Why do some people seem to grow out of attention deficit hyperactivity disorder (ADHD) as they transition into adulthood, but not others? It is a question that has plagued researchers for some time. Studies have already established that gender, ethnicity, socioeconomic status, and symptom severity are not causal factors. In search of an answer, Dr. Philip Shaw and his colleagues at the National Human Genome Research Institute had previously established that adults with ADHD have a thinner cortical structure than their non-ADHD counterparts. To continue their work, Shaw and his colleagues examined how the cortical structure changes over time and how it affects adult ADHD.

While the team’s earlier study had been cross sectional (examining a group at a point in time), they decided to use a longitudinal study to find out how the cortex develops over time in people with ADHD. The research team recruited 92 children—with a mean age of 11—with ADHD, as well as 184 people without ADHD. Over a period of years, the subjects participated in repeated structural imaging scans and clinical assessments until the group reached a mean age of 24 years.

For 40% of the participants with childhood ADHD, the disorder persisted into adulthood. For the adults with ADHD, the cortex exhibited increased thinning over time; however, the adults whose ADHD was in remission had a cortical thickness that gradually developed towards a normal range. These divergent patterns of brain growth are connected to whether a child with ADHD becomes an adult with ADHD, too. The findings suggest that cortex development is the dividing line for adults with ADHD and adults who recover from ADHD.

More research is required to fully understand the relationship between cortical development and adult ADHD. Dr. Shaw concludes that “understanding how differences in brain development are tied to the course of ADHD is the first step in developing tools to help us predict the outcome of childhood ADHD.”

This research is published in the journal Biological Psychiatry.

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