NEUROLOGY ：轻微认知障碍患者的情景记忆与多个颞叶相关通路结构相关

　　轻微认知障碍患者的情景记忆与多个颞叶相关通路结构相关，关联强度用颜色标示 

　　颞叶联系的微结构和情景记忆受损之间的相关模式尚不清楚。情景记忆受损是轻微认知障碍（MCI）的主要特征。英国加地夫大学大脑研究影像中心的Claudia Metzler-Baddeley博士等人进行了一项研究，研究结果在线发表在2012年11月21日的Neurology杂志上。研究结果发现：MCI患者情景记忆与多个颞叶相关路径的结构相关。在MCI患者，由于穹窿异常，替代路径可能对情景记忆的表现影响较大。

　　研究人员对25位MCI和20位匹配的对照进行了弥散MRI和认知评估。通过路径成像重建三个颞叶路径：穹窿、海马周围扣带（PHC）和钩状束。测量组织容量比例（路径萎缩的特异性测量值）和每个路径的微结构值。为了检验特异性相关，对路径（皮质脊髓束）和对照组认知域也进行了比较检验。

　　研究结果显示：在MCI患者，穹窿的组织容量比例降低。钩状体和PHC的轴向与径向弥散度增加，提示存在较多的微结构改变。在对照组，穹窿组织容量比例是轻松回忆的主要相关因素。相反，在MCI，回忆与左侧PHC相关性最强。在MCI患者，钩状体和PHC微结构的改变也和认知记忆和认知信度相关。

　　该研究发现：MCI患者情景记忆与多个颞叶相关路径的结构相关。这些相关性不是局限在穹窿（在健康年轻人和老年人局限在穹窿）。在MCI患者，由于穹窿异常，替代路径可能对情景记忆的表现影响较大。　

Temporal association tracts and the breakdown of episodic memory in mild cognitive impairment

Objective

To examine the pattern of association between microstructure of temporal lobe connections and the breakdown of episodic memory that is a core feature of mild cognitive impairment (MCI).

Methods

Twenty-five individuals with MCI and 20 matched controls underwent diffusion MRI and cognitive assessment. Three temporal pathways were reconstructed by tractography: fornix, parahippocampal cingulum (PHC), and uncinate fasciculus. Tissue volume fraction—a tract-specific measure of atrophy—and microstructural measures were derived for each tract. To test specificity of associations, a comparison tract (corticospinal tract) and control cognitive domains were also examined.

Results

In MCI, tissue volume fraction was reduced in the fornix. Axial and radial diffusivity were increased in uncinate and PHC implying more subtle microstructural change. In controls, tissue volume fraction in the fornix was the predominant correlate of free recall. In contrast, in MCI, the strongest relationship was with left PHC. Microstructure of uncinate and PHC also correlated with recognition memory, and recognition confidence, in MCI.

Conclusions

Episodic memory in MCI is related to the structure of multiple temporal association pathways. These associations are not confined to the fornix, as they are in healthy young and older adults. In MCI, because of a compromised fornix, alternative pathways may contribute disproportionally to episodic memory performance.