Default Mode Network

What is the default mode brain network?

The default mode network (DMN) is the “internal mind.”

When you’re idly daydreaming or thinking about a new idea, the DMN is hard at work.

Though the default mode network is active during rest and sleep,1 it is most active when the mind engages in internal thought or contemplation. When you remember an event from your childhood, imagine a future vacation, or contemplate a family member’s thoughts or feelings, your internal mind drives these perceptions.

When the brain is in a resting state2 and isn’t actively engaged in focused, goal-oriented tasks, “default” or subconscious brain activity increases for internal thought processing,3 which likely evolved from evolutionary self-preservation.

Since we are nearly always thinking to ourselves or subconsciously processing the world around ourselves, the DMN is considered the most active and consistent4 of the seven main brain networks.

Sensorimotor

The role of the DMN

 

Due to its frequent activity, DMN plays an integral role in coordinating with other networks for passive sensory processing.2 These connections often include:

    • Visual processing in conjunction with the visual system when the mind subconsciously appreciates aesthetic beauty,5 like when observing impressive artwork or architecture.
    • Semantic processing6 with the language subnetwork when encoding or translating meaning into spoken or written words.
    • Processing or evaluating personal emotions or the emotions of others, with the limbic system.3

Relationship with the central executive network (CEN)

 

The default mode network was discovered in 2001 as part of a study3 to define a baseline state in the human brain. The study indicated that areas of the brain remain uniformly active in an awake but resting state,3 and there is a decrease in this activity when other brain areas become active for goal-related tasks or the response to external stimuli.1

Through this study, neurologists determined that the brain’s activity switches between the DMN’s internal state and an external processing state in the central executive network (CEN). Together, these two networks are considered the brain’s dominant control networks.

Most importantly, the control networks occur in counterbalance to one another. As soon as the CEN switches into high gear for active and external task processing, the DMN is deactivated.7 The salience network is responsible for the imperceptible switches back and forth — from introspective thinking to external active tasks and back to internal thought.

Imagine a classroom with a student staring longingly out the window at a playground. The default mode network is highly active as the student daydreams. But as soon as the teacher calls the student’s name, the salience network switches from internal thought to the CEN’s external processing. The student’s attention then refocuses on actively finishing an assignment.

The relationship between the DMN and CEN is a critical balance, and the two networks should not be active at the same time. Increased activity in one or both networks has been implicated in multiple mental health disorders.

Disturbance in the DMN

 

Abnormal function in the default mode network is often associated with neuropsychiatric disorders.8 If the network becomes overactive, it can lead to intensified, self-referential thought as a symptom of schizophrenia or negative and disruptive thoughts associated with depression and post-traumatic stress disorder (PTSD).

Altered functional or structural organization of the DMN9 has also been implicated in autism spectrum disorder (ASD).10 Individuals with autism are often characterized by difficulty processing the emotions and feelings of others, in relationship to one’s self. Underlying DMN dysfunction may contribute to an individual’s difficulty processing social situations and information.

It has also been posited that higher functional connectivity between the DMN and other brain networks11 may be an underlying symptom of attention-deficit/hyperactivity disorder (ADHD). This abnormal connectivity may be linked to mind wandering and wavering attention.11 With regard to neurological disease, the earliest stages of Alzheimer’s disease often exhibit degradation of the posterior cingulate cortex.2 This key node in the default mode network is responsible for memory formation and retrieval,2 making it a common target of the disease.12 In some cases, individuals even experience disruption in the DMN prior to showing signs of Alzheimer’s disease.10 With the DMN being a relatively recent discovery for neuroscience, modern research is still uncovering its full implication on mental illness and physical disorders. Fortunately, there is a wide range of possibilities for new treatments and therapies.

 

Where is the default mode network?

 

The default mode network is structurally and functionally connected for internal processes, such as introspective thoughts and imagination.7

DMN_AXI AXIAL VIEW
DMN_SAG SAGITTAL VIEW
DMN_COR CORONAL VIEW

Asymmetry

The DMN also contains a second asymmetry in the connectome. Functional areas 8Av in the frontal lobe and PGs in the parietal lobe are present only in the left hemisphere of the DMN. In the right hemisphere, these areas form functional constituents of the central executive network.

Other structures in the network include the precuneus, the lateral temporal cortex, and the hippocampal formation.13

8Av_a
PGs_a

Left to right: Areas 8Av and PGs, only present in the left hemisphere of the DMN.

Future Impact

 

As our internal mind, areas of the brain associated with the DMN likely have unique functions when they are active in a subconscious state.3 The PCC and the adjacent precuneus are thought to be tonically active regions3 that continually gain information about the external world, without conscious thought processing, but there is still much to explore about this network as the brain’s baseline state.

With the DMN’s prominence as a more recent discovery, as neuroscience continues to explore the subtle intricacies of the human brain, the DMN will offer a unique lens through which to view our own subconscious.

For the larger role the DMN plays in cognition, it will also be exciting to uncover how the DMN coordinates with other brain networks for internal thought processing. Other areas heavily interconnected with the limbic system3 are implicated in processing sensory information, both about the body and externally. With further research, there is potential to identify DMN-targeted therapies that will target the functional connectivity thought to cause mental health disorders and degenerative diseases.

It is our hope that analyzing the “internal mind” will aid in our journey to understand the relationship between our conscious and subconscious minds, as well as the nearly-imperceptible triggers that make up our human perceptions.

Uncover more cutting-edge discoveries about the key brain networks that function alongside the default mode network.

 

Reference list

 

  1. Tryon WW. Core Network Principles: The Explanatory Nucleus. In: Tryon WW, ed. Cognitive Neuroscience and Psychotherapy. Cambridge, Mass: Academic Press; 2014:125-222. doi.org/10.1016/B978-0-12-420071-5.00003-X
  2. Greicius MD, Krasnow B, Reiss AL, Menon V. Functional connectivity in the resting brain: a network analysis of the default mode hypothesis. Proc Natl Acad Sci U S A. 2003;100(1):253-258. doi:10.1073/pnas.0135058100
  3. Raichle ME, MacLeod AM, Snyder AZ, Powers WJ, Gusnard DA, Shulman GL. A default mode of brain function. Proc Natl Acad Sci U S A. 2001;98(2):676-682. doi.org/10.1073/pnas.98.2.676
  4. Lee MH, Hacker CD, Snyder AZ. Clustering of resting state networks. PLoS One. 2012. doi.org/10.1371/journal.pone.0040370
  5. Vessel EA. Isik AI, Belfi AM, Stahl JL, Starr G. The default-mode network represents aesthetic appeal that generalizes across visual domains. Proc Natl Acad Sci U S A. 2019;116(38):19155-19164. doi.org/10.1073/pnas.1902650116
  6. Wirth M, Jann K, Dierks T, Federspiel A, Wiest R, Horn H. Semantic memory involvement in the default mode network: a functional neuroimaging study using independent component analysis. Neuroimage. 2011;54(4):3057-3066. doi:10.1016/j.neuroimage.2010.10.039
  7. Ekhtiari H, Nasseri P, Yavari F, Mokri A, Monterosso J. Neuroscience of drug craving for addiction medicine: From circuits to therapies. In: Ekhtiari H, Paulus M, eds. Progress in Brain Research. Amsterdam, Netherlands: Elsevier. 2016;223:115-141. doi.org/10.1016/bs.pbr.2015.10.002
  8. Whitfield-Gabrieli S, Ford JM. Default Mode Network Activity and Connectivity in Psychopathology. Annu Rev Clin Psychol. 2012;8(1):49-76. doi.org/10.1146/annurev-clinpsy-032511-143049
  9. Padmanabhan A, Lynch CJ, Schaer M, Menon V. The default mode network in autism. Biol Psychiatry Cogn Neurosci Neuroimaging. 2017;2(6):476-486. doi:10.1016/j.bpsc.2017.04.004
  10. Buckner RL, Andrews-Hanna JR, Schacter DL. The brain's default network: anatomy, function, and relevance to disease. Ann N Y Acad Sci. 2008;1124:1-38. doi.org/10.1196/annals.1440.011
  11. Kucyi A, Hove MJ, Biederman J, Van Dijk KR, Valera EM. Disrupted functional connectivity of cerebellar default network areas in attention-deficit/hyperactivity disorder. Hum Brain Mapp. 2015;36(9):3373-3386. doi.org/10.1002/hbm.22850
  12. Chiong W, Wilson SM, D’Esposito M, et al. The salience network causally influences default mode network activity during moral reasoning. Brain. 2013;136(6):1929–1941. doi.org/10.1093/brain/awt066
  13. Know your brain: default mode network. Neuroscientifically Challenged website. https://www.neuroscientificallychallenged.com/blog/know-your-brain-default-mode-network. Published June 16, 2015. Accessed November 10, 2020