Where does intelligence come from? Are a person's mental abilities inborn, or are they shaped by the environment in which they live and grow up? The issue has fascinated researchers for over a century.

Recently, brain-wide association studies using magnetic resonance imaging have allowed researchers to create maps and match different areas of the brain to specific traits such as IQ and mental health. The studies enable researchers to analyze how factors such as experiences and the environment affect children's developing brains.

A family's financial situation and their neighborhood had the strongest association with children's brain development. Socioeconomic factors accounted for more than their IQ, how they were parented or their health history.

An international team of researchers reviewed magnetic resonance imaging scans of nearly 12,000 children between nine and 10 years old who were enrolled in the Adolescent Brain Cognitive Development Study to try to close this knowledge gap.

They found that a family's financial situation and the resources available in the neighborhood had the strongest association with children's brain development. Socioeconomic factors accounted for about 16 percent of the variability in measures of children's brain function, more than their IQ, how they were parented or their health history.

Scott Marek, first author on the study, told TheDoctor he started calling socioeconomic factors ‘The Elephant in the Brain' because studies like this can't be done without considering them. They define members of a community.

“I thought socioeconomic opportunity would matter, but I did not think it would matter this much,” he said.

The researchers divided almost 650 factors into 12 categories: socioeconomics; screen time; cognitive abilities, including test scores and memory; demographic factors such as race and gender; culture and environment, including religion, language and exposure to pollution; physical health; mental health; social adjustment such as friendships and bullying; parenting; substance use and exposure to substance use by others; personality and medical history.

They determined how these factors affected brain development by measuring the thickness of the cortex, the brain's outer layer, and the strength of connections between networks in the brain.

Of the top 40 factors that affected brain function, 37 were socioeconomic, and of the top 40 variables that affected brain structure, 35 were socioeconomic.

Homeownership, family income and access to transportation had a significant effect on brain structure and function. Screen time, the amount of sleep they reported getting and the amount of stress also had an effect.

Children's environments shape their brains in ways that have been misunderstood as being associated with IQ, but really reflect stress and sleep deprivation.

Socioeconomic factors impacted the areas of the brain associated with motor and sensory functions that are sensitive to daily variations in sleep and stress. They did not affect the prefrontal and parietal cortex, the areas of the brain associated with IQ and problem-solving. Children's environments shape their brains in ways that have been misunderstood as being associated with IQ, but really reflect stress and sleep deprivation, Marek said.

The good news for parents is that they can do something about this. “To the extent that you have it in your power to help your kids get more sleep, that is definitely of primary importance,” said Marek, an assistant professor at the Mallinckrodt Institute of Radiology at the Washington University School of Medicine.

Some tips to help kids get more and better sleep include turning off tablets and computers at least 30 minutes before bedtime and following a bedtime routine like taking a warm bath, brushing teeth and listening to stories.

The study and a related editorial are published in Science.