A recent experiment revealed that hormones related to social bonding lead heterosexual men to collaborate more often with female partners in computerized games, regardless of whether the women are presented in sexual terms. The researchers discovered that this hormone specifically encourages men to forgive betrayal under certain conditions, revealing the biological basis of social and mating behavior. These results were published in Psychoneuroendocrinology.
Society is highly saturated with sexual images, prompting psychologists to investigate how emphasizing a person’s sexual nature changes social perceptions. Sexual objectification often leads to sexual objectification. This cognitive shift occurs when individuals reduce to the status of mere objects or body parts, stripped of their humanity and ability to direct their own actions.
Objectification generally has negative social consequences, such as decreased empathy and decreased likelihood of cooperation. When sexualization doesn’t cross the line into objectification, it serves as an extremely valuable social stimulus. In these innocuous scenarios, sexual attractiveness can increase a person’s social value and attract more attention from the opposite sex.
Gonzalo Cosme, a researcher at the University of Lisbon, and Diana Plata, a neuroscientist at the University of Lisbon and King’s College London, wanted to understand what hints at the balance of these interactions. They designed a study to determine whether sexual objectification invites or impedes heterosexual men’s cooperation during economic games. They also sought to test the specific effects of oxytocin on these behaviors.
Oxytocin is a chemical messenger produced in the brain that regulates social cognition, partner bonding, and trust. Oxytocin levels naturally rise during physical intimacy, so the researchers suspected that oxytocin might play a role in getting people through sexual social situations. This hormone is associated with an increased desire to be close to others and form cooperative relationships.
To investigate these dynamics, the researchers recruited 50 heterosexual men and conducted a double-blind, placebo-controlled experiment. Half of the participants self-administered a nasal spray containing synthetic oxytocin, and the other half received a placebo spray containing no active ingredient. Neither the participants nor the researchers knew who received which treatment until the end of the experiment.
Each participant performed a classic game theory exercise called the Prisoner’s Dilemma. The Prisoner’s Dilemma describes a situation in which two individuals must independently weigh the benefits of mutual cooperation against the temptations of selfish betrayal. Participants played multiple rounds of the game with two potential female partners in separate rooms at the university. The researchers required participants to be the first to act in each encounter, putting the men in a vulnerable position that required a base level of trust.
If both players cooperate in the game, they both earn a modest virtual reward. If one side betrays and the other cooperates, the traitor receives the maximum reward, while the victim receives nothing. If both parties betray each other, both receive a very small reward. In this setting, players must consider the possibility that their partner will act honestly.
In reality, the men were competing against a computer algorithm designed to mimic human decision-making patterns. Before each round, participants saw a photo of their opponent. One algorithm was depicted as a sexualized woman wearing heavy makeup, a short dress, and high heels. The other algorithm was represented by a nonsexualized woman wearing a simple sweater, comfortable pants, and flat shoes.
While playing the game, the men wore hats covered with electrodes to measure their brain waves. This recording technique, called electroencephalography, allows researchers to observe how the brain evaluates results in a fraction of a second. The researchers monitored the timing and size of electrical spikes to understand the biological mechanisms that drive behavioral choices in males.
In this experiment, the team monitored two specific electrical events. First, we examined P300 brain waves. This is a sudden positive change in voltage that occurs about a third of a second after a person sees something unexpected or exciting. The second event was a feedback-related negative wave. This includes negative changes in voltage that appear when a person perceives that they have experienced an adverse outcome.
To ensure that the experimental setup worked properly, the researchers asked participants to fill out a questionnaire assessing their opponent’s presumed mental state. Psychological indicators divide the perception of human nature into the capacity to experience emotions and the capacity for personal agency. The latter category assesses the ability to plan, make choices, and exercise self-control.
When someone is completely objectified, observers tend to see that person as having significantly reduced capacity for personal agency. In this study, men rated the women they sexually targeted as more attractive and sexually available. They did not give sexualized women low scores on personal agency, so the results confirmed that although the women were sexualized, they were not deprived of autonomy.
Oxytocin changed the men’s behavior, completely unrelated to the women’s appearance. Men who received the oxytocin spray chose to cooperate more often throughout the Prisoner’s Dilemma game than men who received a placebo. This hormone consistently increased baseline willingness to trust strangers.
This hormone particularly increased the men’s willingness to maintain mutual cooperation after rounds in which both players behaved generously. It also made participants more likely to forgive someone who betrayed them. Choosing to cooperate immediately after being betrayed requires a high degree of tolerance. This act of generosity indicates an internal motivation to repair damaged social bonds.
This permissive behavior was highly dependent on the order in which the enemies appeared during the experiment. Oxytocin-induced forgiveness occurred most often when men first encountered non-sexual women before meeting sexual women. The researchers suspect that encountering a non-sexual partner shortly after a sexual partner may feel like less social reward for participants. This perception of disappointment can reduce the internal motivation to forgive the betrayal.
EEG recordings provided physical evidence of these social evaluations. When men watched the results of their rounds against sexually targeted women, their brains produced higher amplitude P300 electrical signals. This suggests that men paid more cognitive attention to interpreting the behavior of their sexualized partners.
When men under the influence of oxytocin were matched against a non-sexualized woman, their P300 brain signals showed delayed reaction times. Longer delays in this particular brainwave pattern usually indicate that the brain is taking more time to evaluate the feedback. This delay suggests that processing normal social interactions requires a higher cognitive load when participants are biologically primed to form social bonds.
Researchers observed that when men evaluated losing in a match, their negative feedback-related brain waves were much stronger. These negative voltage shifts were also unusually high when men faced a non-sexualized woman as their final opponent. The researchers propose that this spike reflects a subconscious negative evaluation of non-sexualized women following previous interactions with sexualized women.
Although this study provides a biological perspective on social trust, the authors acknowledge that their study has some limitations. This experiment tested only the cooperative behavior of heterosexual men toward their female partners in a controlled environment. Sexualization and oxytocin dynamics may operate differently in women and individuals with other sexual orientations.
The participants all shared a similar demographic background and consisted primarily of young Portuguese university students. Cultural backgrounds shape how people interpret clothing and sexuality. This means that these results may not be fully replicated in other societies. The researchers also used a single standard dose of oxytocin, leaving room for future experiments to test whether different amounts of the hormone produce different effects.
Future research could extend this framework by looking at real social interactions rather than computerized economic games. The current statistical results from EEG data are considered preliminary and require independent replication. Until then, these findings provide the latest perspective on how our neurobiology navigates the boundaries between trust, attraction, and social cooperation.
The study, “Intranasal oxytocin increases cooperation in heterosexual men and women,” was authored by Gonzalo Cosme, Marta Patrocinio, Carlotta Cogoni, Maciej Cocillo, and Diana Plata.
