More recently, our group introduced a novel phase coherence metric, namely the Multivariate Phase Slope Index, to investigate the directionality of functional coupling in MEG and EEG data (Basti et al., 2018). This novel metric has been used to investigate the directionality of functional coupling in the alpha frequency band between the visual network and the whole brain in resting state MEG data from a large cohort of healthy subjects from the Human Connectome Project (Larson-Prior et al., 2013). With this approach, we observed sets of regions belonging to various RSNs which either lead or follow the primary visual cortex (Basti et al., 2018) as shown in Figure 7. For example, we observed coupling between the primary visual cortex (V1) and the Dorsal Attention Network. Parietal areas of the latter lead V1, in line with the notion of a feedback mechanism, while no clear evidence of follower or leader relationship was observed between V1 and the frontal regions in the DAN, suggesting that coupling of V1 to frontal DAN areas observed in Marzetti et al. (2013) can possibly exhibit both feed-forward and feedback characteristics which might lead to the absence of a clear directionality observed in Basti et al. (2018).
