Study Finds Oxytocin Encouraged Heterosexual Men to Trust and Cooperate More With Women

A study published in Psychoneuroendocrinology, titled Intranasal oxytocin increases cooperation of heterosexual men with women, suggests that oxytocin may encourage heterosexual men to cooperate more readily with women during strategic decision-making. Conducted by Gonçalo Cosme, Marta Patrocínio, Carlotta Cogoni, Maciej Kosilo, and Diana Prata, the research found that the hormone promoted cooperative behavior regardless of whether female partners were presented in sexualized or non-sexualized images.

The researchers investigated how oxytocin and sexualized portrayals of women interact to influence trust and cooperation. Their findings add to ongoing discussions about sexualization, objectification, and the biological factors that shape social behavior.

Researchers Explored the Effects of Sexualized Images

Sexualized imagery is common in modern media, prompting researchers to examine how it influences the way people perceive and interact with others. In some situations, sexualization can contribute to objectification, in which a person is viewed primarily in terms of their physical appearance rather than as an individual with thoughts, intentions, and autonomy.

Previous research has linked objectification to reduced empathy and lower levels of cooperation. At the same time, when a person's sense of agency is preserved, physical attractiveness may function as a social reward that attracts attention and encourages interaction.

To better understand these processes, researchers Gonçalo Cosme and Diana Prata examined whether sexualized portrayals of women affect men's willingness to cooperate and whether oxytocin changes that response.

How the Study Was Conducted

The study involved 50 heterosexual men in Portugal who participated in a double-blind, placebo-controlled experiment. Each participant self-administered either an intranasal spray containing synthetic oxytocin or an inactive placebo without knowing which treatment they had received.

Participants then completed multiple rounds of the Prisoner's Dilemma, a well-known game theory task that requires players to choose between cooperation and betrayal. The men believed they were playing against two different women located elsewhere in the building.

In reality, both opponents were computer-controlled programs designed to simulate human decisions. Before each round, participants viewed a photograph representing their partner. One woman was shown in a sexualized outfit consisting of a short dress and high heels, while the other appeared in modest, non-sexualized clothing.

The participants always made the first decision, choosing whether to cooperate or betray their partner. Mutual cooperation produced moderate rewards, betraying a cooperative partner generated the highest payoff, while mutual betrayal resulted in the lowest reward.

Brain Activity and Perceptions Were Also Measured

During the experiment, researchers monitored participants' brain activity using electroencephalography (EEG), which records rapid electrical signals generated by the brain.

The analysis focused on two established EEG responses: the P300 component, associated with attention and the processing of important or unexpected events, and Feedback Related Negativity, which becomes stronger following unfavorable outcomes.

After completing the game, participants rated both female partners on several characteristics, including attractiveness, perceived sexual availability, emotional capacity, and agency, such as the ability to make decisions and exercise self-control.

The sexualized woman was rated as more attractive and more sexually available than the non-sexualized woman. However, participants did not perceive her as having less agency, suggesting that the images increased sexualization without leading to full objectification.

Oxytocin Increased Cooperation

The most consistent behavioral effect came from oxytocin rather than from the appearance of the female partners. Men who received oxytocin cooperated more frequently throughout the game than those who received the placebo.

The hormone appeared to increase participants' general willingness to trust an unfamiliar woman. It also made men more likely to continue cooperating after a previous round in which both players had cooperated.

Oxytocin also increased the likelihood that participants would cooperate immediately after their partner had betrayed them. In the context of the Prisoner's Dilemma, this behavior is considered a form of forgiveness because it reflects a willingness to rebuild cooperation after trust has been broken.

This effect depended on the order in which participants encountered the two women. The increase in forgiving behavior was strongest among men who first played against the non-sexualized woman and later against the sexualized woman.

When the order was reversed, participants were less likely to forgive betrayal. The researchers suggest that moving from a sexualized partner to a non-sexualized one may reduce the perceived social reward, making forgiveness less likely.

Brain Responses Reflected Differences in Social Evaluation

EEG recordings showed that participants devoted more attention to evaluating interactions with the sexualized partner. Outcomes involving the sexualized woman produced larger P300 responses, indicating greater cognitive processing.

Among participants who received oxytocin, the P300 response occurred later when interacting with the non-sexualized partner. According to the researchers, this delay may indicate that oxytocin encouraged men to spend more time processing feedback during less socially rewarding interactions.

Feedback Related Negativity became stronger following losses or unfavorable outcomes, confirming that participants perceived these events as negative. This response was particularly pronounced when the non-sexualized woman appeared as the second partner in the experiment.

The researchers suggest this pattern may reflect a contrast effect, in which interactions with a sexualized partner influence how subsequent interactions with a non-sexualized partner are evaluated.

Researchers Say More Studies Are Needed

The authors emphasize that the findings should be interpreted cautiously because the study involved a relatively small sample of young heterosexual men from Portugal. Cultural differences in attitudes toward clothing, sexuality, and social interaction may influence whether the results apply to other populations.

The experiment also focused exclusively on men interacting with female partners in a controlled laboratory setting. Different findings may emerge in studies involving women, people of different sexual orientations, or real-world social interactions.

In addition, participants received only a single dose of intranasal oxytocin, leaving unanswered questions about how different doses or longer-lasting effects might influence behavior. Previous research has also shown that oxytocin's effects often depend heavily on social context.

Future studies involving larger and more diverse populations, face-to-face interactions, and additional brain imaging techniques will help determine how broadly these findings apply. For now, the study adds to growing evidence that oxytocin can influence trust, cooperation, and forgiveness during social interactions, even when sexualized imagery is present.