Measurements of Sound Pressure in the Cochleae of Anesthetized Cats

A linear mathematical model is proposed which will account for the differences observed between mechanically measured data of Rhode (1971) for basilar membrane motion, and the responses of neural tuning curves (Kiang et al., 1974). We show that theoretical tuning curves may be derived from mechanical responses by forming the difference between the pressure across the basilar membrane and its displacement. Some ramifications of this proposal are discussed. We then propose a hypothetical physical model which could perform such a function.

Section: O(x S)= B(x){0 + •)[A(x)/b(x)] Sz(x S)-•}•t(x S) (5)supporting

confidence: 93%

Cochlear micromechanics—a mechanism for transforming mechanical to neural tuning within the cochlea

Allen¹

1977

“…Such reflection, if present, would have important consequences for understanding the nature of otoacoustic emissions and their contribution to auditory signal processing (Kemp, 1978;Kemp, 1979a). This paper demonstrates, however, that measurements of the cochlear input impedance (Lynch et al, 1982;Nedzelnitsky 1974a;Nedzelnitsky, 1980), which indicate that its phase is nearly zero, imply--when the independent spatial variable is appropriately defined--that the wavelength of the traveling pressure wave changes slowly with position near the stapes. Consequently, reflection of waves traveling in either direction through the basal turn must be small.…”

Section: Introductionmentioning

confidence: 79%

A symmetry suppresses the cochlear catastrophe

Shera¹,

Zweig²

1991

When the independent spatial variable is defined appropriately, the empirical finding that the phase of the cochlear input impedance is small [Lynch et al., J. Acoust. Soc. Am. 72, 108-130 (1982)] is shown to imply that the wavelength of the pressure wave in the cochlea changes slowly with position near the stapes. As a result, waves traveling in either direction through the basal turn undergo little reflection, and the transfer of energy between the middle and inner ears remains efficient at low frequencies. The slow variation of the wavelength implies that the series impedance Z and shunt admittance Y of the cochlear transmission line are approximately proportional at low frequencies and thus requires that the width of the basilar membrane and the cross-sectional areas of the cochlear scalae taper in opposite directions. Maintenance of the symmetry between Z and Y is both necessary and sufficient to ensure that the spatial derivative of the wavelength, and hence the phase of the cochlear input impedance, remains small. Although introduced in another context, the model of Zweig ["Finding the impedance of the organ of Corti," J. Acoust. Soc. Am. 89, 1229-1254 (1991)] manifests the symmetry between Z and Y. In other transmission-line models of cochlear mechanics, however, that symmetry is absent, and the spatial derivative of the wavelength diverges at low frequencies--the "cochlear catastrophe." Those models therefore contradict the impedance measurements and predict little transfer of energy between the middle and inner ears.

“…Their data (dash-dot line in Fig. 13) have been normalized to BM motion by using the CM data of Dallos (1970) and the pressure data of Nedzelnitsky (1974), which are nearly identical, and estimated latencies to rarefaction clicks derived from latencies to condensation clicks (Kim and Molnar, 1979). The similarity of the cat and chinchilla neural data (whether or not normalized to BM motion) probably reflects a similarity in cochlear mechanics, as suggested by Dallos (1970) on the basis of CM recordings.…”

Section: Comparisons With Other Neural Data a Comparison Across Spmentioning

confidence: 92%

Chinchilla auditory-nerve responses to low-frequency tones

Ruggero

Rich

1983

Single unit activity was recorded in the auditory nerves of chinchillas. Period histograms were constructed for responses to tones with frequencies 30-1000 Hz. For low-frequency tones at near-threshold levels, peak period histogram phases for low- and medium-best-frequency (BF) neurons (less than or equal to kHz) ranged from synchronous with condensation at the eardrum to 90 degrees leading it. At near-threshold (but high absolute) levels, high-BF (greater than or equal to 8 kHz) neurons responded in phase with rarefaction. At even higher levels, period histograms for responses of high-BF neurons tended to become bimodal, with one of the modes lagging rarefaction by 90 degrees. Using cochlear microphonics as an indicator of basilar membrane (BM) displacement, at threshold levels, response phase of low- and medium-BF neurons fall within a range between displacement and velocity of the BM toward scala vestibuli. High-BF neurons respond, at threshold (but high) intensities, in phase with BM displacement toward scala tympani. The rates of growth of frequency sensitivity in responses of low-BF (+ 18 dB/oct) and high-BF (+ 12 dB/oct) neurons are consistent with preferred response phases corresponding to BM SV velocity and ST displacement, respectively. At supra-threshold levels high-BF neurons may fire preferentially to both scala tympani displacement and scala vestibuli velocity. These results support the notion that, for high-intensity, low-frequency stimuli, OHC hyperpolarization can induce excitation of the dendrites innervating IHCs.