Functional connectome assessed using graph theory in drug-naive Parkinson's disease

The purpose of this study is to investigate whether the topological organization of whole-brain functional network is disrupted in patients with Parkinson's disease (PD). We employed resting-state functional MRI (R-fMRI) and graph theory to investigate the topological organization of the functional connectome in 47 early-stage drug-naïve PD patients and 47 healthy control subjects. Correlations between network properties and clinical variables were tested. Both the PD and control groups showed small-world architecture in brain functional networks. However, the PD patients had lower clustering coefficient and local efficiency relative to control subjects, indicating disrupted topologic organization and a shift toward randomization in their functional brain network. At node and connection level, reduced node centralities and connectivity strength were found mainly in temporal-occipital regions and also in sensorimotor regions of PD patients. In PD patients, altered global network properties correlated with cognitive function, while motor impairment was correlated with local connection changes. This study demonstrates a disruption of whole-brain topological organization of the functional brain networks in early-stage drug-naïve PD patients and this disruption might contribute to preclinical changes in cognitive process in these patients.