A new study explains why stress makes us both cooperative and defensive

A recent study published in Psychoneuroendocrinology reveals how acute stress influences social behavior in complex ways. Under pressure, individuals may exhibit cooperative and defensive tendencies simultaneously, depending on the social role of their interaction partner. Researchers at the University of Freiburg's led by Laura Oswald investigated whether stress triggers distinct responses based on whether a person is a peer or an evaluator who induced the stressful situation.

The study involved 121 healthy young adults who underwent a five-minute preparation period followed by a 12-minute speech and an eight-minute mental arithmetic task before a panel of white-coated evaluators. Saliva samples, heart-rate monitoring, and self-reported stress levels confirmed the stress response. Participants then engaged in four trust-based games with either a peer or a stressed evaluator, allowing researchers to compare their behavior toward each group.

The findings showed that stressed participants were more likely to cooperate and trust peers, demonstrating the "tend-and-befriend" response. They made an average of 2.52 trusting choices toward peers, compared to 2.02 toward evaluators. Similarly, they exhibited more trustworthy (3.06 vs. 2.40) and sharing (2.83 vs. 2.27) behaviors toward peers. However, they were more punitive toward evaluators, with an average of 0.74 punitive choices versus 0.54 toward peers, also statistically significant.

Interestingly, the size of participants' cortisol, heart-rate, or perceived-stress responses did not clearly predict their differential treatment of peers versus evaluators. The researchers concluded that individual behavior adapts based on the social role of the interaction partner, with cooperation potentially increasing mutual support and defensiveness protecting resources or restoring a sense of control.

However, the study has limitations: all participants experienced the stress procedure, so it cannot prove causation, and interactions always followed the stress test, potentially introducing order effects. Future research should include non-stress controls, friendlier evaluators, and more natural settings. This dual response to stress, cooperating with allies and defending against evaluators, provides a nuanced understanding of how acute stress shapes social behavior.