The experimental OHC elongation phase is not inconsistent with effective transfer of mechanical power to the BM by the active force

Abstract

The amazing development of the OCT techniques permits spatially well-defined measurement of the motion of a number of different solid structures within the Organ of Corti. Recent measurements [1] show the motion of the BM and of the RL in correspondence of each OHC row, as well as the motion of the junction between the OHC body and the Deiter’s cells. In the peak region, at low stimulus levels, the motion of the RL is larger than that of the BM. In a piezoelectric actuator model of the OHCs [2], the electric current is supposed to be proportional to the OHC elongation. Considering the low-pass phase rotation, the OHC force exerted on the BM may act as an anti-damping force, proportional to the RL velocity, and transfer power to both the RL and the BM. In this study, a WKB transmission-line cochlear model with two mechanical degrees of freedom at each tonotopic place is used, in which the OHC force is represented by a low-pass filtered elastic term proportional to the OHC elongation. With respect to our previous studies, this WKB model also includes the fluid focusing effect and the viscous damping effect in the peak region. In the model simulations, with a suitable parameter choice, the phase difference between the RL and the BM near the BF is consistent with some experimental findings, and the OHC power is effectively transmitted to the BM motion.