COMPARISON OF DISTORTION-PRODUCT OTOACOUSTIC EMISSION (DPOAE) AND AUDITORY BRAIN-STEM RESPONSE (ABR) TRAVELING-WAVE DELAY MEASUREMENTS SUGGESTS FREQUENCY-SPECIFIC SYNAPSE MATURATION

Objective: To determine whether the source of age-dependent latency ch anges for ABR wave I results from cochlear mechanics or the haircell-n euron synapse. Design: Cochlear traveling wave delays were estimated o n the basis of derived ABR response latencies and DPOAE phase delays. The difference in travel time between adjacent one octave-separated fr equencies was calculated for four age groups: 30 to 33 wk old, 34 to 3 7 wk old, 38 to 42 wk old (term), and young adults. Results: We found that there were essentially no travel time differences between newborn s in the 34 to 37 and the 38 to 42 wk conceptional age (CA) groups as estimated from DPOAE phase delays. For the 30- to 33-wk-olds, DPOAE tr avel times were increased at all frequencies, likely due to mild (abou t 10 to 15 dB) conductive hearing losses. Differences in travel times between adjacent bands, however, were not different from the other neo natal groups. Estimates an basis of wave I latency showed delays for t he high-frequency region, 6 to 11 kHz, that were still immature at ter m. Conclusions: A comparison of frequency-dependent travel times calcu lated for wave I and DPOAE data in comparable age groups suggests matu re cochlear functioning at 35 wk CA and a delayed maturation for the h aircell-auditory nerve synapses relative to the preneural components f or the basal turn with center frequencies above 6 kHz.