Mapping continued brain growth and gray matter density reduction in dorsalfrontal cortex: Inverse relationships during postadolescent brain maturation

Recent in vivo structural imaging studies have shown spatial and temporal p atterns of brain maturation between childhood, adolescence, and young adult hood that are generally consistent with postmortem studies of cellular matu rational events such as increased myelination and synaptic pruning. In this study, we conducted detailed spatial and temporal analyses of growth and g ray matter density at the cortical surface of the brain in a group of 35 no rmally developing children, adolescents, and young adults. To accomplish th is, we used high-resolution magnetic resonance imaging and novel computatio nal image analysis techniques. For the first time, in this report we have m apped the continued postadolescent brain growth that occurs primarily in th e dorsal aspects of the frontal lobe bilaterally and in the posterior tempo ro-occipital junction bilaterally. Notably, maps of the spatial distributio n of postadolescent cortical gray matter density reduction are highly consi stent with maps of the spatial distribution of postadolescent brain growth, showing an inverse relationship between cortical gray matter density reduc tion and brain growth primarily in the superior frontal regions that contro l executive cognitive functioning. Inverse relationships are not as robust in the posterior temporo-occipital junction where gray matter density reduc tion is much less prominent despite late brain growth in these regions betw een adolescence and adulthood. Overall brain growth is not significant betw een childhood and adolescence, but close spatial relationships between gray matter density reduction and brain growth are observed in the dorsal parie tal and frontal cortex. These results suggest that progressive cellular mat urational events, such as increased myelination, may play as prominent a ro le during the postadolescent years as regressive events, such as synaptic p runing, in determining the ultimate density of mature frontal lobe cortical gray matter.