Two, Not One Networks Rule Brain's Voluntary Chain-of-command

by Medindia Content Team on  June 20, 2007 at 7:06 PM Research News   - G J E 4
Two, Not One Networks Rule Brain's Voluntary Chain-of-command
A recent research, examining the upper echelons of the human brain's chain-of-command, has found that there are not one but two corresponding commanders in charge of the brain.

Neuroscientists at Washington University School of Medicine in St. Louis found that these two commanders are networks of brain regions that do not consult each other but still work toward a common intention i.e. control of voluntary, goal-oriented actions.

This includes an immense range of activities from reading a word to searching for a star to singing a song, but likely does not include uncontrolled behaviors such as control of the pulse rate or digestion.

"This was a big surprise. We knew several brain regions contribute to top-down control, but most of us thought we'd eventually show all those regions linking together in one system, one little guy up top telling everyone else what to do," says senior author Steven Petersen, Ph.D., James S. McDonnell Professor of Cognitive Neuroscience and professor of neurology and psychology.

The findings, published online in the Proceedings of the National Academy of Sciences, may help efforts to comprehend the effects of brain injury and build up new strategies to treat such injuries.

"For example, on rare occasions patients with brain injuries will develop behaviors that are stimulus-bound: Every time they encounter a particular stimulus, they respond exactly the same way," explains first author Nico Dosenbach, an M.D./Ph.D. student. "One man with a brain injury started undressing everytime he saw a bed, regardless of whether it was in a furniture store or his own bedroom. This research may help us understand what's happening to these patients."

For the new study, Dosenbach, Petersen and colleagues including graduate student Damien Fair and Bradley Schlaggar, M.D., Ph.D., used a different brain scanning technique called resting state functional connectivity MRI. For this technique, volunteers 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 a "sustain" signal.

"When you start doing a task, this signal turns on," Petersen explains. "It stays constant while you're doing the task, and then when you're done it turns off."

On the contrary, the front parietal network was constantly active at the start of mental tasks and during the correction of errors.

"This maps very nicely onto another idea that's common in network dynamics and adaptive systems," Dosenbach says. "This is the idea that the factors controlling adaptive systems often act on different time scales. We think the frontoparietal network may be the more online, rapid-adapting controller, while the cinguloopercular network is the more stable, set, in-the-background controller."

This doesn't mean the cinguloopercular network never calls for a change of course.

"It just does that on a slower time scale, to make sure you don't needlessly throw out all the work you've already done," Dosenbach says. "It's amazing: on the one hand, the brain can be very flexible and rapidly adapt to changing feedback, but it can also lock in on something and tune out distractions until the task is finished. And these two separate control systems that work toward the same goal without actually talking to each other likely help create this powerful flexibility."

To follow up, Petersen and colleagues are expanding their investigation to include more brain regions that contribute to control. They are also scanning for differences in these brain networks in volunteers from different age groups and patients with brain injuries or disabilities.

Source: ANI

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