What's New:

 Brain's control network splits in two as children approach adulthood

By Michael Purdy

Aug. 1, 2007 -- Two recently discovered control networks that govern voluntary brain activity in adults start life as a single network in children, report neuroscientists at Washington University School of Medicine in St. Louis.

Researchers previously showed the networks supervise most goal-oriented brain activity, enlisting the specialized talents of multiple brain regions for goal-oriented tasks as diverse as reading a word, listening to music or searching for a star. They were surprised to find the two networks merged together in children.   "This has important implications not only for our thinking about how the architecture of the brain develops, but also for how that same structure breaks down in aging, disease and injury," says senior author Bradley L. Schlaggar, M.D., Ph.D., assistant professor of pediatrics, radiology, neurology and neurobiology and anatomy.

The results appear in the Proceedings of the National Academy of Sciences.   Neuroscientists have spent much of the past few decades pinning brain functions to small brain areas or collaborations between a few of those areas. But scientists have sometimes found it difficult to use this approach to predict how injuries to a given area of the brain will affect a patient's cognitive abilities.   "We're optimistic that answers to these problems and other important questions may lie in a more network-oriented approach that analyzes how several different brain regions regularly work with each other, exchanging data, directives and feedback," says coauthor Steven Petersen, Ph.D., the James McDonnell Professor of Cognitive Neuroscience and professor of neurology and psychology.

In June, Petersen and colleagues at Washington University announced that they had identified two control networks that seem to be in charge of much higher brain function (http://mednews.wustl.edu/news/page/normal/9639.html). The two networks do not consult with each other but still work toward a common purpose: control of voluntary, goal-oriented behavior. This likely does not include involuntary behaviors such as control of the pulse rate or digestion.   One control network, dubbed the cinguloopercular network, is the "stable, sustaining" network, likely to be active during prolonged mental activities, such as reading a text. In contrast, the frontoparietal network is a "more online, rapid-adapting controller," whose active periods include times when the brain recognizes an error and changes its approach to a problem.

Scientists used a new brain scanning technique called resting state functional connectivity MRI to identify the control networks. Instead of analyzing mental activity when a volunteer works on a cognitive task, the new technique scans their brains while they do nothing. The scans reveal changes in the levels of oxygen in blood flowing to different areas of the brain. Researchers interpret correlations in the rise and fall of blood oxygen to different brain areas during inactivity as a sign that those areas likely work together. In neuroscientist's terms, this means the regions have functional connectivity.

A team of researchers led by Petersen and M.D./Ph.D. student Nico Dosenbach analyzed scans of volunteers with an approach called graph theory. They represented various brain regions of interest as shapes, and when two regions met a threshold for functional connectivity, they drew a line between them. The two control networks were distinctly separate even when the connectivity threshold was set to a low level.   For the new study, scientists used the same techniques to analyze the brains of 210 children, adolescents and adults. They found the two control networks are merged in children but begin pulling apart in adolescents, establishing themselves as separate entities and becoming more complex.

The prominent changes add another layer of intricacy to the challenge of predicting how brain injuries will affect patients.   "These networking changes mean a lesion in the same place in the brain could have different consequences depending on when it occurs," Schlaggar says.  

Researchers also found a key component of the sustaining network in adults was closely linked in children to regions that eventually make up the heart of the adaptive network.   "We expected to find some differences in terms of these networks not being fully mature, but a complete switch of allegiance was not something our field would have predicted and is quite provocative," says Petersen.

Given the notoriously short attention span of children, the fact that the core of the sustaining network is stuck in the middle of the adaptive network in kids provides tempting fodder for supposition, according to lead author Damien Fair, a graduate student.   "This is pure speculation, but it could be that this region that forms the heart of the sustaining network is in training for its eventual role in sustaining activities in the adult brain," he says. "It also could be that the sustaining network is just less well-developed in children."   Fair notes that an interesting pattern emerged as scientists looked at their data from a big picture perspective.   "As we get older, connections that are getting weaker tend to be between brain regions located close to each other, while the connections that are getting stronger tend be those between regions that are far apart," he says.   The strengthening of long-range connections may be how the newly established control networks integrate themselves into other brain regions and networks, Petersen says.

Scientists are currently looking to see if other brain regions are part of the control networks. They also plan follow-up studies of the brains of patients with Tourette's syndrome and attention-deficit hyperactivity disorder to learn if their control networks are impaired.

Fair DA, Dosenbach NUF, Church JA, Cohen AL, Brahmbhatt S, Miezin FM, Barch DM, Raichle ME, Petersen SE, Schlaggar BL. Development of distinct control networks through segregation and integration. Proceedings of the National Academy of the Sciences, early online edition.

The National Institutes of Health, the John Merck Scholars Fund, the Burroughs-Wellcome Fund, the Dana Foundation, the Ogle Family Fund, the Washington University Chancellor's Graduate Fellowship and the United Negro College Fund/Merck Graduate Science Research Dissertation Fellowship supported this research.

.