To determine whether low-frequency phase was driving high-frequency amplitude during memory maintenance or vice versa, we calculated the cross-frequency PSI 88. To avoid edge artifacts, we used relatively long segments of 2500 ms (500 to 3000 ms post-target onset), which included at least 5 cycles of the slowest rhythm (6.5 Hz), consistent with previous reports 88. We considered frequencies between 6.5 and 10.5 Hz (0.5-Hz increments) after applying a Hanning window and extracting the complex Fourier coefficients. Significant values above zero indicate that low-frequency components are driving high-frequency activity, while negative values indicate the opposite direction of influence, and values nearest zero suggest no directional coupling.
