Fig. 3

Schematic overview of two cases in which oscillatory activity of a higher-frequency oscillation may be related to the phase of a lower-frequency oscillation. Dark and light boxes separate consecutive cycles of the lower-frequency oscillation. The lower-frequency oscillation of fluctuating amplitude (top) shows phase-amplitude coupling with a higher-frequency oscillation of fluctuating amplitude (middle). In this example, amplitudes of the higher-frequency oscillation are maximal during the up-phase of the lower-frequency oscillation. A higher-frequency oscillation of stable amplitude (bottom), shows phase-phase coupling with the low-frequency oscillation. Here, peaks of the higher-frequency oscillation always coincide with the same phase values of the lower-frequency oscillations. Reproduced from [79]