In this review we will focus on MEG, i.e., the measurement of the magnetic field generated by neural currents. Indeed, MEG has gained an increasing importance in systems neuroscience as testified by the impact of MEG related publications (Baillet, 2017). Magnetoencephalography, being able to track neuronal activity without the filtering effect of the neuro-vascular coupling (Singh, 2012) can provide direct information about neuronal activity and functional connectivity. In the last decade, MEG functional connectivity has contributed to reinforce the concept of Resting State Networks (RSNs) as defined by fMRI (Deco and Corbetta, 2011) by assessing the correlation between the Blood-Oxygen-Level-Dependent (BOLD) time-series of two brain regions. In MEG, initially Amplitude Envelope Correlation (AEC) has been used to assess the level of co-activation between MEG signals of different brain regions. Specifically, MEG AEC has been calculated as the correlation of the slow temporal fluctuations (envelope) of the orthogonalized MEG signals (for a review see O'Neill et al., 2015). Moreover, MEG is able to track neuronal activity at its characteristic time scale, i.e., milliseconds, and it is thus ideally suited to assess
