‘Drug use makes people make bad decisions’

An excess of the signalling molecule dopamine in the brain can have a negative influence on our ability to make decisions. This occurs during drug use, in the manic phase of bipolar disorder and as a side effect of dopamine replacement therapy in Parkinson’s disease. In these situations, people often display overly optimistic, reckless and self-destructive behaviour. Neurobiologists Jeroen Verharen, Roger Adan and Louk Vanderschuren from the Faculty of Veterinary Medicine and UMC Utrecht describe a mechanism behind this phenomenon in a publication in the influential journal Nature Communications.

Dopamine is a signalling molecule in the brain that plays an important role in emotional and cognitive processes. One of the most important functions of dopamine is its role in our capacity to learn from positive and negative experiences.
Verharen: “When something nice happens, like when you’re being served a tasty dessert, your brain releases dopamine. That teaches you to repeat the actions that preceded that pleasant experience. But if your behaviour leads to something unpleasant, such as hurting yourself, then the release of dopamine is inhibited. You learn that the action in question is not something to be repeated. Until recently, however, we did not know exactly where dopamine mediates these learning processes in the brain.”

Contribute to improved treatments for addiction, bipolar disorder and Parkinson’s disease.

Studies in rats

By using modern neuroscience techniques, the researchers stimulated different groups of dopamine cells in rats, and measured the activity of these cells. They then assessed the behaviour of rats when performing tasks in which they had to earn as much sugar as possible.

Vanderschuren: “One remarkable finding was that when we activated the cells that release dopamine in a specific structure of the brain, called the ‘nucleus accumbens’, the rats were not able to adapt their behaviour to changes in the task. Interestingly, this learning problem only related to learning from negative experiences, such as pain or not receiving a reward, but not to positive experiences. As a result, the rats made worse decisions in the tasks we gave them.”

Bad decisions

The researchers concluded that when humans and rats no longer learn from negative feedback, they make bad decisions that seem to be overly optimistic, which can have extremely unpleasant consequences. This is observed during drug use, during the manic phase of bipolar disorder and as a side effect of dopamine replacement therapy in Parkinson’s disease. In their publication in Nature Communications, the researchers describe the brain mechanism of this reduced decision-making ability . This knowledge may contribute to the development of improved treatments for addiction, bipolar disorder and Parkinson’s disease.