Serotonin and dopamine play a major role in social decisions

summary: A new study has revealed the complex role of dopamine and serotonin in social decision-making, using Parkinson's disease patients as subjects.

Through the “ultimatum game,” the team discovered that people's choices differ dramatically when interacting with humans versus computers, influenced by the dynamic interplay between these neural modulators. This neurochemical dance, observed through innovative electrode technology, highlights how dopamine and serotonin levels fluctuate during social interactions, providing new insights into human behavior and potential implications for treating various brain disorders.

The research not only sheds light on basic decision-making processes, but also opens doors to understanding and treating psychological conditions more accurately.

Key facts:

1. The study reveals a new mechanism explaining how dopamine and serotonin interact to influence decision-making in social contexts.
2. Innovative carbon fiber electrodes allowed the simultaneous measurement of these neuromodulators in the human brain, providing a rare glimpse into the dynamic relationship between them.
3. This research could have profound implications for understanding and treating psychiatric disorders, because it provides a deeper understanding of the neurochemical basis of social behavior.

source: Virginia Tech University

In study a day The nature of human behaviorScientists delve into the world of chemical neuromodulators in the human brain, specifically dopamine and serotonin, to uncover their roles in social behavior.

The research, conducted on Parkinson's patients who underwent awake brain surgery, focused on the brain's substantia nigra, an important region associated with motor control and reward processing.

The international team led by Reed Montagu, a computational neuroscientist at Virginia Tech, has uncovered a previously unknown neurochemical mechanism for a known human tendency to make decisions based on social context – people are more likely to accept offers from computers while rejecting identical offers from human players.

Insight into the ultimatum game

In this study, four patients receiving deep brain stimulation surgery to treat Parkinson's disease were immersed in a take-it-or-leave-it ultimatum game, a scenario in which they had to accept or reject varying splits of $20 from both human and computer players. For example, one player might suggest keeping $16, while the patient gets the remaining $4. If the patient refuses to divide, neither of them gets anything.

“You can teach people what they should do in these types of games — that they should accept even small rewards rather than getting no reward at all,” said Montagu, the Virginia Tech Carilion Mountcastle Professor at the Fralin Biomedical Research Institute at VTC. Study author.

“When people know they are playing with a computer, they play perfectly, just like mathematical economists – they do what they should do. But when they play a human, they can't help themselves. They are often driven to punish the smaller offer by rejecting it.”

The dance of dopamine and serotonin

The idea that people make decisions based on social context is not a new idea in neuroeconomic games. But now, for the first time, researchers have shown that the effect of social context may stem from the dynamic interactions of dopamine and serotonin.

When people make decisions, dopamine seems to closely track and react to whether the current offer is better or worse than the previous one, as if it were a continuous tracking system. Meanwhile, serotonin seems to focus only on the current value of the specific offer at hand, suggesting a more case-by-case evaluation.

This fast dancing occurs against a slower background, with dopamine generally being higher when people play the role of other human beings — in other words, when justice comes into play. Together, these signals contribute to our brain's overall assessment of our value during social interactions.

“We shed light on different cognitive processes and finally receive answers to questions in finer biological detail,” the study said. At the Fralin Institute for Biomedical Research.

“Dopamine levels are higher when people interact with another human being rather than a computer,” Pang said. “Here it was also important to measure serotonin to give us confidence that the overall response to the social context is dopamine-specific.”

Seth Batten, a senior research associate in the Montagu lab and first author of the study, built carbon fiber electrodes that were implanted in patients receiving deep brain stimulation surgery, and helped collect data at Mount Sinai Health System in New York.

“The unique development of our method is that it allows us to measure more than one neurotransmitter at a time — and the impact of that should not be lost,” Patten said. “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.”

Discovering the meaning of electrochemical signals recorded from patients during surgery has been a major challenge that has taken years to solve.

“The preliminary data we are collecting from patients is not specific to dopamine, serotonin, or norepinephrine — it is a combination of those,” said Ken Kishida, study co-author and associate professor of translational neuroscience. Neurosurgery, at Wake Forest University School of Medicine.

“We're basically using machine learning tools to separate what's in the raw data, understand the signature, and decode what's going on with dopamine and serotonin.”

In the Study of the nature of human behaviorResearchers have shown how the rise and fall of dopamine and serotonin are intertwined with human cognition and behavior.

“In the world of model organisms, there's a candy store full of fancy techniques for asking biological questions, but it's harder to ask questions about what makes you, you,” said Montagu, who is also director of the Center for Human Neuroscience Research. and the Human Neuroimaging Laboratory of the Fralin Biomedical Research Institute.

Treatment of Parkinson's disease

“At some point, after we evaluate enough people, we will be able to address the pathology of Parkinson's that gave us this window of opportunity,” said Montagu, who is also a professor in Virginia Tech's College of Science.

In Parkinson's disease, significant loss of dopamine-producing neurons in the brainstem is a major feature that usually coincides with the onset of symptoms.

This loss affects the striatum, an area of ​​the brain strongly affected by dopamine. As dopamine decreases, serotonin terminals begin to grow, revealing a complex interplay, as observed in rodent models.

“There's already preclinical evidence that depletion of the dopamine system tells the serotonin system: Hey, we've got to do something.” “But we never got to see the dynamics,” Montagu said.

“What we are doing now is the first step, but we hope that once we reach hundreds of patients, we will be able to correlate this with symptoms and make some clinical data about Parkinson's disease.”

In this regard, the researchers said that there is an open window to identify a wide range of brain disorders.

“The human mind is like a black box,” Kishida said. “We have developed another way to look inward and understand how these systems work and how they are affected by different clinical situations.”

“This work changes the entire field of neuroscience and our ability to inquire about the human mind and brain — using the technology that has been developed,” said Michael Friedlander, executive director of the Fralin Biomedical Research Institute and a neuroscientist who was not involved in the study. This would not have been even imaginable many years ago.

Psychiatry is an example of a medical field that could benefit from this approach, he said.

“We have an enormous number of people in the world with a variety of psychiatric conditions, and in many cases, drug solutions don't work well,” said Friedlander, who also serves as vice chair of the Department of Health Sciences and Psychiatry at Virginia Tech. technology.

“Dopamine, serotonin and other neurotransmitters are closely related to these disorders in some ways. This effort adds real precision and quantity to understanding those issues. The one thing I think we can be sure of is that this work is going to be very important in the future for developing treatments.”

More than a decade in the making

Efforts to measure real-time neurotransmitters in the human brain began more than 12 years ago when Montague assembled a team of experts who “think big about thinking.”

In the first-ever observations of the human brain, scientists published in… nervous cells In 2020, researchers revealed that dopamine and serotonin work at sub-second speeds to shape how people perceive the world and take action based on their perceptions.

More recently, in a study published in October in the journal Current biologyThe researchers used their method of recording chemical changes in awake humans to gain insight into the brain's noradrenaline system, which has long been a target of drugs to treat psychiatric disorders.

And in December in the magazine Advancement of science, The team revealed that the rapid changes in dopamine levels reflect specific calculations related to how humans learn from rewards and punishments.

“We have performed active measurements of neurotransmitters many times in different areas of the brain, and we have now reached the point where we are addressing the critical elements that make us human,” Montagu said.

About this neuroscience research news

author: John Pasteur
source: Virginia Tech University
communication: John Pastor – Virginia Tech
picture: Image credited to Neuroscience News

Original search: Open access.
“Dopamine and serotonin in the human substantia nigra track social context and value signals during economic exchange“By Reed Montague et al. The nature of human behavior

a summary

Dopamine and serotonin in the human substantia nigra track social context and value signals during economic exchange

It is assumed that dopamine and serotonin guide social behaviors. However, in humans, we have not yet been able to study the dynamics of neuromodulation with the development of social interaction. Here, we obtained sub-second estimates of dopamine and serotonin from human subject nigra pars reticulata during the ultimatum game.

The participants, who were patients with Parkinson's disease and undergoing awake brain surgery, had to accept or reject financial offers of varying degrees from human and computer players. They rejected offers more in the human condition than in the computer condition, an effect of social context associated with higher levels of dopamine but not serotonin.

Regardless of social context, relative changes in dopamine tracked changes in trial-by-trial display value—similar to reward prediction errors—while serotonin tracked current display value.

These results show that dopamine and serotonin fluctuations in one of the major production structures of the basal ganglia reflect distinct social context and value signals.