Detection of Cochlear Amplification and Its Activation

Dong, Wei; Olson, Elizabeth S.

doi:10.1016/j.bpj.2013.06.049

Cited by 138 publications

(147 citation statements)

References 43 publications

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“…The space constant is~80 mm (11,23). In addition, at frequencies above the BF, the STP response becomes dominated by the fast, compression pressure mode, which is not involved in cochlear excitation, at least to first order (24)(25)(26).…”

Section: Resultsmentioning

confidence: 99%

“…The experiments were performed in young adult gerbils anesthetized with pentobarbital and euthanized at the end of the experiment. The cochlea was exposed by opening the bulla via a ventral approach and the dual pressure-voltage sensor was inserted into a handdrilled hole,~200 mm in diameter, made in the ST of the basal turn of the cochlea where the BF is~20 kHz (11). The dual sensor is based on fiber-optic pressure sensors (19,20).…”

Section: Methodsmentioning

confidence: 99%

“…1 F). Both the pressure sensor and the wire electrode had frequency responses that were approximately flat over the frequency range of measurement (11). A silver reference electrode for the voltage sensor was connected to the neck muscle.…”

Section: Methodsmentioning

confidence: 99%

“…1 F). STP is a mechanical drive to organ of Corti motion and thus hair cell stimulation, and in a broad frequency range that includes the BF peak, is approximately proportional to BM displacement (11,27).…”

Section: An Example Of Single-tone Responsesmentioning

confidence: 99%

“…Pressure and voltage responses were measured simultaneously, at the same location close to the BM, as described in Dong and Olson (11) and Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

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Two-Tone Suppression of Simultaneous Electrical and Mechanical Responses in the Cochlea

Dong

Olson

2016

Biophysical Journal

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Cochlear frequency tuning is based on a mildly tuned traveling-wave response that is enhanced in amplitude and sharpness by outer hair cell (OHC)-based forces. The nonlinear and active character of this enhancement is the fundamental manifestation of cochlear amplification. Recently, mechanical (pressure) and electrical (extracellular OHC-generated voltage) responses were simultaneously measured close to the sensory tissue's basilar membrane. Both pressure and voltage were tuned and showed traveling-wave phase accumulation, evidence that they were locally generated responses. Approximately at the frequency where nonlinearity commenced, the phase of extracellular voltage shifted up, to lead pressure by >1/4 cycle. Based on established and fundamental relationships among voltage, force, pressure, displacement, and power, the observed phase shift was identified as the activation of cochlear amplification. In this study, the operation of the cochlear amplifier was further explored, via changes in pressure and voltage responses upon delivery of a second, suppressor tone. Two different suppression paradigms were used, one with a low-frequency suppressor and a swept-frequency probe, the other with two swept-frequency tones, either of which can be considered as probe or suppressor. In the presence of a high-level low-frequency suppressor, extracellular voltage responses at probe-tone frequencies were greatly reduced, and the pressure responses were reduced nearly to their linear, passive level. On the other hand, the amplifier-activating phase shift between pressure and voltage responses was still present in probe-tone responses. These findings are consistent with low-frequency suppression being caused by the saturation of OHC electrical responses and not by a change in the power-enabling phasing of the underlying mechanics. In the two-tone swept-frequency suppression paradigm, mild suppression was apparent in the pressure responses, while deep notches could develop in the voltage responses. A simple analysis, based on a two-wave differencing scheme, was used to explore the observations.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: An Example Of Single-tone Responsesmentioning

confidence: 99%

“…Pressure and voltage responses were measured simultaneously, at the same location close to the BM, as described in Dong and Olson (11) and Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

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Two-Tone Suppression of Simultaneous Electrical and Mechanical Responses in the Cochlea

Dong

Olson

2016

Biophysical Journal

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Hair Cell Transduction, Tuning, and Synaptic Transmission in the Mammalian Cochlea

Fettiplace

2017

Comprehensive Physiology

284

273

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Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the inner ear. Recordings of hair cell electrical responses have shown that they transduce sound via sub-micrometer deflections of their hair bundles, which are arrays of interconnected stereocilia containing the mechanoelectrical transducer (MET) channels. MET channels are activated by tension in extracellular tip links bridging adjacent stereocilia, and they can respond within microseconds to nanometer displacements of the bundle, facilitated by multiple processes of Ca2+-dependent adaptation. Studies of mouse mutants have produced much detail about the molecular organization of the stereocilia, the tip links and their attachment sites, and the MET channels localized to the lower ends of each tip link. The mammalian cochlea contains two categories of hair cells. Inner hair cells relay acoustic information via multiple ribbon synapses that transmit rapidly without rundown. Outer hair cells are important for amplifying sound-evoked vibrations. The amplification mechanism primarily involves contractions of the outer hair cells, which are driven by changes in membrane potential and mediated by prestin, a motor protein in the outer hair cell lateral membrane. Different sound frequencies are separated along the cochlea, with each hair cell being tuned to a narrow frequency range; amplification sharpens the frequency resolution and augments sensitivity 100-fold around the cell’s characteristic frequency. Genetic mutations and environmental factors such as acoustic overstimulation cause hearing loss through irreversible damage to the hair cells or degeneration of inner hair cell synapses.

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