Linking neuronal avalanches with oscillatory and broadband 1/f activities in the resting human brain

Objective: Brain oscillations, broadband 1/f activity and neuronal avalanches (NA) are valuable conceptualizations extensively used to interpret brain data, yet, these perspectives have mainly progressed in parallel with no current consensus on a rationale linking them. This study aims to reconcile these viewpoints using source-reconstructed MEG data obtained in healthy humans during eyes-closed resting state. Methods: We analyzed NA in source-reconstructed MEG data from 47 subjects. For this, we introduced custom measures and a comprehensive array of features characterizing the statistical, spatiotemporal and spectral properties of NA. By using the complex baseband representation of signals we provide an analytical description of the mechanisms underlying the emergence of NA from the Fourier spectral constituents of the brain activity. Results: The observed NA disclose a significant spectral signature in the alpha band, suggesting that the large-scale spreading of alpha bursts occurs mainly via brain avalanches. Besides, the NA detected in our MEG dataset can be segregated based on their spectral signature in two main groups having different propagation patterns, where cluster 2 avalanches is mainly related to the spread of narrowband alpha bursts across the brain network, whereas cluster 1 avalanches correspond to more spatially localized fluctuations promoted by the broadband 1/f activity. We also provide an analytical framework for the evidence showing that a) spectral group delay consistency in specific narrow frequency bands, b) transient cross-regional coherent oscillations and c) broadband 1/f activity, are all key ingredients for the emergence of realistic avalanches. Significance: The proposed analytical arguments, supported by extensive model and experimental evidence, show how NA emerge from narrowband oscillations and broadband arrhythmic activity co-existing in the human brain. Our results suggest that large-scale spreading of specific narrowband oscillations takes place in a transient manner mainly via NA, which may play a functional role as a long-range interaction mechanism in the resting human brain. ### Competing Interest Statement The authors have declared no competing interest.