qEEG coherence is a measure of the consistency of the phase relationship between two signals and uses surface EEG to make inferences about underlying brain functional connectivity [49]. Coherence was calculated between pairs of nodes, and represents a normalized measure of the functional coupling between the signals at the nodes at any given frequency [60]–[62]. Coherence was calculated as a function of the power spectral outputs for the signals from the separate nodes for each frequency λ:or the square of the cross-spectrum of the two signals x and y divided by the product of the spectra of the individual channels, at the frequency λ. This procedure yields a real number between 0 (no coherence) and 1 (maximal coherence). Coherence values from individual bins within a frequency band were averaged to obtain the coherence value for that band.
