The default mode network (DMN) is a network of brain regions that are highly active when an individual is at rest and not engaged in any specific task. This network is involved in internal mental processes such as mind-wandering, daydreaming, and self-referential thoughts. The DMN is also thought to play a role in social cognition, empathy, and moral reasoning. Abnormal activity in the DMN has been linked to various psychiatric and neurological disorders, such as depression, schizophrenia, and Alzheimer's disease. Research on the DMN has provided valuable insights into the functioning of the brain and how it relates to our everyday thoughts and behaviors.