The posterior cingulate cortex (PCC), a core region of the default mode network (DMN), shows distinct roles in attention depending on its dorsal and ventral parts. Using fMRI during a working-memory task, standard subtraction analysis showed overall deactivation with increasing difficulty. However, dual-regression functional connectivity revealed a dissociation: the ventral PCC reduced integration with the DMN and anticorrelation with the cognitive control network (CCN) as task demands rose, while the dorsal PCC increased DMN integration and anticorrelation with the CCN. At rest, the dorsal PCC connected with both DMN and attentional networks. These results indicate the PCC supports internally directed thought at low demands and that the dorsal PCC modulates dynamic interactions between networks for attention allocation.
During an attentionally demanding task, brain activity becomes more synchronized and less variable over time compared to rest. This shift is linked to increased activity in the frontoparietal control/dorsal attention network and decreased activity in the default mode network. A computational model confirmed that activating the frontoparietal network increases synchrony and reduces variability, while activating the default mode network does the opposite. The balance between these networks may control how the brain shifts between an unfocused, exploratory state with high variability and a focused, constrained state with low variability.