Location-dependent Organ of Corti Mechanics in the Mammalian Cochlea

Yanju Liu, Ph.D. Defense

Hopeman 224

The sensory epithelium in the cochlea, called the organ of Corti provides amplification critical to our hearing. It is believed that outer hair cell generates forces and injects power into the organ of Corti to amplify its vibrations. Even though that the organ of Corti stiffness varies two to three orders of magnitude along the cochlear length, the force capacity of the outer hair cell is nearly constant. It is puzzling how actuators with a constant force capacity can operate under such a wide stiffness range. Further, the amplification of sound provided by outer hair cell electromotility is dependent on location, such that: high frequency sounds encoded in the basal cochlea are amplified more than low frequency sounds encoded in the apical cochlea. However, there is so far no detailed and convincing explanation for the location-dependent cochlear amplification. To investigate these two unresolved problems in cochlear amplification, a computational model: ‘Virtual Cochlea’, was developed. This model enabled us to study the roles of organ of Corti micromechanics in cochlear amplification. The responses predicted from the model revealed that (1) the stiffness of the organ of Corti complex felt by the outer hair cells remains between 1.5 and 0.4 times of the outer hair cell’s own stiffness and that (2) that the organ of Corti micro-mechanics facilitate outer haircell power generation in the high frequency basal region.