Graph Theory Reveals Two Independent Command Centers in Brain

July 2, 2007

Two networks within the brain work toward a common purpose — the control of voluntary, goal-oriented behavior. Graph theory, the branch of mathematics that characterizes links between pairs of objects, helped uncover this unexpected dual structure.

Neuroscientists at the Washington University School of Medicine in St. Louis used MRI scans to identify pairs of brain regions where blood oxygen levels increased and decreased simultaneously. Such roughly synchronized behavior suggested that these pairs of regions, though independent of each other, were working in a complementary fashion.

To find out how these regions are linked, the scientists graphed the results, representing each region with a distinctive shape, then drew lines connecting regions if there was a correspondence between their oxygenation levels.

"You might expect that everything is connected to everything, and you would get sort of a big mess and not much information," Nico Dosenbach said. Instead, "even at low levels of correlation, there were two sides to these graphs. Brain regions on either side had multiple connections to the other regions on their side, but they never connected on the opposite side."

The results indicate that the brain has two independent control networks, making it an example of a complex adaptive system.

The findings, published online in the Proceedings of the National Academy of Sciences, may aid efforts to understand and treat brain injuries.

Source: Washington University School of Medicine, June 18, 2007; Proceedings of the National Academy of Sciences, June 18, 2007