Developmental Changes of Mechanics Measured in the Gerbil Cochlea |
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Authors: | Gulam Emadi Claus-Peter Richter |
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Institution: | (1) Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA;(2) Department of Otolaryngology Head- and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, USA;(3) Auditory Physiology Laboratory (The Hugh Knowles Center), Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, USA |
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Abstract: | This report describes stiffness and best frequency measurements obtained in vitro from the basilar membrane of the gerbil
cochlea at the onset of hearing, during hearing maturation, and after hearing has matured. Our stiffness data constitute the
first direct experimental evidence of developmental stiffness changes in the basal and middle turns. Stiffness changes by
a factor of 5.5 in the basal turn between postnatal day 11 and adult, and the difference from adult is statistically significant
for all ages measured up to postnatal day 16. For the middle turn, stiffness changes by a factor of 1.6 between postnatal
day 11 and adult. Whereas for postnatal day 12 and beyond there is no statistically significant difference from adult, our
data suggest that there may be a significant difference of stiffness between day 11 and adult in the middle turn. For the
basal turn, our motion measurements confirm a passive component to the developmental best frequency shift. For the middle
turn, changes in best frequency are not statistically significant. Best frequency was determined by stimulating the tissue
at audio frequencies with a glass paddle and measuring motion with a computer-based imaging system. Tissue stiffness was measured
with a piezoelectric-based sensor system. Tissue stiffness changes have previously been postulated to contribute to the best
frequency shift observed in the cochlear base. Incorporating our data into a simple spring-mass resonance model demonstrates
that our experimentally measured stiffness change can account for the change of best frequency. These results suggest that
a stiffness change is, in fact, a critical component of the best frequency shift observed in the basal turn of the gerbil
cochlea after the onset of hearing. |
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Keywords: | cochlea mechanics development stiffness basilar membrane best frequency |
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