An important limiting factor in some EEG-FC studies is that the majority of connectivity measures are based on scalp sensors, which may cause spurious connectivity patterns due to the vulnerability of EEG signal to volume conduction phenomena (Nolte et al., 2004). To address this issue, a number of electrical source imaging methods have been proposed as a valid alternative to channel-related FC (Thatcher et al., 2007; Schoffelen and Gross, 2009; Sakkalis, 2011). In this context, an index of physiological “lagged connectivity” between pairs of brain sources capable of minimizing non-cerebral artifacts and that is not affected by active reference electrodes was recently proposed (Pascual-Marqui et al., 2011). This method has been successfully applied to investigate EEG Source Functional Connectivity (EEG-SFC) between cortical regions in health (Stein et al., 2013) and disease (Canuet et al., 2011, 2012; Clemens et al., 2011; Pagani et al., 2012; Olbrich et al., 2014).
