Default state of the human brain

What does the brain do when you're not doing anything in particular? That's when the brain's "default mode network" really kicks into gear. This series of connected regions in the brain is apparently a hot topic for cognitive neuroscientists. This week's issue of Science News surveys research on the default mode network, which apparently is responsible for allowing your mind to "wander." But it also seems to have a much more important role. From Science News:

Default brain settings may lead to daydreaming and mind-wandering, but the network also conducts serious business. Neuroscientists still hotly debate the network’s exact functions, however. Among its jobs may be running life simulations, providing a sense of self and maintaining crucial connections between brain cells. A few researchers doubt the network is anything special at all.

But evidence suggests that a malfunctioning default network is involved in diseases and disorders as diverse as Alzheimer’s disease, autism, depression, post-traumatic stress disorder, Tourette syndrome, amyotrophic lateral sclerosis, schizophrenia and attention-deficit/hyperactivity disorder.

Despite its laid-back name, which neuroscientist Marcus Raichle coined in a 2001 paper, the default mode network is one of the hardest-working systems in the brain. It was discovered accidentally by researchers watching the activity of brains at work on various tasks.

Neuroscientists use PET (short for positron emission tomography) and functional MRI scanners to image and gauge brain activity. To tell which areas of the brain become more active during a mental task, scientists compare brain activity during the task with activity when the person is at rest, either with eyes closed or while staring at a dot or cross. Raichle, of Washington University in St. Louis, and others saw that every time a person engaged in a mental activity such as memorizing a list of words, a collection of brain regions consistently decreased activity compared with their resting levels. Only when people recall autobiographical memories or imagine alternative situations is the network more active than it is at rest, scientists have since found. (In this context, “rest” refers to a state in which the brain is not engaged in a mental task but is still monitoring the body and the world around it.) Raichle hypothesized that the network is more active when the brain is at rest and has to dial back its activity to let people concentrate on specific tasks.

"You Are Who You Are by Default"

• [Garmt]

  #6, I can top that. I went to bed with one last night. Unfortunately, her field of study doesn’t apply to “learning through osmosis”, so I’m still as dumb as I ever was, but hey.

  I do second #5′s opinion, though. I felt just like a little schoolkid again just now, pointing out the article to her. She went “Apparently. Indeed-e-o. Pff.” and went back to something far more interesting, which is fixing breakfast. (indeed-e-o is cognitiveneuroscientistsslang, btw).

• [The Unusual Suspect]

  “Raichle hypothesized that the network is more active when the brain is at rest and has to dial back its activity to let people concentrate on specific tasks.”

  Much like focusing attention to X is actually the act of ignoring Not-X.

  Great! Another reason to light my mind wander!

• [FoetusNail]

  This is where ideas pop from, when they suddenly bubble to the surface. I’ve always known this network as the back burner.

• [Anonymous]

  I’m NOT a brain scientist but I have seen one up close. Of course when it comes to brain science I only cite the emminent Dr. Anonymous’ articles in my own exposition (published in classified sections of many local newspapers and Craiglist ‘Missed Connections’).

  FYI: Here is another fine review on Default Networks by Mezmer et al.

  A Default mode of the brain function of Britney Spears
  (Lagado University, Laputa, KS)

• [gtllama]

  So if the default mode network provides your sense of self, and activity there decreases when you are focused on a task, that means they have objectively measured the subjective experience of “losing yourself” in something interesting. Far out, man.

• [sonipitts]

  Probably also explains some of the benefits of meditation and sitting zazen. Lots of network-friendly time.

• [Anonymous]

  I’m a brain scientist, and I should point out that “hotly debated” is an understatement for describing what much of the field thinks about this network. While it seems to be accepted that its existence is not a statistical anomaly, ascribing function to it is still an long way off. So suggesting it is representing functions such as “mental time travel” etc. as Raichle has is extremely premature. (For starters, the links between any behavior and this network are only correlational, so *no causality* can be concluded.) The brain is complicated and making such claims for some observed deactivations (something which we also don’t understand, btw) is naive from people who are supposed to be smart. I would instead argue that this is a “novel” topic for an over-hyped field (fMRI of the human brain).