The influence of cochlear shape on low-frequency hearing

doi:10.1073/pnas.0710037105

The influence of cochlear shape on low-frequency hearing

*Department of Mathematics, Vanderbilt University, Nashville, TN 37240;
^†Department of Sciences, Technical University of Crete, Hania, Greece 73100;
^‡Auditory Mechanics Section, National Institute on Deafness and Other Communication Disorders, and
^††Laboratory of Bioengineering and Physical Science, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892;
^¶Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02114;
^‖Woods Hole Oceanographic Institution, Woods Hole, MA 02543; and
**Massachusetts Ear and Eye Infirmary, Boston, MA 02114

Edited by Jon H. Kaas, Vanderbilt University, Nashville, TN, and approved February 13, 2008 (received for review October 22, 2007)

Abstract

The conventional theory about the snail shell shape of the mammalian cochlea is that it evolved essentially and perhaps solely to conserve space inside the skull. Recently, a theory proposed that the spiral's graded curvature enhances the cochlea's mechanical response to low frequencies. This article provides a multispecies analysis of cochlear shape to test this theory and demonstrates that the ratio of the radii of curvature from the outermost and innermost turns of the cochlear spiral is a significant cochlear feature that correlates strongly with low-frequency hearing limits. The ratio, which is a measure of curvature gradient, is a reflection of the ability of cochlear curvature to focus acoustic energy at the outer wall of the cochlear canal as the wave propagates toward the apex of the cochlea.

Footnotes

^§To whom correspondence should be addressed. E-mail: chadwick{at}helix.nih.gov
Author contributions: D.M. and R.S.C. designed research; D.M., R.S.C., D.R.K., J.A., and J.T.O. performed research; D.M., R.S.C., and E.K.D. contributed new reagents/analytic tools; D.M., R.S.C., D.R.K., J.A., and J.T.O. analyzed data; and D.M., R.S.C., and D.R.K. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Freely available online through the PNAS open access option.