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It is not unusual to have mixed emotions when hearing an ADHD diagnosis. While there may be relief at finally being able to place a name to the problem, there may also be confusion and even guilt. The social stigma attached to ADHD leads many, especially parents, to wonder whether they are somehow responsible through poor parenting or poor nutrition. However, brain research on ADHD is revealing that there may be physical causes for attention disorders.
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Are ADHD Brains Different?
According to the National Institute of Mental Health (NIMH), there is no definite answer to the question, “What causes ADHD?" Scientists have speculated that genes, environmental factors and food additives may all play a role in the development of attention disorders. However, without the evidence of a single ‘smoking gun,’ some argue the disorder is a fabricated condition intended to excuse bad behavior allowed by permissive parents and frazzled teachers.
Although conventional wisdom may place the bulk of the blame with parents, science points to very real differences in the brains of children diagnosed with ADHD. More than a decade ago, the earliest studies found that ADHD brains not only reacted to situations differently, they were also physically different.
A 1998 study published in the Proceedings of the National Academy of Sciences of the United States of America found an abnormal increase in activity in the frontal lobe and a decrease in activity in the underlying striatal areas of the brain in ADHD children. Another 1998 study – this one published in Current Opinion in Neurobiology – discovered the frontal lobes and basal ganglia regions of the brain were 10 percent smaller in children diagnosed with ADHD.
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Brain Research, ADHD and Developmental Delays
More recently, a 2007 study commissioned by NIMH provides some hope to parents who may be concerned about their child’s prospects in the future. The study confirmed there are differences between the brains of ADHD children and those of non-ADHD children. However, the study concluded that brain development of children with ADHD follows a normal developmental pattern, but that growth is roughly three years behind that of children without the disorder.
“Finding a normal pattern of cortex maturation, albeit delayed, in children with ADHD should be reassuring to families and could help to explain why many youth eventually seem to grow out of the disorder," said Philip Shaw, M.D., who led the research team . According to the research, approximately half the cortex sites monitored in ADHD children reached their peak thickness at an average age of 10.5. Meanwhile, other children saw their cortex sites reach that level of thickness by 7.5 years of age.
The cortex is important because it is the region of the brain responsible for controlling thinking, attention and planning. A February 2011 editorial in The American Journal of Psychiatry referenced studies indicating a thinning of the cortex is related to an increase in the severity of ADHD behaviors.
A 2010 study published in Molecular Psychiatry also supports earlier brain research that ADHD is a physical problem instead of an emotional or behavioral one. In this study, PET scans of adults diagnosed with ADHD revealed decreased function in the brain’s dopamine reward pathways. Essentially, those with ADHD don’t get the same boost of feel-good dopamine as those with normal brain functions. Researchers hypothesize the reduced level of dopamine explains why those with ADHD often appear to lack motivation and have difficulty staying on task for extended periods of time.
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The Future of Brain Research on ADHD
Research on ADHD continues through government sources such as NIMH and the Centers for Disease Control and Prevention (CDC) as well as through private entities. For parents of ADHD children, and adults suffering from the disorder, brain research on ADHD is a reason for hope. If researchers are able to pinpoint the cause of ADHD, improved treatments are likely to follow. In addition, with increased understanding of the disorder, it may become easier to identify children likely to suffer from ADHD and begin interventions earlier.
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Vaidya, CJ et al. “Selective effects of methylphenidate in attention deficit hyperactivity disorder: a functional magnetic resonance study." Proceedings of the National Academy of the United States of America. November 24, 2998
Swanson, J et al. "Cognitive neuroscience of attention deficit hyperactivity disorder and hyperkinetic disorder." Current Opinion on Neurobiology. April 8, 1998
"Brain Matures a Few Years Late in ADHD, But Follows Normal Pattern," National Institute of Mental Health. November 12, 2007
Klein, Rachel G. "Thinning of the Cerebral Cortex During Development: A Dimension of ADHD," The American Journal of Psychiatry. February 2011
Volkow, ND et al. "Motivation deficit in ADHD is associated with dysfunction of the dopamine reward pathway." Molecular Psychiatry. September 21, 2010