Biology Behind ADD/ADHD

Several months ago I wrote a column highlighting new research into attention deficit/hyperactivity disorder (ADHD).

That new research looked into the biological basis behind the condition and is beginning to point us toward possible new treatments that don't rely solely on the traditional stimulant medications.

Today I will add to that subject by discussing some even more current discoveries about the neural circuits involved in the brains of those with the condition.

One new study using magnetic resonance imaging (MRI) examined the brains of adolescents while they completed a set task. This study compared the results of those with untreated ADHD to the brains of volunteers without the disorder.

All study volunteers were matched for age and gender to ensure that results showed only differences due to ADHD. Importantly, the ADHD subjects in this study had never used medication so the effects cannot be attributed to previous treatment.

The subjects were asked to do a task that required the withholding of a behavioral response. Specifically, the subjects were asked to push a button with their right or left thumb depending on the direction of a displayed arrow. Periodically, the arrow was followed rapidly by a signal to stop before pushing the required button. The tasks were manipulated so that each subject failed on 50 % of the trials, ensuring that subjects worked at the edge of their own ability to do this.

Medication naive subjects with ADHD showed significantly reduced brain activity in certain brain regions when they failed to perform the stop action required by the task. The extent of these reductions in brain activity correlated with the behavioral scores of ADHD severity.

Another study examined brain activity among siblings with the disorder. Similar to the study mentioned above, results were measured as the study subjects were asked to complete tasks. These were also stop and go tasks where subjects were asked to do something and then stop doing it.

This study found that when two siblings both had ADHD they both showed some inhibitory control impairment compared to volunteers without ADHD. As in the first study, those with ADHD had difficulty stopping the tasks.

Also, in siblings where one had the disorder and one did not, the one without the disorder still showed some impairment - although not as much as the sibling with ADHD. These siblings fell somewhere between the normal controls and the brother or sister with ADHD.

If these findings are replicated in other studies, this could be a useful marker in determining a genetic predisposition to ADHD and perhaps in measuring response to treatment. The tests used to measure response inhibition are relatively simple and could be administered in an office setting.

These results go further in confirming our initial thoughts about the neurological basis of ADHD. As we continue to study brain functioning, it is becoming increasingly clear that ADHD is not simply the result of bad parenting or inconsistency, but is a disorder with a biological and genetic basis.

This is a message which bears repeating because many parents and teachers still think the disorder does not even exist. High profile skeptics like Tom Cruise do a lot of damage to the cause of de-stigmatizing mental illness and encouraging people to seek the help that is available, as imperfect as it is.


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