Research over the last 20 years has shown a strong biological basis for the disorder but no one knows for sure what causes it. What is known is that it is more common in some families than others. There appear to be reductions in neurological activity for those with the disorder, primarily the frontal areas of the brain, which are responsible for the control of attention. There may also be some differences in some of the neurochemicals with people with ADHD.
The human brain is the most complex structure in the universe. Because that is true it is also true that no one knows what causes ADHD. Theories abound. The science is growing and we may one day discover the gene or the biological cause for the disorder. That day has not arrived at present. Finding the explanation involving specific genes, the role of a variety of neurotransmitters, differences in brain function, relating that to behaviors and understanding why specific medicines impact that function is a complex task.
The basic theories at present are as follows:
1) ADHD is a primary problem related to the ability to self regulate. The ADHD client has problems controlling attention, managing impulses, mood and activity level. What this results in is that the person with ADHD can’t think, process information, restrain their impulses or organize at a level that would be expected given their age and level of intelligence. ADHD children often appear more immature than other children their own age.
2) ADHD is a limited ability to have appropriate executive functioning. Basically the ability to control impulses, limit distractions, delay gratification, make decisions and solve problems. It is likely that those with ADHD have limited working memory. The basic function of working memory is that it allows a person to see the past, flip it forward to be able to predict future events based on similar experiences. Limited working memory often causes a repeat of past negative behaviors because the person can’t remember the negative results of the last time it happened.
3) Genetic causes. ADHD does tend to run in families. Our first question after determining if a child has ADHD is to ask “which parent” has the disorder. In one study of identical twins, if one had the disorder, 81 % of those identical twins also had the disorder. Only 29% of paternal twins share the disorder. First degree relatives have a five times greater chance than if no close relatives have symptoms. Current studies are focusing on several specific genes as the culprits.
4) Anatomical differences. The research here is not clear and there is a lot of conflicting data at present. Current theories is that there may be differences in both the corpus callosum and an asymmetry in the basal ganglia of ADHD clients.
5) Functional. Several research studies report that it may be caused by differences in the say the brain functions. Daniel Amen has reported significant differences in blood flow patters in the brains of ADHD children and adults. Dr. Joel Lubar has documented differences in electrical activity with higher rates of slow wave activity. A New York University study identified 11 different patterns of brain wave activity using a QEEG scan.
6) Chemical causes. The brain has an amazing variety of neurotransmitters in the brain that are responsible for how it functions. Two key chemicals are norepinephrine and dopamine. The current theory is that there may be an imbalance of those two chemicals, primarily in the area of the prefrontal cortex.
Considering all the evidence, we can be confident in saying that ADHD is a biologically based brain disorder.