Difference in the metabolic response to photic stimulation of the lateral geniculate nucleus and the primary visual cortex of infants: a fMRI study.

The metabolic change that occurs during early development of the human brain was studied with functional magnetic resonance imaging (fMRI), in which the signal change reflects the balance between the supply and the demand of oxygen during stimulus-related neuronal activation. The subjects were 16 infants, aged < 1 year. They were sedated with pentobarbital, and 8-Hz flickering light was intermittently projected onto their eyelids. Two age groups were analyzed: infants < 60 days old and > 60 days old (corrected for gestational age at birth). The stimulus-related signal change was positive in the lateral geniculate nucleus regardless of the infants' age, but in the primary visual cortex reversed from positive in the younger group to negative in the older group. It is known that synaptogenesis in the lateral geniculate nucleus peaks before birth, and in the primary visual cortex accelerates in the second month after birth. Hence, the inversion of the stimulus-related signal change in the primary visual cortex may be due to an increased demand for oxygen owing to rapid synaptogenesis.