ADHD and Brain Development

Attention deficit hyperactivity disorder (ADHD) is one of the most common disorders of childhood that continues into adulthood. Symptoms of ADHD like inattention, impulsiveness, and hyperactivity can lead to difficulty in the person’s emotional, social, and academic functioning.

Deviation or delay?

Experts are somehow divided as to the nature of ADHD. On the one hand, they say that the brains of those having this disorder develop in abnormal ways. On the other hand, they suggest that their brain development is just delayed.

Latest evidence from a brain-imaging study supports the later theory. This study, which was published in the Proceedings of the National Academy of Sciences (online edition) points to patterns in development that could help explain why people with ADHD exhibit impulsive behavior.

Cortical thickness

Philip Shaw, a psychiatrist at the National Institute of Mental Health (Child Psychiatry Branch) led the research team, which studied children with ADHD over a 15-year time frame. They tracked changes in the cortical thickness of the brain of the participants with the help of magnetic resonance imaging (MRI).

Usually, cortical thickness is at its peak at age 7 or 8. Cortices then become thinner as the child ages. The researchers found, however, that this peak thickness in children with the disorder does not occur until age 10.

Developmental delay

Shaw and the researchers found that the general pattern of development was the same. This does not suggest abnormal development, but developmental delay in ADHD. However, they found that children diagnosed with ADHD hit a developmental milestone that is a little earlier than children who are developing normally: maturation of the motor cortex, the one that controls voluntary muscle movements.

Brain imaging

According to Shaw, this finding (plus the fact that development in the brain’s frontal cortex is delayed in ADHD) helps explain some of the restlessness and fidgeting typical in children with ADHD. While these findings look promising, the researchers say MRI will not be used as a diagnostic tool for ADHD anytime soon. In the future, however, this brain imaging may bring the disorder into clearer focus.

Shaw says, "I think in the future, [brain] imaging will help with tailoring treatments for people with ADHD and for refining our knowledge about how it develops."