Behavioural Differences and Neural Substrates of Altruistic and Spiteful Punishment

Altruistic punishment following social norm violations promotes human cooperation. However, experimental evidence indicates that some forms of punishment are spitefulrather than altruistic. Using two types of punishment games and seven non-strategic games, we identified strong behavioural differences between altruistic and spitefulpunishers. Altruistic punishers who rejected unfair offers in the ultimatum gameand punished norm violators in the third-party punishmentgame behaved pro-socially in various non-strategic games. Spitefulpunishers who rejected unfair offers in the ultimatum gamebut did not punish norm violators in the third-party punishmentgame behaved selfishly in non-strategic games. In addition, the left caudate nucleuswas larger in spitefulpunishers than in altruistic punishers. These findings are in contrast to the previous assumption that altruistic punishers derive pleasurefrom enforcement of fairness norms, and suggest that spitefulpunishers derive pleasurefrom seeing the target experience negative consequences.