You Are Who You Are by Default

It may be off when you’re on, but the brain network behind daydreams and a sense of self is no slacker.

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By Tina Hesman Saey, Science News

You may not be riding the latest social wave on Facebook or MySpace, or tweeting your every impulse to fans on Twitter. But your brain is hooked on networking.

Vision works because different brain regions link up to connect the dots of light and color into a meaningful picture of the world. Language depends on networks of neural circuitry that make sense of the words you hear or see and that help you generate your side of the conversation. Networks of nerves control the motion of your muscles, allowing you to move smoothly and, when necessary, swiftly.

Networks are the “in” thing for brain scientists, as surely as they have been for online social butterflies.

Scientists learn about the brain’s networks by asking people to perform all sorts of mental acrobatics — interpreting optical illusions, solving riddles, taking tests of mental or muscular skills. But some neuroscientists think they can learn even more about the brain by asking volunteers to just lie back, close their eyes and let their minds wander.

Such unstructured journeys of the mind — be they planning tonight’s dinner, thinking about that meeting at work and what your boss said afterward, debating whether to drive or fly for your next vacation, or recalling that day in your childhood when you first sat in your new tree house listening to birds chirp —turn out to offer clues about one of the most important, mysterious and well-connected networks of all. It’s called the default mode network, and it’s responsible for what the brain does when it is doing nothing in particular. It’s the brain’s core, both physically and mentally, and it’s better connected to the brain’s system of circuits than Kevin Bacon is to movie stars.

“I think the default mode network is the most exciting thing that has happened in cognitive neuroscience in quite some time,” says Peter Fransson, a neuroscientist at the Karolinska Institute in Stockholm.

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.

Busy behind the scenes
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.

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