During the first five years of life, more than half of the calories consumed by a growing child are used to fuel massive construction projects inside the skull. Building the brain (all the neural connections that form memories, store language, perceive the world, and control bodily movements) is a unique, energy-intensive creative act. The unique structure of a child’s mind, which defines how he or she thinks and feels, is constantly being shaped by the interaction of the environment and the genetic blueprint enmeshed within the developing organization.
Scientists have long wondered which aspects of childhood most influence neurodevelopment. However, it is only in the last few years that collections of data large enough to begin to answer these questions have emerged. Now, after analyzing the brain scans of nearly 12,000 9- and 10-year-old children, researchers at the University of Washington School of Medicine have found that the biggest environmental factor influencing brain structure and function is the child’s family’s socioeconomic status, more than IQ, parenting style, or health history.
Household income, local poverty rates and other neighborhood-level indicators of economic activity accounted for about 16% of the variation in children’s brain function, according to a new study published Thursday in the journal Science. The findings suggest that these differences in measures of brain function are likely due to chronic stress and sleep disturbances, both of which are associated with a more adverse environment.
“The great power of a population epidemiology framework like this is that it acts as a great signpost to where we should focus our resources,” said Scott Marek, a pediatric neuroimaging researcher who co-led the study, and said efforts to understand the mechanisms that drive brain changes should focus. “And overwhelmingly, this data suggests that it’s related to classwork. But specifically, and I hope this is a more powerful message, it seems to be related to sleep, stress, and potentially screens, which, you know, are things that people have at least some control over.”
Independent experts told STAT that the new study provides important evidence that early life environment is a key driver of individual differences in brain organization. But some caution against jumping from this evidence to the conclusion that interventions that improve sleep or eliminate stress will help develop the brain.
“If we could follow people over time, would we find that changes in neighborhood socioeconomic status predicted changes in brain development?” said Janet Currie, a health economist at Yale University and co-director of the Family and Children Program at the National Bureau of Economic Research. “This is really an important question to answer before deciding to intervene.”
The research is called brain-wide association studies (BWAS), in which scientists use statistical methods to link individual differences in living conditions and behavioral characteristics to variation in brain structure and function in large datasets. In this case, the paper emerges from an analysis of the Adolescent Brain and Cognitive Development (ABCD) Study, a large-scale longitudinal brain imaging project supported by the National Institutes of Health at more than 20 sites across the United States.
Starting in 2017, ABCD began recruiting 9- and 10-year-old children to undergo neuroimaging tests every 10 years for the next 10 years. Participants also provide blood and other biological specimens for analysis and undergo exhaustive and repeated behavioral and other assessments, including language, memory, and IQ tests.
Brain scans allow researchers to observe cortical thickness and resting brain activity (a measure of the brain at rest) and build connectivity maps of the brain to find patterns in how different areas of the brain interact with each other. Malek and his colleagues worked with various ABCD collaborators to explore associations between these measures of brain function and 649 variables representing different aspects of children’s lives, including mental and physical health, parenting and peer relationships, drug use, exposure to noise and pollution, cognitive ability, screen time, and cultural and socio-economic factors.
Across data from 11,878 children, researchers found 40 variables related to brain function, 37 of which fell into socioeconomic categories, including measures such as overall wealth in the child’s neighborhood, family income and home ownership, and access to transportation. Socioeconomic influences also accounted for 35 of the top 40 variables related to brain structure. The remaining top variables were related to sleep, screen time, and stress.
Neurologist Nico Dosenbach, who co-led the study, explained that the brain patterns associated with low socio-economic status are very similar to those that occur during sleep deprivation or stimulant use. Areas of the brain associated with sensory and motor functions are activated, making you more responsive to your surroundings. It is very different from the brain patterns associated with higher cognition and other measures of intelligence, which involve the frontal cortex and other areas involved in executive function.
“I was surprised at first,” Dosenbach said. But then it started to make sense when you consider that sleep and stress are downstream consequences of low socio-economic status. Although this evidence is still circumstantial, he stressed, it suggests that socio-economic status “is an indicator of many variables that change the brain, and IQ is only one influence.”
Previous research has linked IQ to physical characteristics of the brain, such as the thickness of the cortex, the outer gray layer of the brain. Dosenbach and Marek believe that these studies incorrectly focused on socio-economic factors. When the researchers adjusted for differences in children’s socio-economic status, the association between brain structure and IQ scores dropped to the point where 70% of the associations were no longer statistically significant. “It’s so intertwined with socio-economics that it’s almost useless,” Malek said.
Malek and his colleagues replicated their study with a sample from the UK Biobank, which is comprised primarily of white people of British or Irish descent, and saw the same pattern. The research team discovered brain differences in the ABCD study data.
Those associated with socio-economic factors were independent of participants’ genetic ancestry.
The discovery comes at an interesting time for the field of exposomics, a science that seeks to investigate the role of the physical and social environment in determining a person’s health.
Secretary of Health Robert F. Kennedy Jr. supported the “Make America Healthy Again” movement and pushed for more research into the environmental causes of chronic disease, autism, and other neurodevelopmental conditions. Last year, the National Institutes of Health committed $50 million to research the link between autism and environmental exposures. President Kennedy and MAHA officials have raised concerns about everything from pesticides to ultra-processed foods, fluoride in drinking water, and childhood vaccines. Less attention has been paid to the health effects of stress and sleep deprivation, and how they can lead to socio-economic disadvantage.
