Cross-frequency coupling reflects a relation between brain oscillations. Here the phase of slow frequency oscillation in the alpha range (~10Hz) modulates broadband power activity in gamma frequency (~60Hz).
The image presents time-frequency representation of gamma power time-locked to the troughs of alpha rhythm. It shows that bursts of high activity are inhibited by the phase of slow oscillation. Alpha phase in each cycle inhibits gamma activity and firing rate providing a mechanism of pulsed, phase-dependent neural inhibition.
The cross-frequency coupling has been observed across many brain regions such as hippocampus, prefrontal cortex, primary visual, auditory and somatosensory cortices and across several species. Theoretical work suggests it is important for various aspects of cognition like memory or attention.
The causal relation between involved frequencies is to be discovered. It is currently unknown if the phase of alpha drives the increase of power or whether the increase of power triggers preferred phase of slow frequency oscillation.