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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 ADHD. 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 areas.

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 activities.

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

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