Two-Dimensional Cochlear Micromechanics Measured In Vivo Demonstrate Radial Tuning within the Mouse Organ of Corti

Area of Science:

• Auditory Neuroscience
• Mechanobiology
• Biophysics

Background:

• Mammalian hearing relies on exquisite sensitivity and frequency discrimination for speech comprehension, especially in noise.
• Cochlear outer hair cells (OHCs) amplify the basilar membrane traveling wave, but the mechanism for sharp frequency tuning remains unclear.

Purpose of the Study:

• To investigate the origin of frequency tuning in the cochlea.
• To measure sound-induced 2-D vibrations within the mouse organ of Corti in vivo.
• To determine the transfer function relating radial shear to transverse basilar membrane motion.

Main Methods:

• In vivo measurement of sound-induced 2-D vibrations in the mouse organ of Corti.
• Analysis of radial vibrations of the tectorial membrane and reticular lamina.
• Comparison of vibration patterns in live, dead, and genetically modified mice (Tecta(C1509G/C1509G)).

Main Results:

• Normalized radial vibrations of the tectorial membrane and reticular lamina showed sharp tuning.
• Radial tuning peaked at a higher frequency than transverse basilar membrane tuning in passive conditions.
• Radial tuning was similar in dead mice and in mice lacking a tectorial membrane, indicating passive mechanics.

Conclusions:

• Passive mechanics within the organ of Corti contribute to cochlear filtering, independent of basilar membrane filtering.
• These passive mechanics sharpen frequency selectivity by determining which OHCs are activated.
• This process tunes the gain of cochlear amplification, enhancing speech discrimination in noise.