Mother nurture and the social definition of neurodevelopment.

The quality of family life in childhood predicts the risk for multiple mental disorders, implying sustained effects on relevant brain circuits. Indeed, there is evidence for the idea that the social environment shapes individual differences in brain development and function. A limitation of this evidence is that most studies focus on extreme social adversity, such as parental deprivation (i.e., institutional rearing) or childhood maltreatment. Whether variations in parental carewithin the normal range are similarly relevant for human neurodevelopment remains unclear. Studies with rodents suggest so, but human brain development occurs within a more complex environmental context and over a longer period. In PNAS, Luby et al. (1) report the results of a prospective, longitudinal study that examined the association of maternal support at preschool and school ages, with hippocampal volume usingMRI at three time points. A strength of the study is the laboratorybased assessment of maternal support during mildly stressful conditions, which very nicely mimics the challenges parents regularly face in child rearing. Maternal support at neither preschool nor school age emerged as a significant predictor of hippocampal volume, a finding consistent with cross-sectional studies showing that variations inmaternal influences do not necessarily emerge as main effects in studies of neurodevelopment (2, 3). However, the unique, longitudinal approach of Luby et al. (1) reveals a compelling association between maternal support and hippocampal growth trajectories: hippocampal volume increased faster with age among subjects with higher levels of maternal support. In addition, hippocampal growth trajectories predicted emotional regulation, an important endophenotype for virtually all commonmental disorders.