( lunteers are asked to calm down while t...)Two, Not One Networks Rule Brain's Voluntary Chain-of-command,Health

lunteers are asked to calm down while their brains are scanned instead of working on a task.

Researchers in the labs of coauthor Marcus Raichle, M.D., and elsewhere have shown that variations in MRI scan results take place even when volunteers are inactive, and that these variations can be studied for positive insights into brain function and architecture.

To develop their analysis, Dosenbach and Petersen turned to graph theory, a branch of mathematics that visually graphs relationships between pairs of objects.

"A similar approach is used in the party game Six Degrees of Kevin Bacon. You use paired connections - appearances in the same movie, marital relationships - to go from one actor or actress to another until you've identified a chain of connections linking Kevin Bacon and another performer that wasn't immediately obvious," Petersen says.

Using an analytic technique initially developed by Raichle's group, scientists employed resting state functional connectivity MRI to discover pairs of brain regions where blood oxygen levels rose and fell more or less in synch with each other, implying the regions likely work together. They graphed the results, representing each brain region with a shape. They drew a line between paired brain regions if their blood oxygenation patterns correlated tightly enough.

"You might expect that everything is connected to everything, and you would get sort of a big mess and not much information," Dosenbach says. "But that's not at all what we found. Even at low levels of correlation, there were two sides to these graphs. Brain regions on either side had multiple connections to other regions on their side, but they never connected to regions on the opposite side."

Having established that two control networks existed, researchers turned back to their functional brain scans for insight into the networks' roles. One network, dubbed the cinguloopercular network, was linked to
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