A team of Hungarian researchers scanned the brains of people who got high scores on a test for Machiavellianism (yes, this is a clinical term for a personality trait) while they played a game of trust. “They found that Machiavellians’ brains went into overdrive when they encountered a partner who exhibited signs of being fair and cooperative. Why? … Because the Machiavellians are immediately figuring out how to exploit the situation for their own gain.”