Responses of peripheral auditory neurons to two-tone stimuli during development: I. Correlation with frequency selectivity.

The responses of peripheral auditory neurons to two-tone stimuli were used to inferentially examine the nature of cochlear processing during development. Rate suppression was not seen in the youngest animals, and was first observed at 77 gestational days, in units exhibiting adultlike frequency selectivity. Suppression was highly correlated with the degree of tuning, and neurons were segregated into three classes based on these responses. Broadly tuned neurons (type IB) with low characteristic frequencies (CFs) did not exhibit suppression, and were observed early in postnatal life. Sharply tuned, but still immature neurons (type IS) exhibited suppression, but to a lesser degree than mature neurons (type M). One interpretation of these results is that basilar membrane mechanics are linear during the final stages of cochlear development, indicating that the immature signal transduction process is fundamentally different from that of adults.