original version of this story Appeared in Quanta Magazine.
Whenever you are active For example, when you perform a task, such as lifting weights at the gym or taking a difficult exam, the electrical activity of neurons increases and the parts of the brain necessary for the task are “activated.” But is your brain still active when you're lazing around on the couch?
Researchers have found that the answer is yes. Over the past 20 years, they have defined what is known as the default mode network. This is a collection of seemingly unrelated areas of the brain that are activated when you are doing nothing. This discovery provides insight into how the brain functions outside of well-defined tasks and also sheds light on the role of brain regions, as well as brain networks, in managing our internal experiences. We also promoted research on
In the late 20th century, neuroscientists began using new techniques to take images of people's brains as they performed tasks with scanning machines. As expected, activity in certain brain areas increased during the task, but to the researchers' surprise, activity in other brain areas also decreased at the same time. Neuroscientists were intrigued to find that the very same brain regions consistently suppressed their activity during different tasks.
It was as if these areas were active when the person was doing nothing, and deactivated when the mind had to focus on something external.
The researchers called these areas “task negative.” When these regions were first identified, Marcus Reichl, a neurologist at Washington University School of Medicine in St. Louis, suspected that these task-negative regions played an important role in the resting mind. “This raised the question, 'What is baseline brain activity?'” Reichl recalls. In his experiments, he had people wearing scanners measure their brain activity while they closed their eyes and simply let their minds wander.
He found that when you're at rest, or mentally turned inward, task-negative areas expend more energy than other parts of your brain. In a 2001 paper, he called this activity “the default mode of brain function.” Two years later, after generating higher-resolution data, a team at Stanford University School of Medicine discovered that this task-negative activity defined a coherent network of interacting brain regions, making this the default mode. It was called a network.
The discovery of the default mode network has sparked curiosity among neuroscientists about what the brain does in the absence of an outwardly focused task. Some researchers believed that the primary function of networks was to create our mind-wandering or daydreaming experiences, but there were many other speculations. Perhaps it controlled the stream of consciousness or activated memories of past experiences. Default mode network dysfunction has then emerged as a potential feature of nearly all psychiatric and neurological diseases, including depression, schizophrenia, and Alzheimer's disease.
Since then, a flurry of research on default modes has complicated our initial understanding. “Over the past 20 years, it's been really interesting to see the types of different tasks and paradigms that engage the default mode network,” said Lucina Uddin, a neuroscientist at the University of California, Los Angeles.
