Functional magnetic resonance imaging of the normal and abnormal visual system in early life

Functional magnetic resonance imaging (fMRI) in young children may provide information about the development of the visual cortex, and may have predic tive value for later visual performance. The purpose of this study was to e valuate the usefulness of fMRI for examining cerebral processing of vision in very young infants and in infants with brain damage. We examined 15 pret erm infants, 12 children suspected of having a cerebral visual impairment a nd 10 children with a normal visual system, all of whom were either spontan eously asleep or sedated with chloral hydrate. Cortical response to strobos copic light stimulation could be demonstrated in all technically acceptable data sets from children with a post-menstrual age (PMA) of >41 weeks, but not in younger infants. Children <60 weeks PMA showed either a blood oxygen ation level-dependent (BOLD) signal increase or decrease, while all older c hildren showed a signal decrease. The activated cortical volumes showed a l inear relation to age for healthy children younger than 90 weeks PMA, but w ere small in children with visual impairment. In two children with unilater al damage to the optic radiations, activation was strongly asymmetrical wit h greatest activation on the healthy side. In future prospective studies, r esults from the period from birth to six months of age should be interprete d with caution, as inter-individual variation of cortical development may b e confused with functional deficit.