Effectiveness of Outer Hair Cells as Cochlear Amplifier: Coupled Oscillator Models

Outer hair cells (OHCs) are essential for the sensitivity and frequency specificity of the mammalian ear. To perform this function, OHCs need to amplify the motion of the basilar membrane, which is much stiffer than themselves. OHCs must overcome this impedance mismatch for their amplifying function particularly at high frequencies, where the mismatch is largest. This issue could be solved by the existence of multiple modes of motion. Here, systems of two coupled oscillators are examined as the simplest of such cases. It is found that some of these model systems indeed make OHCs function as an effective amplifier by overcoming the impedance mismatch. This result suggests that the elaborate structure of the organ of Corti, which can support multiple modes of motion, is a key to the high frequency performance of the mammalian ear. SignificanceThe mammalian ear depends on outer hair cells, which work as the cochlear amplifier. The mechanism, with which outer hair cells perform this biological function, is of great interest. The present paper addresses a question, how soft outer hair cells can amplify the vibration of the much stiffer basilar membrane. It shows that the elaborate structure of the cochlea, which supports multiple modes of motion, must be a key to the exquisite performance of the mammalian ear. It also shows that the properties of outer hair cells obtained from isolated cell preparations are compatible with their physiological function.