Source: Science Mag

Stark and rising inequality plagues many countries, including the United States, and politicians, economists, and—fortunately—scientists, are debating its causes and solutions. But inequality’s effects may go beyond simple access to opportunity: a new study finds that family differences in income and education are directly correlated with brain size in developing children and adolescents. The findings could have important policy implications and provide new arguments for early antipoverty interventions, researchers say.

Researchers have long known that children from families with higher socioeconomic status do better on a number of cognitive measures, including IQ scores, reading and language batteries, and tests of so-called executive function—the ability to focus attention on a task. More recently, some studies have found that key brain areas in children of higher socioeconomic status—such as those involved in memory or language—tend to be either larger in volume, more developed, or both. However, these studies have suffered from some important limitations: For one thing, they don’t adequately distinguish socioeconomic status from racial background, which in the United States are difficult to tease apart because nonwhite groups tend to have higher poverty levels. And few studies treat family income and education levels as independent factors, even though they can act differently on the child’s developing brain. For example, income may be a better indicator of the material resources (such as healthy food and medical care) available to a child, whereas more highly educated parents may be better able to stimulate their child’s intellectual development.

To get around some of these limitations, a research team scanned the brains of 1099 children and young adults, ranging from 3 to 20 years old, using MRI. The researchers, led by Kimberly Noble of Columbia University and Elizabeth Sowell of Children’s Hospital Los Angeles in California, both cognitive neuroscientists specializing in child development, recruited subjects in collaboration with researchers at nine U.S. universities and hospitals, using Internet and community advertising as well as word of mouth.

The MRI scans allowed the team to measure the surface area of the subjects’ cerebral cortices, the outer layer of the brain where most advanced cognitive processing takes place, including language, reading, and executive functions. The researchers chose to measure cortical surface area because previous research had shown that it increases throughout childhood and adolescence as the brain develops, thus making it a potentially sensitive indicator of intellectual abilities. Studies in both animals and humans have suggested that the cortex can grow larger as a result of life experiences, although genetic factors may partly influence its overall size. The team also administered a battery of standard cognitive tests to the subjects and took DNA samples to control for the factors of race and genetic ancestry.

The results, published online this week in Nature Neuroscience, showed that cortical surface area was indeed correlated with different measures of socioeconomic status. Parental education—the number of years that parents had gone to school—showed a linear correlation with overall cortical surface area, especially for regions of the brain involved in language, reading, and executive functions. As a rough approximation, the children of parents with only a high school education (12 years of education or less) had 3% less cortical surface area than children whose parents had attended universities (15 years or more), Noble and Sowell told Science.

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