Light-induced basilar membrane vibrations in the sensitive cochlea

It is commonly believed that the exceptional sensitivity of mammalian hearing depends on outer hair cells which generate forces for amplifying sound-induced basilar membrane vibrations, yet how cellular forces amplify vibrations is poorly understood. In this study, by measuring subnanometer vibrations directly from the reticular lamina at the apical ends of outer hair cells and from the basilar membrane using a custom-built heterodyne low-coherence interferometer, we demonstrate in living mouse cochleae that the sound-induced reticular lamina vibration is substantially larger than the basilar membrane vibration not only at the best frequency but surprisingly also at low frequencies. The phase relation of reticular lamina to basilar membrane vibration changes with frequency by up to 180 degrees from ∼135 degrees at low frequencies to ∼-45 degrees at the best frequency. The magnitude and phase differences between reticular lamina and basilar membrane vibrations are absent in postmortem cochleae. These results indicate that outer hair cells do not amplify the basilar membrane vibration directly through a local feedback as commonly expected; instead, they actively vibrate the reticular lamina over a broad frequency range. The outer hair cell-driven reticular lamina vibration collaboratively interacts with the basilar membrane traveling wave primarily through the cochlear fluid, which boosts peak responses at the best-frequency location and consequently enhances hearing sensitivity and frequency selectivity.

Download Full-text

A self-mixing laser-diode interferometer for measuring basilar membrane vibrations without opening the cochlea

Journal of Neuroscience Methods ◽

10.1016/j.jneumeth.2005.04.014 ◽

2005 ◽

Vol 148 (2) ◽

pp. 122-129 ◽

Cited By ~ 35

Author(s):

Andrei N. Lukashkin ◽

Mikhail E. Bashtanov ◽

Ian J. Russell

Keyword(s):

Laser Diode ◽

Basilar Membrane ◽

Membrane Vibrations

Download Full-text

Loud Sound-Induced Changes in Cochlear Mechanics

Journal of Neurophysiology ◽

10.1152/jn.00192.2002 ◽

2002 ◽

Vol 88 (5) ◽

pp. 2341-2348 ◽

Cited By ~ 14

Author(s):

Anders Fridberger ◽

Jiefu Zheng ◽

Anand Parthasarathi ◽

Tianying Ren ◽

Alfred Nuttall

Keyword(s):

Inner Ear ◽

Time Course ◽

Basilar Membrane ◽

Organ Of Corti ◽

Compound Action Potential ◽

Cochlear Microphonic ◽

Cochlear Function ◽

Loud Sound ◽

Induced Changes ◽

Membrane Vibrations

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.

Download Full-text