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Basilar membrane mechanics at the base of the chinchilla cochlea. I. Input–output functions, tuning curves, and response phases
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1986
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Mössbauer TechniqueCompound Action PotentialBasilar MembraneChinchilla CochleaAuditory ScienceHealth SciencesAuditory ModelingCochlear NucleiCochlear AnatomyResponse PhasesHuman HearingNervous SystemAuditory Hair CellsBiologyNeurophysiologyNeuroanatomyPhysiologyAuditory PhysiologyCochlear PhysiologyElectrophysiologyCochlear DevelopmentAuditory ComputationNeuroscienceMedicineBasilar Membrane MechanicsAuditory SystemAuditory Neuroscience
Basilar membrane velocity was measured 3.5 mm from the basal end of the chinchilla cochlea using the Mössbauer technique, and cochlear physiological state was inferred from the round‑window compound action‑potential threshold to tone bursts. The basilar membrane exhibits a compressive nonlinearity near its characteristic frequency (8–8.75 kHz) but linear behavior elsewhere, with sharply tuned isovelocity curves (Q10≈6, minima≈13 dB SPL, tip‑to‑tail ratios 56–76 dB, high‑frequency slopes ≈300 dB/oct) that match auditory‑nerve tuning, yet sensitivity at CF progressively declines over time while the nonlinearity can persist, and high‑frequency plateaus appear in both tuning and phase curves.
Basilar membrane (BM) velocity was measured at a site 3.5 mm from the basal end of the chinchilla cochlea using the Mössbauer technique. The threshold of the compound action potential recorded at the round window in response to tone bursts was used as an indicator of the physiological state of the cochlea. The BM input-output functions display a compressive nonlinearity for frequencies around the characteristic frequency (CF, 8 to 8.75 kHz), but are linear for frequencies below 7 and above 10.5 kHz. In preparations with little surgical damage, isovelocity tuning curves at 0.1 mm/s are sharply tuned, have Q10's of about 6, minima as low as 13 dB SPL, tip-to-tail ratios (at 1 kHz) of 56 to 76 dB, and high-frequency slopes of about 300 dB/oct. These mechanical responses are as sharply tuned as frequency-threshold curves of chinchilla auditory nerve fibers with corresponding CF. There is a progressive loss of sensitivity of the mechanical response with time for the frequencies around CF, but not for frequencies on the tail of the tuning curve. In some experiments the nonlinearity was maintained for several hours, in spite of a considerable loss of sensitivity of the BM response. High-frequency plateaus were observed in both isovelocity tuning curves and phase-frequency curves.