The evolution of multi-compartment cochlear models

A major goal in cochlear modeling is to account for the functional mechanism of the cochlear amplifier (CA). Although numerous hypotheses have been presented, many are based on addons to the fundamental one-dimensional model, which assumes only the basilar membrane between two fluid-filled channels, scala vestibuli and scala tympani. Another class of models assumes more than two wave propagation channels (modes), and we call them multicompartmental models, a concept that originated with de Boer [1, 2, and 3]. Using a multicompartmental formulation, we put forward the hypothesis that the CA function is due to a combination of forces on the reticular lamina and the basilar membrane coming from both local hair cells and from a pressure wave that propagates in the fluid-filled spaces between the reticular lamina and the basilar membrane. A generic version of the model has been used to match data from various species. An improved model with parameters based on anatomical data from the gerbil can better match physiological data from the gerbil. A more advanced model that separates arcuate and pectinate regions of the basilar membrane shows the phase angle of the response of the arcuate region to low-frequency probe tones reverses at about midway down the cochlea. Overall, the models provide an explanation of how the CA might work.