Two perspectives to investigate the intrinsic organization of the dynamic and ongoing spontaneous brain activity in humans

Spontaneous brain activity studies have revealed `small-world' property in functional networks based on correlated or positively-correlated relationships. However, studies neither investigated negatively-correlated functional networks, nor checked the `dynamic' properties of the whole functional organization. After subjects performed a specific task, what changes will be caused in the intrinsic organization? In this study, we examined pre-task and post-task resting brains using functional MRI (fMRI). Then we suggested two perspectives with positively-correlated brain functional network (PCBFN) and negatively-correlated brain functional network (NCBFN), by testing whether correlation coefficients were positive or negative. The major findings were: 1) the PCBFN was with small-world architecture but the NCBFN was not, with different motifs, and the PCBFN showed stronger small-world effect at the post-task resting state; 2) Both PCBFN and NCBFN followed an exponentially truncated power law degree distribution. This study may offer a framework to investigate the intrinsic organization of spontaneous brain activity.