Socioeconomic status shapes brain networks in different ways for boys and girls

A child’s socioeconomic environment shares a measurable relationship with their physical brain architecture and cognitive test scores. A large study of elementary schoolers has found that while biological sex fundamentally alters these relationships, socially constructed categories like race do not. The findings suggest that unequal access to resources is what truly drives most observed racial differences in brain development. The study was published in Developmental Cognitive Neuroscience.

A child’s socioeconomic status encompasses more than just household income. It includes a variety of environmental factors, such as parental education, food security, neighborhood safety, and the emotional environment at home. Researchers know that children from lower socioeconomic backgrounds often experience different developmental trajectories than their wealthier peers. These differences show up in cognitive test scores and in the physical structure of the brain itself.

In the United States, systemic inequalities have led to a reality where race and socioeconomic status are heavily intertwined. Because of this, it can be difficult for researchers to isolate the effects of environmental resources from other demographic factors. Previous research often treated race as a simple statistical adjustment. But scientists have grown increasingly concerned that this approach might obscure important nuances in how poverty and resources interact with childhood development.

To understand how the environment alters the brain, scientists look at white matter. The brain’s white matter acts as the physical communication network between different gray matter regions. Researchers evaluate this network by looking at two main properties known as integration and segregation.

Integration describes the global efficiency of the network. A highly integrated brain resembles a system of long-distance highways that allows information to travel quickly across the entire brain with very few stops. Segregation refers to localized efficiency. A segregated network is similar to tight-knit local neighborhoods, where nearby brain regions communicate heavily with one another rather than reaching out across the brain.

To explore how these environmental and physical factors overlap, lead author Jaden Kropf and senior author Donald J. Mabbott, both based at The Hospital for Sick Children in Toronto, worked alongside their colleagues to analyze child brain data. They used information from the Adolescent Brain Cognitive Development study. This produced a large study of 8,064 nine- and ten-year-old children from across the United States.

The researchers gathered information on sixteen different measures of socioeconomic status. They grouped these measures into four distinct categories. These categories included general resources like parental education, material resources like food security, non-material resources like school engagement, and household dynamics like living with two parents.

The team then evaluated diffusion magnetic resonance imaging scans to map the white matter networks of each child. This imaging technique works by tracking the movement of water molecules along the brain’s fibrous pathways. Finally, they recorded general cognitive ability using a standardized battery of tests that assess memory, language, and attention. By building statistical models, the researchers could look at the associations between socioeconomic status, brain network organization, and cognitive scores.

The researchers found that all categories of socioeconomic status were linked to general cognitive ability. Increased general resources, non-material resources, and household stability were associated with higher cognitive scores. Conversely, higher material resources actually predicted lower cognitive scores. The study authors note that this specific negative association contradicts some previous research, pointing to the varied nature of socioeconomic measures.

In looking at the brain, the team uncovered unexpected patterns. They originally suspected that decreased socioeconomic status would be linked to lower levels of white matter integration and segregation. Instead, they found the opposite. Children with lower socioeconomic status tended to have more highly integrated and segregated white matter networks.

Because integration and segregation usually increase as a person ages, this means the brain networks of low-income children appeared more mature than their peers. The authors suggest this aligns with the stress acceleration hypothesis. This theory proposes that children facing early environmental adversity may experience faster biological development. In a stressful environment, the brain might accelerate its maturation to adapt to immediate survival challenges.

While a highly organized brain network is typically a sign of healthy development in adults, premature maturation might come with trade-offs. In this age group, the researchers found that increased network segregation was associated with lower cognitive test scores. Ultimately, the way the brain wired itself into segregated networks partially explained the link between socioeconomic status and cognitive ability.

After establishing these baseline associations, the researchers set out to see if demographic factors changed the modeled relationships. They first grouped the participants by race. They wanted to know if being part of a specific racial group altered how resources, brain wiring, and cognition interacted.

When the researchers simply grouped the children by race, they observed some group-specific associations. However, because wealth and resources are distributed so unequally across racial lines in the United States, the scientists ran a second analysis. In this analysis, they artificially balanced the sample so that each racial group had an equal number of participants from the exact same income brackets.

Once the socioeconomic distributions were equalized, nearly all unique racial differences vanished. The relationships between resources and cognitive ability were largely the same regardless of a child’s race. The study notes that white matter differences previously attributed to race are likely just the result of unequally distributed socioeconomic resources.

The scientists then examined biological sex, which they recorded as sex assigned at birth. Unlike race, sex is a fundamentally biological characteristic. When the researchers ran their models comparing male and female participants, they found distinct patterns.

Biological sex meaningfully changed how the environment was tied to brain development and cognition. For instance, living in a two-parent household was linked to higher cognitive ability in boys, but the results were not statistically significant for girls. Alternatively, having more non-material resources was associated with network segregation only in girls. The brain’s network segregation mediated the link between socioeconomic status and cognition in boys, but it did not do the same in girls.

These sex-based divergences might reflect different biological timelines for boys and girls. Nine- and ten-year-old children are at the onset of puberty. The authors point out that puberty has sex-specific influences on white matter development, and children in lower socioeconomic environments often enter puberty earlier.

The authors acknowledge a few limitations in their work. Because the study relies on data taken from a single point in time, it cannot demonstrate that a lack of resources causes specific changes in the brain. The associations highlight a pattern, but developmental trajectories can only be confirmed through studies that follow the same children over many years.

The mathematical models used to represent brain networks are also simplifications. Brain connectivity involves actual hierarchies that graph-based metrics do not completely capture. The researchers also note that cognitive tests inherently favor the cultural assumptions of the majorities they were designed around, meaning cultural biases could still influence test scores.

These findings advocate for a customized approach when scientists evaluate demographics. Socially constructed categories like race might not act as biological variables, but they do dictate access to resources. In contrast, biological traits like sex can fundamentally alter the pathways through which the environment shapes the growing brain.

The study, “Demographics Change the Relationships Between Socioeconomic Status, White Matter Network Organization, and Cognition in Children,” was authored by Jaden Kropf, Busisiwe Zapparoli, Julie Tseng, Amy S. Finn, Anne L. Wheeler, Nomazulu Dlamini, and Donald J. Mabbott.