Auditory nerve fibre responses in the ferret

The ferret (Mustela putorius) is a medium-sized, carnivorous mammal with good low-frequency hearing; it is relatively easy to train, and there is therefore a good body of behavioural data detailing its detection thresholds and localization abilities. However, despite extensive studies of the physiology of the central nervous system of the ferret, even extending to the prefrontal cortex, little is known of the functioning of the auditory periphery. Here, we provide an insight into this peripheral function by detailing responses of single auditory nerve fibres. Our expectation was that the ferret auditory nerve responsiveness would be similar that of its near relative, the cat. However, by comparing a range of variables (the frequency tuning, the variation of ratelevel functions with spontaneous rate, and the high-frequency cut-off of phase locking) across several species, we show that the auditory nerve (and hence cochlea) in the ferret is more similar to that of the guinea-pig and chinchilla than to that of the cat. Animal models of hearing are often chosen on the basis of the similarity of their audiogram to that of the human, particularly in the low-frequency region. We show here that whereas the ferret hears well at low frequencies, this is likely to occur via fibres with higher characteristic frequencies. These qualitative differences in response characteristics in auditory nerve fibres are important in interpreting data across all of auditory science, as it has been argued recently that tuning in animals is broader than in humans.