Investigating the spectral features of the brain meso-scale structure at rest

Recent studies provide novel insights into the meso-scale organization of the brain, highlighting the co-occurrence of different structures: classic assortative (modular), disassortative and core-periphery. However, the spectral properties of the brain meso-scale remain mostly unexplored. To fill this knowledge gap, we investigated how the meso-scale structure is organized across the frequency domain. We analyzed the resting state activity of healthy participants with source-localized high-density electroencephalography signals. Then, we inferred the community structure using weighted stochastic block-modelling to capture the landscape of meso-scale structures across the frequency domain. We found that meso-scale modalities were mixed over the frequency spectrum, with a core-periphery structure predominance. Nevertheless, we also highlighted a selective increase of disassortativity in the delta and theta bands, and of assortativity in the low gamma band (30-50 Hz). We further described other features of the meso-scale organization by identifying those brain regions which, at the same time, i) exhibited the highest degree of assortativity, disassortativity and core-peripheriness (i.e. participation), ii) were consistently assigned to the same community, irrespective from the granularity imposed by WSBM (i.e. granularity-invariance). We defined those brain areas as Participation and Granularity Invariant. In conclusion, we observed that the brain spontaneous activity shows frequency-specific meso-scale organization which may support spatially distributed and local information processing.