Minimum spanning tree reflects the alterations of the default mode network during Alzheimer's disease

This study analyzes the connectivity pattern of the default mode network (DMN) in patients with Alzheimer's disease (AD) in comparison with young and elderly controls using the minimum spanning tree (MST). This tree is a tool from graph theory and connects all the nodes of a graph with the minimum cost. The findings revealed that the alterations of the basic structure represented by the MST might provide valuable insights about the physiopathology of the disease. Additionally, by making use of the MST for functionally clustering the DMN, it was shown that the functional subnetworks comprising the DMN differed among the three subject groups. Nonetheless, there were intact prefrontal and temporal networks in elderly controls and AD patients, as well. The analysis shows that although the topologies of the MST characterized by the degree distributions do not differ significantly among the groups, the DMN of the AD patients exhibits a higher segregation, insomuch that posterior cingulate/precuneus and hippocampus/parahippocampus are heavily isolated from rest of the network. We conclude that the MST can be used effectively for analyzing cortical networks.