ADHD Dopamine Theory
A study by US researchers at the Brookhaven National Laboratory,
published in Journal of the American Medical Association, in November
2009 found levels of dopamine correlated with ADHD (Attention Deficit
Hyperactivity Disorder). This is in support of the dopamine theory of
They found ADHD patients lack dopamine, which normally allows us to
experience a sense of reward and motivation. Using a PET scan (positron
emission tomography), the researchers focused on the chemical dopamine, a
key regulator of mood, as the cause of ADHD.
In particular they measured levels of dopamine receptors and dopamine
transporters, which dopamine needs to function effectively. ADHD
patients had lower levels of both dopamine receptors and transporters
two areas of the brain’s limbic system, responsible for the emotions,
and sensations such as motivation and reward. Patients with more
pronounced ADHD symptoms had the lowest levels of the proteins in these
This study shows that ADHD is more than just the attention systems of the brain, but also in the motivation and emotion centers.
The Dopamine System
The dopamine system, and in particular the dopamine D2 receptor, have
been implicated in reward mechanisms of the brain. When dopamine is
released into the synapse, it stimulates a number a dopamine receptors
(D1 to D5, but mainly the D2) and a reward system is started. Dopamine
is commonly associated with the pleasure system of the brain, giving us
our feelings of enjoyment and motivates us to perform certain
This theory is confirmed by the use of drugs such as cocaine and
amphetamines, which lead to an increase of dopamine in the reward
pathway of the brain. Amphetamines raise dopamine levels by forcing
dopamine molecules out of the vesicles where dopamine is stored, and
into the synaptic gap. Making the dopamine transporters to work in
reverse does this.
Under normal conditions dopamine works to maintain our normal drives
and reduces stress. A large proportion of people with ADHD also suffer
from anxiety and stress. Anxiety and stress also cause ADHD behavior, so
increasing the dopamine effect, as with amphetamine ADHD stimulant
drugs, is meant to serve three purposes: stimulating the brain,
decreasing stress and giving a feeling of wellbeing.
Unfortunately not all people get a feeling of wellbeing, suffering
from the medications’ side effects. There other therapies can get the
same result. Training the working memory and excercises, which use the
brain, especially co-ordination excercises, raises dopamine levels in
the brain. Then we utilize the natural dopamine our bodies produce.
The dopamine theory is an integral part of other ADHD theories, such
as the Executive Dysfunction theory of ADHD, the ADHD gene theory and
the Dynamic Developmental Theory of ADHD.
While the dopamine theory is supported by genetic and stimulant
medication studies, other studies show that the stress hormone,
norepinephrine affects parts of the brain where attention and response
actions are controlled.
The pharmaceutical company Shire release a new drug in November 2009,
based on the norepinephrine system, called INTUNIV. This is a blood
pressure medication, Guanfacine, which according to Shire, is thought to
work directly by binding selectively to alpha-2A adrenergic receptors
located in the prefrontal cortex an area of the brain that has been
linked to ADHD. This is a different route than the amphetamines.
So although dopamine does seem to play a role in ADHD, it is not the whole story.