A recently developed measure of nonlinear functional connectivity called “lagged phase synchronization”, implemented in the eLORETA statistical package, is resistant to non-physiological artifacts, in particular low spatial resolution and volume conduction, that usually affect previously published connectivity indices (e.g., phase coherence, imaginary component of coherence, classic phase synchronization) [24], [41], [42]. This lagged connectivity measure is thought to be accurately corrected as it represents the connectivity between two signals after the artifactual instantaneous zero-lag contribution has been excluded. For instance, the connectivity patterns of the classic phase synchronization (which include the instantaneous artifact) are dominated by the locations of maximum activity, which are seen as common instantaneous sources, and therefore are not often related to true physiological connections [24]. Compared to the imaginary part of the coherence proposed by Nolte et al. [42] as a conservative index of connectivity, the lagged connectivity measure has the important property of being relatively robust to the strength of the instantaneous component, i.e. it can still detect physiological “non-zero” lagged connectivity even in the presence of large instantaneous artifacts, while the imaginary part of
