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Scientists have found that the brain development of children with attention deficit hyperactivity disorder (ADHD) is delayed but otherwise typical, according to a new study by researchers at the National Institutes of Health (NIH). Comparing brain scans of children aged 6 to 16 who had the common psychiatric disorder with scans of those who did not, researchers found that some areas in the ADHD brain — particularly those involved in thinking, attention and planning — matured an average of three years later than "healthy" brains, but otherwise followed normal patterns of development.

The results, which were published today in the online edition of the Proceedings of the National Academy of Sciences (PNAS), offer new insight into why kids usually seem to outgrow their ADHD, says Dr. Philip Shaw, who led the research team at the Child Psychiatry Branch of the National Institute of Mental Health (NIMH). "It doesn't mean we can just sit back and do nothing," Shaw says, but the findings complement "what psychiatrists have been telling parents for years," that most kids with ADHD do get better.

Shaw and his colleagues compiled data from the brain scans of 446 children, half of whom had ADHD. The scans used new imaging technology that allowed researchers to "watch" some 40,000 points in the subjects' brains over time, and to figure out which specific regions of the brain developed, or thickened, at different rates. On average, in children with ADHD, the age at which 50% of the 40,000 points on the cortex — the brain's outer mantle — achieved peak thickness was 10 1/2, three years behind the typically developing kids whose cortex matured at age 7 1/2. The lag was most obvious in the prefrontal cortex, the study found, the area of the brain critical to cognitive functions like memory, attention focusing, higher-order motor control and the ability to suppress inappropriate responses and thoughts. One region, however, appeared to develop faster in the ADHD brain: the primary motor cortex. Combined with the delay in higher-order motor control, researchers theorize, it could explain why kids with ADHD are so fidgety and restless.

Aside from the timing of maturation, the brains of children with ADHD appear to develop the same way typical brains do, from back to front. "Do [kids with ADHD] have basically have the same sequence of brain development? That's a yes," says Shaw. "Do they completely catch up with other kids? That's what we're looking at now."

ADHD is the most common psychiatric childhood disorder in the United States, but it's not bound by geography; diagnosis of ADHD is increasing globally. Since 1993, use of stimulant drugs to treat ADHD has more than tripled worldwide, according to one study. Symptoms for the disorder include impulsiveness, hyperactivity and poor concentration, and can develop over several months. Though most people outgrow the hyperactivity aspect — characterized by having trouble sitting still, moving around when others are seated, or talking while others are talking — about a quarter to a third of children and teenagers carry their ADHD into adulthood. Some environmental factors like lead exposure, smoking during pregnancy and food additives have been linked with increased risk of the disorder, but there's still debate in the mental health community about whether the cause is mostly genetic or environmental. What's clear, though, is that ADHD is highly heritable — if one parent has or had the condition, their child has about a 70% chance of inheriting it.

Though the new study may eventually help scientists identify why ADHD causes the brain to develop slower and how kids can get better sooner, Shaw says it won't help doctors diagnose the disorder today. ADHD diagnoses still have to made through clinical evaluations, and for now, treatment still means the widely used psycho-stimulant drugs, like Ritalin, and behavioral therapy.

As doctors continue learning about the ADHD brain, however, more and more alternative treatments, such as attention training and psychotherapy, are gaining traction. Research shows that the brain is not static — that it can physically change with experience. Studies reveal that the brains of some piano players, for instance, are more developed in the areas responsible for finger movement, while in the brains of people who have practiced meditation long-term, the attention centers are physically larger than average.

The ability to pay better attention is one of those things that people can consciously and physically improve in themselves, says Dr. Lidia Zylowska, who heads a program for ADHD patients at the UCLA Mindful Awareness Research Center. Zylowska's early research in meditation — one technique within the larger practice of mindful awareness — suggests that it can improve older ADHD patients' ability to stay focused. The practice may also work for kids. "We always think that our brain makes our mind, but it may work the other way," says Zylowska. "You can have an impact on your biology."

• Krista Mahr
• A new study finds that the brains of kids with ADHD mature more slowly than average. The question is, do they catch up?