Department of Psychology, University of Michigan, Ann Arbor, MI 48109, USA.
Department of Epidemiology and Biostatistics, Michigan State University, East Lansing, MI 48824, USA.
Cereb Cortex. 2021 Jul 5;31(8):3881-3898. doi: 10.1093/cercor/bhab056.
Aging is associated with widespread alterations in cerebral white matter (WM). Most prior studies of age differences in WM have used diffusion tensor imaging (DTI), but typical DTI metrics (e.g., fractional anisotropy; FA) can reflect multiple neurobiological features, making interpretation challenging. Here, we used fixel-based analysis (FBA) to investigate age-related WM differences observed using DTI in a sample of 45 older and 25 younger healthy adults. Age-related FA differences were widespread but were strongly associated with differences in multi-fiber complexity (CX), suggesting that they reflected differences in crossing fibers in addition to structural differences in individual fiber segments. FBA also revealed a frontolimbic locus of age-related effects and provided insights into distinct microstructural changes underlying them. Specifically, age differences in fiber density were prominent in fornix, bilateral anterior internal capsule, forceps minor, body of the corpus callosum, and corticospinal tract, while age differences in fiber cross section were largest in cingulum bundle and forceps minor. These results provide novel insights into specific structural differences underlying major WM differences associated with aging.
衰老是与脑白质（WM）广泛改变相关的。大多数关于 WM 年龄差异的先前研究都使用了弥散张量成像（DTI），但典型的 DTI 指标（例如分数各向异性；FA）可以反映多种神经生物学特征，这使得解释变得具有挑战性。在这里，我们使用基于固定点的分析（FBA）来研究在使用 DTI 的 45 名老年人和 25 名年轻健康成年人样本中观察到的与年龄相关的 WM 差异。与年龄相关的 FA 差异广泛存在，但与多纤维复杂性（CX）的差异密切相关，这表明它们反映了交叉纤维的差异，而不仅仅是单个纤维段的结构差异。FBA 还揭示了与年龄相关的额叶边缘效应的位置，并提供了对其潜在的不同微观结构变化的深入了解。具体而言，穹窿、双侧内囊前肢、小内囊脚、胼胝体体部和皮质脊髓束中的纤维密度差异在年龄上较为显著，而在扣带束和小内囊脚中的纤维横截面积差异在年龄上最大。这些结果为与衰老相关的主要 WM 差异的基础上的具体结构差异提供了新的见解。
