IV for children from one-year~ to 2 years of age. Only the absolute latency and interpeak latency (mean, S/D, ranges) are shown. Figure I shows how systemitically the values for interpeak latency gets decreased as the age advances. Representative tracings of wave patterns at different ages upto 2 years are shown in the figure. Comments The cochlea develops fully at birth and it produces responses equi57
1 Year
,ii l
, 6 Month
TTI
tO.
2~ Yeor (
C
C
=
1
~
C
,
I
,r, E
w
0
=
J'¢
. . . . . . .
L . . . .
t4ONTX5 - - - - - -
VELR A G E
Figure 1. Shows how systemetically the values for interpeak latency gets decreased as the age advances, in the latency age curve. Representativetracing of wave patterns at different ages upto 2 years are also shown in the figure with that of an adult control. valent to those seen in adults The myelination of the 8th nerve and maturation of th.~ brainstem takes time. From 1 month to 6 months, the latency values indicate almost the same findings, whereas thereafter the maturation and myelination become evident and it is almost complete by about 2 years of age. By then the values are comparable to those of adults. This indicates that complete myelination and maturation of the 8th nerve and brainstem occur at 2 years of age. Fujikawa and Weber (1977) observed such findings in infants. Hecox (1975) and Salamy et al. (1978)also noted this prc,longation of latency values in infants. These auditory brainstem changes as observed during the
early months of life can b~ explained by the ongoing myelination processes, increasing fibre diameter and increasing efficiency of the symp~tic mechanism (Hecox 1975); Starrelat (1971) Age related such changes in childhood are also mentioned by many authors Fabiani et al. (1979); O'Donovan et. al. (1980) ; Suzuki et. al. (1982) ; and Chiappa, (1983). Disease conditions can affect a child more adversely during the early childhood and cause deafness resulting in speech and language development problem and then the education of such a child becomes difficult. Adequate caution should therefore be exercised in dealing with children in this are group while treating them for other diseases and illnesses. Ototoxic drugs, used in Paediatric
Indian Journal of Otolaryngology, Volume 38, No. 2, June, 1986
MATURATION
OF C O C H L E A ,
BRAINSTEM
EVOKED
AUDITORY
POTENTIALS
NERVE A N D B R A I N S T E M IN H U M A N
INFANTS
TABLE 1 S h o w i n g the absolute latency values in msec (1 months to 6 months of age 6 infants/9 years.) I
II
III
AND
A S O B S E R V E D BY A U D I T O R Y CHILDREN--DEKA
et al.
practices need m o n i t o r i n g in these children. It can be d o n e by a u d i t o r y brainstem evoked potentials.
IV
V References
Mean
1.79
2.8
4.42
5.87
6.75
S/D
0,08
0.09
0.22
0,44
0.17
Range
(1.7-l.9)
(2.7-3.0)
(4.0-4.7)
(5.1-6.5)
(6.6-7.1)
22 TABLE II S h o w i n g the interpeak Latency Values in msec (1 to 6 months of age, 6 infants/9 years).
I-III
IIl-V
I-V
Mean
2.63
2.33
4.99
SD
0.17
0.12
0.13
Range
(2.3-2.8)
(2.2-2.6)
Range
(2.3-2.8)
1.
Chiappa, K.H. (1983). Evoked potentials in clinical Medicine, pp. 138-180, Raven Press, New York.
2.
Deka, R.C. (1985). Auditory brainstem evoked potentials in at-risk children (under preparation).
3.
Deka, R.C., Kacker, S.K. (1985). ABER in Meniere's Disease. Indian J. Otolaryngology, (in press).
4.
Fujikawa, S.K., Weber, B.A. (1977) . Effects of increased stimulus on human brainstem electric response audiometry as a function of age. J. Am. Audio// Soc. 3 : 14.7-150.
5.
Hecox (1975). Electrophysiological correlates of human auditory development. In infant perception ; From sensation to cognitionl: Vol. II : Perception of space, speech and sound. Edited by L. B. Cohen and P. Salapatek, pp. 151-191. Academic Press, New York.
6.
Hecox, K'., Galambos, R. (1974). Brainstem auditory evoked response in human infants and adults. Archives of Otolaryngology. 99 : 30-33.
7.
Mokotoff, B., Shulman--Galambos, C., Galambos, R. (1977). Brainstem auditory evoled responses in children. Arch. Otolaryngol. 103 : 38-43.
8.
O'Donovan, C.A., ' Beagley, H.A. H.A. Shaw, M. (1980). Latency of brainstem response in children. British -. Audiology 14 : 23-29.
9.
Smith, L.E., Simmons, F.B. (1982). Accuracy of auditory brainstem evoked response with hearing level unknown. Ann. Otol. Rhino/. Laryngo/. 94 : 266-267.
10.
Sohmer, H., Feinmesser, M. (1973). Routine use of electrocochleography on human subjects. Audiology 12 : 167-173.
11.
Starr, A., Amile, R.N., Martin, W.H., Sanders, S. (1977). Development of auditory function in newborn newborn infants, revealed by auditory brainstem potentials. 60 : 831839.
12.
Suzuki, J.l., Kodera, K., (1982). Auditory evoked response, Assessment in gology, Ann. N. Y. A. Vol. 388 : 487-495.
(4.4-85.2)
(2.2-2.6)
(4.8-5.2)
TABLE III S h o w i n g the absolute latency values in msec
(1 year to 2 years of age--5 Children/10 years) I
II
III
IV
V
Mean
1.66
2.62
3.93
4.86
5.78
S/D
0,05
0.08
0.11
0.26
0.19
Range
(1.6-1.7)
(2.5-2.7)
(3.8-4.1)
(4.5-5.3)
5.6-6.1 )
TABLE IV S h o w i n g t h e Inter Peak Latency Values in msec
(1 year to 2 years of age, 5 children/10 years)
Mean
I--III 2.27
III--V 1.85
I--V 4.12
S/D
0.11
0.13
0.19
Range
(2.2-2.4)
(1.7-2.0)
(3.9-4.2)
t= P <
..
5.41
t =
8.37
t =
11.47
0.001
P <
0.001
P<
0.001
Indian Journal of Otolaryngology. Volume 38, No. 2, June, 1986
Kaga, K. brainstem Otolaryncad. Sci.
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