A provocative new study suggests that poverty affects brain structure in children and teenagers, with children growing up in the poorest households having smaller brains than those who live in affluence.

The study, published this week in the journal Nature Neuroscience, was led by Kimberly Noble, who teaches at both Teachers College, Columbia University and at the university’s medical school. Elizabeth Sowell of Children’s Hospital Los Angeles in California was the senior author.

In the largest study of its kind to date, the researchers worked with a team of neuroscientists around the country to record the brain images of 1,099 children and teens from ages 3 to 20. The researchers spent three years analyzing the magnetic resonance imaging scans.

They measured the surface area of the cerebral cortices, the outer layer of the brain that controls the most sophisticated cognitive functions such as language, reading, decision-making and spatial skills. Prior studies have shown that the cortex can grow as a result of experiences and stimulation. The researchers also administered cognitive tests to the children.

They found that the brains of children in families that earned less than $25,000 a year had 6 percent less surface area than those whose families earned $150,000 or more. The poor children also scored lower on the battery of cognitive tests.

“We see that children’s brain structure varies with parents’ educational attainment and income,” said Noble, who stressed that researchers cannot say whether poverty causes smaller brain structures.

“Correlation is not causation,” she said. “We can talk about links between parent education and family income and children’s brain structure but we can’t say for sure these differences are causing differences in brain structure.”

The researchers have two theories about why poor children have smaller brains. One is that poor families lack access to material goods that help healthy development, like good nutrition and higher quality health care. The other theory is that poor families tend to live more chaotic lives, and that stress could be inhibiting brain development in children.

Noble has embarked on a new study to try to answer that question. She has begun a pilot study to investigate whether giving low-income mothers a small or large monthly sum impacts the cognitive development of their children in their first three years of life. She plans to recruit 1,000 low-income mothers from around the country, half of whom would receive $333 a month, while the other half receive $20 a month for three years. That research is expected to take five years.

Among the poor children studied, small differences in family income were associated with relatively large differences in brain surface area. But among wealthier children, those same small differences in family income were linked to smaller differences in brain surface area.

But brain size — and cognitive ability — can grow, Noble said. “The brain is in­cred­ibly plastic, in­cred­ibly able to be molded by experience, especially in childhood. These changes are not immutable. ”