Suppression in auditory-nerve fibers of cats using low-side suppressors. III. Model results

A phenomenological model which simulates auditory-nerve (AN) two-tone suppression was developed. The model uses the output of the outer hair cell (OHC) to control the gain of the cochlear amplifier, which presumably affects only frequencies near the characteristic frequency (CF). Among other things, the model can simulate basic AN suppression patterns including the 1/4 to 1/2 cycle relationships which exist between phase of suppression and phase of excitation to the suppressor (SUP) tone alone (Cai and Geisler, 1996a). Without any changes, it is also able to simulate the experimental low-frequency biasing data and the suppression of CF component by the low-frequency SUP tone in the OHC outputs (Cheatham and Dallos, 1994). These successful simulations of the suppression patterns support the basic assumption in the model, that the saturation of OHC transduction current produces two-tone suppression. However, the amplitude behavior of the model fits that obtained only from AN fibers with high spontaneous rates (and from inner hair cells (IHC)), but not fibers with lower spontaneous rates. It appears, therefore, that other unknown mechanism(s) operating at stages following the IHC potential are important in determining the magnitude of low-side suppression.