By Dr Yaara Yeshurun
We don’t often give much thought to not thinking. Increasingly, though, research is showing us that it’s a surprisingly eventful state, and how well it’s working—or not—can be related to a wide array of mental illnesses that can greatly affect a person’s life.
The term “default mode network” was coined in 2011 by neuroscientist Marcus Raichle, because it describes a system that turns on (to oversimplify it) when nothing else is happening: It’s the default in the absence of anything else. In other words, the DMN is what’s working when a person is not focusing on what’s around them in the present moment. The DMN is for daydreaming and being creative; for imagining someone else’s perspective; for self-focus; and for what could be called “mental time travel,” both for planning and for remembering.
Recent research suggests that the DMN is also involved in integrating external information with internal information (for example one’s beliefs, emotions and prior knowledge) in order to make sense out of events occurring in the outside world. (For more on the DMN, click here.)
The purpose of the DMN: social hard-wiring
As UCLA’s Matt Lieberman has put it, “The brain has a major system that seems predisposed to get us ready to be social in our spare moments.” The DMN is a major part of that system—the wiring by which we create narratives about the world and how all of us fit into it and fit together.
Consider the name. The DMN—the default mode. We, as humans, are wired to make everything we see fit into a story of people and what they’re thinking. Social cognition is literally the default state of the brain.
Consider your own experiences, even the simplest. If you see a human face, you probably can’t stop yourself from inferring what the person’s expression means about what they’re likely to be thinking and feeling. You probably don’t automatically infer emotional states onto a tree in the same way. We’re hard-wired from birth (though it does develop, with the rest of the brain, throughout childhood and adolescence) to understand our human world socially, differently from how we understand the rest of the world.
And consider the research. We have learned that the DMN is sensitive to how we socially understand the world. For example, in one of our studies, we asked participants to listen to a short story by JD Salinger in an MRI scanner so that we could measure their brain response at the same time. Before listening to the story, each participant was presented with one of two different contexts that shaped their interpretation of the characters’ behavior throughout the story.
We found that the response of the auditory cortex (a brain region that processes sound) was similar, no matter how participants interpreted the story. This makes sense, as the auditory input was exactly the same. However, this was not the case in the DMN. The way participants interpreted the story—the emotions, beliefs, and intentions they attributed to the characters—shaped the response of the DMN.
DMN dysregulation: When the trains don’t run on time
Think of the brain as a busy city’s complicated subway map. At any moment, there are many journeys happening along many overlapping routes, for many purposes. The brain’s DMN is one of the subway lines. It connects areas that include the medial prefrontal cortex, the posterior cingulate cortex, and the angular gyrus. When the DMN is functioning properly, travel on this line makes it possible for the brain to process and integrate information, from the outside world and inside the mind, in order to create a narrative to help to understand the world.
But, like any rail line, it doesn’t always work perfectly. If our imaginary subway line was not connecting well enough, we can imagine that problems would arise. Similarly, in the DMN, hypoactivity can correlate with Alzheimer’s disease, Parkinson’s disease, or autism spectrum disorder.
Conversely, we can imagine the difficulties if our imaginary train network were to be overloaded. And similarly, a hyperactive DMN can correlate to depression, anxiety, loneliness, or schizophrenia.
Whether DMN dysregulation causes, is a result of, or correlates with the mental illnesses is difficult to say with certainty based on research to date, but the relation is clear. Increasingly clear, too, is the fact that there are behavioral and pharmacological interventions that can help the DMN to down-regulate and re-regulate.
Meditation has repeatedly been found to down-regulate DMN activity—not only during the act of meditating itself but also beyond the specific practice. Research into some serotonergic psychedelics is also promising; For example, psilocybin is being studied in clinical trials for its potential to act as a reset in some severe mental health conditions, such as depression that has not responded to traditional SSRI or antidepressant treatment (known as treatment-resistant depression, or TRD).
Investigational therapies like these may alter the response of the DMN, and manipulation of the DMN offers promising pathways for the treatment of these debilitating illnesses.
The DMN hard-wires humans to be social. We plan ahead; we think back. We conjecture about what others are thinking; We think about what we’re thinking. We imagine. When the DMN works, it’s integrating information from our own thoughts and feelings as well as from the outside world, to try to make sense of it all. When it isn’t working properly, we can get too lost in thoughts—or not connect enough with them.
The DMN, working away in the background, was an unsung hero for part of the history of psychiatric research. It is finally getting the attention it deserves for its quiet but an important role in our mental health.
Dr. Yaara Yeshurun
Source: Used with permission.
Dr Yaara Yeshurun is a social neuroscientist and assistant professor in the School of Psychological Sciences and the Sagol School of Neuroscience at Tel-Aviv University, and the director of their Social & Cognitive Neuroscience Laboratory. Dr Yeshurun received her Ph.D. in Neurobiology from the Weizmann Institute of Science. Her research focuses on social neuroscience “in the wild.” Using behavioral studies, fMRI (functional magnetic resonance imaging), and fNIRS (functional near-infrared spectroscopy), her lab studies the neural mechanisms underlying individual differences in the way people interpret external situations and the role of brain-to-brain synchronization in real life interactions