Sex differences in the effects of acute stress on behavior in the ultimatum game.

Acute stress affects human decision making. It has been argued that there are systematic sex differences in behavioral responses to acute stress, with males showing a 'fight or flight' and females showing a 'tend and befriend' response. A 'tend and befriend' response would suggest that women become more cooperative under acute stress, while men do not. We investigated the effects of acute stress on social behavior. We induced stress via the Trier Social Stress Test (TSST) and then immediately after measured how participants reacted to offers made in the ultimatum game by a male proposer. We found that female participants were less likely to reject offers under stress (n = 25) vs. no stress (n = 37), p = 0.009, independent of how fair these offers were, cooperative behavior consistent with the 'tend and befriend' hypothesis. Male participants when stressed (n = 30) did not show differences in rejections rates compared to the control condition (n = 26), p = 0.41. Our results provide support for a qualitatively different behavioral response to acute stress among men and women.