Sociality, cooperation and “prosocial” behaviors are the foundation of human society (and of the extraordinary development of our brain) and yet, taken individually, people often show huge variation in terms of altruism/egoism, both among individuals and in the same individual at different moments in time. What causes these differences in behavior? An answer may be found by observing the activity of the brain. The brain circuits that are activated suggest that each of the two behavior types corresponds to a cognitive analysis that emphasizes different aspects of the same situation.