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A dance of dopamine and serotonin influences social behavior

In a new study published in Nature Human Behavior on Monday, February 26, scientists have made significant strides in understanding the role of chemical neuromodulators, specifically dopamine and serotonin, in shaping social behavior

This research, which involved Parkinson’s disease patients undergoing awake brain surgery, focused on the brain’s substantia nigra, a key area for motor control and reward processing.

Neurochemical mechanism 

Led by Read Montague, a computational neuroscientist at Virginia Tech, the international team uncovered a neurochemical mechanism underlying the human propensity to make decisions based on social context. This mechanism explains why individuals are more inclined to accept offers from computers than from human counterparts in decision-making games.

“When people know they’re playing a computer, they play perfectly, just like mathematical economists – they do what they should do. But when they’re playing a human being, they cannot help themselves. They are often driven to punish the smaller bid by rejecting it,” Montague explained.

Chemical influence on decision-making 

The study utilized the “ultimatum game” to analyze patients’ responses to offer splits of $20 from both human and computer players. This setup allowed the researchers to observe the dynamic interplay between dopamine and serotonin in real-time, offering new insights into how these chemicals influence decision-making in social contexts.

“Dopamine levels are higher when people interact with another human as opposed to a computer,” said study co-author Dan Bang, an associate professor at Aarhus University in Denmark. “And here it was important that we also measured serotonin to give us confidence that the overall response to social context is specific to dopamine.”

Distinguishing the roles of two neurotransmitters 

“The unique twist with our method is that it allows us to measure more than one neurotransmitter at a time – the impact of that should not be lost. We’ve seen these signaling molecules before, but this is the first time we’ve seen them dance. No one has ever seen this dance of dopamine and serotonin in a social context before,” said study co-author Seth Batten, senior research associate in Montague’s lab.

Ken Kishida, a co-author and associate professor at Wake Forest University School of Medicine, discussed the challenges of interpreting the electrochemical signals, which were addressed through advanced machine-learning tools. These tools helped distinguish the specific roles of dopamine and serotonin from the raw data collected during surgery.

Broader implications 

The implications of this research extend beyond understanding social behavior, offering potential insights into Parkinson’s disease pathology and other brain disorders. Montague expressed hope that their findings could eventually contribute to better clinical outcomes for Parkinson’s patients, given the disease’s impact on dopamine-producing neurons.

Michael Friedlander, executive director of the Fralin Biomedical Research Institute, praised the study’s potential to revolutionize neuroscience and psychiatric treatment. He highlighted the importance of dopamine, serotonin, and other neurotransmitters in psychiatric disorders, suggesting that this research could lead to more precise and effective treatments.

“We have an enormous number of people in the world who suffer from a variety of psychiatric conditions, and, in many cases, the pharmacological solutions do not work very well,” said Friedlander, who is also Virginia Tech’s vice president of health sciences and technology. 

“Dopamine, serotonin, and other neurotransmitters are in some ways intimately involved with those disorders. This effort adds real precision and quantitation to understand those problems. The one thing I think we can be sure of is this work is going to be extremely important in the future for developing treatments.”

Study significance 

This study marks a culmination of over a decade of effort by Montague and his team to measure neurotransmitters in real-time in the human brain, opening new avenues for understanding the neurochemical underpinnings of human cognition and behavior.

“We’ve made active measurements of neurotransmitters multiple times in different brain regions, and we have now reached the point where we’re touching on crucial elements of what makes us human beings,” Montague concluded.

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