Recent developments in cochlear physiology.

Abstract

Recent findings in cochlear physiology have caused many of our long held ideas about how sound is analyzed by the ear to be reevaluated. This article describes changes which have occurred in three classical ideas of cochlear transduction: (1) There is a gradient of frequency representation along the cochlea with high frequencies being represented at the base and lower frequencies represented progressively toward the apex. It is now known that the specific frequency which is represented at a given location along the cochlea is not invariant but changes systematically during the normal development of hearing. (2) The place code and frequency tuning along the cochlea are due to the conventional traveling wave of von Békésy and basilar membrane mechanics. Experiments in nonmammalian vertebrates which lack a traveling wave have shown that other mechanisms, including the mechanical resonance of hair cell stereocilia, may contribute to tonotopic organization and frequency tuning. It is possible that hair cell stereocilia also contribute to frequency representation and tuning in the mammalian cochlea. (3) The vibration of the basilar membrane to sound is determined by its passive mechanical properties. It is now known that the response of the basilar membrane, and that of the cochlear partition as a whole, is influenced by physiological processes which utilize metabolic energy. The active processes are likely expressed through the motile activity of outer hair cells.