Different But Equal

Kids often claim they are just as smart—if not smarter—than their parents. Childish nonsense? Perhaps not, according to a recent study. It turns out that young children’s brains are as efficient in solving information-processing tasks as their adult versions, despite being very differently organized. This finding could improve our understanding of normal brain development as well as of disorders such as autism and Tourette syndrome.

 

This figure shows how the functional networks in the brain evolve during development. In each case, 34 key regions from four brain lobes are linked to each other based on mutual correlation into four functional networks. Regions are color-coded based on their anatomical locations (pastel rings) and functional network membership (solid dots). The top row shows how anatomically close regions—such as those from the frontal lobe, highlighted in turquoise—segregate into different functional networks with age. In contrast, the bottom row (the same data points) shows how anatomically distant regions integrate into a functional network—illustrated by the red-highlighted regions from the frontal, parietal, and temporal lobes, which integrate into the "default" network. Observe also how the cerebellar network (four blue dots with pink rings), initially isolated, gets integrated into the overall network with age. Reprinted from: Fair, DA, et al., Functional Brain Networks Develop from a “Local to Distributed” Organization, PLoS Computational Biology 5(5): e1000381. doi:10.1371/journal.pcbi.1000381 (2009).“Whether you are a kid or an adult your brain is organized in a pretty damn efficient way,” says Steven Peterson, PhD, a neurophysiologist at the Washington University School of Medicine in St. Louis, and senior author of the study which appeared in the May 2009 issue of PLoS Computational Biology.

 

By seven years of age, a typical human brain has already attained 95 percent of its adult size and most of the wiring that connects neurons to each other is already in place. As the brain matures further, two things happen: its wires (axons) get better at transmitting signals and its unused junctions (synapses) are progressively trimmed out. Along with these physical changes, the brain changes the way it configures its various regions into functional networks during resting, reading, singing, walking, or other tasks. This phenomenon is a key to both normal and abnormal brain development, but until now it has been difficult to quantify.

 

In the new study, Petersen and his team used magnetic resonance imaging to study functional brain connectivity in a sample population of 210 subjects aged 7-31 years. When they cross-correlated the temporal activity of 34 key brain regions in each subject while resting, a clear pattern emerged: brain regions in children interacted mostly with their neighbors while those in adults enjoyed longer-range interactions. While this confirmed prior theories, further quantitative analyses turned up a surprise. Functional brain networks in both adult and child subjects proved to consist of tightly knit communities loosely linked to each other—both possessing a “small world” structure that typifies efficiently connected systems such as social networks and the Internet. Although these communities start off being spatially localized in children and grow more diffuse with maturity, measures of computational efficiency remain high throughout. “All of us were surprised when those numbers came out,” says Petersen, who notes that these findings have now been replicated by Stanford University neuroscientist Vinod Menon’s research team in the July 2009 issue of PLoS Biology.

 

Petersen and his colleagues, including pediatric neurologist Bradley Schlaggar, MD, PhD, have applied this methodology to study Tourette syndrome, a neurological disorder characterized by physical and vocal tics. Brain connectivity patterns in adolescent Tourette sufferers appear to lag by 2-3 years compared to normal, says Petersen. “The context we got from studying normal development allowed us to interpret what we observed in Tourette subjects.”

 

“This study is incredibly innovative in providing original and direct evidence about how circuits are formed in the brain,” says Beatriz Luna, PhD, a developmental psychologist at the University of Pittsburgh Medical Center. Luna suggests that the method could next be applied to study subjects engaged in specific activities. BJ Casey, PhD, a neuroscientist at the Weill Medical College of Cornell University in Ithaca, New York, finds the study to be “a very novel characterization of neural system development” ideally suited to study developmental disorders such as autism. “It’s going to drive a lot of research,” she says.
 



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