During the first five years of life, more than half the calories a growing child consumes go to fueling the massive construction project inside their cranium. Building a brain — all the neuronal connections that form memories, store language, perceive the world, control bodily movements — is an energy-intensive act of singular creation. The unique architecture of a child’s mind — what defines how they think and feel — is constantly being shaped by the interplay of the surrounding environments and the genetic blueprints spooled inside their developing tissues.
Scientists have long wondered which aspects of childhood most influence neural development. Only in the last few years have collections of data large enough to start answering those questions emerged. Now, after analyzing brain scans from nearly 12,000 children ages 9 and 10, a group of researchers at Washington University School of Medicine has found that the leading environmental factor influencing brain structure and function — more than IQ, parenting style, or health history — is the socioeconomic status of a child’s family.
Household income, local poverty rates, and other neighborhood-level measures of economic activity accounted for about 16% of the variability in children’s brain function, according to the new study, which was published Thursday in Science. Its findings suggest that these differences in measures of brain function probably stem from chronic stress and disrupted sleep, both of which are associated with more disadvantaged surroundings.
“The big power in population epidemiological frameworks like this one is, it acts as a major signpost for where we should be pouring our resources” or focusing efforts to understand the mechanisms driving brain changes, said Scott Marek, a pediatric neuroimaging researcher who co-led the study. “And overwhelmingly, this data is suggesting it’s, yes, it’s related to class. But specifically — and I hope this is where a more empowering message comes in — it seems like it has to do with sleep, stress, potentially screens. These are things that people at least have some control over.”
Independent experts told STAT that the new research provides important evidence for childhood environment being a key driver of individual differences in brain organization. But some cautioned leaping from this evidence to conclusions that interventions to improve sleep or remove stress would help brain development.
“If you could follow people over time, would you find that changes in neighborhood socioeconomic status predicted changes in brain development?” said Janet Currie, a health economist at Yale University who co-directs the program on families and children at the National Bureau of Economic Research. “This is really the key question that needs to be answered before deciding on interventions.”
The study is what’s called a brain-wide association study, or BWAS, in which scientists use statistical techniques to link individual differences in living conditions or behavioral traits with variability in brain structure and function inside a large dataset. In this case, the paper emerged from an analysis of the Adolescent Brain Cognitive Development (ABCD) Study, a large, longitudinal brain-imaging project backed by the National Institutes of Health, with more than 20 sites around the U.S.
Starting in 2017, ABCD began recruiting 9- and 10-year-old kids to receive neuroimaging every other year for the next decade of their lives. Participants also provide blood and other biospecimens for analysis, and they repeatedly go through a deep battery of behavioral and other evaluations, including language, memory, and IQ tests.
The brain scans allow researchers to look at cortical thickness and resting-state activity — a measure of the brain during rest — and build brain connectivity maps to look for patterns in how different regions of the brain talk to one another. Working with various ABCD collaborators, Marek and his colleagues looked for connections between these measures of brain function and 649 variables representing various aspects of children’s lives, including mental and physical health, parenting and friendships, substance use, exposure to noise or pollution, cognitive abilities, screen time, and cultural and socioeconomic factors.
Across data from 11,878 children, they found 40 variables linked to brain function, and 37 of those fell into the socioeconomic category, including measures of the overall wealth of a child’s neighborhood, family income and homeownership, and access to transportation. Socioeconomic influences also accounted for 35 of the top 40 variables associated with brain structure. The remaining top variables were related to sleep, screen time, and stress.
Nico Dosenbach, a neurologist who co-led the study, described how the brain patterns associated with low socioeconomic status looked a lot like what happens during sleep deprivation, or during the consumption of stimulant drugs. Areas of the brain associated with sensory and motor functions get activated, heightening one’s reactivity to one’s surroundings. It looks very different from brain patterns associated with higher-order cognition and other measures of intelligence, which involve the frontal cortex and other areas related to executive functioning.
“I was surprised at first,” Dosenbach said. But then it started to make sense as they thought about sleep and stress being a downstream consequence of low socioeconomic status. The evidence of this is still circumstantial, he stressed, but it suggests that socioeconomic status “indexes a bunch of variables that change the brain, and that IQ is just along for the ride.”
Prior research has linked IQ with physical brain features such as the thickness of the brain’s outer gray layer, the cortex. Dosenbach and Marek believe those studies were mistakenly picking up on socioeconomic factors instead. When they ran an analysis that adjusted for differences in children’s socioeconomic status, the associations between brain structures and IQ scores dropped to the point where 70% of those associations were no longer statistically significant. “It goes to almost nothing, because it’s so deeply confounded with socioeconomics,” Marek said.
Marek and his colleagues saw the same patterns when they replicated their study in a sample from the U.K. Biobank, which is predominantly made up of individuals with white British or Irish backgrounds. Within the ABCD Study data, the research team found that the brain differences associated with socioeconomic factors were unrelated to the genetic ancestry of the participants.
The findings come at an interesting time for the field of exposomics — science that seeks to explore the role of the physical and social environments in determining a person’s health.
In embracing the Make America Healthy Again movement, Health and Human Services Secretary Robert F. Kennedy Jr. has pushed for more research into environmental causes of chronic diseases, autism, and other neurodevelopmental conditions. Last year, the National Institutes of Health poured $50 million into studying the links between autism and environmental exposures. Kennedy and the MAHA crowd have voiced concern over everything from pesticides to ultra-processed foods to fluoride in drinking water and childhood vaccines. The health impacts of stress and sleep deprivation — and their roots in socioeconomic disadvantage — have received far less attention.