EEG/MEG holds the promise to reveal dynamic connectivity since it is sensitive to transient neural activities occurring on the order of milliseconds [202–204]. A variety of techniques have been used, most of which have amounted to evaluating the cross-correlation or phase synchronization of signals between pairs of scalp electrodes or sensors [205]. Graph-theory-based tools from the study of complex network have also been developed to describe the connectivity of large-scale networks [206]. However, the relationship between the observed connectivity pattern in the sensor space and that in the source space is complicated by the dispersion of electromagnetic signals from the cortex to the sensors.
