Alzheimer病视觉注意缺陷的功能MRI研究

Visual attention deficits in Alzheimer′s disease——a fMRI study

目的 采用功能磁共振成像(functionalMRI, fMRI)技术考察Alzheimer病(AD)视觉注意缺陷的原因,并对其相应的神经解剖基础进行初步探讨。方法 13例临床诊断可能为AD的患者和13例年龄、性别与之相匹配的健康老年人参加了2种不同视觉搜索的实验测试(即联合特征搜索和子集搜索任务:其中的靶刺激均具有2个特征,但前者是通过特征捆绑策略,后者是通过项目分组形成子集来完成任务)。同时采用SiemensSonata1 5T成像系统, 采集其脑部fMRI数据,通过功能神经成像分析软件SPM 99 (statisticalparametricmappingsoftware, SPM)进行统计分析得到脑功能活动的图像。结果 尽管2个研究组在完成不同搜索任务时的脑区大部分相互重叠,包括顶叶、额叶、颞枕交界区、原始视皮层和皮层下结构等脑区,但不同脑区的激活强度和范围明显不同,AD组主要表现为双侧顶叶和左侧额叶激活减少,并以子集搜索任务时的组间差异更显著。结论 AD患者在项目分组和特征捆绑方面均存在一定程度功能失调,其视觉注意缺陷可能是由于顶叶病变使注意焦点在不同空间位置转换困难所致,同时伴有前扣带回和前额叶功能不良。

Objective To investigate the attention level and probe the neuro-anatomic basis of visual attention deficits, and to identify its essential causes in AD patients by using functional MRI. Methods Thirteen patients with AD and 13 healthy subjects of similar age and gender ratio participated in the experiment designed with two visual search tasks. The first was a conjunction task, where two features were presented in the array and spatial attention and feature binding were required. The second task was subset search, where two features were also presented but only one of them was needed in order to group stimuli together (the subset) without the need for feature binding. The fMRI data were collected on a Siemens 1.5 T Sonata MRI system and analyzed by statistical parametric mapping software (SPM 99) to generate the activation map. Results Although two groups revealed similar networks engaged in different search tasks, including the parietal lobe, frontal lobe, occipital regions, primary visual cortex, and some subcortical structures, there were remarkable differences in the extent of activation of these brain regions between patients and controls. The less activation was demonstrated in the bilateral parietal lobes and left frontal regions, especially in the subset search, in AD patients. Conclusion The attention deficits in AD patients were caused by “feature binding” problem and “grouping” inefficiency. The less activation mainly located in the parietal cortex (unable to switch the focus of their attention “window” in different spatial locations), with anterior cingulate and the frontal lobes dysfunction.