In the last decades, systems neuroscience has made it clear that brain functioning requires the cooperation of several spatially separated brain regions to allow for integrative functions (e.g., vision, audition), as well as for higher order functions (e.g., understanding of actions), for a review see e.g., Rizzolatti et al. (2018). The reliable estimation of this cooperation, i.e., of functional connectivity between brain areas, is thus of primary importance to disclose the physiological and pathological organization of the human brain. To this end, several non-invasive imaging techniques and novel analysis methods have contributed to the examination of whole-brain functional connectivity patterns: functional Magnetic Resonance (fMRI) and functional Near Infrared Spectroscopy (fNIRS) have investigated the level of co-activation between brain regions as a proxy for functional communication (e.g., Smith et al., 2013; Wang et al., 2017), while electrophysiological techniques such as ElectroEncephaloGraphy (EEG) and MagnetoEncephaloGraphy (MEG), have characterized both the level of co-activation between brain regions and the coupling of their respective signals, i.e., the statistical relationship between time-series of neuronal signals. A recent review on the theory and algorithms of electrophysiological brain connectivity analysis can be found in He et al. (2019).
