| 1. |
- Burwood, George, et al.
(författare)
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Best frequencies and temporal delays are similar across the low-frequency regions of the guinea pig cochlea
- 2022
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 8:38
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Tidskriftsartikel (refereegranskat)abstract
- The cochlea maps tones with different frequencies to distinct anatomical locations. For instance, a faint 5000-hertz tone produces brisk responses at a place approximately 8 millimeters into the 18-millimeter-long guinea pig cochlea, but little response elsewhere. This place code pervades the auditory pathways, where neurons have "best frequencies" determined by their connections to the sensory cells in the hearing organ. However, frequency selectivity in cochlear regions encoding low-frequency sounds has not been systematically studied. Here, we show that low-frequency hearing works according to a unique principle that does not involve a place code. Instead, sound-evoked responses and temporal delays are similar across the low-frequency regions of the cochlea. These findings are a break from theories considered proven for 100 years and have broad implications for understanding information processing in the brainstem and cortex and for optimizing the stimulus delivery in auditory implants.
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| 2. |
- Burwood, George W. S., et al.
(författare)
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Revealing the morphology and function of the cochlea and middle ear with optical coherence tomography
- 2019
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Ingår i: QUANTITATIVE IMAGING IN MEDICINE AND SURGERY. - : AME PUBL CO. - 2223-4292 .- 2223-4306. ; 9:5, s. 858-881
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Forskningsöversikt (refereegranskat)abstract
- Optical coherence tomography (OCT) has revolutionized physiological studies of the hearing organ, the vibration and morphology of which can now be measured without opening the surrounding bone. In this review, we provide an overview of OCT as used in the otological research, describing advances and different techniques in vibrometry, angiography, and structural imaging.
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| 3. |
- Chen, Fangyi, et al.
(författare)
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A differentially amplified motion in the ear for near-threshold sound detection
- 2011
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Ingår i: Nature Neuroscience. - : Springer Science and Business Media LLC. - 1097-6256 .- 1546-1726. ; 14:6, s. 770-774
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Tidskriftsartikel (refereegranskat)abstract
- The ear is a remarkably sensitive pressure fluctuation detector. In guinea pigs, behavioral measurements indicate a minimum detectable sound pressure of ∼20 μPa at 16 kHz. Such faint sounds produce 0.1-nm basilar membrane displacements, a distance smaller than conformational transitions in ion channels. It seems that noise within the auditory system would swamp such tiny motions, making weak sounds imperceptible. Here we propose a new mechanism contributing to a resolution of this problem and validate it through direct measurement. We hypothesized that vibration at the apical side of hair cells is enhanced compared with that at the commonly measured basilar membrane side. Using in vivo optical coherence tomography, we demonstrated that apical-side vibrations peaked at a higher frequency, had different timing and were enhanced compared with those at the basilar membrane. These effects depend nonlinearly on the stimulus sound pressure level. The timing difference and enhancement of vibrations are important for explaining how the noise problem is circumvented.
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| 4. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Alterations of basilar membrane response phase and velocity after acoustic overstimulation
- 2002
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Ingår i: Hearing Research. - : Elsevier. - 0378-5955 .- 1878-5891. ; 167:1-2, s. 214-222
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the physiology of noise-induced hearing loss, the sound-induced vibrations of the basilar membrane (BM) of the inner ear were measured in living anesthetized guinea pigs before and after intense sound exposure. The vibrations were measured using a laser Doppler velocimeter after placing reflective glass beads on the BM. Pseudo-random noise waveforms containing frequencies between 4 and 24 kHz were used to generate velocity tuning curves. Before overstimulation, sharp response peaks were seen at stimulus frequencies between 15 and 17 kHz, consistent with the expected best frequency of the recording location. The response to low level stimuli lagged the high level ones by up to 90 degrees at the characteristic frequency. Following exposure to loud sound, the BM vibrations showed a pronounced reduction in amplitude, primarily at low stimulus levels, and the best frequency moved to approximately 12 kHz. At higher levels, the reduction was either absent or much smaller. In addition to the amplitude changes, increased phase lags were seen at frequencies near the characteristic frequency. In animals with more severe exposures, response phases were altered also at frequencies showing no change of the amplitude. The phase was independent of stimulus level after severe exposures.
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| 5. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Loud sound-induced changes in cochlear mechanics
- 2002
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 88:5, s. 2341-2348
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the inner ear response to intense sound and the mechanisms behind temporary threshold shifts, anesthetized guinea pigs were exposed to tones at 100-112 dB SPL. Basilar membrane vibration was measured using laser velocimetry, and the cochlear microphonic potential, compound action potential of the auditory nerve, and local electric AC potentials in the organ of Corti were used as additional indicators of cochlear function. After exposure to a 12-kHz intense tone, basilar membrane vibrations in response to probe tones at the characteristic frequency of the recording location (17 kHz) were transiently reduced. This reduction recovered over the course of 50 ms in most cases. Organ of Corti AC potentials were also reduced and recovered with a time course similar to the basilar membrane. When using a probe tone at either 1 or 4 kHz, organ of Corti AC potentials were unaffected by loud sound, indicating that transducer channels remained intact. In most experiments, both the basilar membrane and the cochlear microphonic response to the 12-kHz overstimulation was constant throughout the duration of the intense stimulus, despite a large loss of cochlear sensitivity. It is concluded that the reduction of basilar membrane velocity that followed loud sound was caused by changes in cochlear amplification and that the cochlear response to intense stimulation is determined by the passive mechanical properties of the inner ear structures.
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| 6. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Organ of Corti potentials and the motion of the basilar membrane
- 2004
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 24:45, s. 10057-10063
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Tidskriftsartikel (refereegranskat)abstract
- During sound stimulation, receptor potentials are generated within the sensory hair cells of the cochlea. Prevailing theory states that outer hair cells use the potential-sensitive motor protein prestin to convert receptor potentials into fast alterations of cellular length or stiffness that boost hearing sensitivity almost 1000-fold. However, receptor potentials are attenuated by the filter formed by the capacitance and resistance of the membrane of the cell. This attenuation would limit cellular motility at high stimulus frequencies, rendering the above scheme ineffective. Therefore, Dallos and Evans (1995a) proposed that extracellular potential changes within the organ of Corti could drive cellular motor proteins. These extracellular potentials are not filtered by the membrane. To test this theory, both electric potentials inside the organ of Corti and basilar membrane vibration were measured in response to acoustic stimulation. Vibrations were measured at sites very close to those interrogated by the recording electrode using laser interferometry. Close comparison of the measured electrical and mechanical tuning curves and time waveforms and their phase relationships revealed that those extracellular potentials indeed could drive outer hair cell motors. However, to achieve the sharp frequency tuning that characterizes the basilar membrane, additional mechanical processing must occur inside the organ of Corti.
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| 7. |
- He, Wenxuan, et al.
(författare)
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An outer hair cell-powered global hydromechanical mechanism for cochlear amplification
- 2022
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Ingår i: Hearing Research. - : ELSEVIER. - 0378-5955 .- 1878-5891. ; 423
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Forskningsöversikt (refereegranskat)abstract
- It is a common belief that the mammalian cochlea achieves its exquisite sensitivity, frequency selectiv-ity, and dynamic range through an outer hair cell-based active process, or cochlear amplification. As a sound-induced traveling wave propagates from the cochlear base toward the apex, outer hair cells at a narrow region amplify the low level sound-induced vibration through a local feedback mechanism. This widely accepted theory has been tested by measuring sound-induced sub-nanometer vibrations within the organ of Corti in the sensitive living cochleae using heterodyne low-coherence interferometry and optical coherence tomography. The aim of this short review is to summarize experimental findings on the cochlear active process by the authors group. Our data show that outer hair cells are able to gener-ate substantial forces for driving the cochlear partition at all audible frequencies in vivo. The acoustically induced reticular lamina vibration is larger and more broadly tuned than the basilar membrane vibration. The reticular lamina and basilar membrane vibrate approximately in opposite directions at low frequen-cies and in the same direction at the best frequency. The group delay of the reticular lamina is larger than that of the basilar membrane. The magnitude and phase differences between the reticular lamina and basilar membrane vibration are physiologically vulnerable. These results contradict predictions based on the local feedback mechanism but suggest a global hydromechanical mechanism for cochlear amplifi-cation. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam. (c) 2021 Elsevier B.V. All rights reserved.
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| 8. |
- He, Wenxuan, et al.
(författare)
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The reticular lamina and basilar membrane vibrations in the transverse direction in the basal turn of the living gerbil cochlea
- 2022
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Ingår i: Scientific Reports. - : NATURE PORTFOLIO. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The prevailing theory of cochlear function states that outer hair cells amplify sound-induced vibration to improve hearing sensitivity and frequency specificity. Recent micromechanical measurements in the basal turn of gerbil cochleae through the round window have demonstrated that the reticular lamina vibration lags the basilar membrane vibration, and it is physiologically vulnerable not only at the best frequency but also at the low frequencies. These results suggest that outer hair cells from a broad cochlear region enhance hearing sensitivity through a global hydromechanical mechanism. However, the time difference between the reticular lamina and basilar membrane vibration has been thought to result from a systematic measurement error caused by the optical axis non-perpendicular to the cochlear partition. To address this concern, we measured the reticular lamina and basilar membrane vibrations in the transverse direction through an opening in the cochlear lateral wall in this study. Present results show that the phase difference between the reticular lamina and basilar membrane vibration decreases with frequency by similar to 180 degrees from low frequencies to the best frequency, consistent with those measured through the round window. Together with the round-window measurement, the low-coherence interferometry through the cochlear lateral wall demonstrates that the time difference between the reticular lamina and basilar membrane vibration results from the cochlear active processing rather than a measurement error.
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| 9. |
- Nuttall, Alfred L., et al.
(författare)
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A mechanoelectrical mechanism for detection of sound envelopes in the hearing organ
- 2018
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- To understand speech, the slowly varying outline, or envelope, of the acoustic stimulus is used to distinguish words. A small amount of information about the envelope is sufficient for speech recognition, but the mechanism used by the auditory system to extract the envelope is not known. Several different theories have been proposed, including envelope detection by auditory nerve dendrites as well as various mechanisms involving the sensory hair cells. We used recordings from human and animal inner ears to show that the dominant mechanism for envelope detection is distortion introduced by mechanoelectrical transduction channels. This electrical distortion, which is not apparent in the sound-evoked vibrations of the basilar membrane, tracks the envelope, excites the auditory nerve, and transmits information about the shape of the envelope to the brain.
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| 10. |
- Nuttall, Alfred L, et al.
(författare)
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Instrumentation for studies of cochlear mechanics : from von Békésy forward
- 2012
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Ingår i: Hearing Research. - : Elsevier BV. - 0378-5955 .- 1878-5891. ; 293:1-2, s. 3-11
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Tidskriftsartikel (refereegranskat)abstract
- Georg von Békésy designed the instruments needed for his research. He also created physical models of the cochlea allowing him to manipulate the parameters (such as volume elasticity) that could be involved in controlling traveling waves. This review is about the specific devices that he used to study the motion of the basilar membrane thus allowing the analysis that lead to his Nobel Prize Award. The review moves forward in time mentioning the subsequent use of von Békésy's methods and later technologies important for motion studies of the organ of Corti. Some of the seminal findings and the controversies of cochlear mechanics are mentioned in relation to the technical developments.
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