Fig. 2: Change in phase-amplitude coupling (PAC) across task states.

a The time-frequency representation of PAC showing that the phase of alpha (9 Hz) modulates the amplitude of gamma (31–90 Hz). This average PAC was obtained from the Oz electrode, and it appears to be modulated by cognitive load. b Average PAC curves calculated from Oz electrode based on the phase of low-frequency oscillation at different frequencies (4–20 Hz, with a step of 1 Hz) and the amplitude of gamma (31–90 Hz). A relatively consistent maximum strength of PAC was shown at the phase of 9 Hz oscillation. c The amplitude of gamma as a function of the phase of the 9 Hz oscillation represented in a polar coordinate system. This is a visualization of the result in (B) at 9 Hz. d The average modulation index of the PAC calculated based on the phase of different frequencies (1–20 Hz, with a step of 0.1 Hz). The amplitude for calculating PAC was always based on the gamma band (31–90 Hz). e, f The distributions of the average modulation index obtained using the phase of 9 Hz oscillation and the amplitude of gamma (31–90 Hz) from each electrode in each task state. It shows that the average modulation index was the strongest in the occipital area. Note: a.u. refers to arbitrary unit.