Matijevic Stephanie, Ryan Lee
Cognition and Neuroimaging Laboratory, Department of Psychology, University of Arizona, Tucson, AZ, United States.
Front Aging Neurosci. 2021 Mar 15;13:628865. doi: 10.3389/fnagi.2021.628865. eCollection 2021.
Well-established literature indicates that older adults have poorer cerebral white matter integrity, as measured through diffusion tensor imaging (DTI). Age differences in DTI have been observed widely across white matter, although some tracts appear more sensitive to the effects of aging than others. Factors like APOE ε4 status and sex may contribute to individual differences in white matter integrity that also selectively impact certain tracts, and could influence DTI changes in aging. The present study explored the degree to which age, APOE ε4, and sex exerted global vs. tract specific effects on DTI metrics in cognitively healthy late middle-aged to older adults. Data from 49 older adults (ages 54-92) at two time-points separated by approximately 2.7 years were collected. DTI metrics, including fractional anisotropy (FA) and mean diffusivity (MD), were extracted from nine white matter tracts and global white matter. Results showed that across timepoints, FA and MD increased globally, with no tract-specific changes observed. Baseline age had a global influence on both measures, with increasing age associated with lower FA and higher MD. After controlling for global white matter FA, age additionally predicted FA for the genu, callosum body, inferior fronto-occipital fasciculus (IFOF), and both anterior and posterior cingulum. Females exhibited lower global FA on average compared to males. In contrast, MD was selectively elevated in the anterior cingulum and superior longitudinal fasciculus (SLF), for females compared to males. APOE ε4 status was not predictive of either measure. In summary, these results indicate that age and sex are associated with both global and tract-specific alterations to DTI metrics among a healthy older adult cohort. Older women have poorer white matter integrity compared to older men, perhaps related to menopause-induced metabolic changes. While age-related alterations to white matter integrity are global, there is substantial variation in the degree to which tracts are impacted, possibly as a consequence of tract anatomical variability. The present study highlights the importance of accounting for global sources of variation in DTI metrics when attempting to investigate individual differences (due to age, sex, or other factors) in specific white matter tracts.
成熟的文献表明，通过扩散张量成像（DTI）测量，老年人的脑白质完整性较差。DTI中的年龄差异在整个白质中广泛存在，尽管某些纤维束似乎比其他纤维束对衰老的影响更敏感。APOE ε4状态和性别等因素可能导致白质完整性的个体差异，这些差异也会选择性地影响某些纤维束，并可能影响衰老过程中的DTI变化。本研究探讨了年龄、APOE ε4和性别对认知健康的中老年至老年人DTI指标产生整体影响与特定纤维束影响的程度。收集了49名年龄在54 - 92岁之间的老年人在两个时间点（间隔约2.7年）的数据。从九个白质纤维束和全脑白质中提取DTI指标，包括各向异性分数（FA）和平均扩散率（MD）。结果显示，在各个时间点，FA和MD整体上增加，未观察到特定纤维束的变化。基线年龄对这两个指标都有整体影响，年龄增加与较低的FA和较高的MD相关。在控制了全脑白质FA后，年龄还可预测胼胝体膝部、胼胝体体部、额枕下束（IFOF）以及前扣带回和后扣带回的FA。与男性相比，女性平均全脑FA较低。相比之下，与男性相比，女性前扣带回和上纵束（SLF）的MD选择性升高。APOE ε4状态对这两个指标均无预测作用。总之，这些结果表明，在健康的老年人群体中，年龄和性别与DTI指标的整体及特定纤维束改变均相关。老年女性的白质完整性比老年男性差，这可能与绝经引起的代谢变化有关。虽然与年龄相关的白质完整性改变是全身性的，但各纤维束受影响的程度存在很大差异，这可能是纤维束解剖结构变异性的结果。本研究强调了在试图研究特定白质纤维束中的个体差异（由于年龄、性别或其他因素）时，考虑DTI指标整体变异来源的重要性。
