Exploring dopamine, serotonin and social behavior during deep brain stimulation in Parkinson's patients.

The neurotransmitters dopamine and serotonin in the brain have a significant influence on our social behavior, as new research shows. For the first time, their interaction has been directly observed thanks to the participation of four Parkinson's patients in an experiment during brain surgery. Dthe resultate reveal a neurochemical mechanism that explains our tendency to make decisions in a social context. Additionally, in the long term, this technique could help to better understand changes in brain chemistry associated with Parkinson's disease.

A classic experiment in behavioral psychology served as the basis: A person is asked to divide 20 dollars between themselves and another person. If the other person accepts the proposed offer, both will receive the agreed amount. If the other person refuses, both of them come away empty-handed. Economically, it would be advantageous for the second person to accept any offer, even if it is just one dollar. However, most people show a tendency to reject unfair offers and thus punish the other person for what they perceive as an outrageous offer. But what exactly happens in the brain during such decision-making processes?

To answer this question, a team led by Seth Batten from Virginia Tech turned to an unusual method. Four Parkinson's patients undergoing brain surgery while awake were asked to take part in the ultimatum game. The operation was carried out to implant electrodes for deep brain stimulation and to relieve the symptoms of the disease. The researchers also inserted an electrode into the open brain to measure the ratio of the brain messengers dopamine and serotonin while the subjects made decisions in the ultimatum game.

The measurements of brain messengers revealed a biological mechanism that explains why people incorporate social contexts into their decisions. Dopamine levels respond to the fairness of the offer, while serotonin levels respond to the absolute value of the offer. Interestingly, dopamine levels are higher when people interact with other people than with a computer. These findings could not only explain behavior in the ultimatum game, but also contribute to research into Parkinson's disease.

One of the fundamental features of Parkinson's disease is the loss of dopamine-producing neurons in the brainstem. Although the current study did not involve the brainstem, further research could provide a better understanding of the altered interactions of dopamine and serotonin in Parkinson's disease. The results are a first step towards linking the dynamics of these neurotransmitters with the symptoms of the disease and possibly enable clinical statements on Parkinson's pathology.

Summary

Source: Seth Batten (Virginia Tech) et al., Nature Human Behavior, doi: 10.1038/s41562-024-01831-w

Jürgen Zender, Munich in March 2024