Lagged phase synchronization, a measure that quantifies the non-linear relationship between two regions after removal of the instantaneous contribution, was then computed across DMN and FPN ROIs. Instantaneous measures of EEG-based connectivity are known to be susceptible to the effects of volume conduction, which can lead to the detection of spurious functional coupling among separate regions. However, lagged connectivity corrects for this as it represents the connectivity between two regions after this zero-lag contribution has been excluded. In this respect, lagged connectivity is considered to represent a true measure of physiological connectivity. Lagged phase synchronization between ROIs was computed for each artifact-free EEG segment in the frequency domain using normalized Fourier transforms. Based on prior factor analyses of distinct frequency bands [45], the frequency ranges were: delta (1.5–6 Hz), theta (6.5–8 Hz), alpha-1 (8.5–10 Hz), alpha-2 (10.5–12 Hz), beta-1 (12.5–18 Hz), beta-2 (18.5–21 Hz) and beta-3 (21.5–30 Hz). For additional details see Supplement.
