There may be several different "causes of ADHD" just as there are different types of ADHD. The most recent research models describing "Attention Deficit Hyperactivity Disorder" suggest that several areas of the brain may be affected by ADHD. These include the
Each of these areas of the brain is associated with various functions, or qualities, or abilities.
The most recent models describing what is happening neurologically in the brains of people with Attention Deficit Disorder suggest that several areas of the brain may be affected by the disorder, including the Frontal Lobes, the Inhibitory Mechanisms of the Cortex, the Limbic System, and the Reticular Activating System. Each of these areas or systems of the brain is associated with various functions of the brain.
Neurotransmitters such as Dopamine work to activate brain cells, and regions of the brain. Too much activation, or too little, can cause ADHD symptoms. One-third of the neurotransmitters in the brain are glutamate, and brain research is now looking at the intricate relationships between glutamate, dopamine, and norepinephrine in the functioning of the pre-frontal cortex. Glutamine is the pre-curser of glutamate. Research is revealing that the glutamate network neurotransmissions from the pre-frontal cortex to other areas of the brain are enhanced by dopamine and norepinephrine. Too little dopamine or norepinephrine is a problem, and too much is a problem. And the importance of glutamate in PFC functioning is beginning to come to the forefront in research.
Brain imaging gives new insight into underlying cause of ADHD
Brain imaging gives new insight into underlying cause of ADHD
The frontal lobes help us to pay attention to tasks, focus concentration, make good decisions, plan ahead, learn and remember what we have learned, and behave appropriately for the situation.
The inhibitory mechanisms of the cortex keep us from being hyperactive, from saying things out of turn, and from getting mad at inappropriate times, for examples. They help us to "inhibit" our behaviors.
When the inhibitory mechanisms of the brain aren't working as hard as they ought to, then we can see results of what are sometimes called "dis-inhibition disorders" such as impulsive behaviors, quick temper, poor decision making, hyperactivity, and so on.
Here is a video from YouTube with a simple explanation of ADHD and what causes ADHD.
The limbic system is the base of our emotions and our highly vigilant look-out tower. If over-activated, a person might have wide mood swings, or quick temper outbursts. He might also be "over-aroused," quick to startle, touching everything around him, hyper-vigilant.
A normally functioning limbic system would provide for normal emotional changes, normal levels of energy, normal sleep routines, and normal levels of coping with stress. A dysfunctional limbic system results in problems with those areas.
The frontal lobes help us to pay attention to tasks, focus concentration, make good decisions, plan ahead, learn and remember what we have learned. The frontal lobes also help us to behave appropriately for a given situation. Emotional issues such as anger, frustration, and irritability that come on impulsively in some types of ADHD probably come from the pre-frontal cortex.
The inhibitory mechanisms of the cortex keep us from being hyperactive, from saying things out of turn, and from getting mad at inappropriate times, for examples. These inhibitory mechanisms of the cortex help us to "inhibit" our behaviors. When the inhibitory mechanisms of the brain aren't working as efficiently as they ought , then we can see results of what are sometimes called "dis-inhibition disorders" such as impulsive behaviors, quick temper, poor decision making, hyperactivity, and so on.
Attention Deficit Disorder might affect one, two, or all three of these areas, resulting in several different "styles" or "profiles" of children (and adults) with Attention Deficit Hyperactivity Disorder.
Researchers at Cardiff University have recently published a study in The Lancet claiming that they have found the first direct evidence of a genetic link, or genetic cause for attention-deficit hyperactivity disorder in children, teens, and adults. The research team also reports that this is evidence for ADHD being a neurological disorder, such as autism, and not due to environmental factors such as bad parenting.
However, their research study was immediately countered in Britain by those who insist that ADHD is due primarily to environmental factors, primarily stress and the release of cortisol in young children.
The Cardiff University study examined the DNA from 366 children who had been diagnoses with ADHD, and compared their DNA to over 1,000 children without the disorder. They found significant differences in the DNA of 15% of the ADHD group, specifically in regions of the chromosomes previously identified with autism and schizophrenia, which are other neurological disorders. This compared to finding these same variations in only 7% of the control group.
In her interview with the BBC, professor Anita Thapar said, “Here we have very clear evidence for ADHD being a genetic disorder.” However, she also went on to say that there are several factors that contribute to ADHD, and the severity of the disorder in any individual. “It’s a complicated mix.”
The study also went on to stress that as of yet there has not been one single gene identified as the cause of ADHD, but they hope that in the future some of the biological mysteries of ADHD will be solved, leading to new and better treatments.
The flip-side to this study is that they only found the DNA variations in 15% of the children diagnosed with ADHD – which means that in 85% of the children diagnosed with ADHD in this study there was no genetic variation identified. So what are the implications for those children? Does that mean that there are no genetic factors causing their ADHD?
While we believe from our clinical experiences that genetics play a large part in all of the ADHD in the world, we don’t believe that it necessarily is the cause for your individual child’s ADHD. Through the years we estimated that in about 80% of the cases that we treated (well over 1,000 children, teens, and adults) there was at least one close relative who had either ADHD, Tourettes Syndrome, Obsessive-Compulsive Disorder, or Alcoholism. So we “believe” (just on our experience) that there is a genetic component in most cases.
However, we also know that many children who have been diagnosed with ADHD actually have some other condition that looks like ADHD but is not, such as a head injury, fetal alcohol syndrome, in utero drug exposure, Tourettes Syndrome, depression, environmental allergies, or have been exposed to environmental toxins as children.
We have no doubt that part of this conflict involves the accuracy of a diagnosis of ADHD, or lack thereof. For example, if a child who is inattentive, impulsive, and hyperactive because of fetal alcohol syndrome is incorrectly diagnosed with ADHD, there would be no “genetic” cause, or “genetic link” to be discovered for their “ADHD” disorder.
Also interviewed by the BBC was Child Psychologist Oliver James, who disputed the conclusions of the study’s authors. Dr. James comes from a primarily environmental side of the debate on the causes of ADHD, and he stated on the BBC interview that in his opinion the findings of the study “have been hyped in the most outrageous fashion.” He especially focused on the 85% of the children diagnosed with ADHD for whom no genetic differences could be found. “What is really significant is the role of the environment.” He believes that the primary cause of ADHD in children is “children being very stressed out” which results in high levels of cortisol being released into they bodies. He believes that parents can help their children to learn to deal with the stress, and decrease the cortisol levels and therefore their ADHD symptoms.
Professor Tim Kendall of the National Collaborating Centre for Mental Health is another skeptic of the study’s results. He is of the opinion that there may be a number of factors that cause ADHD, and that putting the cause purely on genetics might lead to children being given incorrect or unnecessary treatments. "…(The cause of ADHD is) a mixture of genetic and environmental factors, and the important thing is that we don't end up thinking this is a biological problem which is only subject to biological treatments like Ritalin."
We would expect that as technology advances the study of the brain, and human genetics, that we would find out a lot more about the biology of ADHD. But with so many being given the diagnosis, rightly or wrongly, we would also expect that until some very great advancements are made in the diagnosis of ADHD at the level of the doctor’s office, or therapist’s office, that this conflict between nature or nurture in ADHD will continue in full force.