How well do we understand the cochlea?

Nobili, Renato; Mammano, Fabio; Ashmore, Jonathan

doi:10.1016/s0166-2236(97)01192-2

Cited by 171 publications

(133 citation statements)

References 72 publications

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“…We have shown that transmission-line models successfully capture long-range fluid coupling in the cochlea, contrary to the claims of Nobili et al (1998Nobili et al ( , 2000Nobili et al ( , 2003aNobili et al ( , 2003b. Indeed, we have established that the long-range component of Nobili et al's threedimensional force propagator is functionally equivalent to the hydrodynamic Green's function of a onedimensional tapered transmission line (see the Appendix).…”

Section: Discussionmentioning

confidence: 85%

“…In particular, they claim that transmission-line models ''reduce fluid coupling to a sort of local interaction, thus failing to represent adequately its long-range character.'' This same criticism also surfaces in a recent review (Nobili et al 1998), in which the authors remark that ''instantaneous hydrodynamic coupling among different basilar membrane portions has a long-range character that is only approximately represented by nearest-neighbour transmission-line interactions.'' As we explain below, these statements misrepresent the nature of the fluid coupling in the one-dimensional model.…”

Section: Are Wave-equation Formulations Unphysical?mentioning

confidence: 80%

“…In recent years, however, Nobili and colleagues have criticized wave-equation formulations of cochlear mechanics on the grounds that they fundamentally misrepresent the hydrodynamics of the cochlea (Nobili 2000;Nobili et al 1998Nobili et al , 2003a. They write, for example, that ''the solutions of the BM [basilarmembrane] motion equation are not of the bi-directional wave-propagation type'' and can ''in no way ... be represented as the superposition of progressive and regressive wave components.…”

Section: Introductionmentioning

confidence: 99%

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Do Forward- and Backward-Traveling Waves Occur Within the Cochlea? Countering the Critique of Nobili et al.

Shera

Tubis

Talmadge

2004

JARO

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The question of whether or not forward-and backward-traveling waves occur within the cochlea constitutes a long-standing controversy in cochlear mechanics recently brought to the fore by the problem of understanding otoacoustic emissions. Nobili and colleagues articulate the opposition to the traveling-wave viewpoint by arguing that wave-equation formulations of cochlear mechanics fundamentally misrepresent the hydrodynamics of the cochlea [e.g., Nobili et al. (2003) J. Assoc. Res. Otolaryngol. 4:478-494]. To correct the perceived deficiencies of the wave-equation formulation, Nobili et al. advocate an apparently altogether different approach to cochlear modeling-the so-called ''hydrodynamic'' or ''Green's function'' approach-in which cochlear responses are represented not as forward-and backward-traveling waves but as weighted sums of the motions of individual basilar membrane oscillators, each interacting with the others via forces communicated instantaneously through the cochlear fluids. In this article, we examine Nobili and colleagues' arguments and conclusions while attempting to clarify the broader issues at stake. We demonstrate that the one-dimensional wave-equation formulation of cochlear hydrodynamics does not misrepresent longrange fluid coupling in the cochlea, as claimed. Indeed, we show that the long-range component of Nobili et al.'s three-dimensional force propagator is identical to the hydrodynamic Green's function representing a one-dimensional tapered transmission line. Furthermore, simulations that Nobili et al. use to discredit wave-equation formulations of cochlear mechanics (i.e., cochlear responses to excitation at a point along the basilar membrane) are readily reproduced and interpreted using a simple superposition of forward-and backward-traveling waves. Nobili and coworkers' critique of wave-equation formulations of cochlear mechanics thus appears to be without compelling foundation. Although the traveling-wave and hydrodynamic formulations impose strikingly disparate conceptual and computational frameworks, the two approaches ultimately describe the same underlying physics.

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Section: Discussionmentioning

confidence: 85%

Section: Are Wave-equation Formulations Unphysical?mentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Do Forward- and Backward-Traveling Waves Occur Within the Cochlea? Countering the Critique of Nobili et al.

Shera

Tubis

Talmadge

2004

JARO

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“…The concept assumes that the cochlea is endowed with a biological energy source that amplifies the ear's input by pumping mechanical energy into the vibrations inside the ear (1)(2)(3)(4)(5)(6). The validity of the concept is supported by the mechanics of the cochlea and its mechanosensory cells.…”

mentioning

confidence: 99%

“…Hair cells, the cochlear mechanosensory cells, provide a source of mechanical energy. In addition to transducing mechanical vibrations into electrical responses, some hair cells are equipped with molecular motors that convert metabolic or electrical energy into mechanical energy, resulting in active movements of the cells (1,(3)(4)(5)(6)(7). These cellular movements, in turn, exert positive feedback on the cochlear mechanics.…”

mentioning

confidence: 99%

Power gain exhibited by motile mechanosensory neurons in Drosophila ears

Göpfert

Humphris²,

Albert³

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

120

137

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In insects and vertebrates alike, hearing is assisted by the motility of mechanosensory cells. Much like pushing a swing augments its swing, this cellular motility is thought to actively augment vibrations inside the ear, thus amplifying the ear's mechanical input. Power gain is the hallmark of such active amplification, yet whether and how much energy motile mechanosensory cells contribute within intact auditory systems has remained uncertain. Here, we assess the mechanical energy provided by motile mechanosensory neurons in the antennal hearing organs of Drosophila melanogaster by analyzing the fluctuations of the sound receiver to which these neurons connect. By using dead WT flies and live mutants (tilB 2 , btv 5P1 , and nompA 2 ) with defective neurons as a background, we show that the intact, motile neurons do exhibit power gain. In WT flies, the neurons lift the receiver's mean total energy by 19 zJ, which corresponds to 4.6 times the energy of the receiver's Brownian motion. Larger energy contributions (200 zJ) associate with self-sustained oscillations, suggesting that the neurons adjust their energy expenditure to optimize the receiver's sensitivity to sound. We conclude that motile mechanosensory cells provide active amplification; in Drosophila, mechanical energy contributed by these cells boosts the vibrations that enter the ear.cochlear amplifier ͉ hearing ͉ auditory mechanics ͉ cell mobility ͉ hair cell T he cochlear amplifier is the dominant unifying concept in cochlear mechanics (1). The concept assumes that the cochlea is endowed with a biological energy source that amplifies the ear's input by pumping mechanical energy into the vibrations inside the ear (1-6). The validity of the concept is supported by the mechanics of the cochlea and its mechanosensory cells. Hair cells, the cochlear mechanosensory cells, provide a source of mechanical energy. In addition to transducing mechanical vibrations into electrical responses, some hair cells are equipped with molecular motors that convert metabolic or electrical energy into mechanical energy, resulting in active movements of the cells (1, 3-7). These cellular movements, in turn, exert positive feedback on the cochlear mechanics. By nonlinearly undamping the cochlear resonances as the stimulus intensity declines, this feedback selectively improves the ear's sensitivity to small vibrations induced by faint sound (1, 3-6). Notably, this hair cell-based feedback occasionally becomes unstable, leading to self-sustained feedback oscillations within the cochlear duct. Such self-sustained feedback oscillations may account for the ear's ability to generate spontaneous otoacoustic emissions, i.e., to spontaneously emit sound (8, 9).Collectively, the hair cells' motility, the cochlea's nonlinearity, and the ear's spontaneous otoacoustic emissions document the presence of hair cell-based mechanical feedback inside the cochlear duct. Yet, whether this feedback brings about power gain by expending biological energy, as assumed by the concept of the cochlear ampli...

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