The relationship of low-frequency phase to high-frequency amplitude has gained greater theoretical importance given recent findings that low-frequency brain rhythms are often entrained by external sensory and motor events as well as internal cognitive processes associated with decision making, motivation, and memory [23]. That is, low-frequency phase entrainment combined with phase-amplitude CFC provides a plausible mechanism to coordinate fast, spike-based computation and communication with slower external and internal state events guiding perception, cognition, and action. To clarify this connection, this review examines the different varieties of CFC, current empirical evidence of phase-amplitude CFC and methods to assess it, the relation of high frequency power to local cortical activity, the dynamic entrainment of low-frequency phase, the transient and task-relevant modulation of CFC strength, and the role of CFC in learning and memory.
