Multiple modes of inner hair cell stimulation

Most current theories of cochlear mechanics assume that the pattern of coch lear partition vibration is simple, similar to that of a bending beam. Rece nt evidence suggests, however, that the vibration of the organ of Corti can be complex and that multiple vibrational modes may play an important role in cochlear transduction. Inner hair cell (IHC) and auditory nerve response s to pure tones can exhibit large phase shifts and complex response wavefor ms with increasing stimulus level. In contrast, the comparable basilar memb rane (BM) responses are much less complex, exhibiting only small phase shif ts and relatively sinusoidal waveforms. To reconcile the differences observ ed between the published BM data and the IHC data, we have recorded recepto r potentials from IHCs and compared these waveform data to the output of tw o computational models:a traditional linear model where IHC excitation depe nds only on BM displacement and a new model that assumes that outer hair ce ll (OHC) force production provides the major mechanical input to the IHC al ong with two additional mechanical components. Comparisons of the output of the two models with the experimental data show that the new model is capab le of reproducing the very complex voltage responses of the IHC recorded in vivo whereas the traditional model performed poorly. (C) 1999 Published by Elsevier Science B.V. All rights reserved.