Oxytocin influences intuitions about the relationship between belief in free will and moral responsibility

Philosophers have proposed that laypeople can have deterministic or indeterministic intuitions about the relationship between free will and moral responsibility. However, the psychophysiological mechanisms that generate these extreme intuitions are still underexplored. Exogenous oxytocin offers a unique opportunity to gain a deeper understanding of these underlying mechanisms, since this neuropeptide influences a wide range of outcomes related to social cognition and prosociality. This study investigated the effects of intranasal oxytocin on intuitions about the relationship between free will and moral responsibility by applying a randomized, double-blind, placebo-controlled, between-subject design. Healthy male participants rated the moral responsibility of a hypothetical offender, who committed crimes in either a primed deterministic or an indeterministic universe. Under placebo, participants held the offender more morally responsible when acting in an indeterministic compared to a deterministic universe, which could be accredited to recognition of the offender's freely chosen action to commit the crimes. Under oxytocin, participants rated the offender's actions with greater leniency and similarly assigned lower moral responsibility in both universes. These findings strengthen the assumption that a person can have different intuitions about the relationship between free will and moral responsibility, which can be presumably dependent on motivational states associated with affiliation.