Phase-amplitude CFC has been observed in the rodent hippocampus [34–39], rodent basal ganglia [37], and macaque neocortex [5]. In humans, phase-amplitude CFC has been observed across multiple cortical and subcortical sites under a variety of experimental conditions [40–55] and using a variety of different measures (see Box 1). For example, Figure 1A is a phase-locked time-frequency plot showing that high frequency amplitude is modulated by low frequency (theta, 4–8 Hz) phase. Figure 1B shows that across a wide range of phase and amplitude frequency pairs, theta/high-gamma phase-amplitude CFC is strongest. This example of theta/high gamma phase-amplitude coupling in human neocortex is consistent with the theta/gamma coupling observed in rodent hippocampus, and may have similar cellular and network origins.
