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The hormone oxytocin changes how the brain learns and retrieves information about where people stand in social hierarchies. A recent study published in PNAS reveals that oxytocin boosts neural activity associated with learning social ranks and improves memory for networks that do not directly involve the observer. These results outline the biological mechanisms that help humans navigate social environments.
Social dominance hierarchies dictate who gets access to resources, mating opportunities, and who wields social influence. These hierarchies generate systematic asymmetries in behavior, physiology, and decision-making across many different species. To succeed in these environments, people must track their own status and the relationships among third parties. Tracking one’s own position typically engages different brain areas than evaluating others from a third-party perspective.
Past research mostly focused on simple, linear hierarchies, where one person is at the top and others follow in a straight line. Real social networks feature equal ranks and branching connections. The researchers wanted to understand the brain mechanisms used to learn these more intricate structures.
The study was conducted by Jiawei Liu and Chen Qu of South China Normal University, along with several colleagues in China and France. They focused on oxytocin, a hormone known to affect social memory and dominance behaviors in animals. The team wanted to see if the hormone alters how humans learn and remember social ranks.
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The researchers recruited 60 healthy young men for the experiment, two of whom were later excluded for insufficient performance, leaving 58 in the final analysis. Only men were included to avoid gender-based variations in hormone response and attitudes toward the male faces used in the visual tasks. Participants were randomly assigned to receive either an oxytocin nasal spray or a placebo spray containing no active ingredients.
Participants then played a computer game where they learned the ranks of individuals in two different fictional corporate departments. One department included the participant, acting as a self-oriented network. The other department centered around a stranger, acting as an other-oriented network.
During the initial training phase, participants saw pairs of faces and guessed their rank relationship. They had to decide who was superior or if the two individuals held an equal rank. They received immediate feedback on whether they were right or wrong, allowing them to deduce the hidden social structure through trial and error.
As the training progressed, participants improved their accuracy. They learned the ranks within their own department faster than the stranger’s department. The participants also learned the relationships between people of high status and low status faster than they learned the relationships of people with intermediate status.
The researchers used mathematical modeling to track the underlying learning process. They tested different models, including those based purely on structural mapping and those based on associative learning. The data best fit a hybrid model. This model showed that people learn social networks through two interacting mental processes.
First, participants track the likelihood that any two people belong to an “equal” rank category based on direct feedback. Second, they assign a hidden rank value to each person that adjusts over time. These hidden values drift apart for unequal pairs and move closer together for equal pairs. By combining these processes, the brain builds a coherent hierarchical representation without needing to see the entire network at once.
Functional magnetic resonance imaging, or fMRI, measured blood flow in the participants’ brains during the training task. When participants selected the correct rank relationship, two brain areas became highly active. These were the ventromedial prefrontal cortex and the posterior cingulate cortex.
These brain regions are located near the center of the brain and help process social information and rewards. Participants who received oxytocin showed heightened activity in these areas compared to the placebo group. The hormone appeared to amplify the brain signals required to map the social network.
Next, participants completed a test phase to measure transitive inference. This is the ability to deduce relationships between items that have not been explicitly linked. They were shown pairs of faces that had never appeared together during training and had to infer the rank relationship based on what they had learned earlier.
The researchers did not provide feedback during this test phase. Oxytocin altered performance during this phase, but the effect depended on the social network in question. The hormone improved accuracy when participants made inferences about the stranger’s department. It did not improve performance for the department that included the participant.
During the test phase, brain scans revealed additional differences in how the brain handles these two networks. The dorsal anterior cingulate cortex was more active when participants made inferences about the stranger’s network. This brain region is known to help facilitate social interactions by tracking the value and cost of options for other people.
Brain scans during the test phase also showed that the amygdala and the parahippocampal region responded differently under the influence of oxytocin. These temporal lobe structures are involved in processing emotions and memory. In the oxytocin group, these memory centers reacted more strongly when retrieving information about the stranger’s network than the participant’s own network.
The researchers suggest that oxytocin makes people less self-centered in their social memory. It amplifies the recall of relationships that are relevant to others, shifting the brain’s focus away from the self. This aligns with past research showing that oxytocin can promote prosocial behaviors and alter how the brain values other people.
The study comes with certain limitations regarding the participant pool. The researchers only tested healthy men. The hormone affects men and women differently, meaning these results might not apply to women. The study also used male faces for the hierarchy tasks, which could influence how ranks are perceived.
Another limitation involves the route of hormone administration. The study relied on a nasal spray to deliver oxytocin to the brain. While research indicates that nasal oxytocin does reach the central nervous system, some of the behavioral changes might stem from indirect effects in the rest of the body.
Future research will need to untangle how central and peripheral oxytocin systems interact during social learning. Scientists also need to test how these mechanisms operate in different demographics and real-world social settings.
The study, “Oxytocin modulates the neurocomputational mechanisms engaged in learning rank relationships in social networks,” was authored by Jiawei Liu, Chen Qu, Rémi Philippe, Siying Li, Edmund Derrington, and Jean-Claude Dreher.
