A recent study has found a significant link between the brain chemical dopamine and our ability to understand and attribute mental states to ourselves and others, a process known as mentalizing. Led by researchers at the University of Birmingham, the study shows that altering dopamine levels in the brain affects these mentalizing abilities. These findings are detailed in the journal PLOS Biology.
The study was motivated by the observation that people with disorders characterized by dopamine dysfunction, such as Parkinson’s disease, Huntington’s disease, Tourette’s syndrome and schizophrenia, often have difficulty mentalizing. This disorder can lead to serious social problems, including social isolation and a reduced quality of life.
Despite these links, dopamine’s role in mentalizing has not been directly tested in healthy individuals. The researchers wanted to fill this gap by examining whether manipulating dopamine levels could causally influence mentalizing abilities.
“Although the mentalizing abilities of people with Parkinson’s disease are not the primary focus of treatment, they do have a significant impact on people with the disease,” said Bianca Schuster, lead author of the study. “So understanding how dopamine imbalances can affect mentalizing processes in the brain could be very important for individuals, as well as for understanding the side effects of medications prescribed for Parkinson’s disease and other disorders.”
The study involved 43 healthy volunteers, with an average age of 26, who took part in two testing sessions. Participants were given either a dopamine-blocking drug called haloperidol or a placebo in a double-blind design, meaning neither the participants nor the researchers knew which drug was being given on which day. Haloperidol works by blocking dopamine receptors, reducing dopamine activity in the brain.
Each participant was given a series of tasks designed to measure mentalizing, emotion recognition, working memory, and motor function. The primary mentalizing task involved interpreting short animations in which geometric shapes interacted in ways that implied various mental states or simple goal-directed actions.
The results are clear: haloperidol reduced participants’ ability to accurately identify mental states depicted in animations. This suggests a direct role for dopamine in mentalizing. Specifically, when participants took haloperidol, their accuracy in identifying mental states was significantly lower than that of participants taking the placebo.
Interestingly, this impairment is not limited to mental animations but also extends to goal-directed actions. This implies that dopamine could influence general cognitive functions such as attention and working memory, which are essential for drawing conclusions about the actions of others.
Additionally, the study found that the similarity between participants’ movements and those seen in the animations affected their mentalizing accuracy. Under placebo, participants who moved in a manner similar to the animations were better able to identify the mental states depicted. However, this effect disappeared under haloperidol, suggesting that dopamine disruption affects the use of motor codes in social cognition.
Although the study provides strong evidence for the causal role of dopamine in mentalizing, several limitations must be considered. First, the tasks used in the study, although well-established, may not fully capture the complexity of real-world social interactions. Future research could explore how dopamine influences mentalizing in more natural contexts, such as face-to-face interactions.
Second, the study did not examine potential interactions between dopamine and other neuromodulators like serotonin, which are also known to affect social cognition. Understanding how these systems work together could provide a more complete picture of the neurochemical basis of mentalizing.
Additionally, the study results are based on a healthy population. It remains to be seen how these findings translate to people with dopamine-related disorders, who may have additional complexities that impact their mentalizing abilities.
“The main conclusion of our work is that in disorders associated with dopamine dysfunction, in addition to producing the primary symptoms associated with these disorders (such as the motor symptoms of Parkinson’s disease), dopamine imbalance also affects individuals’ sociocognitive abilities,” Schuster added. “This work could have implications for how we treat Parkinson’s disease in the future, but also for how we use drugs that affect dopamine action in the brain.”
The study, “Disruption of Dopamine D2/D3 System Function Impairs Human Ability to Understand Others’ Mental States,” was authored by Bianca A. Schuster, Sophie Sowden, Alicia J. Rybicki, Dagmar S. Fraser, Clare Press, Lydia Hickman, Peter Holland, and Jennifer L. Cook.
