MAPPING THE COCHLEAR PARTITIONS STIFFNESS TO ITS CELLULAR ARCHITECTURE

The mechanical properties of the cochlear partition are fundamental to auditory transduction. We measured the point stiffness of the partiti on, in vivo, at up to 17 radial positions spanning its width, in the b asal turn of the gerbil cochlea. We found the linear stiffness at the position that is most likely under the outer pillar cells to be 1.5 ti mes greater than adjacent positions toward the ligament, in the pectin ate zone, and five times greater than adjacent positions toward the la mina, in the arcuate zone. This radial variation seems to reflect the cellular geometry of the partition: The pillar cell is positioned as a structural element, and the basilar membrane supports a rich cellular structure in the pectinate zone, whereas it borders a fluid-filled sp ace in the arcuate zone. The radial variation in partition stiffness w e find will influence passive cochlear mechanics, and also bears on ac tive cochlear mechanics, since it supports the plausibility of cells a s effective force generators. Our results from measurements made in vi vo extend the findings of previous measurements made in excised cochle ae, in which the cellular contribution to stiffness was less evident.