Poor Children May Have Smaller Brains Than Rich Children. Does That Tell Us Anything?

A young Professor X.

Photo by Oli Scarff/Getty Images

Social scientists have found that by the time children enter kindergarten, there is already a large academic achievement gap between students from wealthy and poor families. We still don’t know exactly why that’s the case. There’s a sense that it at least partly has to do with the fact that affluent mothers and fathers have more intensive parenting styles—they’re more likely to read to their kids, for instance—and have enough money to make sure their toddlers grow up well-nourished, generally cared for, and intellectually stimulated. At the same time, poor children often grow up in chaotic, food-insecure, stressful homes that aren’t conducive to a developing mind.

A new study in the journal Nature Neuroscience adds an interesting biological twist to this issue. Using MRI scans of more than 1,000 subjects between the ages of 3 and 20, it finds that children with poor parents tend to have somewhat smaller brains, on some dimensions, than those who grow up affluent. Specifically, low-income participants had less surface area on their cerebral cortexes—the gray matter responsible for skills such as language, problem solving, and other higher-order functions we generally just think of as human intelligence. Poorer individuals in the study also fared worse on a battery of cognitive tests, and a statistical analysis suggested the disparities were related to brain dimensions. 

How big a difference are we talking about? According to the researchers, children whose parents earned less than $25,000 per year had 6 percent less surface area on their cortex than those whose parents earned at least $150,000.

This is the largest published study of its kind, and it could well help us understand more about why low-income children start off behind academically. But it’s also a little early to be drawing much in the way of conclusions from the paper, especially about the causes behind its findings. Lead author Kimberly Noble, a professor at Columbia University’s medical school and Teachers College, believes that physical differences between rich and poor kids’ brains may trace back to the environments in which they grow up and is beginning a new research project to test that theory.* But that didn’t stop Charles Murray, the conservative author of the discredited book The Bell Curve, from basically telling the Washington Post that the gaps must be the result of genetic inheritance:

“It is confidently known that brain size is correlated with IQ, IQ measured in childhood is correlated with income as an adult, and parental IQ is correlated with children’s IQ,” Murray wrote in an e-mail. “I would be astonished if children’s brain size were NOT correlated with parental income. How could it be otherwise?”

That there is what one calls irresponsible science commentary.

It’s also important to note that while Noble and her co-authors found a statistically significant correlation between income and brain size, it was not particularly strong. As you can see on the graph below, there were plenty of low-income subjects with relatively large brains, and lots of high-income subjects with relatively small brains. The relationship between income and neural growth seems to be tighter at the very bottom of the income distribution, where children may well be subject to extreme degrees of deprivation. But as Noble put it to me, “You would never be able to look at a child’s family income and from that information alone predict their cortical surface area.”  

In other words, when it comes to brain development, poverty isn’t destiny.  

*Correction, April 20, 2015: This post originally misidentified Columbia’s Teachers College as Teacher’s College.