What is the Default Mode Network?

The term default mode network (DMN) was coined by Marcus Raichel. In a seminal paper, he noticed that the resting state of brain utilizes just as much energy as active tasking brain. The DMN is primarily focused on the medial prefrontal cortex, posterior cingulate cortex (PCC) and angular gyrus. The DMN is best known for being active when a person is not focused on the outside world, and the brain is at rest, such as during mind-wandering and daydreaming.

The default mode network (DMN) is primarily responsible for:

•Autobiographical information: Memories of collection of events and facts about one's self.

•Self-reference: Referring to traits and descriptions of one's self.

•Emotion of one's self: Reflecting about one's own emotional state.

•Projection: Remembering the past and projecting into the future.

•Time: Episodic memory

Mental Chatter & Electric Shock: An inability to sit alone with our thoughts

In a fascinating paper by Timothy Wilson’s group at University of Virginia, they found that participants typically did not enjoy spending 6 to 15 minutes in a room by themselves with nothing to do but think. Study participants enjoyed doing mundane external activities much more than sit alone with their thoughts, and that many preferred to administer electric shocks to themselves instead of being left alone with their thoughts.

In the initial part of the study, students were told to sit in an empty room for 15 minutes without any way to distract themselves. The only condition was that they had to stay seated and not fall asleep. The students were questioned when the time was up. Most of the people in the study reported that they did not enjoy the experience. To remove the bias of an unfamiliar setting, the researchers ran the experiment again with people at home. Unsurprisingly, the people found the experience even more miserable, and often cheated by getting up from their chair or checking their phones. To see if the effect was found only in students, Timothy Wilson’s group recruited more than 100 people, aged 18-77, and found the same results.

But the most astounding result was yet to come. To check whether people might actually prefer something unpleasant to nothing at all, the study participants were given the option of administering a mild electric shock. Earlier, they were asked to rate the unpleasantness of the shock alongside other options, such as looking at pictures of cockroaches or hearing the sound of a knife rubbing against a bottle. All the students picked for the test said they would pay to avoid mild electric shocks after receiving a demonstration. To the researchers' surprise, 65% of men & 25% of women preferred mild electric shock than sit alone with their thoughts..

It is highly probable that DMN is what makes meditation so difficult. The constant mental chatter and stream of thoughts make sitting still in meditation or in silence very difficult.

Default Mode Network Imaged: John Graner, Neuroimaging Department, National Intrepid Center of Excellence, Walter Reed National Military Medical Center 8901 Wisconsin Avenue, Bethesda, MD 20889, USA. - http://www.frontiersin.org/Neurotrauma/10.3389/fneur.2013.00016

Adaptive Value of the DMN: Markov Process

The question then arises, if the DMN is so difficult to deal with, why was it conserved in evolution in the first place? My hypothesis is that having a DMN has adaptive value for the growth and survival of the human race. It is useful to think of the DMN as a random walk or Markov process. Thoughts are randomly moving in various directions, and for particularly difficult problems you get creative insights that are not accessible to the normal everyday tasking network. This has adaptive value from a evolutionary perspective because being still, and sitting in one place is not a good strategy for the survival of the species.

A lot of scientific breakthroughs and advancements happen when seemingly random thoughts coalesce and give rise to new insights. For example, in 1865 the German chemist August Kekulé proposed a ring structure of benzene after dreaming of a snake eating its own tail. Elias Howe got the inspiration for a new design of the sewing machine through a dream. Historically, the eye of the needle had always been at the top, as it still is today on hand sewing needles. Elias dreamt that cannibals surrounded him, and prepared to cook him as they waved spears. When he awoke from the, he remembered the spears, which had holes in the shaft and moved up and down. This was the inspiration for the new design of the sewing machine that was completely different from conventional design of sewing machines.

DMN in Experienced Meditators

One common comment that I get from multiple people who try to meditate is the constant stream of thoughts that crop up when they try to sit still. This is because of the DMN being active, and trying to will and stop the DMN is a foolhardy endeavor. Judson Brewer’s group, has published multiple studies which show that in experienced meditator there is a significant decrease in DMN activity and reduction of self-referential thoughts.

In my next blog post I will detail some strategies from my practice that can deal with the problem of the DMN when meditating.

Mystical Experiences and DMN

My hypothesis which is based on my reading of mystical literature, and personal practice is that a lot of references to the mind dying or becoming quiet are references to the DMN stopping in individuals. One hallmark that is frequently reported in these mystical awakenings is the absence of self-referential thoughts, and freedom from the incessant chatter of the mind. The mind becoming silent and quiet is something that is often mentioned in mystical literature. This common across multiple traditions and transcends cultural barriers.

The thought-free experience of the Self is silence. Ramana Maharishi

When you have space, the mind naturally becomes silent. When the mind has space, which means no direction, no operation of will and therefore no fear, then in that space there is silence. J. Krishnamurti

To the quiet mind all things are possible. The quieter the mind, the more powerful, the worthier, the deeper, the more telling and more perfect the prayer is. To the quiet mind all things are possible. Meister Eckhart

Last night, I begged the Wise One to tell me the secret of the world. Gently, gently, he whispered, Be quiet, the secret cannot be spoken, It is wrapped in silence. Rumi

References

1. The brain's default mode network. Annu Rev Neurosci 2015 Jul 8;38:433-47.

2. Social psychology. Just think: the challenges of the disengaged mind. Science 2014 Jul 4;345(6192):75-7.

3. Meditation experience is associated with differences in default mode network activity and connectivity PNAS. 2011 Dec 13;108(50):20254-9.