Study tracks brains response to economic exchange in first-in-human discovery

Brain’s response to economic offers

Scientists made the first discovery in humans by watching what happens in the brains of people playing a game where they must decide whether to accept or reject money offers. 

They compared how people reacted when playing against a computer versus playing against another person, only to find that when people played against a person, they were more likely to reject offers, even if it meant they would get less money. 

During the study, the patients were presented with different divisions of $20 by both human participants and computer players. For example, one player might suggest keeping $16, leaving the patient with the remaining $4. If the patient refused this division, neither party received any money.

They also discovered that dopamine, one of the chemicals in the brain, increased when people played against another person, suggesting that it was linked to social interactions. 

On the other hand, serotonin, another brain chemical, stayed the same regardless of who they played against.

The study showed that dopamine reacted to whether the offer was better or worse than before, like keeping track of surprises or changes in the game. Serotonin, however, only seemed to care about the value of the offer right at that moment.

“You can teach people what they should do in these kinds of games — they should accept even small rewards as opposed to no reward at all,” stated Montague, the Virginia Tech Carilion Mountcastle professor with the Fralin Biomedical Research Institute at VTC and the senior author of the study. 

“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.”

Neurotransmitter levels observed in real-time

This study reveals that changes in dopamine and serotonin in a specific part of the brain are linked to how we perceive social situations and decide whether to accept or reject offers.

Scientists employed deep brain stimulation surgery in Parkinson’s disease patients to measure neurotransmitter levels, particularly dopamine and serotonin, in real-time, noted the statement.

Additionally, they used carbon-fiber electrodes to collect data and employed machine-learning tools to analyze and interpret the electrochemical signals recorded by patients. This allowed them to observe the dynamic interactions of dopamine and serotonin in the brain during social interactions and decision-making processes.

First author Dan Bang, associate professor of clinical medicine and Lundbeck Foundation Fellow at Aarhus University in Denmark, and an adjunct associate professor at the Fralin Biomedical Research Institute, expressed:

“We are shining a spotlight on various cognitive processes and finally receiving answers to questions in finer biological detail.”

Bang noted that dopamine levels are higher when people interact with another human instead of a computer and asserted that it was imperative also to measure the serotonin to provide confidence that the overall response to social context is specific to dopamine.

Seth Batten, a senior research associate in Montague’s lab and one of the study’s primary authors, constructed the carbon-fiber electrodes used in patients undergoing Deep Brain Stimulation surgery.

Batted stated that the unique twist with the method is that it allowed the scientists 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.”

However, the challenge was comprehending the recorded electrochemical signals from patients in surgery, which took years to unravel.

“The raw data that we’re collecting from patients isn’t specific to dopamine, serotonin, or norepinephrine – it’s a mixture of those,” stated Ken Kishida, a co-author of the study and an associate professor of translational neuroscience and neurosurgery, at Wake Forest University School of Medicine.  

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

The findings of this study offer promising avenues for understanding human behavior and advancing clinical applications. 

Promising treatment approaches for those with cognition deficit

The revelations could enhance the understanding of the human brain, potentially leading to personalized treatment approaches and targeted therapeutic interventions, improving outcomes for individuals affected by conditions with social cognition deficits. 

Additionally, the study’s methodology contributes to the advancement of neuroscience research by providing a deeper understanding of neurotransmitter dynamics in the human brain, paving the way for further investigations into the role of other neurotransmitters and brain regions in complex behaviors and cognitive processes. 

These findings also hold promise for developing novel pharmacological interventions, personalized medicine strategies, and enhanced diagnostic tools to improve human health and well-being.

Michael Friedlander, executive director of the Fralin Biomedical Research Institute and a neuroscientist, remarked that this work is changing the entire field of neuroscience and our ability to query the human mind and brain — with a technology that was just not even imagined many years ago.

“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,” Friedlander added.

“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.”

The study was published in the journal–Nature Human Behavior earlier today [February 26, 2024].

Study abstract:

Dopamine and serotonin are hypothesized to guide social behaviours. In humans, however, we have not yet been able to study neuromodulator dynamics as social interaction unfolds. Here, we obtained subsecond estimates of dopamine and serotonin from human substantia nigra pars reticulata during the ultimatum game. Participants, who were patients with Parkinson’s disease undergoing awake brain surgery, had to accept or reject monetary offers of varying fairness from human and computer players. They rejected more offers in the human than the computer condition, an effect of social context associated with higher overall levels of dopamine but not serotonin. Regardless of the social context, relative changes in dopamine tracked trial-by-trial changes in offer value—akin to reward prediction errors—whereas serotonin tracked the current offer value. These results show that dopamine and serotonin fluctuations in one of the basal ganglia’s main output structures reflect distinct social context and value signals.