Columella footplate motion and the cochlear microphonic potential in the embryo and hatchling chicken

摘要

A piezoelectric (PZE) vibrator was used to mechanically drive the columella footplate and stimulate the cochlea of chicken embryos and hatchlings. Our objectives were to characterize the motion of the PZE driver and determine the relationship between columella footplate motion (displacement/ velocity) and the cochlear microphonic recorded from the recessus scala tympani (CM,,,). At each frequency, displacement of the PZE driver probe tip was linearly related to the applied voltage over a wide range of attenuation levels (-60 to -20 dBre: 50 Vp-p). The mean displacement across frequencies (100-4000 Hz) was 0.221 +/- 0.042 mu m(p-p) for a constant applied voltage level of -20 dBre: 50 Vp-p. Displacement was within 1.5 dB of the mean for this stimulus level at all frequencies except for 4000 Hz, where it was similar to 3 dB higher (p < 0.01). CMrst amplitudes in hatchlings were larger than amplitudes in embryos (p=0.003). For a given frequency, CM was linearly related to footplate displacement and velocity at both ages. The transform ratio of CMrst/A (CM amplitude/displacement) increased at similar to 6 dB/octave at frequencies between 100 and 1000 Hz in hatchlings suggesting that cochlear impedance (Zc) was resistive at these frequencies. In a large fraction of the embryos, Zc exhibited reactive behavior. (c) 2006 Acoustical Society of America.