It is critical to distinguish between two different ways of thinking about CFC: 1) as an observed statistical dependence between filtered signals derived from electrical brain activity, and 2) as a transient but mechanistic coupling (mediated by spikes and synaptic activity) between the functionally distinct neuronal subpopulations that give rise to recorded electrical activity. CFC can have a functional role under option 2, but not under option 1. Therefore, saying that theta/gamma phase-amplitude CFC has a functional role is equivalent to saying that dynamic interactions between the pyramidal-interneuron cell sub-networks that give rise to theta and gamma frequency activity has a functional role. So first, how are these different brain rhythms generated, and second, what is the mechanism of their interaction?
