Brain oscillations of different frequencies can coexist and influence each other. A cross-frequency interaction occurs when a feature from one oscillation (i.e., instantaneous amplitude, phase, or frequency) depends on a feature from another oscillation at a distinct frequency. These phenomena have been collectively called cross-frequency coupling (CFC). There are multiple types of CFC, such as phase-amplitude coupling, amplitude-amplitude coupling, and n:m phase-locking. Several metrics have been devised to quantify CFC.
