Frequency distribution of synchronized spontaneous
otoacoustic emissions showing sex-dependent differences and asymmetry
between ears in 2- to 4-day-old neonates
Liu J, Wang N, Li J, Shi B, Wang H
Int J Pediatr Otorhinolaryngol. 2009 May;73(5):731-6
Department of Otorhinolaryngology Head and Neck Surgery, Beijing Chaoyang
Hospital, Capital Medical University, PR China
OBJECTIVE: The mature pattern of frequency distribution of synchronized
spontaneous otoacoustic emissions (SSOAEs) has been reported to be bimodal
in adults and children between 5 and 11 years of age; however, little
is known about the distribution in neonates between 2 and 4 days after
birth. Furthermore, overall differences in frequency distribution resulting
from difference in sex and asymmetry between ears have not been carefully
examined. The aim of this study is to determine the frequency distribution
of SSOAEs in neonates at 2 to 4 days of age, evaluate the maturity
of the pattern of distribution in this age group, and to evaluate the
effects of differences in sex and asymmetry between left and right ears
on the frequency distribution.
METHODS: We evaluated 224 ears in 112 newborns (59 girls, 53 boys)
whose ages ranged from 2 to 4 days. The SSOAEs were measured using ILO96.
RESULTS: Most of the SSOAEs (86.5%) appeared at frequencies between 1.01
and 4.50 kHz. The overall frequency distribution of the SSOAEs showed
a 'peak-valley-peak' pattern when plotted. Two peaks with maxima
at 1.41-1.60 and 3.01-3.20 kHz were separated by a valley with a minimum
at 2.41-2.60 kHz. Both girls and boys had approximate monomodal patterns
in the distribution of SSOAEs. Significant sex-dependent differences were
noted with more SSOAEs at the lower frequencies (<or=2 kHz) in boys
(46.1%) than in girls (32.0%) (P<0.05) and more SSOAEs at the higher
frequencies (2.51- 4.50 kHz) in girls (50.9%) than in boys (37.5%) (P<0.05).
Both the right and left ears showed the 'peak-valley-peak' pattern that
was similar to the overall distribution pattern. But, compared with the
peaks measured in the left ears at 1.01-1.50 and 3.01-3.50 kHz, the peaks
of the right ears at 1.51-2.00 and 2.51-3.00 kHz were much closer to the
CONCLUSIONS: The overall distribution of frequency of SSOAEs in 2-
to 4-day-old neonates had the similar mature 'peak-valley-peak' distribution
pattern seen in adults. Significant sex-dependent differences of the
SSOAEs frequency distributions have been found. However, only slight ear
asymmetries of the SSOAEs frequency distributions can observed in this
age group. (Bold text emphasis by Martin Braun)
Three years after the first report on the occurrence of the octave distance
in the distribution of spontaneous otoacoustic emissions (SOAEs) by Braun
(2006) we have now a replication of these findings by Liu et al. (2009).
Here the frequency distribution of 769 SOAEs from 224 ears again showed
a clear concentration in the 2-octave range between 1 kHz and 4 kHz,
which corresponds to the range between C6 and C8 in musical terms.
And again the distribution in this range was not normal, but bimodal with
peaks at 1.5 kHz and 3 kHz, corresponding to F#6 and F#7 in musical terms.
Interestingly, the valley between the two peaks was not as deep in the
new data from neonates as it was in the previous data from children and
adults. Also the valley appeared at slightly higher frequencies in the
new neonate data. This indicates that the mechanism which causes the bimodality
is not yet fully mature at birth. Braun's hypothesis that the octave-spaced
peaks at F#6 and F#7 are caused by descending neural input upon the
SOAE generating outer hairs cells in the cochlea is thus supported
by the new data, because this neural system is known to be fine-tuned
As shown in Figs. 2-4 of the new study, effects of side and sex modulate
the distribution pattern. But they cannot be candidates for the cause
of the bimodality, because this is present in all subgroups of the data.
Also, effects of side and sex are fully absent in the previous data from
children and adults (Braun, 2006). These effects are therefore a further
indication of the immaturity of the neonate cochlea. Overall, the concept
that SOAE probability in humans reflects octave-based
processing in the auditory thalamus has gained further strength.
(Comment Martin Braun)