Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA, USA.
Neuropsychologia. 2013 Jul;51(8):1435-44. doi: 10.1016/j.neuropsychologia.2013.03.005. Epub 2013 Mar 16.
Although aging is associated with changes in brain structure and cognition it remains unclear which specific structural changes mediate individual cognitive changes. Several studies have reported that white matter (WM) integrity, as assessed by diffusion tensor imaging (DTI), mediates, in part, age-related differences in processing speed (PS). There is less evidence for WM integrity mediating age-related differences in higher order abilities (e.g., memory and executive functions). In 165 typically aging adults (age range 54-89) we show that WM integrity in select cerebral regions is associated with higher cognitive abilities and accounts variance not accounted for by PS or age. Specifically, voxel-wise analyses using tract-based spatial statistics (TBSS) revealed that WM integrity was associated with reasoning, cognitive flexibility and PS, but not memory or word fluency, after accounting for age and gender. While cerebral fractional anisotropy (FA) was only associated with PS; mean (MD), axial (AD) and radial (RD) diffusivity were associated with reasoning and flexibility. Reasoning was selectively associated with left prefrontal AD, while cognitive flexibility was associated with MD, AD and RD throughout the cerebrum. Average WM metrics within select WM regions of interest accounted for 18% and 29% of the variance in reasoning and flexibility, respectively, similar to the amount of variance accounted for by age. WM metrics mediated ~50% of the age-related variance in reasoning and flexibility and different proportions, 11% for reasoning and 44% for flexibility, of the variance accounted for by PS. In sum, (i) WM integrity is significantly, but variably, related to specific higher cognitive abilities and can account for a similar proportion of variance as age, and (ii) while FA is selectively associated with PS; while MD, AD and RD are associated with reasoning, flexibility and PS. This illustrates both the anatomical and cognitive selectivity of structure-cognition relationships in the aging brain.
尽管衰老与大脑结构和认知变化有关，但仍不清楚哪些特定的结构变化介导个体认知变化。一些研究报告称，弥散张量成像（DTI）评估的白质（WM）完整性部分介导了与年龄相关的处理速度（PS）差异。WM 完整性介导与年龄相关的更高阶能力（例如记忆和执行功能）差异的证据较少。在 165 名典型衰老成年人（年龄范围为 54-89 岁）中，我们表明，选择大脑区域的 WM 完整性与更高的认知能力相关，并解释了 PS 或年龄无法解释的差异。具体而言，使用基于体素的空间统计学（TBSS）的体素分析表明，在考虑年龄和性别后，WM 完整性与推理、认知灵活性和 PS 相关，但与记忆或词汇流畅性无关。虽然脑区分数各向异性（FA）仅与 PS 相关；平均（MD）、轴向（AD）和径向（RD）扩散与推理和灵活性相关。推理与左前额叶 AD 选择性相关，而认知灵活性与整个大脑的 MD、AD 和 RD 相关。在选择的 WM 感兴趣区域内的平均 WM 指标分别解释了推理和灵活性方差的 18%和 29%，与年龄解释的方差量相似。WM 指标介导了推理和灵活性的约 50%的年龄相关差异，以及 PS 解释的方差的不同比例，推理为 11%，灵活性为 44%。总之，（i）WM 完整性与特定的更高认知能力显著相关，但具有可变性，可以解释与年龄相似比例的方差，（ii）FA 与 PS 选择性相关；而 MD、AD 和 RD 与推理、灵活性和 PS 相关。这说明了衰老大脑中结构-认知关系的解剖学和认知选择性。
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