(a) Synthetic data of different CFD made following [29]. The θ signal was generated by concatenating sinusoidal segments of mean amplitude 10 and different periods drawn from a Gaussian of mean 125ms. The γ signal is an 80Hz sinuisoidal coupled to the trough of θ. Then, θ and γ are added together to create 3 timeseries with different theta-gamma relationship: in the blue line γ is lagged 10ms behind θ, in the green timeseries γ is not lagged whereas for the red line θ laggs behind γ by 10 ms. (b) Top: Cross Frequency Coupling of the timeseries in (a). Notice that independently of the time difference between theta and gamma all timeseries have identical CFC peaking at (8Hz,80Hz). (c) Bottom: Cross Frequency Directionality of the lines in (a). CFD is able to detect the time delay between the γ amplitude and θ phase. (tiff)
