Center for Vital Longevity, School of Behavioral and Brain Sciences, The University of Texas at Dallas, Dallas, Texas.
Hippocampus. 2019 Dec;29(12):1206-1223. doi: 10.1002/hipo.23133. Epub 2019 Jul 23.
Advancing age is associated with both declines in episodic memory and degradation of medial temporal lobe (MTL) structure. The contribution of MTL to episodic memory is complex and depends upon the interplay among hippocampal subfields and surrounding structures that participate in anatomical connectivity to the cortex through inputs (parahippocampal and entorhinal cortices) and outputs (fornix). However, the differential contributions of MTL system components in mediating age effects on memory remain unclear. In a sample of 177 healthy individuals aged 20-94 we collected high-resolution T1-weighted, ultrahigh-resolution T2/PD, and diffusion tensor imaging (DTI) MRI sequences on a 3T Phillips Achieva scanner. Hippocampal subfield and entorhinal cortex (ERC) volumes were measured from T2/PD scans using a combination of manual tracings and training of a semiautomated pipeline. Parahippocampal gyrus volume was estimated using Freesurfer and DTI scans were used to obtain diffusion metrics from tractography of the fornix. Item and associative episodic memory constructs were formed from multiple tests. Competing structural equation models estimating differential association among these structural variables were specified and tested to investigate whether and how fornix diffusion and volume of parahippocampal gyrus, ERC, and hippocampal subfields mediate age effects on associative and/or item memory. The most parsimonious, best-fitting model included an anatomically based path through the MTL as well as a single hippocampal construct which combined all subfields. Results indicated that fornix microstructure independently mediated the effect of age on associative memory, but not item memory. Additionally, all regions and estimated paths (including fornix) combined to significantly mediate the age-associative memory relationship. These findings suggest that preservation of fornix connectivity and MTL structure with aging is important for maintenance of associative memory performance across the lifespan.
随着年龄的增长，情景记忆会衰退，内侧颞叶（MTL）结构也会退化。MTL 对情景记忆的贡献很复杂，取决于海马亚区之间的相互作用以及与皮质通过输入（海马旁回和内嗅皮质）和输出（穹窿）进行解剖连接的周围结构。然而，MTL 系统成分在调节年龄对记忆的影响方面的差异贡献仍不清楚。在一个由 177 名年龄在 20-94 岁的健康个体组成的样本中，我们在 3T Phillips Achieva 扫描仪上采集了高分辨率 T1 加权、超高分辨率 T2/PD 和弥散张量成像（DTI）MRI 序列。使用手动跟踪和半自动流水线的培训相结合，从 T2/PD 扫描中测量海马亚区和内嗅皮质（ERC）的体积。使用 Freesurfer 估计海马旁回的体积，并使用弥散张量成像从穹窿的轨迹获得弥散指标。项目和联想情景记忆结构由多个测试形成。指定并测试了竞争结构方程模型，以估计这些结构变量之间的差异关联，以调查穹窿扩散和海马旁回、ERC 和海马亚区的体积是否以及如何调节年龄对联想和/或项目记忆的影响。最简约、拟合最好的模型包括 MTL 内的解剖路径以及一个组合所有亚区的单个海马结构。结果表明，穹窿的微观结构独立调节了年龄对联想记忆的影响，但不能调节项目记忆。此外，所有区域和估计的路径（包括穹窿）联合起来，显著调节了年龄与联想记忆的关系。这些发现表明，随着年龄的增长，穹窿连接和 MTL 结构的保留对于维持整个生命周期的联想记忆表现很重要。
