Centre for Functional MRI of the Brain, University of Oxford, Oxford, UK.
Neuroimage. 2010 Jan 1;49(1):94-103. doi: 10.1016/j.neuroimage.2009.08.003. Epub 2009 Aug 11.
Brain development continues actively during adolescence. Previous MRI studies have shown complex patterns of apparent loss of grey matter (GM) volume and increases in white matter (WM) volume and fractional anisotropy (FA), an index of WM microstructure. In this longitudinal study (mean follow-up=2.5+/-0.5 years) of 24 adolescents, we used a voxel-based morphometry (VBM)-style analysis with conventional T1-weighted images to test for age-related changes in GM and WM volumes. We also performed tract-based spatial statistics (TBSS) analysis of diffusion tensor imaging (DTI) data to test for age-related WM changes across the whole brain. Probabilistic tractography was used to carry out quantitative comparisons across subjects in measures of WM microstructure in two fiber tracts important for supporting speech and motor functions (arcuate fasciculus [AF] and corticospinal tract [CST]). The whole-brain analyses identified age-related increases in WM volume and FA bilaterally in many fiber tracts, including AF and many parts of the CST. FA changes were mainly driven by increases in parallel diffusivity, probably reflecting increases in the diameter of the axons forming the fiber tracts. FA values of both left and right AF (but not of the CST) were significantly higher at the end of the follow-up than at baseline. Over the same period, widespread reductions in the cortical GM volume were found. These findings provide imaging-based anatomical data suggesting that brain maturation in adolescence is associated with structural changes enhancing long-distance connectivities in different WM tracts, specifically in the AF and CST, at the same time that cortical GM exhibits synaptic "pruning".
大脑在青春期仍持续活跃地发育。先前的 MRI 研究表明，脑灰质（GM）体积出现明显损失，白质（WM）体积和各向异性分数（FA）增加，后者是 WM 微观结构的指标，呈现复杂的模式。在这项对 24 名青少年的纵向研究（平均随访 2.5+/-0.5 年）中，我们使用基于体素的形态测量学（VBM）分析方法和常规 T1 加权图像，测试 GM 和 WM 体积与年龄相关的变化。我们还对弥散张量成像（DTI）数据进行基于束的空间统计学（TBSS）分析，以测试整个大脑中与年龄相关的 WM 变化。使用概率追踪来进行定量比较，比较两个对支持言语和运动功能很重要的纤维束（弓状束[AF]和皮质脊髓束[CST]）的 WM 微观结构的测量值。全脑分析确定了与年龄相关的 WM 体积和 FA 双侧增加，在许多纤维束中，包括 AF 和 CST 的许多部分。FA 变化主要是由平行扩散性增加驱动的，这可能反映了形成纤维束的轴突直径增加。在随访结束时，左右 AF（而不是 CST）的 FA 值均明显高于基线。在此期间，还发现皮质 GM 体积广泛减少。这些发现提供了基于影像学的解剖学数据，表明青春期大脑成熟与结构变化有关，这些变化增强了不同 WM 束中的远距离连通性，特别是在 AF 和 CST 中，同时皮质 GM 表现出突触“修剪”。
