The Default Mode Network and Its Implications

Dr. Adel Rasheed,
MBBS

‘Stimulus-independent thought’ or ‘mind wandering’ appears to be the brain’s default mode of operation” -Killingsworth and Gilbert, 2010

You are sitting in a lecture hall, confined to a chair of questionable reliability, kept from speaking, and asked to focus on a rather monotonous lecture. During this kind of “attention-demanding’ activity, the mind tends to wander into internal thought, “What will I be doing tonight?” “That person was rude to me yesterday.” “Why did she leave me?” and so on. You find yourself ‘zoning out’ into a world of self-reflection, mental time travel, mental reasoning, and theory of mind (our ability to imagine the world from someone else’s perspective) before returning to the task at hand.

 Today, there is a rapidly growing body of evidence attributing such mind wandering to one part of a newly recognized, specific, anatomically defined brain system that is preferentially active when individuals are not focused on the external world, called the Default Mode Network (DMN). Simply put, when left undisturbed, this is the network people engage in by default. Its roles and functions are still being defined through ongoing research. However, the DMN has great intrinsic value because of its association with what it means to create a sense of self.
  Basic Areas Part of DMN:

DMN regions include but are not limited to the posteromedial cortex (PMC), the medial prefrontal cortex (MPFC), the angular gyrus (AG), the middle temporal cortex (MTC), the middle frontal gyrus (MFG), and the inferior frontal gyrus (IFG). The DMN is a recent concept, and because of this, there is not a complete consensus on which brain regions should be included in a definition of it.

Its discovery was an unexpected consequence of brain-imaging technologies used in research in which various novel, attention-demanding, and non-self-referential tasks were compared with brain imaging done in between those tasks during which participants were not doing much of anything. In 2001, Marcus Raichle observed that several areas in the brain exhibited heightened activity when the subjects were doing nothing mentally. The findings were published in a paper titled “A Default Mode of Brain Function,” which unbeknown to him would catch on and be referred to as the default mode network. The initial publication has over 13,600 citations today. Treading with caution about the risk of oversimplifications and premature conclusions, the exploration of the implications of the DMN is one of endless fascination.

Mind wandering and unhappiness: Killingsworth

“The ability to think about what is not happening is a cognitive achievement that comes at an emotional cost.”

In a 2010 paper published in Science assessing the effect of mind-wandering, a behavior attributed to the Default Mode network, researchers asked over 13,000 participants through their phones at random moments during their waking hours, presenting them with the following questions:

How are you feeling right now?
What are you doing right now?
and a mind-wandering question (“Are you thinking about something other than what you’re currently doing?”)

Here is what they found:

• First, people’s minds wandered frequently, regardless of what they were doing. Mind wandering occurred in 46.9% of the samples. i.e., nearly half the time, people were thinking about something other than the task they were in the middle of.
•  People were less happy when their minds were wandering than when they were not.
• What people were thinking was a better predictor of their happiness than what they were doing.
  
  

Although this study reveals a close connection between mind-wandering and unhappiness, the exact nature of this relationship is up for debate. For example, mind-wandering has been shown to aid in creativity, learning from past mistakes, playtesting future plans, and building our narrative identities. DMN activity appears to be altered by meditation.

Psychedelics and the DMN

The topic of psychedelics and their potential therapeutic uses is gaining traction in pop science culture today. Described by journalist Michael Pollan in the New York Times bestseller 2018 book, “How to Change Your Mind…,”’ and its remake as a Netflix docuseries by the same name, it chronicles the history of psychedelics and the involvement of the DMN in various aspects of their effects. A separate meta-analysis concluded “associations between a psychedelic’s ability to reduce the functional connectivity within the DMN (and increase its connectivity to other networks), altered states of consciousness, and therapeutic outcomes.”

The DMN is becoming increasingly relevant in the pathophysiology of many mental illnesses such as depression, Alzheimer’s, autism, schizophrenia, and many more.

Dr. Adel Rasheed,
MBBS

Sources:

•  Self-projection and the brain, Buckner and Carol 2007
• A default mode of Brain Function, Raichle et al 2001
• Annual review of Neuroscience, Raichle 2015
• A wandering Mind is an Unhappy mind, Killingsworth and Gilbert 2010
• Distinct electrophysiological signatures of task-unrelated and dynamic thoughts (Julia W. Y. Kam Zachary C. Irving Caitlin Mills,and Robert T. Knight PNAS January 18, 2021)
• Meditation experience is associated with differences in default mode network activity and connectivity Judson A. Brewera,1, Patrick D. Worhunskya, Jeremy R. Gray, Yi-Yuan Tang, Jochen Weberd, and Hedy Kobera).
• Neural Correlates of the psychedelic state as determined by fMRI studies with psilocybin, Carhart-Harris 2012 PNAS.
• Default Mode Network Modulation by Psychedelics: A Systematic Review. James J Gattuso, et al. International Journal of Neuropsychopharmacology, Volume 26, Issue 3, March 2023, Pages 155–188,
• The default mode network and self-referential processes in depression Yvette I. Shelinea et al.
• Molecular, Structural, and Functional Characterization of Alzheimer’s Disease: Evidence for a Relationship between Default Activity, Amyloid, and Memory, buckner et al 2005.