Stress from Poverty Decreases Child Brain Sizes—Even at Birth

The size of a child’s brain may be determined before he or she is even born.

Though the idea has been controversial, some scientists have long suspected a link between socioeconomic class and cognitive ability—but they’ve never unearthed clear-cut, biological proof of it. A new study, published yesterday in Nature Neuroscience, might be the closest experts have ever come to defining such a connection. Led by neuroscientists Kimberly Noble of Columbia University and Elizabeth Sowell of Children’s Hospital in Los Angeles, California, the team examined 1,099 individuals between the ages of three and 20 years old, and found that income was logarithmically associated with brain surface area. In other words, as income increased, brain surface area increased as well.

While not irreversible, the effects of socioeconomic status on cognitive ability are more pronounced than scientists imagined.

Perhaps the most significant achievement of this study is that it eliminated differences due to ethnicity. In this way, the study is an exclusive glimpse into the brain’s size across a population, independent of genetic ancestry. Here’s Sara Reardon, writing for Nature News:

Because people with lower incomes in the United States are more likely to be from minority ethnic groups, the team mapped each child’s genetic ancestry and then adjusted the calculations so that the effects of poverty would not be skewed by the small differences in brain structure between ethnic groups.

The brains of children from the lowest income bracket — less than US$25,000 — had up to 6% less surface area than did those of children from families making more than US$150,000, the researchers found. In children from the poorest families, income disparities of a few thousand dollars were associated with major differences in brain structure, particularly in areas associated with language and decision-making skills. Children’s scores on tests measuring cognitive skills, such as reading and memory ability, also declined with parental income.

It will be important to follow this cohort over time, but the conclusions of this study strongly support another piece of unpublished work that looked at the brains of 44 African-American girls, each about a month old, born to families with different incomes. There, the link was found, too, even at that very early age. The researchers suggest the effects may be seen as early as birth, too, due to environmental factors like nutrition in-utero and maternal stress.

Epigenetics could play a role, too. “People’s experiences exert a strong influence on their biology by silencing genes or turning them back on, significantly changing the way a cell functions without changing its DNA sequence,” wrote Eleanor Nelson for NOVA Next last year. Stress, anxiety, and even trauma may be passed down through these subtle genetic mechanisms, and that may affect a child’s brain structure, as well.

Still, the disadvantages of being born in poverty are not irreversible, the experts say. With quality care and nutrition, a child born in destitution can have the same potential as the highly privileged.