Hydromechanical Structure of the Cochlea Supports the Backward Traveling Wave in the Cochlea In Vivo

Figure 1

BM and stapes vibration spectra induced by a point stimulation of the BM. (a) The opened cochlea with stimulator and reflective beads in place. The stimulator probe is a blunt pipette driven by a piezoelectric stack. Reflective beads are placed on the BM, labeled as apical, middle, or basal, in the direction away from the stimulator. A bead was also placed on the stapes for recording its vibration. Vibration amplitude (b) and phase (c) of the middle (solid), basal (dash), and the stapes (circle) beads, relative to that of the apical bead. (d) Phase difference (solid) between the middle and basal beads and the calculated group delay (dash). (e) Wave velocity and the wavelength, calculated from the phase difference in . The negative delay value at lower frequencies (<14 kHz) in both (d) and (e) is likely due to a local disturbance, such as the local reflection with the insertion of the stimulator. The wave speed is high at lower frequencies, and the distance between these two beads is small. Both effects make it vulnerable to the disturbance. For a wider range, apical to stapes, this small negative delay is absent (g). (f) Phase difference (solid) between the middle and basal beads and the calculated phase delay (dash). (g) Phase of the stapes vibration (solid) relative to the apical bead and the calculated phase delay (dash).

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