Your education, your job, your income, the neighborhood in which you live are markers of socioeconomic status (SES). First-of-its-kind research shows that SES contribute to physical and mental health, educational achievement, and cognitive capacities. The brain acts as a mediator between socioeconomic status and many outcomes. Scientific studies, however, have previously failed to show whether SES’s impact on the brain is primarily genetic, or primarily environmental.
An international research team led by scientists at the University of Pennsylvania and Vrije Universiteit Amsterdam are trying to determine the relative contributions of genes and environment. The team found evidence that both genetics and environmental influences contribute to the neurological socioeconomic impact. That is not new knowledge, nor a surprise.
“What we saw in the study is that some of the relationship between the brain and socioeconomic status could be explained by genetics, but there is a lot more to that relationship that remains even after you account for genetics,” says Gideon Nave, a marketing professor in Penn’s Wharton School. “This suggests that socioeconomic conditions, in some way, can negatively influence the social and economic disparities which plague our American culture.”
A significant body of research has shown that socioeconomic status has a signature in the brain.
“I study the relation between SES and the brain,” says Farah. “A question that always comes up is: What causes these differences? Are characteristics of SES encoded in the genome, or does life experience at different levels of SES have these effects on the brain? We were able to show that it is both, and that genes and environment seem to exert different effects on different parts of the brain.”
Each participant was assigned two socioeconomic “scores.” One combined income, occupation, and education. The second combined neighborhood and occupation. The two scores accounted for about 1.6 percent of variation in total brain volume.
Scrutinizing the brain scan data, they found a host of brain regions related to SES. The cerebellum showed a substantial connection to SES. Located near the brainstem, the cerebellum is responsible for movement and balance as well as higher level functions involving cognition and learning.
“We see correlations popping up all over the brain between SES and gray matter volume,” says Nave. “They’re small, but with the large sample size of our study, we can be confident that they’re real.”
Hyeokmoon Kweon, a doctoral student at Vrije Universiteit Amsterdam, adds: “Importantly, these small regional correlations do not imply that the overall relationship between gray matter of the brain and SES is also small. In fact, we can predict a sizable amount of SES differences by aggregating these small brain-SES relationships.”
The researchers looked for evidence of the genetic influence of socioeconomic status in the brain. They found that genetics could explain slightly more than half of the relationship between gray matter volume and SES in some regions. The prefrontal cortex and insula were particularly strongly governed by genetic influence. The relationship between SES and gray matter volume in other brain regions was not as consistently correlated with genetics, a sign that alterations there may be environmentally influenced.
Underscoring the influence that the environment can have, the researchers look at another variable in the data: body mass index (BMI). While genetics plays a role in BMI, BMI also arises from non-genetic factors, including nutrition and physical activity. Even after controlling for the known genetic linkages between brain anatomy and socioeconomic status, they found BMI could account for an average of 44% of the relationship between SES and gray matter volume.
The finding suggests that the environmental factors, not just genetic determinants, that can contribute to elevated BMI—such as poor nutrition and insufficient physical exercise—may also manifest in brain structure.
The researchers say that their findings, far from suggesting that there’s nothing to be done to ameliorate the impact of socioeconomic status impact on the brain, instead underscore that thoughtful policymaking should address health and social disparities connected to SES differences.
One solution could be policy interventions, the researchers say, addressing, for example, environmental justice concerns that are linked with poorer neighborhoods. “If air quality is worse in lower-SES neighborhoods, that can be triggering inflammation and other negative effects in the brain,” says Nave. “As just one example, regulations that mitigate air pollution could remove that harm and improve health and well-being across the board, no matter what neighborhood one lives in. Free, high-quality preschool can do the same thing. Genetics, in these cases, is not destiny.”
More studies are needed, the team says, to move from identifying correlations to pinning down causations, in terms of understanding the environmental effects of socioeconomic status on the brain. “With more and more data becoming available,” says Kweon, “I expect we will soon be able to produce such studies, which will help shape targeted interventions.”
The research is published in the journal Science Advances.