Effects of preterm extrauterine visual experience on the development of the human visual system: a flash VEP study.

To compare the functional maturation of the human visual system between intra- and extrauterine course flash visual evoked potentials (VEPs) in preterm infants (gestational age 24 to 36 weeks). Previously established normal values, with special reference to the two components of the N1 wave, were employed (Tsuneishi 1995). A cross-sectional analysis of 124 infants at 36 weeks postmenstrual age (PMA), showed that there are no differences in the absolute values of VEP peak latencies depending on the postnatal age (PNA). Conversely, the N1 wave form changes with increasing PNA from a wave in which the early peak (N1a) has a higher amplitude than the late peak (N1b) into the reverse situation with a higher amplitude of the N1b as compared to N1a. This observation may correlate with the maturation of the neuronal networks in the visual cortex. In a longitudinal analysis of 50 infants followed for more than 5 sessions of weekly recordings, we found that the individual rapid decrease in the N1a latency, which may reflect the initiation of myelination in the optic radiation, most frequently occurs at around 37 weeks PMA, regardless of PNA. Preterm extrauterine visual experience has little effect on the myelination process in the visual pathway, but has a marked effect on the developmental changes in VEP wave form which reflect the developmental changes of the neuronal networks in the visual cortex.