Default Mode Network, or DMN, refers to the neural network in the human brain in the resting state. When people turn to specific tasks, brain activity differs from the resting state, which is characterized by daydreaming, loose associations, and digressive thoughts. The specific brain activity pattern of the resting state was not discovered until 2001.
What is the default mode network?
The default mode network is a brain anatomical finding. Brain regions that are separated from each other are simultaneously activated in the resting state and show the activity patterns characteristic of DMN. The diagnostic technique used to visualize DMN is functional magnetic resonance imaging. Hemoglobin, the oxygen transport molecule in blood, emits different magnetic signals depending on the oxygen charge. Therefore, functional magnetic resonance imaging illustrates blood flow changes and metabolic processes in individual brain areas, leading to the discovery of the DMN. The idea that the brain never rests is an old one. Earlier, the electrical activity of the brain could be visualized by electroencephalography. However, the anatomical description of the DMN is a fairly recent research finding: Marcus E. Raichle and colleagues coined the term in a 2001 scientific publication. With the description of a normal resting state of the brain, the discovery of aberrant, possibly pathological states has also become possible. Current research examines the effects of drugs, neurological diseases, and certain behaviors, such as meditation, on the DMN.
Anatomy and structure
An important part of the DMN is the medial temporal lobe. Related to this is activity in the medial prefrontal cortex. Integration of the two distinct subsystems in the brain occurs via the posterior cingulate. The angular gyrus also plays a role. In addition to this frontal part of the DMN, there are other parts that perform specific functions at rest. Thus, there is an interconnected system of activities in the medialdorsal part of the brain. This includes the dorsal medial part of the prefrontal cortex, the temporoparietal junction area, and the lateral temporal cortex. The frontal temporal lobes are also part of this subsystem. Another activity system includes the hippocampus, parahippocampus, and retrosplenial cortex. The posterior parietal lobe also contributes to this subsystem. The activity patterns in the listed anatomical areas are integrated primarily via the frontal region. Anatomical evidence of the DMN is also successful in monkeys. Humans do not have a DMN until about 9 to 12 years of age.
Function and tasks
The DMN is active when the brain is not being used to complete specific tasks. When specific tasks begin, parts of the DMN are deactivated. A new pattern of activity, the Task Positive Network, or TPN, is created to complete the specific tasks. Thus, an important function of the DMN is to enable this transition between resting state and TPN in the first place. The brain areas needed for the completion of tasks are only freed up for these tasks via the deactivation of the DMN. In addition to this dynamic function for the orderly transitions between DMN and TPN, the DMN performs important tasks in the resting state. When people daydream and let their thoughts wander seemingly aimlessly, their identity is consolidated. On the one hand, they think about themselves and thus form an autobiographical memory; on the other hand, they also think about other people and thus strengthen their capacity for empathy. Finally, aimless thoughts also lead to a better understanding of the past and plans for the future. In yoga and meditation, there is even an intentional activation of the DMN. During sleep, the DMN is associated with the occurrence of dreams.
Diseases
Medications, drugs, and certain diseases alter the appearance of the DMN. In schizophrenia, there may be insufficient deactivation of the DMN during the transition to the working state (TPN) of the brain. Presumably, autistic patients have only a weakly developed DMN. An altered DMN activity pattern occurs in patients with Alzheimer’s disease. Many other diseases and pathologies manifest similarly to schizophrenia by incomplete deactivation of the DMN during the transition to the TPN.Although the subject is not well researched, there are data pointing in this direction, including for attention deficit/hyperactivity disorder (ADHD), depression, and post-traumatic stress disorder. Presumably, all illicit drugs and permitted medications affecting the state of consciousness and sleep have one influence or another on the DMN. Codeine, an opiate found in numerous, everyday medicines, for example, in some cough syrups, has been shown to influence DMN activity patterns. Presumably, the numerous psychotropic drugs, i.e., sleeping pills, tranquilizers, and antidepressants, also have negative effects on DMN and TPN. The hallucination-inducing drug psilocybin interferes with DMN deactivation during the transition to TPN. Perhaps drug and intoxication experiences in general also have their origin in a dysfunction of the DMN and TPN networks. So what do psychiatrically healthy people who are not taking drugs or medications do with the research findings on the DMN? The central message to all healthy people is that on the one hand there are times when thoughts are free in the literal sense, and on the other hand there are times when increased attention to complete a particular task requires shutting down overly associative thoughts. Modern work environments are designed to prevent employees from becoming distracted while completing certain tasks. Extra spaces are available to let the mind wander. Multitasking is for computers, but not for the human brain.
