Theta-gamma coupling.

Three gamma cycles are sequentially “embedded” in a theta cycle. (A), (B), and (C) depict the temporal activity pattern of three different neuronal assemblies oscillating in the gamma range. Each is phase-locked to the underlying theta rhythm with a different phase offset, as indicated by the dashed lines. This type of coupling is known as phase-amplitude coupling, because the amplitude modulation of each gamma pattern is locked to a particular phase of the theta pattern (S).