1. This study used fMRI to scan 153 men and 151 women playing an iterated Prisoner's Dilemma game with both human and computer partners. Participants were randomized to receive intranasal oxytocin, vasopressin, or placebo. 2. The researchers found different neural correlates of cooperation depending on sex and outcome of previous moves. In men, cooperation after experiencing betrayal was correlated with activation in prefrontal regions involved in emotion regulation. In women, cooperation after betrayal was correlated with less activation in stress-related areas like the amygdala. 3. Men showed a positive correlation between caudate activation after mutual cooperation and subsequent cooperative choices, while women showed a negative correlation. This suggests sex