The studies presented above have all focused on the maintenance phase of the WM. Kaplan et al. (2014) focused on the retrieval phase of spatial memory. The phase coupling was assessed by calculating PLV between a seed voxel in the medial Pre-frontal Cortex (mPFC) and all the other voxels in the brain. Significant increase (compared to baseline) in theta coupling was found between right anterior medial temporal lobe (aMTL) and the seed voxel and this theta coupling was argued to play a role in mnemonic functions. The phase coupling was also analyzed with PLI and this analysis confirmed that the increase in theta coupling was not an artifact of volume conduction. The PLI analysis also showed increased theta coupling between the seed and nearby anterior cingulate cortex. However, the authors acknowledged that the phase coupling between so nearby regions should be interpreted with caution (Kaplan et al., 2014). The evidence indicates that phase coupling within different frequency bands plays a role in WM processes. Siebenhühner et al. (2016) expanded the perspective by showing that during the maintenance period of DMS
