To determine the directionality of the long-range connections in source space, we computed PSI 90, an estimate of the direction of information flow between two signals. PSI was computed between voxels that showed a significant difference in PLV between memory and control blocks. For each considered voxel pair, the PLV was calculated at each frequency bin within the frequency band of interest for both blocks, separately. Then, the PSI was computed for each block, stimulation condition, and age group across all frequency bins within this frequency band as described by Nolte et al. (2008) 90. A positive PSI indicates that the seed region acts as a sender, and negative values provide evidence for the seed region acting as a receiver.
