Changes in dopamine levels in the brain affect thinking ability

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Mentalizing refers to the act of attributing and understanding the mental states (thoughts, emotions, intentions, etc.) of others and oneself. Researchers at the University of Birmingham have demonstrated that changes in dopamine levels in a person's brain affect their mentalizing ability. The results were announced today. in PLOS Biology.

Dopamine is a neurotransmitter, a chemical messenger in the brain, well known for its role in pleasure, motivation, and learning. Moreover, researchers know that low levels of dopamine in areas of the brain that control movement are a major cause of symptoms in diseases such as Parkinson's.

At the same time, social-cognitive problems, such as difficulties with emotion recognition and mentalizing, have also been associated with Parkinson's disease, although no clear link has been shown between these problems and dopamine imbalance.

Indeed, difficulties with Theory of Mind are commonly associated with psychosocial changes such as isolation and social withdrawal, which are common features of dopamine-related disorders.

Lead author Dr Bianca Schuster, from the University of Birmingham's School of Psychology, said: “Though thinking abilities in people with Parkinson's may not be the main focus of treatment, it still has a major impact on those with the disease. A better understanding of how dopamine imbalances affect thought processes in the brain is hugely important for patients, as is a better understanding of the secondary effects of medications prescribed for Parkinson's and other conditions.”

In this study, researchers conducted a double-blind, placebo-controlled experiment on a group of 33 healthy volunteers. Participants were given haloperidol, a drug that blocks dopamine receptors in the brain. The volunteers took part in the same experiment over two days, receiving the drug on the first day and a placebo on the other day.

Participants were asked to complete an animation task in which they were shown short videos of triangles “interacting” with each other. They were asked to interpret the videos by selecting the label they thought best described the unfolding scene. In a separate experiment, the researchers also investigated participants' ability to judge emotions expressed in full-body point-light displays (videos of actors in which only their joint movements were visible; published here: Schuster et al., 2021, Journal of Neuroscience).

The researchers found that after taking haloperidol, participants were significantly less able to accurately associate the animated interactions with mental states, which was linked to the drug's effect on emotion recognition.

“A major implication of our study is that in diseases involving dopamine dysfunction, in addition to causing the core symptoms associated with these diseases (such as the motor symptoms of Parkinson's disease), dopamine imbalance also impacts an individual's social-cognitive abilities,” Dr. Schuster added.

“This research could have an impact not only on how we treat Parkinson's disease in the future, but also on how we use any medication that affects how dopamine works in the brain.”

reference: Schuster BA, Sowden S, Rybicki AJ, et al. “Impaired dopamine D2/D3 system function reduces humans' ability to understand the mental states of others.” PLOS Biol2024;22(6):e3002652. doi: 10.1371/journal.pbio.3002652

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