Modeling of auditory nerve fiber input/output functions near threshold

The instantaneous discharge rate of auditory nerve fibers (ANFs) near their threshold exhibits an approximately exponential relationship to the instantaneous pressure at the eardrum after compensating for the discharge latency. Some simplified models of the pressure-to-discharge transduction process in the cochlea have attributed this exponential relationship to an inner hair cell (IHC) transduction current that is either an exponential function with a level-dependent slope parameter or a first-order Boltzmann function (which is approximately exponential around the zero-input point) followed by a low-pass filter. However, such IHC transduction functions do not produce level-dependent changes in the AC and DC components of the IHC potential that match the behavior observed in physiological recordings. In this study, we show that retaining the physiologically-accurate IHC transduction model of Bruce et al. (Hear. Res., 2018) and following it by an exponential or exponential-like function that maps the IHC potential to the input of the synaptic power-law adaptation in that model produces the desired exponential input/output behavior near threshold while preserving the appropriate level-dependent changes in ANF discharge rate and phase-locking. [Work supported by NSERC Discovery Grant #RGPIN-2018-05778.]