Connectivity is a hot topic in neuroscience these days. Instead of trying to figure out what individual brain regions do, researchers are focusing more on how regions work together as a network to enable memory, language, and decision-making. Now, a study of more than 100 children finds that interconnected brain regions develop in concert through childhood and adolescence. The researchers say their work could have implications for understanding various puzzles in neuroscience, such as what goes wrong in autism or why adolescent boys are prone to risky behavior.
To look for evidence of coordinated development across brain regions, Armin Raznahan, a child psychiatrist and neuroscientist at the National Institute of Mental Health in Bethesda, Maryland, and his colleagues tapped into a long-running NIMH project that has been collecting magnetic resonance imaging scans of brain anatomy in children at different ages. They analyzed scans from 108 healthy children who'd had at least three scans taken between the ages of 9 and 22. The researchers calculated the thickness of the cerebral cortex, the brain's outermost layer of tissue, which is involved in virtually every aspect of cognition and behavior. In general, the cortex thickens in early childhood and thins in adolescence or adulthood, Raznahan says. He and his colleagues hypothesized that these changes might happen simultaneously in interconnected brain regions.
That's exactly what they found. For example, the team will report tomorrow in Neuron, they saw this pattern in the so-called default mode network, which becomes active when people let their minds wander. "These regions are firing together for a lot of one's life," Raznahan says. "What we've shown is that these regions also seem to mature in close synchrony with each other."
Overall, the study found that brain regions that talk to each other a lot appear more likely to mature in synchrony. These include regions of the temporal and frontal cortex that contribute to sophisticated functions, such as language, abstract reasoning, and decision-making. In contrast, parts of the cortex involved in narrowly focused tasks—such as making sense of sights and sounds or telling muscles what to do—appear to mature more independently.
The team also found one notable difference between the boys and girls in the study. Girls exhibited more coordinated development in regions of the prefrontal cortex implicated in complex decision-making. "That's really intriguing to us," Raznahan says. Adolescent boys are more likely than girls to engage in risky or violent behavior, and one prominent hypothesis holds that differences in the maturation of the prefrontal cortex might account for these tendencies, Raznahan says.
"This encourages us to look past the notion that regions of the brain develop in isolation," says Bradley Schlaggar, a child neurologist and developmental cognitive neuroscientist at Washington University School of Medicine in St. Louis in Missouri. "I think that's really an important insight." Schlaggar thinks similar methods could be useful in studies of autism and other neurodevelopmental disorders. It's possible that normal brain development depends on certain brain regions maturing in synchrony, Schlaggar says. Alan Evans, a neuroimaging scientist at the Montreal Neurological Institute and Hospital in Canada, agrees, noting that many researchers think autism arises when brain development goes awry, resulting in abnormal connectivity among brain regions. "I would bet that you'd see significant differences between an autistic population and an age-matched normal population using this methodology," he says.
Both Schlaggar and Evans find the sex-difference findings less compelling, though. "It's intriguing," Evans says, "but that particular result needs further exploration."
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