RESPONSES OF PERIPHERAL AUDITORY NEURONS TO 2-TONE STIMULI DURING DEVELOPMENT .3. RATE FACILITATION

Approximately 25% of peripheral auditory neurons having low characteri stic frequencies (CFs) and bread tuning, and recorded from immature an imals, responded to two-tone stimuli with increases in discharge rate greater than predicted by linear summation of the responses to probe t ones (facilitation), in contrast to the two-tone suppression observed in adult animals and in more sharply tuned immature neurons. Facilitat ion was not seen after 81 gestational days and was not observed when t est tones produced a substantial increase in rate when presented alone . The fact that some neural responses were facilitated under condition s of two-tone stimulation during the final stages of cochlear differen tiation provides additional evidence that signal transduction is funda mentally different in neonatal kittens than in adults. A linear model of basilar membrane mechanics coupled to nonlinear neural processes is proposed which can account for the production of facilitation.