Via NOVA Next | PBS: ‘Some scientists are arguing that our new understanding of a particular network in the brain is allowing neuroscientists, psychologists, and psychiatrists—even artists and writers—to understand each other in ways that wouldn’t have made sense ten years ago. Called the default mode network, or DMN, it’s a set of brain regions that are typically suppressed when a person is engaged in an external task (playing a sport, working on a budget), but activated during a so-called “resting state” (sitting quietly, day-dreaming).

“It’s an extremely important platform for any kind of thought that is disengaged from the ‘here-and-now,’ ” says Mary Helen Immordino-Yang, assistant professor of psychology at the University of Southern California’s Brain and Creativity Institute. That includes processing other people’s stories, reflecting on our own lives, planning for the future, or making important decisions. Immordino-Yang says the default mode network is “metabolically expensive.” In other words, when your head is lost in the clouds, your brain is hard at work.The default mode network, which is hyperactive in schizophrenic people, plays an important role in self-reflection, identity, and mind-wandering. Though not the only “resting state” network that’s active when we’re staring off into space, the DMN is unusual in that it is reliable and identifiable, making it easy for scientists to study. Like a web of taut ropes overlaying and intersecting one another, the regions of the DMN–which include the medial prefrontal cortex and the posterior cingulate, both of which are involved in self-awareness, self-reflection, and so on–light up in concert, despite any distance separating them.

When neurologist Marcus Raichle and his colleagues discovered the DMN in 2001, it took the scientific community by surprise. How could rest and self-reflection excite the same brain regions in us all? Why are those regions so intimately correlated? Wouldn’t a brain scan vary more from person to person depending on the content of an individual’s thoughts? It turned out that the DMN has nothing to do with content and everything to do with context. This network is functioning all the time–focusing on a task merely tempers and subdues it.

“This is first time we’ve found a neural system that actually reveals your inner self,” says Susan Whitfield-Gabrieli, a research scientist at MIT. In 2009, she and her colleagues found that in schizophrenic people, the DMN operates on overdrive. When clinically diagnosed patients enter an fMRI scanner and are asked to perform various tasks, the dial on their DMN doesn’t turn down like it should. And when the patients are at rest, their DMN is hyper-connected, buzzing with surplus energy. What’s more, they lack the ability to toggle out of the DMN, this highly self-referential state of being. “They’re actually stuck in their default mode network,” Whitfield-Gabrieli says.’