A new study published in Nature Mental Health has found that children growing up in states with higher income inequality show measurable differences in brain structure and function that may contribute to mental health problems later on. The findings are based on brain scans and psychological assessments of thousands of children aged 9 to 10 in the United States. The results suggest that inequality is associated with thinner and smaller brain regions as well as altered brain network communication.
Adolescence is a period of rapid brain development and increased vulnerability to mental health issues. Previous research has focused heavily on how a family's income or education levels can influence children's mental health and brain development. However, the broader effects of structural inequality -- the extent to which income is unevenly distributed across a population -- have not been thoroughly examined. This study aimed to fill that gap by asking whether state-level income inequality is linked to changes in the developing brain and whether those changes could help explain mental health risks in adolescents.
The authors were motivated by growing evidence that unequal societies tend to have higher rates of mental health problems. These outcomes are not limited to those living in poverty. Rather, inequality itself appears to influence social experiences such as perceived social status, comparisons with others, and feelings of belonging.
These social processes can be stressful, especially for children, and prolonged stress is known to affect the brain. By identifying whether inequality leaves a detectable imprint on the brain during early development, the researchers hoped to better understand one potential biological pathway connecting social conditions to psychological outcomes.
"While numerous studies have examined links between individual socioeconomic status (like family income or parent education), whether macroeconomic factors can also get under the skin and become biologically embedded was unknown," said study author Divyangana Rakesh (@divyangana), a lecturer at King's College London. "Our paper is an important contribution as it links a structural characteristic of a society to children's brain structure and function. Our findings highlight that structural inequality, over and above family income, is associated with children's brains."
The researchers used data from the Adolescent Brain Cognitive Development Study, a long-term project tracking nearly 12,000 children across the United States. For this analysis, they focused on a subset of more than 8,000 children from 17 states who had usable brain scans and mental health assessments. The children were between 9 and 10 years old at the time of the brain imaging and came from a variety of racial, ethnic, and socioeconomic backgrounds.
State-level income inequality was measured using the Gini coefficient, a standard tool in economics. A Gini score of 0 means perfect equality, while a score of 1 means perfect inequality. The researchers compared children's brain images and psychological symptoms with the level of income inequality in the states where they lived. Importantly, the analysis adjusted for a wide range of other variables, including family income, parental education, mental health, and state policies like Medicaid expansion.
The researchers found that children in states with higher income inequality tended to have thinner and smaller brains overall. These effects were widespread, appearing across many regions involved in decision-making, emotional regulation, attention, and sensory processing.
Children from more unequal states also showed altered patterns of communication between major brain networks. In particular, connections between the default mode network, which is active during inward thought, and the dorsal attention network, which helps focus on external tasks, were different in these children.
To find out whether these brain differences helped explain the link between inequality and mental health, the researchers followed up with participants six months and 18 months after the initial scan. They found that lower brain volume, reduced surface area, and changes in communication between specific brain networks partly mediated the connection between growing up in an unequal state and experiencing more mental health symptoms over time. These symptoms included trouble with attention, mood, and behavior.
"These findings add to the growing literature which demonstrates how social factors, in this instance income inequality, can influence well-being through pathways which include structural changes in the brain," said co-author Vikram Patel, a professor of Harvard University.
Co-author Kate Pickett, a professor at the University of York, added: "Our paper emphasizes that reducing inequality isn't just about economics - it's a public health imperative. The brain changes we observed in regions involved in emotion regulation and attention suggest that inequality creates a toxic social environment that literally shapes how young minds develop, with consequences for mental health and impacts that can last a lifetime. This is a significant advance in understanding how societal-level inequality gets under the skin to affect mental health."
The researchers emphasize that these associations held even after accounting for family-level economic status. This suggests that inequality itself -- how resources are distributed across society -- has a unique influence on developing brains and mental wellbeing.
The study is large and comprehensive, but it also has limitations. The authors caution that the findings are correlational. That means they show associations between inequality, brain development, and mental health, but they do not prove that inequality directly causes these changes. Experimental or longitudinal research would be needed to establish causality.
The study also focused only on state-level inequality, which may not fully capture children's local environments. Smaller-scale factors like neighborhood segregation or school resources could also play a role. Additionally, the researchers did not measure stress directly, so while chronic stress is a likely explanation for the brain changes observed, it remains a hypothesis to be tested in future work.
The results are also based on average effects. While the associations are statistically significant, they represent modest differences that may accumulate over time or interact with other risk factors in complex ways.
Another limitation is that the brain measures were averaged across both hemispheres, which might have missed important differences between the left and right sides of the brain. The mental health outcomes were also broad, combining symptoms from multiple categories into a single score. Future research could explore whether specific brain changes are linked to particular types of mental health issues, such as anxiety or attention problems.
Finally, the researchers acknowledge that inequality itself is a multi-dimensional construct. The Gini coefficient captures income distribution but does not include information about wealth, access to resources, or economic mobility. Including additional measures in future studies may offer a more complete picture of how inequality shapes development.
"I would like to replicate it in the United Kingdom and using international data if possible, as well as test associations with longitudinal brain development," Rakesh said. "I'm also interested in elucidating the pathways through which this happens."
The study, "Macroeconomic income inequality, brain structure and function, and mental health," was authored by Divyangana Rakesh, Dimitris I. Tsomokos, Teresa Vargas, Kate E. Pickett, and Vikram Patel.