Brain areas more integrated for complex tasks: study

Researchers at Stanford University have learned that the integration between different areas of the brain fluctuates and people do better on complex tasks when the brain is more integrated.

The findings build on the understanding in the past 100 years that different brain areas serve unique purposes and on the recent knowledge that rather than having strictly defined routes of communication between different areas, the level of coordination between different parts of the brain seems to ebb and flow.

"The brain is stunning in its complexity and I feel like, in a way, we've been able to describe some of its beauty in this story," said Mac Shine, a postdoctoral researcher at Stanford and lead author of a study published in Neuron. "We've been able to say, 'Here's this underlying structure that you would never have guessed was there, that might help us explain the mystery of why the brain is organized in the way that it is.'"

While working in the lab of Russell Poldrack, a Stanford professor of psychology, Shine and his colleagues used open source data from the Human Connectome Project to examine how separate areas of the brain coordinate their activity over time, both while people are at rest and while they are attempting a challenging mental task.

For the resting state condition, the researchers used a novel analysis technique to examine functional magnetic resonance imaging (fMRI) data, which shows in real time which areas of the brain are active. The analysis estimates the amount of blood flow in pairs of brain regions and then uses the mathematics of graph theory to summarize the way that the whole network of the brain is organized. They found that even without any intentional stimulation, the brain network fluctuates between periods of higher and lower coordinated blood flow in the different areas of the brain.

To determine whether these fluctuations were relevant for the function of the brain, the researchers used fMRI data from people who had successfully performed a challenging memory test. They found that the brains of participants were more integrated while working on this complicated task than they were during quiet rest, indicating that the brain was most interconnected in people who performed the test fastest and with the greatest accuracy.

As a final step in their study, the researchers measured pupil size to try and tease out how the brain coordinates this change in connectivity. Pupil size is an indirect measure of the activity of a small region in the brainstem called the locus coeruleus that is thought to amplify or mute signals across the entire brain. Up to a certain point, increases in pupil size likely indicate greater amplification of strong signals and greater muting of weak signals across the brain. The researchers found that pupil size roughly tracked with changes in brain connectivity during rest, in that larger pupils were associated with greater connectedness.

This suggests that the noradrenaline coming from the locus coeruleus might be what drives the brain to become more integrated during highly complicated cognitive tasks, allowing a person to perform well on that task.

"This research shows these really clear relationships between how the brain is functioning at a network level and how the person's actually performing on these psychological tasks," noted co-author Poldrack.

The researchers plan to further investigate the connection between neural gain and integration in the brain and to figure out how universal these findings are to other behaviors, such as attention and memory. "I think we were really lucky here, in that we had an exploratory question that bore fruit," said Shine. "Now, we're in a position where we can ask new questions that will hopefully help us to make progress in understanding the brain." Endit