It has been suggested that the disturbed synchrony in neural oscillations may reflect dysfunction within RSNs in subjects with MDD [45]. Most studies of neural synchrony in MDD, however, have examined brain function within a single region over a relatively short distance. Few studies have examined synchronous oscillations from sites spanning greater distances, across brain regions, to provide information regarding the neurophysiology of larger scale networks [37], [43], [46]–[47]. qEEG coherence is a measure that is well suited to examine synchrony across brain regions. While a peak in qEEG power indicates oscillatory synchrony at a single point, coherence is a well-established indicator of connectivity between two points, or “nodes,” that have a fixed oscillatory phase relationship. Coherence therefore represents the coupling of activity between two nodes that are functionally linked, but not time-locked to a specific event [48]–[50]. Coherence values range between 0 (no shared activity between nodes) and 1 (completely synchronous). This measure thus is well-adapted for assessing functional connectivity in RSNs: it has been successfully used to examine spatial integration both at short- and long-distances in the brain
