Dopamine

Kowal conducted experiments on 40 regular users of cannabis. The control group of 20 non-users were given a placebo. Kowal studied the direct and chronic effects of marijuana on dopamine-related functions, such as creative thinking and the ability to recognize one’s own mistakes. The brain chemical dopamine is important for the proper working of the brain and also plays a role in learning performance.

Less good at brainstorming

Kowal’s research showed that cannabis users were less able to brainstorm, a mental process that is crucial for creative performance:

There is a widespread belief among users that these drugs enhance creativity. This experiment disproves that belief.

Poor at recognizing mistakes

Kowal also demonstrated that for chronic users the brain processes involved in monitoring mistakes also work less effectively. A high dose of marijuana seems to influence both the unconscious processing of mistakes and also the later and more conscious stages of error processing.

It is important that we gather more knowledge about the effects of cannabis on a person’s ability to detect mistakes. This can help with putting together a treatment program for drug addiction.

Lower dopamine production

The research also indicated clear long-term effects: cannabis disrupts the activity of dopamine in the brain. With chronic users a significant reduction was seen in the frequency of spontaneous eye blinking, an indication of a reduction in dopamine production.

More Research Required

The conclusions from other scientific research is that regular marijuana use does not necessarily have extremely negative effects for the take-up of dopamine. It may well be that the age at which cannabis is first used is a crucial factor, Kowal suggests. The type of cannabis and the way neurobiological processes interact with one another can also result in individual difference.

More research is needed on the effects of cannabis and on the individual consequences it can have on mental functions.

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Anissa Abi-Dargham, MD, said, “In light of the more widespread acceptance and use of marijuana, especially by young people, they believe it is important to look more closely at the potentially addictive effects of cannabis on key regions of the brain. She is a professor of psychiatry (in radiology) at Columbia University Medical Center (CUMC) and a lead author of the paper.

The study included 11 adults between the ages of 21 and 40 who were severely dependent on cannabis and 12 matched healthy controls. On average, the cannabis use group started using as early as age 16, became dependent on cannabis by age 20, and have been dependent for the past 7 years. In the month prior to the study, nearly all users in this study smoke marijuana on a daily basis.

Using positron emission tomography (PET) to track a radiolabelled molecule that binds to dopamine receptors in the brain, the scientists measured dopamine release in the striatum and its subregions, as well as in several brain regions outside the striatum, including the thalamus, midbrain, and globus pallidus. The cannabis users in this study stayed in the hospital for a week of abstinence to ensure that the PET scans were not measuring the acute effects of the drug. Participants were scanned before and after being given oral amphetamine to elicit dopamine release. The change in the binding of the raiotracer was taken in percentages as an indicator of capacity for dopamine release.

Compared to the control group, the cannabis users had significantly lower dopamine release in the striatum, including subregions involved in associative and sensorimotor learning, and in the globus pallidus.

The scientists also explored the relationship between dopamine release in a key area of the striatum and cognitive performance on learning and working memory tasks. Although there was no difference between groups in task performance, lower dopamine release in all participants was associated with worse performance on both tasks.

“We don’t know whether decreases dopamine was a preexisting condition or the result of heavy cannabis use,” said Dr. Abi-Dargham. “But the bottom line is that long-term, heavy cannabis use may impair the dopaminergic system, which could have a variety of negative effects on learning and behavior.”

Jeffrey Lieberman, MD, Chair of Psychiatry at CUMC and past president of the American Psychiatric Association, noted that “these findings add to the growing body of research demonstrating the potentially adverse effects of cannabis, particularly in youth, at the same time that government policies and laws are increasing access and use.”

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