How do we represent what others do and receive?
I’ve been fascinated with social interactions all my life. During my Ph.D. research, I discovered a neuronal signal related to who is responsible for self reward (Baez-Mendoza PNAS 2013). However, the problem with this interpretation is that the experimental design could not generate a neuronal signal that can differentiate between an individual and another agent.
To test a social agent identity signal, I needed to test three agents simultaneously. The task is deviously simple; three monkeys sit around a rotary table and take turns to offer a reward (such as an apple slice) 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 was 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. Then, using machine learning algorithms, we could read what happened in the previous interaction from the neuronal population. Furthermore, we could decode from the neuronal population whom the animal would give an apple slice to before they even performed the action. This finding suggested that this brain area plays a role in strategic decisions, and helps an individual answer the question “with whom it is more advantageous to reciprocate”.
Together, these findings suggest that the dmPFC plays a vital role in mapping out our actions and outcomes, as well as mapping out what others are doing.