Demystifying Series (DS #1): Default Mode Network (DMN)

Does our brain really rest when we sleep or when we're not doing anything that requires focus? What does the brain do when we are sitting idle or when we are not engaged by any external stimulus?

The answer to all these questions is the Default Mode Network (DMN).

In this article, we will try to understand what the DMN is and the key theories around it.

In simple terms, we can say that the brain network that remains active when we are at rest and not engaged in any specific activity is the Default Mode Network (DMN).

Earlier, it was believed that the brain remained inactive while we were resting. In the late 1990s, research on the aspect of brain during the resting phase began gaining momentum. In 1997, Gordon Shulman came across an interesting fact that certain regions of the brain remained inactive while we are doing goal-oriented tasks. This research was further taken forward by Neurologist Marcus Raichle, who coined the term “Default Mode" in 2001. They were clearly able to see that a certain section of the brain, which was remaining inactive when goal-oriented tasks were performed, became active when the individual was in a resting phase. Mainly, the regional blood flow and oxygen consumption in these regions of the brain were measured to understand which parts of the brain were active.

DMN exists not only in humans, but also in animals. DMN becomes very crucial in terms of self-reflection, emotional processing, social interaction, and mental exploration. It also plays a very important role in episodic memory (a long-term form of memory that keeps a record of personal events that have happened in your life) and helps in building mental narratives.

DMN does not work in silos; it interacts actively with other brain networks as needed. When we are doing tasks that need close attention, it is seen that the DMN takes a back seat, and the Executive Control Network (ECN: The network of the brain mainly responsible for goal-oriented behaviour, executive functioning, cognitive control, error monitoring, working memory, and attention) kicks in to do the task. This shows the reciprocal interactions exhibited by the DMN.

This switch is mainly made possible promptly with the help of the Salience Network (SN), which detects the stimuli and deactivates the DMN and activates the ECN to get the activity completed successfully.

Multiple theories are being proposed around the DMN; some of the prominent theories are:

1. Sentinel Hypothesis: This theory mainly suggests that even when we are resting and not interacting with the external world, the DMN is working in the background, assessing the environment around us so that we can quickly respond to any relevant stimuli represented to us. This becomes very important in terms of survival and adaptation.

2. Social Connection Hypothesis: This theory suggests that the DMN has a great deal to do with how a person socially interacts and is able to understand another person’s mind. Various functional neuroimaging studies have pointed towards the fact that DMN areas and other brain regions are activated during social interactions such as observing facial expressions and the mental state of others. Clinical research has shown that patients with autism spectrum disorders who normally present with difficulty in social interaction have altered connectivity and activity in the DMN.

3. Creative Imagination Hypothesis: Suggests that the DMN is involved in facilitating creativity and helping in creating brand new ideas. The notion of this hypothesis is that when a person is in the rest phase or not engaged in an external activity, the DMN becomes active, helping the mind to explore different mental scenarios, thus helping the person to be more creative, come up with new ideas, and solve complex problems. Watch this video to explore more on this theory: https://www.youtube.com/watch?v=hAM_ujHG9Ns

Studies conducted via functional magnetic resonance imaging (fMRI) and other techniques have suggested that variance in the performance of the DMN has been found to trigger various conditions such as Alzheimer’s, Depression, Schizophrenia, Anxiety Disorders, Post-Traumatic Stress Disorder (PTSD), and Attention Deficit Hyperactivity Disorder (ADHD).

Research on the DMN is an ongoing process and has even extended to animals, providing more insights into the evolution and adaptive nature of the neural networks. The study of the DMN has huge possibilities in neuropsychiatric treatment as well as mental well-being.