Origins of charity and deception in the brain Michael L. Platt Duke University Human nature is fundamentally contradictory. We are the most charitable species on the planetÑoften giving to others we donÕt even know. We are also the most deceptiveÑmisleading, lying, and cheating to further our own ends. People also differ in how charitable and how deceptive they are. How the brain shapes these behaviors remains poorly understood. In my talk, I will describe recent work using a new model of social cognition in which pairs of monkeys interact through a computer device while we either monitor or manipulate their brains. We found that monkeys favor giving rewards to another monkey, particularly if he is more familiar or subordinate, rather than give the rewards to no one. OxytocinÑa hormone implicated in social bondingÑmakes monkeys more giving to each other. We also found that giving behavior selectively activated cells in the medial frontal cortex, previously implicated in empathy in humans. By contrast, when monkeys played a competitive game against each other, they rapidly developed unpredictable behaviors that served to deceive the other monkey. We found that deceptive behavior selectively activated a specific population of cells in the lateral frontal cortex. Inactivating these cells impaired the ability to act deceptively. Together, these discoveries define part of a network of brain areas specialized for complex social behavior and cognition. They also show that monkeys spontaneously engage in charity and deception depending on context, just as humans do.