Early maternal support predicts larger brain volumes at school age.

Luby et al. offer a compelling study showing the importance of maternal nuturing in young humans.Maternal support is predictive of hippocampus volume measured at school age. From their introduction:

Animal studies have shown that maternal nurturance...promotes adaptive programming of the hypothalamic–pituitary–adrenal axis stress response and hippocampal development. Improvements in the capacity for stress modulation have been shown to be related to epigenetic modifications whereby methylation of multiple genes results in changes in gene expression for glucocorticoid and mineralcorticoid receptors. These changes are associated with increases in dendritic branching and neurogenesis and related increases in hippocampal volumes. Consistent with this phenomenon and conversely, the stress of early maternal deprivation has been shown to have negative effects on this cascade. A similar relationship between early nurturance and stress modulation has also been reported in nonhuman primates.

Their abstract:

Early maternal support has been shown to promote specific gene expression, neurogenesis, adaptive stress responses, and larger hippocampal volumes in developing animals. In humans, a relationship between psychosocial factors in early childhood and later amygdala volumes based on prospective data has been demonstrated, providing a key link between early experience and brain development. Although much retrospective data suggests a link between early psychosocial factors and hippocampal volumes in humans, to date there has been no prospective data to inform this potentially important public health issue. In a longitudinal study of depressed and healthy preschool children who underwent neuroimaging at school age, we investigated whether early maternal support predicted later hippocampal volumes. Maternal support observed in early childhood was strongly predictive of hippocampal volume measured at school age. The positive effect of maternal support on hippocampal volumes was greater in nondepressed children. These findings provide prospective evidence in humans of the positive effect of early supportive parenting on healthy hippocampal development, a brain region key to memory and stress modulation.