Brain Organization Changes As We Enter Adulthood

A new study finds that children’s brains are organized differently than those of adults.  Specifically, the neural connections within a child’s brain are more a function of proximity to one another than is the case with adult brains.

The research also showed that despite these differences, one of the most important core principals of adult brain organization is present in the brains of children as young as 7 years old.

"Regardless of how tempting it might be to assume otherwise, a normal child’s brain is not inherently disorganized or chaotic," said the study’s senior author Steven E. Petersen of the Washington University School of Medicine in St. Louis.

"It’s differently organized but at least as capable as an adult brain,” he added.

Petersen and his colleagues study normal brain organization and development to learn more about the ways in which developmental disorders and brain injury can impair mental capabilities.  They plan to apply their knowledge towards the development of new treatments for such disorders.

The researchers used resting-state brain scans to identify and study brain networks.  Instead of recording mental activity when volunteers work on a cognitive task, resting-state connectivity scans the spontaneous activity that takes place in the brains as they do nothing.
When this brain activity rises and falls at the same time in different brain regions, researchers conclude that those areas likely work together.

Using this technique, scientists had previously discovered four brain networks with varying responsibilities in the adult brain.  The networks typically involve tight links between several brain regions that are physically distant from each other.  In the current study, these networks are where the organizational contrasts arise.  

Petersen and his team scanned the brains of 210 subjects ranging from 7 to 31 years of age.   The researchers set the lower limit for study subjects at 7 years of age because the brain is approximately 95 percent of its adult size at this age.

The scientists found that instead of having networks made of brain regions that are distant from each other but functionally linked, most of the tightest connections in a child’s brain are between brain regions that are physically close to each other.

However, that doesn’t mean that children are more scatter-brained than adults.

"Regardless of how tempting it might be to assume otherwise, a normal child’s brain is not inherently disorganized or chaotic," Petersen said.

"It’s differently organized but at least as capable as an adult brain."

The scans also showed how the brain’s organization changes as we age.

"We took a group of the youngest subjects, analyzed their results, then dropped data from the youngest and added data from the next-oldest and redid the analysis until we had worked our way through all subjects," said Damien A. Fair, Ph.D., one of the study’s leaders.

"The result was a detailed movie of how the organizational transition from a child’s brain to an adult’s brain takes place. It clearly shows a switch from localized networks based on physical proximity to long-distance networks centered on functionality,” added Fair, a former Washington University graduate student now at Oregon Health and Science University.

“As a person ages, those long-range networks become more efficient and then brain can use more of them,” explained Alexander L. Cohen, another study leader and a current graduate student at Washington University.

"They’re trying to solve the task of being a brain in a human body,” he added.

The researchers also examined children’s brains for "small-world" organization, a quality present in adult brains and sometimes referred to as the "Kevin Bacon" organization after the trivia game "six degrees of Kevin Bacon”.  The game demonstrates how easy it is to connect any actor to Kevin Bacon in six movies or less through links among various co-stars.

"It’s the idea of a large network that lets you connect one node with another in a relatively short number of steps via special nodes," Fair said.

"Like Kevin Bacon, these special nodes have many connections to other nodes, allowing them to help shorten the amount of steps that have to be taken when connecting nodes."

Scientists had already known that children had far fewer long-distance links among brain regions than adults.  However, when researchers looked more closely they discovered there were enough of these links and nodes with multiple connections to establish small-world organization.

The researchers are now considering ways to adapt their study to the changing physical geography of even younger brains. They have also started to examine the same phenomena in subjects with brain injuries and developmental disorders.

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