Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta T6G 2V2, Canada.
J Neurosci. 2011 Jul 27;31(30):10937-47. doi: 10.1523/JNEUROSCI.5302-10.2011.
Healthy human brain development is a complex process that continues during childhood and adolescence, as demonstrated by many cross-sectional and several longitudinal studies. However, whether these changes end in adolescence is not clear. We examined longitudinal white matter maturation using diffusion tensor tractography in 103 healthy subjects aged 5-32 years; each volunteer was scanned at least twice, with 221 total scans. Fractional anisotropy (FA) and mean diffusivity (MD), parameters indicative of factors including myelination and axon density, were assessed in 10 major white matter tracts. All tracts showed significant nonlinear development trajectories for FA and MD. Significant within-subject changes occurred in the vast majority of children and early adolescents, and these changes were mostly complete by late adolescence for projection and commissural tracts. However, association tracts demonstrated postadolescent within-subject maturation of both FA and MD. Diffusion parameter changes were due primarily to decreasing perpendicular diffusivity, although increasing parallel diffusivity contributed to the prolonged increases of FA in association tracts. Volume increased significantly with age for most tracts, and longitudinal measures also demonstrated postadolescent volume increases in several association tracts. As volume increases were not directly associated with either elevated FA or reduced MD between scans, the observed diffusion parameter changes likely reflect microstructural maturation of brain white matter tracts rather than just gross anatomy.
人类大脑的健康发育是一个复杂的过程，在儿童期和青春期仍在继续，这一点已被许多横断面和一些纵向研究证明。然而，这些变化是否在青春期结束尚不清楚。我们使用弥散张量纤维束追踪技术，对 103 名年龄在 5 岁至 32 岁的健康受试者进行了纵向白质成熟度研究；每位志愿者至少接受了两次扫描，总共进行了 221 次扫描。各向异性分数（FA）和平均弥散度（MD）是髓鞘和轴突密度等因素的指标，在 10 条主要白质束中进行了评估。所有束都显示出 FA 和 MD 的显著非线性发展轨迹。大多数儿童和青少年的大多数白质束都出现了显著的个体内变化，这些变化在大多数投射束和连合束中在青春期后期基本完成。然而，联合束表现出 FA 和 MD 的青春期后个体内成熟。扩散参数的变化主要归因于垂直方向扩散性的降低，尽管平行方向扩散性的增加也导致了联合束 FA 的延长增加。大多数束的体积都随年龄显著增加，纵向测量也表明在几个联合束中，青春期后体积仍在增加。由于两次扫描之间的 FA 升高或 MD 降低与体积增加没有直接关系，因此观察到的扩散参数变化可能反映了脑白质束的微观结构成熟，而不仅仅是大体解剖。
