Hierarchical organization of the functional brain identified using floating aggregation of functional signals

A novel method is proposed to parcellate the cerebral cortex into functionally homogenous regions at multiple scales with a hierarchical organization based on resting-state fMRI data. The cortical vertices are clustered according to inter-vertex functional similarity measures progressively at multiple spatial scales from fine to coarse by a procedure referred to as floating aggregation. The floating aggregation takes into consideration both the inter-regional functional similarity and the consistency of intra-regional functional homogeneity measures at every level of the resulting parcellation hierarchy. This aggregation procedure does not require to specify the number of regions for the parcellation, and could help identify proper spatial scales for the brain parcellation based on the overall region homogeneity changes across levels of the hierarchy. The experimental results on a resting-state fMRI dataset have demonstrated that the proposed method could not only obtain brain parcellation results with better functional homogeneity measures than state-of-the-art techniques, but also identify a hierarchical functional organization of the brain at multiple spatial scales.