Pioneering Stanford study shows how children's brain signaling differs from adults

- By Erin Digitale

STANFORD, Calif. — The first-ever comparison of synchronization of brain signals in children and young adults helps explain why children are less adept at multitasking, emotion regulation and other behaviors that come with maturity, according to researchers at the Stanford University School of Medicine.

The study, published July 21 in PLoS-Biology, offers unexpected insights into how the brain matures. It also lays the groundwork for understanding neurodevelopmental problems such as autism and attention deficit-hyperactivity disorder.

“We were surprised to see that by the age of 7 to 9, the brain's overall basic architecture is already so well-formed,” said senior study author Vinod Menon, PhD, associate professor of psychiatry and behavioral sciences and of neuroscience. His team demonstrated that school-aged children’s brain traffic is already organized along a general, efficient and fault-tolerant network plan found in adults’ brains. Their findings also uncovered new information about how signaling develops between distant brain regions.

Marsel Mesulam, MD, a professor of neurology, psychiatry and psychology at Northwestern University who was not involved in the study, called the results “exciting.” The findings, he said, “provide entirely new ways of thinking about how brain connections become remodeled as children become adolescents and adults.” He noted that no one had previously compared the functional integration between different regions of the gray matter in children and adults. “This work will be able to frame and guide our thinking on these issues for many years to come,” he said.

Earlier studies showed that in adult brains, neural signals are synchronized in a way that resembles a small-world network, Menon said. In these networks, each part of the brain is connected to nearby brain regions by lots of short, local fibers, similar to city streets. Distant brain regions are linked by a few large “highways” of connections. The connections meet at many hubs, or intersections, and signals are efficiently transmitted along the shortest path to their destinations. This organization allows detailed communication in local, specialized parts of the brain, and efficient signaling between regions.

By measuring changes in brain structure during development, scientists had previously deduced that the immature brain has excess connections that are selectively pruned away as it matures. “This structure reduces the wiring cost for communicating signals between different parts of the brain,” said Kaustubh Supekar, a graduate student in biomedical informatics who is the paper’s first author.

However, no one had examined the functional development of the brain’s communication networks. Adults often draw on many brain regions simultaneously. Menon and his colleagues wondered if children’s brains make the same synchronous functional connections.

To watch brain networks interact with their near and distant neighbors in real time, the team used two kinds of brain scans in 23 awake but resting children aged 7 to 9 and 22 young adults aged 19 to 22. Functional magnetic resonance imaging tracked neural activity, allowing the team to calculate an overall map of the organization of brain networks. Diffusion tensor imaging traced the anatomical pathways to help the team infer how the interaction of brain regions changes with wiring distance.

The brains of children showed stronger short-distance synchronization while adults had stronger long-distance synchronization. Adults also had stronger synchronization between multiple cortical regions responsible for complex information processing and decision-making. Children, in contrast, drew more upon links between the sub-cortex and various regions of the cortex. The findings help explain a wide range of prominent changes observed in children’s behavior as they mature, Menon said.

“For instance, links between the paralimbic system, which governs emotional and motivational regulation, and the emotion-processing region in the limbic system get significantly stronger in young adults,” Menon said. “We know that emotion regulation is one of the key functions that develops in late childhood and adolescence, and our findings provide a new approach for understanding this.”

And the strengthened functional links between cortical regions could explain why adults are better than children at multitasking, said Mesulam. “There’s that phrase, ‘Think globally, act locally,’” he said. “It’s that sort of distinction. In the immature brain, local processes dominate, and as the brain matures, it creates this ability to react globally.”

The next step in the research, Menon said, will be to compare the brain signaling and synchronization in children with neurodevelopmental disorders to that of typically developing children. Such comparisons could eventually illuminate the origins of autism, ADHD and schizophrenia, for example.

Menon and Supekar collaborated with Mark Musen, MD, PhD, a professor of medicine at the Center for Biomedical Informatics Research at Stanford. The research was funded by grants from the National Institutes of Health and the National Science Foundation.

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