ORIENTATION-REVERSAL AND PHASE-REVERSAL VISUAL-EVOKED POTENTIALS IN FULL-TERM INFANTS WITH BRAIN-LESIONS - A LONGITUDINAL-STUDY

The onset and maturation of visual cortical mechanisms can be recorded by using steady-state Visual evoked potentials. The aim of this study was to evaluate and compare orientation-reversal (OR) and phase-rever sal (PH) VEP as indicators of the maturation of cortical function in a population of fullterm infants with brain lesions on neonatal MRI. Fo rty-six infants with brain lesions on neonatal MRI were tested on both PH and OR VEP at 8 reversals/second at the age of 5 months and, if th e responses were not significant, at a lower temporal frequency (4 rev ersals/second). Children whose VEPs were not significant at 5 months w ere tested longitudinally at 6, 9, 12 and 18 months. The results showe d that 23 of the 46 infants (50 %) did not show significant responses at 5 months and that while in 7 of the 23 (14 % of the whole cohort) t he responses became significant between 5 and 12 months, in the other 16 infants (34 %) the VEP responses were persistently abnormal. Childr en with focal lesions, such as focal infarction or haemorrhages, tende d to show normal or only mildly delayed VEP while more generalised les ions, such as the ones seen in infants with hypoxic-ischaemic encephal opathy grade 2 and 3, tended to be associated with abnormal VEP respon ses. The involvement of the optic radiations and occipital cortex was not always associated with abnormal VEP responses but the concomitant involvement of the basal ganglia was always associated with abnormal V EP. We were also able to demonstrate that VEP can be also used as a pr ognostic indicator: while normal OR VEP are reliably associated with a normal visual and neurodevelopmental outcome, abnormal 4 OR or 8 PH a t 5 months are consistently associated with abnormal outcome.