Abstract：Studies have shown that dysfunctions of the default mode network (DMN) are associated with Alzheimer′s disease. In this work, in order to further find out the abnormal connective structure of default mode network in patients with Alzheimer′s disease, an unbiased brain network was constructed by using the minimum spanning tree method and tree hierarchical clustering method was used to analyze community structure of DMN in patients with early mild cognitive impairment (EMCI), lately mild cognitive impairment (LMCI), Alzheimer′s disease (AD) and normal controls (NC). In addition, the difference between gyrus rectus and superior frontal gyrus of orbital part, and precuneus and posterior cingulate gyrus was analyzed. At the same time, the centrality of superior temporal gyrus was analyzed. The results showed that DMN was divided into 5 clusters in NC and EMCI, and it was divided into 7 clusters in the LMCI, but it was divided into 9 clusters in AD. There was significant difference between LMCI and AD in the connection between gyrus rectus and superior frontal gyrus of orbital part (P=0.048), LMCI and EMCI in the connection between precuneus and posterior cingulate gyrus (P=0.042). There was a significant difference between LMCI and NC in the connection between precuneus and posterior cingulate gyrus (P=0.016). There was a significant difference in betweenness of superior temporal gyrus between AD and LMCI (P=0.028), LMCI and NC (P=0.001), EMCI and NC (P=0.048). The results showed that with the progress of the disease, the structure of DMN was gradually dispersed, the connection between the brain regions and the centrality were changed. These brain regions mainly include hippocampus, parahippocampal gyrus, precuneus, posterior cingulate gyrus, superior frontal gyrus of orbital part, middle frontal gyrus of orbital part, gyrus rectus and superior temporal gyrus.
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