The present article overviewed many studies on the brain functions affected by the social experiences in infants, especially focusing on the mother-infant bonding in early infants and the stress vulnerability in infants with immature brain functions developed by the maltreated maternal care. In order to explain the relationships between the emotion and stress vulnerability from neuropsychological point of view in developmental process, this article showed that it is significant to examine hemispheric asymmetries of brain activations of maltreated and normal infants in the mother-infant interaction settings. On the basis of our pilot study for the cerebral blood flow of normal infants in the mother-infants interaction setting, it was suggested that the application of near-infrared spectroscopic topography to the investigation for the stress vulnerability in infants could become useful in future.