Fig. 5.
Principles underlying 3 phase-amplitude cross-frequency coupling (CFC) measures. A: the heights ratio measure can be straightforwardly defined in a phase-amplitude plot, as indicated. B: the power spectral density (PSD) of the instantaneous amplitude envelope can be used to assess phase-amplitude coupling. In this example, a theta–LG coupling measure can be defined by integrating the power values over the theta band. C: a phase-amplitude coupling measure can be defined as the length of the mean vector (arrow) of a time series defined in the complex plane by AfAei∗ϕfp (black dots connected with line). Notice the existence of asymmetry around zero in this example, which characterizes the existence of phase-amplitude coupling in this analysis.