Endeavors magazine: Brain Size and Autism

Brain Size and Autism

Bigger brains can mean big problems.

by Mark Derewicz

At six months, the babies were smiling and laughing, even with strangers. At twelve months — nothing.

“It was like someone pulled down a curtain,” says psychiatrist Joseph Piven. “The babies were not interested in social interaction. There was no back-and-forth, no eye contact.”

When Piven saw a video of these children, who were later diagnosed with autism, he also saw a possible shift in his field. What if people aren’t born with autism? What if babies develop the disorder during the second half of their first year of life?

Piven then considered another fact: autistic kids have brains that are 5–10 percent larger than normal. His team studied fifty autistic two-year-olds and found that the toddlers’ heads were indeed larger than normal. Then Piven studied the head circumferences of 113 autistic kids from birth to three years old. Head circumference is a good indicator of brain volume in young children. During the first year of life, the babies who eventually developed autism had normal-sized heads. But beginning at twelve months, the heads of autistic kids grew at an accelerated rate.

“Presumably this brain overgrowth originated just prior to twelve months, or at the end of the first year of life,” Piven says.

So what’s going on?

No one knows, but there’s lots of speculation. As a baby ages, everyday experiences help remodel any synaptic connections in the brain that aren’t necessary anymore. This remodeling helps shape the mind. But in autistic babies, remodeling might not happen correctly, and that could lead to the overgrowth of neural connections and a larger-than-normal cerebral cortex. All this could bog down the brain’s communication network, causing autistic behavior.

Piven cautions that this theory oversimplifies complex brain functions and development. Although faulty remodeling might account for larger brains and cause autistic behavior, it might not. The problem could be in some other process in development.

Piven is now leading a six-university research project to study brain development in children at risk for autism: kids whose older siblings have autism. Using magnetic resonance imaging, researchers will scan the brains of children at six months, twelve months, and twenty-four months to show exactly how the brains of autistic babies and toddlers change over time.

“Right now we’re starting to measure particular fiber tracts in the brain, the different neural circuitry,” he says. “We want to see what parts of the brain are associated with what sorts of autistic behavior.”

Joseph Piven, the Sarah Graham Kenan Professor of Pediatrics and Psychiatry in the School of Medicine, is director of the Autism Centers of Excellence, a ten-million-dollar program funded by the National Institutes of Health.