Critical ages in brainstem development revealed by neonatal 3-channel Lissajous' trajectory of auditory brainstem...

Auditory brainstem evoked potentials (ABEPs) were recorded from 91 newborns from 7 age groups between 26 to 43 weeks of gestation. In addition to the widely used vertex-mastoid derivation, potentials were recorded from three orthogonal electrode configurations, and represented in 3 dimensional voltage-space as three-channel Lissajous' trajectories (3CLTs). ABEPs were evoked by alternating polarity, monaural 75 dBnHL clicks presented at rates of 10/s, 55/s and 80/s. Potentials were also recorded to 45 dBnHL and 15 dBnHL clicks presented at 10/s. 3CLT point by point (apex latencies, amplitudes and orientation) as well as planar segment (planar segment position and duration) descriptors, along with peak latencies of the vertex-mastoid peaks, were followed for effects of age, stimulus intensity and rate. ABEPs began to appear consistently at 29 weeks of gestation to high stimulus intensities, with a rapid decrease of ABEP thresholds up to 34 weeks. At 35 weeks, thresholds stabilized approximately at adult values. The results indicate a significant effect of stimulus rate and intensity as well as of gestational age group on apex latencies. The findings also showed changes in apex orientations associated with stimulus rate and intensity interacting with gestational age. 3CLT descriptors enhanced the understanding of these results in relation to developmental and maturational aspects of the auditory system. The results may be explained by maturational change in relative contributions of constituents of the complex ABEP generators.