What is it that hold us in the grip of unpleasant, stressful mental states? Why do we do this to ourselves? One answer may lie in the nature of the brain itself.

While observing patients’ brains during MRI and PET scans, researchers from various laboratories were surprised by a shared observation. Although patients and research subjects were told to “rest” and not given anything to do, they engaged in free-ranging mind-wandering during which certain parts of their brains were surprisingly active. These parts represented a network of interconnected structures.

Identified as the Default Network or the Default Mode Network, this network of brain structures has been associated with self-referential thinking as opposed to thinking about externally-focused tasks. Think of replaying a time you felt criticized by someone compared to thinking about your grocery list.

The default network is not without its benefits. It allows for creativity, introspection, and problem solving. But impaired DN functioning is considered a transdiagnostic risk factor for maladaptive stress reactivity and mental disorders because when the DN is overly active and in control, there could be problems. In healthy individuals who are stressed, the DN can be suppressed so the person can focus on the threats and take effective action. But when the DN is not adequately suppressed, the self-referential and internal focus is maintained through rumination.