Read the paper here: https://www.science.org/stoken/author-tokens/ST-116/full. This is what Raymundo had to say about the study:

Q: Why did you decide to conduct this study, and how would you summarize the most important points?

A: I’ve been fascinated with social interactions all my life. During my PhD research I discovered a neuronal signal related to who is responsible for my reward. Sort of, a signal related to who bought a round of drinks. But the problem was that this signal couldn’t really dissociate who bought the round of drinks, only that someone else other than me bought the drinks. To test a social agent identity signal, a signal telling me exactly who bought the drinks, I needed to test three agents simultaneously. We had the idea of using a rotary apparatus to have three monkeys interact, and that’s how we got started. The task is deviously simple, three monkeys sit around a rotary table and take turns to offer an apple slice, or reward, to one of the other two monkeys. At the same time we recorded single neuronal activity from a brain area known to play a role in social cognition, the dorsomedial prefrontal cortex or dmPFC.

In the end we found a much richer brain representation of social interactions in the dmPFC than what I initially anticipated. First, we found a signal related to the social agent identity for reward or action. This type of signal is a building block for social exchange. It is a representation of who performs an action or who receives a reward. If you know who acts and receives reward, then you can be specific about who you interact with. Using machine learning algorithms, we were able to then read from the neuronal population what happened on the previous interaction. Furthermore, we were able to decode from the population who the animal would give an apple slice before they even did it. This finding suggested that this brain area plays a role in strategic decisions – with whom it is more advantageous to reciprocate. To test this idea, we disrupted the normal activity in this area and found that the animals were less likely to reciprocate. Together, these findings suggest that the dmPFC plays an important role in mapping out our actions and outcomes as well as that of others.

Q: How might your findings be put to use or be applied to humans?

A: Our results suggest that the dmPFC is crucial for mapping out what others are doing. In neuropsychiatric conditions in which this ability is compromised, treatments aimed at improving the functioning of this brain area, either directly or indirectly, might improve peoples’ lives.