Maturational changes of VEPs in normal premature neonates: a longitudinal study

In order to clarify the maturational changes of visual evoked potentials (VEPs) in normal premature neonates, longitudinal recordings were obtained for 11 normal premature neonates at low risk, at intervals of mainly 1 week and occasionally 2 weeks. Positive waves around 200 ms, P200, negative waves around 300 ms, N300, and positive waves around 400 ms, P400, were recognized. Since P200 and P400 exhibited more variability in latency and appearance than N300, maturational changes in the N300 component were analyzed. The latency of monophasic N300 showed transient prolongation from 32 to 35 weeks gestational age (GA) and re-shortening after 35 weeks GA, or slow regression from 32 to 35 weeks GA and a steady decrease after 35 weeks GA. The bifid N300 showed a shift of dominancy from the first negative peaks to the second peaks, and after 35 weeks GA latency shortening of the second peaks. These findings suggested that the decrease in N300 latency in the premature period may comprise two stages, a slow regression rate or reverse stage from 32 to 35 weeks GA, and a fast regression rate stage from 35 to 38 weeks GA, and that N300 may consist of two components, early and late ones, with the same polarity. This study indicates that careful attention should be paid to evaluation of VEPs in premature neonates.