Diffusion imaging studies have observed age-related degradation of white matter that contributes to cognitive deficits separately in younger-old (ages 65–89) and oldest-old (ages 90+) adults. But it remains unclear whether these age effects are magnified in advanced age groups, which may reflect disease-related pathology. Here, we tested whether age-related differences in white matter microstructure followed linear or nonlinear patterns across the entire older adult lifespan (65–98 years), these patterns were influenced by oldest-old adults at increased risk of dementia (cognitive impairment no dementia, CIND), and they explained age effects on episodic memory. Results revealed nonlinear microstructure declines across fiber classes (medial temporal, callosal, association, projection and/or thalamic) that were largest for medial temporal fibers. These patterns remained after excluding oldest-old participants with CIND, indicating that aging of white matter microstructure cannot solely be explained by pathology associated with early cognitive impairment. Moreover, finding that the effect of age on episodic memory was mediated by medial temporal fiber microstructure suggests it is essential for facilitating memory-related neural signals across the older adult lifespan.

弥散成像研究观察到与年龄相关的白质退化会分别导致较年轻（65-89 岁）和最年长（90 岁以上）成年人的认知缺陷。但尚不清楚这些年龄效应是否在高龄组中被放大，这可能反映了与疾病相关的病理学。在这里，我们测试了白质微观结构的年龄相关差异在整个老年人寿命（65-98 岁）中是否遵循线性或非线性模式，这些模式受到老年痴呆症风险增加（认知障碍无痴呆症）的影响, CIND)，他们解释了年龄对情景记忆的影响。结果显示跨纤维类别（内侧颞叶、胼胝体、联合、投射和/或丘脑）的非线性微观结构下降，其中颞叶内侧纤维最大。这些模式在排除最年长的 CIND 参与者后仍然存在，表明白质微结构的老化不能仅仅用与早期认知障碍相关的病理学来解释。此外，发现年龄对情景记忆的影响是由内侧颞叶纤维微观结构介导的，这表明它对于促进老年人寿命中与记忆相关的神经信号至关重要。