A person’s preference for group-based inequality and social hierarchies may be linked to both brain structure and a personality trait tied to reward seeking. According to a new study published in Current Psychology, young adults who score higher in social dominance orientation tend to have less gray matter in a brain region involved in empathy and emotional processing. The findings hint that social and political worldviews may be tied partly to basic motivational and emotional differences.
Social dominance orientation is a personality trait that captures how much an individual prefers inequality between social groups over equality. People who score high on this trait view society as naturally divided into superior and inferior groups, often supporting social systems and policies that maintain these hierarchies. In contrast, those with lower scores favor egalitarian relationships between groups and oppose group-based dominance.
To explore how this mindset relates to the physical brain, researchers focused on specific areas, including the anterior insula. The insula is an island of brain tissue tucked deep within the lateral groove on each side of the brain, positioned beneath the frontal, parietal, and temporal lobes. Its front portion, the anterior insula, plays a central role in detecting bodily sensations and processing the emotional experiences of others.
The study was led by Jesús Adrián-Ventura, a professor at the University of Zaragoza in Spain and a researcher with the Pseudo-Lab research group.
“Despite Social Dominance Orientation—the ideological belief that some groups should dominate others—being a central construct in social psychology, its neural underpinnings have received very little attention,” Adrián-Ventura told PsyPost. “We aimed to contribute to filling this gap, while also exploring predictors related to personality and motivation. Ultimately, we sought to investigate how stable brain traits (e.g., brain anatomy) and motivational drives jointly predispose individuals to endorse social hierarchies and inequality.”
Earlier psychological work helped establish this line of inquiry. For instance, a 2013 study indicated that people who strongly favor social dominance tend to report lower empathy in general.
Other research suggested that the desire for social hierarchy may be driven less by negative feelings toward other groups than by an appetite for rewards. In particular, a 2013 paper linked social dominance orientation to positive approach motivation, which is the psychological drive to actively pursue rewards. This finding pointed to the possibility that people who endorse hierarchies might find the prospect of higher social rank and power personally rewarding.
Scientists later began asking whether these persistent psychological tendencies correspond to measurable differences in brain anatomy. In a 2023 brain imaging study of adults in Singapore, researchers observed that higher social dominance scores were tied to less gray matter, the brain tissue made up mainly of nerve cell bodies, in the anterior insula and in the ventromedial prefrontal cortex, an area just above the eye sockets involved in weighing values and regulating emotions.
Higher scores were also tied to more gray matter in the amygdala, an almond-shaped structure deep in the brain that helps process emotions such as fear. Some of those results did not hold up under stricter analysis methods, so Adrián-Ventura and his colleagues set out to test them again with refined techniques in a Spanish sample.
The researchers recruited 99 healthy young adults between the ages of 18 and 30, including 62 women and 37 men, from a university campus in Spain. All participants completed cognitive screening and filled out psychological surveys before undergoing brain scans. Two participants showed brain volume values that were potential statistical outliers and were excluded from the neuroimaging analyses, leaving a sample of 97 participants. The researchers had calculated in advance that about 84 participants would be needed to reliably detect a moderate correlation.
Participants completed an eight-item survey measuring social dominance orientation, rating statements about group equality and dominance on a scale from 1 to 7. They also completed a 24-item survey assessing sensitivity to reward, which measures how readily someone acts in response to potential incentives in daily life without worrying about negative outcomes. Brain scans were gathered using high-resolution 3-Tesla magnetic resonance imaging, a technique that produces detailed images of soft tissue without X-rays.
The team analyzed the scans using voxel-based morphometry, a computational approach that measures the volume of gray matter in specific parts of the brain. The authors analyzed predefined regions of interest based on a standardized anatomical brain atlas, adjusting their calculations for participant age and head size. They did not include sex as a separate factor, reasoning that adjusting for head size already captures much of the sex-related variation in brain volume.
The analyses indicated that higher scores on social dominance orientation were linked to less gray matter volume in both the left and right anterior insula. For the left anterior insula, the correlation with social dominance scores was r = -0.30, and for the right anterior insula, it was r = -0.29, representing moderate negative correlations after accounting for age and head size. Because testing several regions raises the odds of a chance finding, the researchers used a stricter threshold for statistical significance, and both insula results passed it.
An exploratory scan of the entire brain found no significant associations with social dominance anywhere, including the insula. The insula link appeared only in the targeted analysis of the three predefined regions.
Unlike the previous study in Singapore, the researchers did not find evidence linking social dominance to the amygdala or the ventromedial prefrontal cortex. The associations between dominance scores and gray matter volume in the amygdala were small and were not statistically significant. Similarly, the correlation with the ventromedial prefrontal cortex was not statistically significant.
“We were somewhat surprised by the absence of significant associations in the amygdala and ventromedial prefrontal cortex, which contradicted the only previous neuroanatomical study on this topic,” Adrián-Ventura noted. “Because that prior study involved Singaporean Chinese adults while ours involved a Spanish sample, we suspect this discrepancy might reflect cultural differences. It suggests that while the anterior insula’s involvement might be a universally preserved pathway, other neural mechanisms of social dominance could be highly sensitive to distinct cultural landscapes.”
In their paper, the authors note that methodological differences, such as how the brain regions were outlined, could also explain the discrepancy, and they describe the cultural explanation as speculative.
At the behavioral level, social dominance orientation was positively related to sensitivity to reward, with a moderate correlation of r = 0.33. The researchers then built statistical models that predicted social dominance scores from anterior insula volume, age, and head size before adding reward sensitivity. Among the 95 participants with complete data, the full model accounted for up to 29 percent of the individual differences in social dominance scores, with reward sensitivity adding about 10 to 11 percentage points beyond what the other factors explained.
“The effects we observed are quite substantial,” Adrián-Ventura pointed out. “Importantly, structural brain features and personality traits are highly heritable and exhibit strong stability across the lifespan. This highlights that preferences for social hierarchies are not merely transient attitudes but may be rooted in early developmental and genetic factors.”
“In this sample, people who more strongly endorsed group-based hierarchies tended to have lower gray matter volume in the anterior insula and to report greater sensitivity to rewards,” said David V. Smith, an associate professor of psychology and neuroscience at Temple University, director of the Temple University Brain Research and Imaging Center, and director of the Neuroeconomics Laboratory, who was not involved in the study.
“These findings offer interesting leads for investigating how motivational processes relate to these attitudes.” “The authors’ comparison with earlier work suggests partial support: they found a similar insula association in a different population, but no significant associations in the other two brain regions tested,” he added. “This is a useful follow-up, although I’d want larger studies before treating the pattern as well established.”
The insula findings sit in tension with earlier work by the same team. In a study covered by PsyPost in 2025, Adrián-Ventura and his colleagues reported that, in nearly the same group of Spanish young adults, higher scores on anti-hierarchical aggression, a facet of left-wing authoritarianism that captures hostility toward established authorities, were linked to a thinner cortex in the right anterior insula. That study measured cortical thickness rather than gray matter volume, and its attitude measure targeted hostility toward those in power rather than a general preference for group hierarchy, suggesting that quite different ideological stances may relate to the structure of the same brain region.
The authors suggest that the anterior insula findings might reflect differences in socio-emotional processing. Because the anterior insula helps people tune into the emotional distress and feelings of others, having less gray matter in this region could relate to reduced empathy. If that is the case, reduced sensitivity to others’ feelings, combined with a heightened drive toward incentives, could make individuals more comfortable endorsing social arrangements where some groups dominate others.
“We found that individuals who strongly endorse social hierarchies tend to have less gray matter volume in the anterior insula, a brain region typically involved in empathy and socio-emotional processing,” Adrián-Ventura said. “Furthermore, these individuals showed a heightened sensitivity to reward, suggesting a strong drive to pursue status that may override the negative social consequences of inequality. Together, our results reveal an underlying neurobiological and motivational predisposition associated with a higher social dominance orientation.”
As with all research, there are some caveats to consider. The study was cross-sectional, meaning it captured a snapshot of brain structure and personality traits at a single moment. These observations cannot establish that smaller insula volume causes someone to favor social hierarchies, nor can they determine whether adopting certain social beliefs alters brain tissue over time.
“A crucial caveat is that our study relies strictly on brain and personality measures, meaning we cannot definitively confirm that mechanisms like empathy directly mediate this relationship, although it is highly plausible,” Adrián-Ventura emphasized. “Furthermore, as this is an observational study, we cannot presume a causal direction between brain anatomy and behavioral outcomes. Finally, because our sample consisted of young Spanish adults (mostly university students), further cross-cultural research is needed to determine how well these neurobehavioral correlates generalize to other populations.”
“Lower gray matter volume does not automatically mean less empathy, and greater general reward sensitivity does not demonstrate that someone finds inequality rewarding,” Smith told PsyPost.
Smith also viewed the structural results with caution. “I would treat the anatomical findings as preliminary,” he said. “The targeted analyses and correction for multiple comparisons are strengths, but 97 participants is a relatively small sample for linking individual differences in brain anatomy to psychological traits, where estimated associations can be unstable in smaller samples. I’d also want to see whether the association holds when sex is included in the models, since adjusting for head size is not the same as adjusting for sex.”
The study was also not pre-registered, meaning the researchers did not publicly record their hypotheses and analysis plan in advance, unlike the Singapore study they sought to replicate. Future research will need to examine how sociodemographic variables such as sex and broader age distributions interact with these brain structures over time.
“More broadly, our research group investigates the neurocognitive factors associated with different belief systems—such as authoritarianism, pseudoscientific doctrines, and conspiracy theories—alongside interventions like empathetic refutation,” Adrián-Ventura said. “To advance this mission, our next steps involve examining new functional brain metrics (e.g., resting-state) and the potential mediating roles of behavioral variables such as empathy or perspective-taking. Finally, we aim to conduct longitudinal studies across more generalizable samples from adolescence to early adulthood, allowing us to track the development of these ideologies and establish causal predictors.”
Empathetic refutation is an approach to correcting false beliefs that first acknowledges the concerns behind them, while resting-state measures track brain activity when a person is not performing any task.
Smith also pointed toward experimental steps that could build upon the current findings. “I’d like to see a substantially larger, preregistered replication that directly measures empathy and tests whether people value their group being ahead of another group, even when their own group’s payoff stays the same,” he explained. “That would help distinguish a preference for relative advantage from a more general tendency to pursue rewards.”
The study, “Neuroanatomical correlates of social dominance orientation and the contributing role of reward sensitivity,” was authored by Jesús Adrián-Ventura, Angelo Fasce, Anna Miró-Padilla, Anastasia Cherednichenko, César Ávila, and Diego Avendaño.
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