Factors that influence rate-versus-intensity relations in single cochlear nerve fibers of the gerbil

The relationship between characteristic frequency (CF) and rate-intensity curve shape was examined in 144 cochlear nerve fibers obtained from 39 Mongolian gerbils. Quasi-steady-state firing rates were measured in response to tone bursts at the CF. From each intensity curve, estimates of slope, firing rate at saturation, and dynamic range were derived using nonlinear curve fitting. Saturation firing rate was depressed for stimuli with a high duty cycle, especially for units with low rates of spontaneous discharge. The distributions of slope and saturation firing rate differed for fibers with CFs above and below 3 to 4 kHz. The interrelation of slope, dynamic range, maximum driven rate, and spontaneous firing rate was also different for fibers with CFs above and below this band. This mid-CF transition is discussed in terms of possible longitudinal changes in the function of the gerbil cochlea.