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Morphological Immaturity of the Neonatal Organ of Corti and Associated Structures in Humans

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Abstract

Although anatomical development of the cochlear duct is thought to be complete by term birth, human newborns continue to show postnatal immaturities in functional measures such as otoacoustic emissions (OAEs). Some of these OAE immaturities are no doubt influenced by incomplete maturation of the external and middle ears in infants; however, the observed prolongation of distortion-product OAE phase-gradient delays in newborns cannot readily be explained by conductive factors. This functional immaturity suggests that the human cochlea at birth may lack fully adult-like traveling-wave motion. In this study, we analyzed temporal-bone sections at the light microscopic level in newborns and adults to quantify dimensions and geometry of cochlear structures thought to influence the mechanical response of the cochlea. Contrary to common belief, results show multiple morphological immaturities along the length of the newborn spiral, suggesting that important refinements in the size and shape of the sensory epithelium and associated structures continue after birth. Specifically, immaturities of the newborn basilar membrane and organ of Corti are consistent with a more compliant and less massive cochlear partition, which could produce longer DPOAE delays and a shifted frequency-place map in the neonatal ear.

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Notes

  1. The sectioning angle could also be off-orthogonal in the other direction (i.e., in the direction which would elongate the organ of Corti height rather than the BM width). However, we are confident that we are safe on that score, because the factor controlling that angle is the tilt of the modiolar axis with respect to the horizontal (see Figure 8). If we were “off” in the neonates, the different turns would not appear concentric in 2D reconstructions. Although we did no 2D reconstructions for the present study, the Liberman lab has completed two prior studies of human neonatal cochleae prepared by standard celloidin techniques and can verify that the spirals were just as concentric in the neonatal 2D reconstructions as in the adults.

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Acknowledgments

We thank the anonymous reviewers for their helpful comments on the manuscript.

Funding

This study was supported by grants DC003552 (CA), DC003687 (CAS), and DC0188 (MCL) from the National Institutes of Health.

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Correspondence to Carolina Abdala.

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Meenderink, S.W.F., Shera, C.A., Valero, M.D. et al. Morphological Immaturity of the Neonatal Organ of Corti and Associated Structures in Humans. JARO 20, 461–474 (2019). https://doi.org/10.1007/s10162-019-00734-2

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  • DOI: https://doi.org/10.1007/s10162-019-00734-2

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