Default mode network (DMN)

The default mode network (DMN) is a set of anatomically connected cortical and subcortical regions — including the medial prefrontal cortex, posterior cingulate cortex, precuneus and angular gyri — that are co-activated at rest and deactivate during externally directed tasks, a pattern first described systematically by Raichle and colleagues in 2001. The DMN supports self-referential thought, episodic memory retrieval, mental simulation and social cognition. In normal aging, DMN connectivity and task-related deactivation weaken, correlating with poorer episodic memory and reduced cognitive flexibility. In Alzheimer's disease, the DMN shows disproportionate amyloid-β deposition and atrophy in its core hubs, consistent with its high baseline metabolic activity and tight coupling to the interstitial fluid dynamics that clear Aβ during sleep.