Alteration in the Local and Global Functional Connectivity of Resting State Networks in Parkinson's Disease

Abstract

Objective: Parkinson's disease (PD) is a neurodegenerative disorder that mainly leads to the impairment of patients' motor function, as well as of cognition, as it progresses. This study tried to investigate the impact of PD on the resting state functional connectivity of the default mode network (DMN), as well as of the entire brain.

Methods: Sixty patients with PD were included and compared to 60 matched normal control (NC) subjects. For the local connectivity analysis, the resting state fMRI data were analyzed by seed-based correlation analyses, and then a novel persistent homology analysis was implemented to examine the connectivity from a global perspective.

Results: The functional connectivity of the DMN was decreased in the PD group compared to the NC, with a stronger difference in the medial prefrontal cortex. Moreover, the results of the persistent homology analysis indicated that the PD group had a more locally connected and less globally connected network compared to the NC.

Conclusion: Our findings suggest that the DMN is altered in PD, and persistent homology analysis, as a useful measure of the topological characteristics of the networks from a broader perspective, was able to identify changes in the large-scale functional organization of the patients' brain.

Keywords: Parkinson’s disease; default mode network; functional connectivity; persistent homology; resting state fMRI.

Figure 1.

Functional connectivity of the DMN with the PCC (left) and mPFC (right) as the seed regions in the NC (first row), PD group (second row), and the difference between them (third row). PCC: posterior cingulate cortex, mPFC: medial prefrontal cortex, NC: normal control, PD: Parkinson’s disease, DMN: default mode network.

Figure 2.

Connectome rings of the PCC (A and B) and mPFC (C and D) with the rest of the brain in the PD (A and C) and NC (B and D) groups. PD: Parkinson’s disease, NC: normal control, PCC: posterior cingulate cortex, mPFC: medial prefrontal cortex.

Figure 3.

Barcode diagram and the brain connectivity visualization at filtrations values 0.2, 0.3, and 0.4 for the NC (green curve) and PD (blue curve) groups. The vertical axis represents the number of connected components (0^th Betti number), while the horizontal axis corresponds to the filtration values. The 3D brain visualization represents the ROIs as spherical nodes and their pairwise connections as edges to represent added connection with changing filtration values; color-coded based on the connection strength. NC: normal control, PD: Parkinson’s disease, ROI: regions of interest.

Figure 4.

Dendrogram for the NC (A) and PD group (B) based on the barcode diagram. The vertical axis represents the node index over the 90 regions of interest, and the horizontal axis represents the filtration values. The coloring of the lines is based on the distance from the giant component. NC: normal control, PD: Parkinson’s disease.