Every day we make decisions based on predicting what someone else will do—from deciding whether the driver approaching an intersection will stop for the red light to determining whether a particular negotiation strategy will result in a desired outcome.

Now a study by Harvard Medical School investigators at Massachusetts General Hospital has discovered two groups of neurons that play key roles in social interactions between primates. One group is activated when deciding whether to cooperate with another individual and another group is involved in predicting what the other will do. The findings appear in Cell.

“For a long time we have been interested in understanding how complex social interactions between individuals are mediated by neurons within the brain,” said Keren Haroush, HMS instructor in neurosurgery at Mass General and lead author of the Cell paper. “We found that part of the frontal lobe called the anterior cingulate cortex plays an essential role in mediating cooperative social interactions in Rhesus monkeys. Some neurons encode the animal’s decision whether or not to cooperate with another monkey, and a separate group of neurons was activated in predicting what the other monkey would do before it had made its decision. The activity of those other-predictive neurons was uniquely affected by the social context of the interaction.”