The goal of this particular study was to see whether impulsivity could be decreased by raising levels of dopamine. The researchers believe the answer is "Yes".
The study was a double-blinded, placebo controlled trial with 23 adult participants. Each volunteer was given either tolcapone, an FDA approved drug that inhibits dopamine, or a placebo. To measure the effects, researchers then gave each participant a hypothetical choice between receiving a large amount of money later or a small amount of money immediately. They were all measured twice, once with a placebo and once with tolcapone.
The study was published in the July 4th issue of the Journal of Neuroscience.
Results showed that participants were more likely to choose the less impulsive option of a large amount later after taking tolcapone than with the placebo. It was also seen via magnetic resonance imaging that in those taking tolcapone, parts of the frontal cortex associated with decision-making were much more active than among the volunteers taking the placebo.
This study was not designed to figure out why reduced dopamine is associated with impulsivity. Lead author Andrew Kayser, PhD, explains that scientists believe impulsivity is due to an imbalance of dopamine in the brain between the frontal cortex and the striatum. Mostly all addictive drugs directly or indirectly impact the dopamine system.
"They tend to increase dopamine in the striatum, which in turn may reward impulsive behavior. In a very simplistic fashion, the striatum is saying 'go,' and the frontal cortex is saying 'stop.' If you take cocaine, you're increasing the 'go' signal, and the 'stop' signal is not adequate to counteract it."
Tolcapone is a drug commonly used to treat Parkinson's disease, a condition where a deficit of dopamine prevents movement. A follow-up study is being planned by Kayser and team to determine what impact tolcapone might have on drinking behavior. Once researchers can determine that tolcapone is safe to take while consuming alcoholic drinks, they will be able to see what effect it has on the decision making of drinkers.
What is dopamine?Dopamine is a neurotransmitter - a chemical released by nerve cells to facilitate communications with other nerve cells. Dopamine occurs in a wide range of animals, including humans. In humans, it activates five types of dopamine receptors - D1, D2, D3, D4, and D5 - as well as their variants. Dopamine is also a hormone which is released in a region of the brain (hypothalamus) to inhibit prolactin release.
Dopamine plays a key role in the brain in a human's:
- working memory
- voluntary movement
- punishment and reward
- inhibition of prolactin synthesis (which is involved in sexual satisfaction and lactation)