An investigation into the functional and structural connectivity of the Default Mode Network

Connectivity analyses based on both resting-state (rs-)fMRI and diffusion weighted imaging studies suggest that the human brain contains regions that act as hubs for the entire brain, and that elements of the Default Mode Network (DMN) play a pivotal role in this network. In the present study, the detailed functional and structural connectivity of the DMN was investigated. Resting state fMRI (35 minute duration) and Diffusion Weighted Imaging (DWI) data (256 directions) were acquired from forty-seven healthy subjects at 3 T. Tractography was performed on the DWI data. The resting state data were analysed using a combination of Independent Component Analysis, partial correlation analysis and graph theory. This forms a data driven approach for examining the connectivity of the DMN. ICA defined regions of interest were used as a basis for a partial correlation analysis. The resulting partial correlation coefficients were used to compute graph theoretical measures. This was performed on a single subject basis, and combined to compute group results depicting the spatial distribution of betweenness centrality within the DMN. Hubs with high betweenness centrality were frequently found in association areas of the brain. This approach makes it possible to distinguish the hubs in the DMN as belonging to different anatomical association systems. The start and end points of the fibre tracts coincide with hubs found using the resting state analysis.