Development of wide-band middle ear transmission in the Mongolian gerbil.
Stapes vibrations were measured in deeply anesthetized adult and neonatal (ages: 14 to 20 days) Mongolian gerbils. In adult gerbils, the velocity magnitude of stapes responses to tones was approximately constant over the entire frequency range of measurements, 1 to 40 kHz. Response phases referred to pressure near the tympanic membrane varied approximately linearly as a function of increasing stimulus frequency, with a slope corresponding to a group delay of 30 micros. In neonatal gerbils, the sensitivity of stapes responses to tones was lower than in adults, especially at mid-frequencies (e.g., by about 15 dB at 10-20 kHz in gerbils aged 14 days). The input impedance of the adult gerbil cochlea, calculated from stapes vibrations and published measurements of pressure in scala vestibuli near the oval window [E. Olson, J. Acoust. Soc. Am. 103, 3445-3463 (1998)], is principally dissipative at frequencies lower than 10 kHz.


CONCLUSIONS
(a) middle-ear vibrations in adult gerbils do not limit the input to the cochlea up to at least 40 kHz, i.e., within 0.5 oct of the high-frequency cutoff of the behavioral audiogram; and (b) the results in both adult and neonatal gerbils are inconsistent with the hypothesis that mass reactance controls high-frequency ossicular vibrations and support the idea that the middle ear functions as a transmission line.
Overstreet
Edward H
EH
Institute for Neuroscience and Hugh Knowles Center, Department of Communication Sciences and Disorders, Northwestern University, Evanston, Illinois 60208-3550, USA.
Ruggero
Mario A
MA
D000818:Animals; D000831:Animals, Newborn; D001307:Auditory Perception / Q000502:physiology; D004432:Ear, Middle / Q000502:physiology*; D005849:Gerbillinae; D006309:Hearing / Q000502:physiology; D013016:Sound; D013199:Stapes / Q000502:physiology; D014732:Vibration