How Dopamine and Serotonin Influence Social Behavior

An international team deciphers the complex dance of dopamine and serotonin in the human brain, shedding light on social decisions.

In a study published in nature human behaviorIn , scientists are delving into the world of chemical neuromodulators in the human brain, particularly dopamine and serotonin, to uncover their role in social behavior.

The study was conducted in Parkinson’s disease patients undergoing brain surgery while awake and focused on the brain’s substantia nigra, a key region associated with motor control and reward processing.

The international team, led by Virginia Tech computational neuroscientist Reed Montague, has identified humans’ well-known tendency to make decisions based on social context: we reject identical offers from human players. However, they uncovered a previously unknown neurochemical mechanism that makes people more likely to accept offers from computers.

Scientists discuss their research to discover insights into the complexities of the brain and mind. Recently, researchers included (from left) Dan Vann of Aarhus University in Denmark, Ken Kishida of Wake Forest University School of Medicine, and Michael Friedlander, executive director of the Fralin Institute for Biomedical Research. Peter Dayan, Managing Director of the Max Planck Institute for Biocybernetics in Tübingen, Germany, and Reid Montague, Director of the Human Neuroscience Research Center at the Fralin Institute for Biomedical Research, reflect on decades of achievements. I did.Credit: Clayton Metz/Virginia Tech

Insights from the Ultimatum Game

In this study, four patients undergoing deep brain stimulation surgery for Parkinson’s disease played a take-it-or-leave-it scenario in which they had to accept or reject various $20 splits from both human and computer players. I was immersed in the ultimatum game. For example, suppose a player offers to keep her $16 and the patient takes his remaining $4. If the patient refuses to split, neither receives anything.

“You can teach people what to do in these kinds of games, and they should receive even a small reward, rather than no reward at all,” said the Virginia Tech professor at VTC’s Fralin Institute for Biomedical Research. Mr Montague, Carillion Mountcastle Professor and Senior Professor, said: Author of the study. “When people know they’re playing a computer, they play perfectly and do what they’re supposed to do, just like mathematical economists. But when they play a human, they play themselves They are often tempted to punish by rejecting smaller bids.”

Reid Montague, who led the research team that documented the chemical underpinnings of social decision-making, talks about tapping into the key elements that make us human.Credit: Clayton Metz/Virginia Tech

dopamine serotonin dance

The idea that people make decisions based on social context is not new in neural economic games. But now researchers have shown for the first time that the effects of social context can result from a dynamic interaction between dopamine and serotonin.

When people make decisions, dopamine seems to be a continuous tracking system, closely following and reacting to whether the current offer is better or worse than previous offers. Serotonin, on the other hand, seems to focus only on the current value of the particular offer at hand, suggesting a more case-by-case evaluation.

This fast dance is performed against a slow background. So when people play other people, when fairness is valued, dopamine is higher overall. Together, these signals contribute to our brain’s overall valuation during social interactions.

“We are shining a spotlight on different cognitive processes and ultimately getting answers to questions about finer biological details,” said co-first author of the study, from Aarhus University in Denmark. said Dan Bunn, associate professor of clinical medicine and Lundbeck Foundation Fellow and adjunct associate professor. At Fralin Biomedical Research Institute.

“Dopamine levels are higher when humans interact with other humans, as opposed to computers,” Bang says. “And here it was important to also measure serotonin to gain confidence that the overall response to social situations was specific to dopamine.”

Seth Batten, a researcher at the Fralin Biomedical Research Institute, created the electrodes used to record the dance of dopamine and serotonin.Credit: Clayton Metz/Virginia Tech

Seth Batten, a senior scientist in Montague’s lab and the study’s lead author, created carbon fiber electrodes that are implanted in patients undergoing deep brain stimulation surgery and is being used at the Mount Sinai Health System in New York. assisted with data collection.

“What’s unique about our method is that we can measure multiple neurotransmitters at once; their impact should not be lost,” Batten says. “We’ve seen these signaling molecules before, but this is the first time we’ve seen them dance. Until now, no one had seen this dance of dopamine and serotonin in a social context. Never.”

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

“The raw data we are collecting from patients is not specific to dopamine, serotonin, or norepinephrine, but a mixture of them,” said Kishida, study co-author and associate professor of translational neuroscience. Ken said. Department of Neurosurgery, Wake Forest University School of Medicine. “We’re basically using machine learning-type tools to isolate the content of the raw data, understand the signatures, and decipher what’s going on with dopamine and serotonin.”

inside natural human behavior researchresearchers showed how the rise and fall of dopamine and serotonin are intertwined with human cognition and behavior.

“The world of model organisms has a candy store full of fancy techniques for asking biological questions, but it’s hard to ask questions about what makes you you.” said Montague, who is also director of the Human Neuroscience Research Center. and the Human Neuroimaging Laboratory at the Fralin Biomedical Research Institute.

Initiatives against Parkinson’s disease

“At some point, after we evaluate enough people, we will be able to address the pathology of Parkinson’s disease that has given us this opportunity,” said Montague, who is also a professor in the Virginia Tech School of Science.

In Parkinson’s disease, a significant loss of dopaminergic neurons in the brainstem is a key feature and usually coincides with the onset of symptoms.

This loss affects the striatum, an area of ​​the brain that is strongly influenced by dopamine. As dopamine decreases, serotonin terminals begin to bud, revealing complex interactions, as observed in rodent models.

“There is already preclinical evidence that a decrease in the dopamine system tells the serotonin system ‘you have to do something,’ but we have never been able to observe that dynamic,” Montague said. Told. “What we are doing now is a first step, but once we have a few hundred patients we will be able to relate this to the symptomology and make some clinical statements about the pathology of Parkinson’s disease. It is expected.”

In this regard, researchers said a window is opening to learn about a wide range of brain disorders.

“The human brain is like a black box,” says Kishida. “We have developed another way to look inside and understand how these systems work and how they are affected by different clinical conditions.”

“This research explores the entire field of neuroscience and the human mind and brain,” said Michael Friedlander, executive director of the Fralin Institute for Biomedical Research and a neuroscientist who was not involved in the study. We are changing capabilities that were unimaginable just a few years ago.”

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

“There are a huge number of people in the world who suffer from a variety of mental illnesses, and pharmacological solutions are often ineffective,” said Friedlander, who is also vice president for health sciences at Virginia Tech. said. technology. “Dopamine, serotonin and other neurotransmitters are in some ways intimately connected to these diseases. This work adds real precision and quantification to understanding these issues. I One thing we can be sure of is that this research will be of great importance in developing treatments in the future.”

Over 10 years in development

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

In unprecedented observations of the human brain, scientists neuron In 2020, researchers revealed that dopamine and serotonin work at subsecond speeds to shape how people perceive the world and take actions based on that perception. .

Recently, in a study published in the journal October current biologyResearchers used a method to record chemical changes in awake humans to gain insight into the brain’s noradrenergic system, a long-standing target of drugs to treat mental illnesses.

And in December’s diary scientific progress, The researchers found that rapid changes in dopamine levels reflect specific calculations about how humans learn from rewards and punishments.

“We’ve made multiple active measurements of neurotransmitters in different regions of the brain, and now we’re at the point where we’re touching on the key elements that make us human,” Montagu said. Told.

Reference: “Dopamine and serotonin in the human substantia nigra track social context and value signals during economic exchanges” Seth R. Batten, Dan Bang, Brian H. Kopell, Arianna N. Davis, Matthew Heflin, Qixiu Fu, Ofer Perl, Kimia Ziafat, Alice Hashemi, Ignacio Saez, Leonardo S. Barboza, Thomas Toomey, Terry Lorenz, Jason P. White, Peter Dayan, Alexander W. Charney, Martin Figge, Helen S. Mayburg, Kenneth T. Kishida, Xiaoshi Gu, P. Reed Montague, February 26, 2024, nature human behavior.
DOI: 10.1038/s41562-024-01831-w