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 int ra- and extrauterine course hash visual evoked potentials (VEPs) in preterm infants (gestational age 24 to 36 weeks). Previously established normal va lues, with special reference to the two components of the N1 wave, were emp loyed (Tsuneishi 1995). A cross-sectional analysis of 124 infants at 36 wee ks postmenstrual age (PMA), showed that there are no differences in the abs olute values of VEP peak latencies depending on the postnatal age (PNA). Co nversely, 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 networ ks 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 mye lination in the optic radiation, most frequently occurs at around 37 weeks PMA, regardless of PNA. Preterm extrauterine visual experience has little e ffect on the myelination process in the visual pathway, but has a marked ef fect on the developmental changes in VEP wave form which reflect the develo pmental changes of the neuronal networks in the visual cortex.