FIGURE 4.

Simulation. Phase‐amplitude coupling (PAC) analysis with neural responses at subdural channel 36 (upper panel) and simulated triangular signals at the gazed frequency (lower panel). (a) Average broadband (4–250 Hz) signal when gazing a 14 Hz stimulus shows a non‐sinusoidal response with sharp transitions. (b) Phase‐amplitude coupling between the phase of the fundamental response (10–16 Hz) and the amplitude of the gamma component (55–125 Hz). Each circular plot shows the average amplitude of the high‐gamma response (indicated by the length of the bars) with respect to the phase of the fundamental component (indicated by the radial angle). Note that the five stimulation frequencies achieve their maximal gamma amplitudes at different phase angles. (c) Time between the minimal and maximal gamma amplitude is largely independent of the gazed frequency. (d) Example of the artificial sawtooth signal used in the simulation. Similar to the real data, the sawtooth signal has sharp transitions from ascending to descending amplitudes. (e) The spurious phase‐amplitude coupling exhibits maximal amplitude at equal phases for all five stimulation frequencies. (f) Time between the minimal and maximal gamma amplitude is strongly correlated with the stimulation frequency. Note that only one point is shown per stimulation frequency since identical results were obtained for each trial at that frequency