A milestone for normal development of the infantile brain detected by functional MRI

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Abstract
Objective: To investigate the relationship between cerebral cortical function and white matter myelination in the visual pathway in the evaluation of normal brain development. Methods: The authors performed quantitative analysis of white matter myelination detected with conventional T1-weighted spin echo (SE) MRI and brain functional MRI (fMRI) using echoplanar imaging with photic stimulation in 27 neurologically normal infants (age range, 0 to 22 weeks). Results: An age-dependent gradual increase in signal intensity was observed in optic radiation on the T1-weighted SE images, indicating progression of white matter myelination. A rapid age-dependent reverse in signal response was observed on fMRI. Infants older than 8 weeks showed a stimulus-induced signal decrease in the visual cortex, whereas infants younger than 7 weeks showed a signal increase. Conclusions: A rapid inversion of response revealed by fMRI with photic stimulation in infants suggests a change in oxygen consumption during neuronal activation, which is related to rapid synapse formation and accompanying increased metabolism. fMRI can detect dynamic metabolic changes during brain maturation, which is a different developmental process from white matter myelination. The metabolic changes detected by fMRI provide a milestone for the evaluation of normal brain development.