VISUAL ACTIVATION IN INFANTS AND YOUNG-CHILDREN STUDIED BY FUNCTIONALMAGNETIC-RESONANCE-IMAGING

The purpose of this study was to determine whether visual stimulation in sleeping infants and young children can be examined by functional m agnetic resonance imaging. We studied 17 children, aged 3 d to 45 mo, and three healthy adults. Visual stimulation was performed with S-Hz f lickering light through the sleeping childs' closed eyelids. Functiona l magnetic resonance imaging was performed with a gradient echoplanar sequence in a 1.5-T magnetic resonance scanner. Six subjects were excl uded because of movement artifacts; the youngest infant showed no resp onse. In 10 children, we could demonstrate areas of signal decrease du ring visual stimulation in the occipital cortex (mean decrease 2.21%), contrary to the signal increase observed in the adult controls (mean increase 2.82%). This decrease may be due to a higher proportional inc rease in oxygen extraction compared with increase in cerebral blood fl ow during activation. The different response patterns in young childre n and adults can reflect developmental or behavioral differences. Loca lization of the activation seemed to be age-dependent. In the older ch ildren and the adults, it encompassed the whole length of the calcarin e sulcus, whereas it was restricted to the anterior and medial part of the calcarine sulcus in the younger infants. This may reflect a diffe rent functional organization of the young child's visual cortex or the on-going retinal development.