This 2016 German human study found:
“Intranasal administration of arginine vasopressin (AVP), a hormone that regulates mammalian social behaviors such as monogamy and aggression, increases humans’ tendency to engage in mutually beneficial cooperation.
AVP increases humans’ willingness to cooperate. That increase is not due to an increase in the general willingness to bear risks or to altruistically help others.”
One limitation of the study was that the subjects were all males, ages 19-32. The study’s title was “human risky cooperative behavior” while omitting subjects representing the majority of humanity.
Although the researchers claimed brain effects from vasopressin administration, they didn’t provide direct evidence for the internasally administered vasopressin in the subjects’ brains. A similar point was made about studies of vasopressin’s companion neuropeptide, oxytocin, in Testing the null hypothesis of oxytocin’s effects in humans.
A third limitation was that although the researchers correlated brain activity with social behaviors, they didn’t carry out all of the tests necessary to demonstrate the claimed “novel causal evidence for a biological factor underlying cooperation.” Per Confusion may be misinterpreted as altruism and prosocial behavior, the researchers additionally needed to:
“When attempting to measure social behaviors, it is not sufficient to merely record decisions with behavioral consequences and then infer social preferences. One also needs to manipulate these consequences to test whether this affects the behavior.”
http://www.pnas.org/content/113/8/2051.full “Vasopressin increases human risky cooperative behavior”