ADHD Brains May Just Be Late-Blooming
> 11/13/2007 2:18:18 PM

All parents dread a report from school that their child is disruptive or inattentive. With nearly 10% of the population eligible for a diagnosis of ADHD, parents feel that they must stay vigilant for any warning signs. However, detecting ADHD symptoms leads to the difficult decision of what exactly can and should be done to correct the problem. A recent study from the National Institute of Mental Health  (NIMH) offers not a new treatment, but the hope that the problem is one of slower development rather than permanent abnormality.

In September, we wrote an article to highlight the fact that adult ADHD is often not taken seriously. An extensive WHO survey reported that 3.4% of those over 18 had ADHD, a troubling number but significantly smaller than the percentage of children with ADHD.  Why is it that the majority of children with ADHD grow up to be asymptomatic? One explanation could be that ADHD is a developmental delay that usually catches up to the average in the long-term.

Dr. Philip Shaw from the NIMH has long used brain-imaging techniques to study ADHD, but only recently has the technology become precise enough to measure detailed cortical thickness instead of crude lobal volumes. Last year, Dr. Shaw found that the lowest cortical thicknesses corresponded with the worst clinical outcomes. This led him to suspect that cortical thickness problems can explain ADHD symptoms, and so he scanned more than 40,000 regions in the brains of 446 children. Normally, the brain reaches its peak thickness at 7.5 years, and then undergoes a pruning process that optimizes performance. The scans showed that the ADHD group did not reach their thickness peak in many brain regions for an average of 10.5 years. Particularly interesting is the finding that ADHD brains actually developed faster than normal in the motor cortex, but much slower in areas that regulate behavior, such as the frontal cortex. This imbalance could very well explain much of the agitation and impulsivity found in ADHD children.

Aside from the uneven development rate of the motor cortex, ADHD brains followed the same, if slower, pattern of development as normal brains. At 10.5 years, most ADHD brains have begun the healthy pruning process. This observation dovetails with the fact that most patients are able to discontinue medication when they approach adulthood. It is, however, somewhat inconsistent with a study that we covered last week that used fMRI to show that ADHD brains had impaired activation during listening tasks. This discrepancy requires further study, and may possibly be explained by the fact that while ADHD brains eventually develop a normal structure, there are still some lingering functional differences.

Even if ADHD brains do catch up, that does not mean that adults are never burdened by the problems of ADHD. Researchers consistently report that an ADHD diagnosis in childhood is a risk factor for later problems like drug addiction. This is not necessarily inconsistent with Dr. Shaw's contention that ADHD brain structure eventually normalizes. A delayed and partially uneven development could easily cause lasting psychological damage to a child who struggles for years to overcome a handicap that brings disappointment at home and at school. The positive message then to take away from this study is that while parents should certainly intervene, whether it be with medication, therapy, or social support, to ensure that their children are not scarred by development problems, they should not despair that an ADHD diagnosis is a permanent sentence.

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