RESPONSES OF PERIPHERAL AUDITORY NEURONS TO 2-TONE STIMULI DURING DEVELOPMENT .1. 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, a nd was first observed at 77 gestational days, in units exhibiting adul tlike frequency selectivity. Suppression was highly correlated with th e degree of tuning, and neurons were segregated into three classes bas ed on these responses. Broadly tuned neurons (type Ig) with low charac teristic frequencies (CFs) did not exhibit suppression, and were obser ved early in postnatal life. Sharply tuned, but still immature neurons (type I,) exhibited suppression, but to a lesser degree than mature n eurons (type M). One interpretation of these results is that basilar m embrane mechanics are linear during the final stages of cochlear devel opment, indicating that the immature signal transduction process is fu ndamentally different from that of adults.