Development in the frequency selectivity of auditory nerve fibers in the kitten.

The modification of tuning properties in the cochlea has been studied by means of tuning curves from auditory nerve fibers in kittens of various ages. Comparison of tuning curves of three characteristic frequencies (CF) shows that the tuning of high CF units tends to approach adult values by the end of the second postnatal week, whereas medium and low CF units have a delayed maturation. Threshold sensitivity, on the other hand, shows a development inverse to that of tuning. The threshold of low CF units tends to reach adult values before that of medium and high CF units. The development of tuning can be related to the structural maturation of the cochlea, where the most differentiated part is located at the base of the first turn and corresponds to the rapid development of high CF units. In the same way, the second and the third turns show a delayed structural development corresponding to a different maturation of tuning for medium and low CF units.