Prior to any physiological interpretations, PAC is comparable to EEG coherence in that both quantify the statistical relationship between brain signal components. Where EEG coherence is a measure of the consistency of phase differences between two signals oscillating at the same frequency (Srinivasan et al., 2007), PAC measures the relationship between the phase of a lower-frequency oscillation and the amplitude of a higher-frequency oscillation (Canolty & Knight, 2010). Statistical estimates of both PAC and coherence have minimum and maximum possible values with coherence ranging between the absence of synchrony to perfect synchronization, and PAC strength ranging from the absence of any modulatory relationship between the phase of one frequency to the amplitudes at a higher frequency (no coupling) to perfect coupling.
