Why your ‘seesaw’ brain can’t stay on task

U. FLORIDA (US) — When we try to concentrate on a specific task, different parts of our brain are in a constant battle for control behind the scenes.

We’ve all been there: You’re at work deeply immersed in a project when suddenly you start thinking about your weekend plans. Now, researchers are using a new technique to examine how parts of the brain fight for dominance.

Addressing these fluctuations in attention may clarify neurological disorders such as autism, depression, and mild cognitive impairment.


Scientists know different networks within the brain have distinct functions. Researchers used functional magnetic resonance imaging (fMRI) and biostatistical methods to examine interactions between a set of areas they call the task control network and another set of areas known as the default mode network.

The task control network regulates attention to surroundings, controlling concentration on a task such as doing homework or listening for emotional cues during a conversation. The default mode network is thought to regulate self-reflection and emotion, and often becomes active when a person seems to be doing nothing else.

“We knew that the default mode network decreases in activity when a task is being performed, but we didn’t know why or how,” says Mingzhou Ding, a professor of biomedical engineering at the University of Florida. “We also wanted to know what is driving that activity decrease. For a long time, the questions we are asking could not be answered.”

In the past, researchers could not distinguish between directions of interactions between regions of the brain, and could come up with only one number to represent an average of the back-and-forth interactions.

The new technique untangles the interactions in each direction to show how the different brain regions interact with one another.

For the study, published in the Journal of Neuroscience, the researchers examined the brains of people performing a task that required concentration. They were able to see the activity in certain areas of the brain at the same time a person performed a given task and saw which parts of the brain were active, which were not and correlated this to how successful a person was at the given task.

They then applied the Granger causality technique to look at the data they saw in the fMRI. The technique allows scientists to examine how one variable affects another variable; in this case, how one region of the brain influences another.

“People have hypothesized different functions for signals going in different directions,” Ding says. “We show that when the task control network suppresses the default mode network, the person can do the task better and faster. The better the default mode network is shut down, the better a person performs.”

However, when the default mode network is not sufficiently suppressed, it sends signals to the task control network that effectively distract the person, causing his or her performance to drop. So while the task control network suppresses the default mode network, the default mode network also interferes with the task control network.

“Your brain is a constant seesaw back and forth,” even when trying to concentrate on a task, Ding says.

The Granger causality technique may help researchers learn more about how neurological disorders work.

They have found that the default mode network remains unchanged in people with autism whether they are performing a task or interacting with the environment, which could explain symptoms such as difficulty reading social cues or being easily overwhelmed by sensory stimulation. Similar findings have been observed with depression and mild cognitive impairment.

However, until now no one has been able to address what areas of the brain might be regulating the default mode network and which might be interfering with that regulation. “Now we are able to address these questions,” Ding says.

Researchers from Peking University in Beijing contributed to the study.

Source: University of Florida