Visual processing in infants and children studied using functional MRI

We studied the development of visual processing in 58 children, ranging fro m 1 d to 12 y of age (median age 29 mo), using functional magnetic resonanc e imaging. All but nine children had either been sedated using chloral hydr ate (n = 12) or pentobarbital (n = 28). Nine children were studied under a full halothane/ N2O:O-2 anesthesia. In the first postnatal month, 30% of th e neonates showed a positive blood oxygenation level-dependent (BOLD) contr ast signal, whereas, for infants between the ages of 1 mo and 1 y, 27% did so. Thirty-one percent of children between 1 and 6 y of age and 71% of chil dren aged 6 y and above showed a positive BOLD contrast signal change to ou r visual stimulation paradigm. Besides the usual positive BOLD contrast signal change, we also noted that a large portion of the children measured displayed a negative BOLD contrast signal change. This negative BOLD contrast signal change was observed in 3 0% of children up to 1 mo of age, in 27% between 1 mo and 1 y of age, in 47 % between 1 and 6 y of age, and in 14% of children 6 y and older. In the ch ildren in which we observed a negative correlating BOLD contrast signal cha nge, the locus was more anterior and more lateral than the positive BOLD co ntrast signal, placing it in the secondary visual cortical area. The result s indicate that when using functional magnetic resonance imaging on childre n, the primary visual cortical area does not respond functionally in the sa me manner as that of the adult until 1.5 y of age. This supports earlier cl inical and electrophysiologic findings that different cortical mechanisms s eem to contribute to visual perception at different times postnatally.