The default mode network (DMN) is a set of brain regions — medial prefrontal cortex, posterior cingulate cortex/precuneus, lateral temporal cortex, and hippocampal formation — that show increased activity during rest and internally directed thought (mind-wandering, autobiographical memory, imagining the future, considering others' perspectives) and decreased activity during externally demanding tasks. Discovered by Marcus Raichle and colleagues through PET studies showing consistent "deactivation" during cognitive tasks, the DMN has become one of the most studied brain networks.
Functions
The DMN supports a range of internally directed cognitive processes: autobiographical memory retrieval, episodic future thinking, mentalizing (reasoning about others' mental states), self-referential processing, and spontaneous thought (mind-wandering). The coherence of DMN activity may provide a neural substrate for the continuous stream of consciousness and the maintenance of a narrative self-concept.
Altered DMN function has been observed in numerous clinical conditions. In Alzheimer's disease, DMN regions are among the first affected by amyloid deposition. In depression, excessive DMN activity and impaired deactivation during tasks correlate with rumination. In schizophrenia, altered DMN-task network interactions may contribute to psychotic symptoms. In autism, reduced DMN connectivity correlates with social cognitive difficulties. These clinical associations highlight the DMN's importance for normal cognitive and social functioning.