The main DMN regions, posterior cingulate, ventral parietal cortex, and mPFC, showed opposite levels of activity for successful Ext-Enc and successful Ext-Ret, i.e. the encoding/retrieval flip pattern. The finding that these regions show less activity during successful encoding, but increased activity during successful retrieval, confirms our previous findings [21], [25]. Based on the finding that the DMN regions tend to show deactivation during efficient cognitive performance [3], we have proposed that this pattern represents an efficient memory mechanism by which normal default mode processes, such as spontaneous thought [36], are suppressed to allow successful encoding [21], [25]. At the same time, the finding that these regions show more activity during successful retrieval is in line with the view that episodic retrieval constitutes a prominent part of the default mode [6], [26]. The present study provides strong support for this view by showing functional overlap between task-based retrieval success regions and the DMN as defined by a resting-state coherence analysis. Together with the encoding results, our findings support the idea that episodic retrieval is part of the default mode of the brain, whereas episodic encoding is not, and actually benefits from suppression of DMN activity.
