How do brain chemicals shape social choices?

How brain chemicals control our social behaviour has been revealed by a simple game...

Working with patients affected by Parkinson’s disease, who were undergoing brain surgery while they were awake, researchers at Mount Sinai in New York used electrodes to probe a part of the brain called the substantia nigra. This area is involved in initiating movements, and reward sensations.

The subjects played a simple "ultimatum" game. “It’s a social exchange game and it ought to be called take it or leave it,” explains Virginia Tech's Read Montague, who led the study.

Players had to decide whether to accept, or reject, offers of money from either another human participant or a computer. If they reject the offer, both players lose money.

“The interesting thing is, if human beings think that they are playing a human, they will reject non-zero offers. If they think they are playing a computer, then they play almost perfectly, meaning they dont reject any non-zero offers,” explains Montague.

Non-zero offers tend to be low valued offers which should not be rejected from an economical perspective. However, when playing against humans, players reject these non-zero offers to punish the opponent for an unfair offer, underlining that people prefer equal outcomes over personal gain. 

Using electrochemistry, a technique that can identify substances based on electrical currents they produce when a voltage is applied to them, the team identified that the levels of the neurochemicals dopamine and serotonin react to the opposing player. Dopamine tracks whether an offer is better or worse than the previous one, while the serotonin signal focuses only on the scale of each offer in isolation.

“When they are told they are playing a human being, their tonic level in the pool of dopamine goes up measurably; when they are playing a computer, it does not!” says Montague. In other words, dopamine climbs when fairness comes into play.

The results provide better insights into how our brains work during social interactions.

Until now, scientists had not been able to understand the chemical changes happening in the brain during disease or why certain treatments work. This study gives them the opportunity to finally take a look inside the brain and start understanding what makes you, you.

“Our hope is that we can roll these methodologies out to other groups that can use them and can extend them. So there are a lot of people that can ask really clever questions about the cognition of people,” adds Montague.