According to a brain imaging study, some regions of the young ADD/ADHD brain develop up to three years slower than in the brains of youth without ADD/ADHD.

Results of the study, which were released in November 2007, gave details of an ADD/ADHD brain imaging study conducted by researchers at the National Institute of Mental Health (NIMH), part of the U.S. National Institutes of Health. During the study, NIMH doctors scanned the brains of 223 youth with ADHD and 223 youth without ADHD. The 446 total participants ranged in age from preschoolers to young adults.

During the study, doctors compared the thickness of cortex tissue in the ADHD brain and non-ADHD brain. In both the ADHD brain and the non-ADHD brain, cortex tissue becomes thicker during childhood and then thins after puberty. This thinning is normal as the brain gets rid of unneeded neural connections and becomes more efficient during the teen years.

However, brain scans in the study showed that, in the ADD/ADHD brain, the cortex achieved peak thickness at an average age of 10.5. In the brains of children without ADHD, peak cortex thickness occurred at age 7.5. This three-year delay in the ADD/ADHD brain is most prominent in the area of the brain that controls thinking, attention, and planning.

In spite of the delay, the study appeared to show that both the ADD brain and the non-ADD brain developed in the same way, albeit at different times.