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Results: 4

1.
Fig. 2.

Fig. 2. From: Contribution of active hair-bundle motility to nonlinear amplification in the mammalian cochlea.

Effects of interference with active hair-bundle motility and somatic motility. The responses to SPLs from 90 dB to 40 dB are arranged in a chromatic sequence; pale blue shading highlights the range of sensitivities after treatment. (A) After 15 min of perfusion into the perilymph of the scala tympani, 3 mM salicylate reduced the sensitivity to the level characteristic of anoxia. (B) Following 60 min of endolymphatic iontophoresis, BAPTA likewise lowered sensitivity to the anoxic level. (C) Perilymphatic perfusion of 150 mM KCl, which affects both active hair-bundle motility and somatic motility, reduced the sensitivity to that after anoxia. The peaks of the traveling waves in A–C, which are indicated in each panel by arrowheads, shifted basally after each treatment to resemble those after anoxia. (D) Endolymphatic iontophoresis of Ca2+ moderately reduced the traveling wave’s sensitivity and narrowed its range. (E) Rp-cAMPS, which interferes with the activation of protein kinase A, reduced the sensitivity of basilar-membrane oscillation. (F) 8-Br-cAMP, a lipid-soluble analog of cAMP that promotes protein phosphorylation, also diminished the sensitivity. In D–F the peaks of the traveling waves moved basally to a lesser extent and broadened less than during anoxia. Note the different abscissa scales, which reflect the sizes of the apertures through which the interferometric measurements were made.

Fumiaki Nin, et al. Proc Natl Acad Sci U S A. 2012 December 18;109(51):21076-21080.
2.
Fig. 4.

Fig. 4. From: Contribution of active hair-bundle motility to nonlinear amplification in the mammalian cochlea.

Generic behavior near a Hopf bifurcation. (A) Two distinct regimes emerge for a system’s sensitivity near a Hopf bifurcation. The response is linear below a crossover value of the pressure but becomes nonlinear with an exponent of –2/3 for stronger stimulation. (B) Simulations based on the normal form of the Hopf bifurcation at a position near the peak of the traveling wave demonstrate behaviors similar to those observed experimentally. Small values of the linear coefficient a, which correspond to low viscous damping, lead to predominantly nonlinear behavior (red line) similar to that in control experiments. Increasing the coefficient a by a factor of five reduces the sensitivity and renders it constant for most of the range of SPLs (continuous blue line). An additional tenfold increase in a reduces the sensitivity to the level observed after anoxia (black line). For the value of a used for the continuous blue line, reducing the coefficient b that controls the nonlinearity to 10% of its original value does not change the sensitivity for low sound pressures but increases the sensitivity and enhances linearity at high sound pressures (dashed blue line).

Fumiaki Nin, et al. Proc Natl Acad Sci U S A. 2012 December 18;109(51):21076-21080.
3.
Fig. 1.

Fig. 1. From: Contribution of active hair-bundle motility to nonlinear amplification in the mammalian cochlea.

Characteristics of the traveling wave on the chinchilla’s basilar membrane. (A) Schematic illustrations depict the cochlear traveling wave under control conditions (Upper) and after anoxia (Lower). In each diagram the black line shows the instantaneous position of the traveling wave on the basilar membrane and the shaded area represents the envelope through a complete cycle of oscillation. (B) Interferometric measurements indicate the velocities of basilar-membrane oscillation in response to pure-tone stimulation at 9 kHz. The convergence of the curves toward their peaks indicates that the traveling waves under control conditions (Upper) are compressive at stimulus levels exceeding 40 dB SPL. In contrast, the velocities measured after anoxia (Lower) scale linearly with sound pressure and the peaks are shifted basally. The results are plotted in 10 dB decrements in stimulation from 90 dB to 40 dB SPL. In this and subsequent illustrations, levels are arranged in a chromatic sequence and the cochlear base lies to the left. (C) Dividing the velocities by the stimulus pressures yields sensitivity measurements. Because the active process is most effective during weak stimulation, the sensitivities are greatest at low SPLs (Upper). In the absence of the active process, the sensitivity curves of an anoxic preparation are superimposed (Lower). In this and subsequent illustrations, pale red shading indicates the entire range of sensitivities under control conditions and pale gray shading shows that after anoxia.

Fumiaki Nin, et al. Proc Natl Acad Sci U S A. 2012 December 18;109(51):21076-21080.
4.
Fig. 3.

Fig. 3. From: Contribution of active hair-bundle motility to nonlinear amplification in the mammalian cochlea.

Analysis of amplification and nonlinear compression. Level functions relate the sensitivity of traveling-wave responses at a particular location on the basilar membrane to the strength of stimulation. The control data (red) in each panel demonstrate linear behavior for stimuli below 50–60 dB SPL and compressive nonlinearity at higher levels. The responses after anoxia (black) reveal the behavior of the passive cochlea. The difference between the two sets of curves represents the gain at each level of stimulation, with values up to 100× for weak stimuli. (A) Perilymphatic perfusion of 3 mM salicylate for 15 min lowered the sensitivity to the level encountered after anoxia. The blue data in this and subsequent panels represent the responses after treatment. (B) BAPTA iontophoresed into the endolymph eliminated mechanoelectrical transduction and rendered the cochlea passive. (C) A high K+ concentration in the perilymph depolarized hair cells, perturbing both active hair-bundle motility and somatic motility, and lowered the sensitivity to the value after anoxia. (D) Raising the endolymphatic Ca2+ concentration by iontophoresis, a procedure meant to partly block transduction channels, desensitized the traveling wave and rendered its behavior linear. A gain of about 10× nonetheless persisted. (E) Rp-cAMPS reduced the cochlear gain to a similar extent but spared some nonlinearity; (F) 8-Br-cAMP also reduced both the gain and nonlinearity.

Fumiaki Nin, et al. Proc Natl Acad Sci U S A. 2012 December 18;109(51):21076-21080.

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