The search for a biological basis is the heart of the debate on whether or not ADD is a legitimate diagnosis. The problem has been that until recently, results have been inconclusive and in some cases contradictory.
Research by Zametkin, who pioneered the use of PET imaging in ADD patients, seems to indicate that the ADD brain has a strong right brain predominance.
Brain scan images produced by positron emission tomography (PET) (see image below) show differences between the brain of an adult with Attention deficit Hyperactivity Disorder (right) and an adult who is not ADD (left).
These scans showed promise in the search for a biological marker for ADHD. However, Zametkin reported in another study on Brain metabolism in teenagers with affention-deficit hyperactivity disorder that similar scans did not statistically differentiate between normal adolescents and those with ADHD. Zametkin was unable to replicate the previous results.
More research into the biology of ADD, using magnetic resonance imaging (MRI), scans which revealed left-sided brain differences in ADHD and other abnormalities in the ADD brain.
A paper presented at the NIH ADHD Conference titled “Biological Bases of Attention Deficit Hyperactivity Disorder. Neuroanatomy, Genetics, and Pathophysiology” (presented by James Swanson, Ph.D., and F. Xavier Castellanos, M.D.) cites reduced size in specific neuroanatomical regions of the frontal lobes and basal ganglia in the brains of ADHD subjects. They conclude their presentation by saying that “Overall, the recent investigations in these areas have provided considerable evidence of multiple biological bases of ADHD/HKD.”
Even more recently, in a paper made public on November 23, 1998, researchers at Stanford using Functional MRJ (fMRJ) on ADD children reported to have found a biological marker for ADHD specifically in the response of the brain to being medicated with Ritalin, With ADD brains responding differently to Ritalin medication than the brains of Non-ADD control groups.
Finally, genetic evidence of the disorder indicates a strong possibility of ADD being a hereditary condition.