Impulsive children become thoughtful adults only after years of improvements to the brain's information highways, a team reports in Current Biology.
A study of nearly 900 young people ages 8 to 22 found that the ability to control impulses, stay on task and make good decisions increased steadily over that span as the brain remodeled its information pathways to become more efficient.
The finding helps explain why these abilities, known collectively as executive function, take so long to develop fully, says Danielle Bassett, an author of the study and an associate professor of bioengineering at the University of Pennsylvania.
"A child's ability to run or to see is very well developed by the time they're 8," she says. "However, their ability to inhibit inappropriate responses is not something that's well developed until well into the 20s."
The results also suggest it may be possible to identify adolescents at risk of problems related to poor executive function, says Joshua Gordon, director of the National Institute of Mental Health, which helped fund the study. These include "all kinds of disorders such as substance abuse, depression and schizophrenia," he says.
The study is part of an effort to understand the brain changes underlying the development of executive function. It used a technology called diffusion imaging that reveals the fibers that make up the brain's information highways.
"What we were interested in asking is whether that pattern of highway structure changes as children grow, and whether those changes are related to the emergence of executive function," Bassett says.
The team found two important changes. One was that the highways tend to cluster in "modules" of the brain that perform specialized functions, like impulse control. The effect is like building more roads to move traffic inside a city.
At the same time, though, the connections between these specialized modules get stronger, which is a bit like adding lanes to the interstates that let people get from one city to another.
The result of these changes is a brain network in which information flows more efficiently, both within specialized areas and also between areas. And this speedy network is really important when it comes to executive functions like impulse control, Bassett says.
"Being able to inhibit inappropriate behavior requires you to quickly stop yourself from doing something that you might naturally do," she says.
The study had limitations, though, because it did not track the changes in each participant's brain over time. Other studies are underway that will allow scientists to study brain changes in individuals over many years.
Researchers suspect that they will see abnormal changes in the brain pathways involved in executive function in people who go on to develop psychiatric or substance abuse disorders. If so, "this could help in terms of identifying individuals who are at high risk," Gordon says.
Eventually, Gordon says, brain scans might be used to show whether a particular treatment for a psychiatric disorder is working.
AUDIE CORNISH, HOST:
When a toddler gets angry, it's not unusual to see hitting, stomping or biting. That's because of what's happening in the child's brain. It's just beginning to develop the circuits that control impulsive behavior. Now scientists think they know how those circuits take shape. NPR's Jon Hamilton has the story.
JON HAMILTON, BYLINE: A child's brain has to learn a lot - how to recognize faces, grasp objects, control emotions. And Danielle Bassett of the University of Pennsylvania says these abilities don't improve at the same pace.
DANIELLE BASSETT: A child's ability to run or to see is very well-developed by the time they're 8. However, their ability to inhibit inappropriate responses is not something that's well developed until well into the 20s.
HAMILTON: That's probably because impulse control is so complicated. The brain has to figure out what to do, so an area behind the forehead starts making calculations based on information from many other areas - memory, the senses, emotions. Then it has to make a decision. And Bassett says this has to happen really fast.
BASSETT: Being able to inhibit inappropriate behavior requires you to quickly stop yourself from doing something that you might naturally do.
HAMILTON: It's all part of something called executive function, which also helps us plan and focus. Bassett was part of a team that wanted to know how executive function develops. So they studied the brains of nearly 900 young people from 8 to 22. Bassett says the team used a special kind of MRI to reveal the fibers that make up the brain's information highways.
BASSETT: What we're interested in asking is whether that pattern of highway structure changes as children grow and whether those changes are related to the emergence of executive function.
HAMILTON: Bassett says the answer to both questions is yes.
BASSETT: There are two very salient changes in the patterns of these highways.
HAMILTON: One is that the highways tend to cluster in areas of the brain that perform specialized functions, like impulse control. Bassett says it's like seeing more roads appear in each community.
BASSETT: But in addition, we also see the strengthening of connections between those communities.
HAMILTON: Which is a bit like adding lanes to the interstate. The result, described in the journal Current Biology, is a network in which information flows more efficiently both within specialized areas and also between those areas. And that's exactly what the brain needs to stifle the impulse to smack an annoying sibling or send an angry text.
Joshua Gordon directs the National Institute of Mental Health, which helped fund the research. He says understanding the brain changes associated with executive function could shed light on a range of problems that often show up during adolescence.
JOSHUA GORDON: All kinds of nurse neuropsychiatric disorders - substance abuse disorders, schizophrenia, depression.
HAMILTON: And Gordon says there may be distinctive connection patterns associated with each of these problems.
GORDON: This could help in terms of identifying individuals who are at high risk of later developing psychiatric disorders so we can follow them more closely.
HAMILTON: Gordon says brain scans might also someday show whether a particular treatment is working. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.