Abstract
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 - reversal (PH) VEP as indicators of the maturation
of cortical function in a population of full - term infants with brain lesions on
neonatal MRI. Forty - 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 the responses
were not significant, at a lower temporal frequency (4 reversals/second). Children
whose VEPs were not significant at 5 months were tested longitudinally at 6, 9,12
and 18 months. The results showed 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) the responses became significant between 5 and 12 months, in
the other 16 infants (34 %) the VEP responses were persistently abnormal. Children
with focal lesions, such as focal infarction or haemorrhages, tended to show normal
or only mildly delayed VEP while more generalised lesions, such as the ones seen in
infants with hypoxic - ischaemic encephalopathy grade 2 and 3, tended to be associated
with abnormal VEP responses. 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 VEP. We were also able to
demonstrate that VEP can be also used as a prognostic indicator: while normal OR VEP
are reliably associated with a normal visual and neurodevelopmental outcome, abnormal
4 OR or 8 PH at 5 months are consistently associated with abnormal outcome.
Key words
VEP - Infant - Brain - MRI - Vision
