Overman Margot Juliëtte, Zamboni Giovanna, Butler Christopher, Ahmed Samrah
Research Institute for the Care of Older People (RICE), Bath BA1 3NG, UK.
MRC Cognition and Brain Sciences Unit, University of Cambridge, Cambridge CB2 7EF, UK.
Brain Commun. 2021 Apr 28;3(2):fcab060. doi: 10.1093/braincomms/fcab060. eCollection 2021.
Posterior cortical atrophy is an atypical form of Alzheimer's disease characterized by visuospatial impairments and predominant tissue loss in the posterior parieto-occipital and temporo-occipital cortex. Whilst episodic memory is traditionally thought to be relatively preserved in posterior cortical atrophy, recent work indicates that memory impairments form a common clinical symptom in the early stages of the disease. Neuroimaging studies suggest that memory dysfunction in posterior cortical atrophy may originate from atrophy and functional hypoconnectivity of parietal cortex. The connectivity patterns underpinning these memory impairments, however, have not been investigated. This line of inquiry is of particular interest, as changes in white matter tracts of posterior cortical atrophy patients have been shown to be more extensive than expected based on posterior atrophy of grey matter. In this cross-sectional diffusion tensor imaging MRI study, we examine the relationship between white matter microstructure and verbal episodic memory in posterior cortical atrophy. We assessed episodic memory performance in a group of posterior cortical atrophy patients ( = 14) and a group of matched healthy control participants ( = 19) using the Free and Cued Selective Reminding Test with Immediate Recall. Diffusion tensor imaging measures were obtained for 13 of the posterior cortical atrophy patients and a second control group of 18 healthy adults. Patients and healthy controls demonstrated similar memory encoding performance, indicating that learning of verbal information was preserved in posterior cortical atrophy. However, retrieval of verbal items was significantly impaired in the patient group compared with control participants. As expected, tract-based spatial statistics analyses showed widespread reductions of white matter integrity in posterior cortical regions of patients compared with healthy adults. Correlation analyses indicated that poor verbal retrieval in the patient group was specifically associated with microstructural damage of the splenium of the corpus callosum. Post-hoc tractography analyses in healthy controls demonstrated that this splenial region was connected to thalamic radiations and the retrolenticular part of the internal capsule. These results provide insight into the brain circuits that underlie memory impairments in posterior cortical atrophy. From a cognitive perspective, we propose that the association between splenial integrity and memory dysfunction could arise indirectly via disruption of attentional processes. We discuss implications for the clinical phenotype and development of therapeutic aids for cognitive impairment in posterior cortical atrophy.
后部皮质萎缩是阿尔茨海默病的一种非典型形式，其特征为视觉空间障碍以及顶枕叶和颞枕叶皮质的主要组织丢失。虽然传统上认为情景记忆在后部皮质萎缩中相对保留，但最近的研究表明，记忆障碍是该疾病早期阶段常见的临床症状。神经影像学研究表明，后部皮质萎缩中的记忆功能障碍可能源于顶叶皮质的萎缩和功能连接减弱。然而，支撑这些记忆障碍的连接模式尚未得到研究。这一研究方向特别有趣，因为后部皮质萎缩患者白质束的变化已被证明比基于灰质后部萎缩预期的更为广泛。在这项横断面扩散张量成像MRI研究中，我们研究了后部皮质萎缩中白质微观结构与言语情景记忆之间的关系。我们使用自由和提示选择性回忆测试及即时回忆，评估了一组后部皮质萎缩患者（n = 14）和一组匹配的健康对照参与者（n = 19）的情景记忆表现。对13名后部皮质萎缩患者和第二组18名健康成年人进行了扩散张量成像测量。患者和健康对照者表现出相似的记忆编码表现，表明后部皮质萎缩患者对言语信息的学习得以保留。然而，与对照参与者相比，患者组言语项目的检索明显受损。正如预期的那样，基于束的空间统计分析显示，与健康成年人相比，患者后部皮质区域的白质完整性普遍降低。相关性分析表明，患者组言语检索能力差与胼胝体压部的微观结构损伤特别相关。对健康对照者的事后纤维束成像分析表明，这个压部区域与丘脑辐射和内囊后肢相连。这些结果为后部皮质萎缩中记忆障碍的脑回路提供了见解。从认知角度来看，我们认为压部完整性与记忆功能障碍之间的关联可能通过注意力过程的中断间接产生。我们讨论了对临床表型的影响以及后部皮质萎缩认知障碍治疗辅助工具的开发。
