Low frequency phase entrainment to behaviorally-relevant events suggests a functional role for phase-amplitude CFC, but CFC could not serve as an effective control mechanism if CFC strength were constant over time and across different tasks. The findings of Tort and colleagues [37] are illuminating as they show dynamic modulation of CFC strength in rodent hippocampus and striatum during a simple T-maze task. Interestingly, in addition to showing that CFC strength can quickly go from no coupling to strong phase-amplitude coupling and back within hundreds of milliseconds (Figure 3), this study also revealed different patterns of coupling and temporal modulation within different brain structures. In particular, the temporal modulation of phase-amplitude CFC in the hippocampus differed from that in the striatum, as did the high and low frequencies that were coupled. Furthermore, this study showed that CFC can span different areas, with hippocampal low frequency phase affecting high frequency amplitude in the striatum and vice versa. The distinct coupling frequencies observed in each area may provide a form of frequency domain modularity that allows simultaneous communication in independent channels.
