Auditory brain-stem evoked potentials to clicks at different presentation rates: estimating maturation of pre-term and full-term neonates.

Auditory brain-stem evoked potentials ABEPs were recorded from 57 neonates ranging in gestational age between 27 and 43 weeks. Averages and standard deviations of I, III and V peak latencies, I-V, I-III and III-V inter-peak latency differences (IPLDs), for 10/sec and 55/sec clicks were calculated for each age group. An additional measure, the net effect of increasing stimulus rate (ISR), was calculated by subtracting 10/sec measures from their 55/sec counterparts. Correlations between ABEP measures and subject age were determined. The results of this study demonstrate a significant correlation between gestational age and electrophysiological measures of peripheral, as well as central, conduction: an inverse correlation between age and peak latencies as well as IPLDs. The slope of this correlation was steeper for the higher stimulus rate. The slope of 55/sec measures vs. age was the sum of the respective slopes of 10/sec measures and of ISR. The maturation of 10/sec measures may reflect white matter development, while ISR changes with gestational age represent maturation of synaptic efficacy. Thus, the maturation of 55/sec measures reflect the combined maturation of nerve conduction velocity and synaptic efficacy along the neonatal auditory nerve and brain-stem. This differential evaluation may enable more accurate determination of developmental age of neonates, with respect to total maturation as well as its constituents.