Recent research suggests that poverty may have a profound effect on the brain. Imaging studies show that the conditions that go hand-in-hand with poverty — a combination of environmental factors and emotional stressors — can actually slow the development of crucial parts of the brain involved in regulating behavior, impulsivity, and mood. And lacking resources appears to promote certain behaviors (such as excessive borrowing) that perpetuate the poverty cycle.
How Poverty Impacts Brain Development
Children from low-income households tend to have poorer academic performance and lower standardized test scores than kids from higher-income families, as well as more emotional and behavioral problems, including ADHD, depression, and anxiety. In adulthood, they typically hold fewer advanced degrees and have truncated earning potential. New research suggests this may, in part, be attributed to the way growing up in an impoverished home changes the brain.
A study published Monday in the journal JAMA Pediatrics followed 389 kids and teens, aged 4 to 22, from a range of socioeconomic backgrounds between 2001 and 2006. The researchers, including Jamie Hanson, Ph.D., a postdoctoral fellow at Duke University and the University of North Carolina-Chapel Hill’s Center for Developmental Science, and Barbara Wolfe, Ph.D., a professor of economics, population health sciences, and public affairs at the University of Wisconsin-Madison, found that kids living in households just above the federal poverty level had gray matter volumes that were 3 to 4 percentage points below the norm for their age group. The lower volume was concentrated in the brain's frontal and temporal lobes, regions that are implicated in behavioral and learning problems. Among kids living below the federal poverty line, gray matter volumes were 8 to 10 percent below the norm. On average, these kids performed 4 to 7 points worse on standardized tests.
Hanson, Wolfe, and their colleagues calculated that as much as 20 percent of the disparity in test scores could be explained by these maturation gaps.
“We’re still charting what this truly means for behavior, but we’re starting to try to connect it to the various outcomes you often see, things like educational achievement and health-related behaviors and outcomes,” Hanson tells ATTN:. “The hope is that we’ll find neural signatures of that, and then use them to develop interventions and argue for public policy measures that would help families in need.”
Earlier work by Hanson and Wolfe, published in the journal PLOS ONE in 2013, found similar neurodevelopmental disparities between lower- and higher-income children. That study followed 77 kids from a few months after birth until age 4. They found that children born into families with incomes under 200 percent of the federal poverty level had lower gray matter volumes than kids from high-income families. Gray matter volume in kids from middle-income families did not statistically significantly differ from that of their richer peers, suggesting a poverty-specific effect.
These differences weren’t present at birth, Wolfe says. “We found that before age 1, infants’ brains were basically the same, regardless of whether or not they were growing up in a poor family. But then as we traced them to age 4, we found areas that were developing more slowly among infants in low-income families.”
The brain regions that are suffering are critical, Hanson adds. “The frontal lobe, the region that helps with self-control and strategy and planning, had a slower growth rate for kids in lower-income households.”
Similarly, in a paper published in Nature Neuroscience in March, Kimberly Noble, MD, Ph.D., an associate professor of neurosciences and education at Columbia, and her colleagues imaged the brains of 1,099 kids, teens, and young adults aged 3 to 20. They found that those who came from families with a yearly income of less than $25,000 had 6 percent less total brain surface area than kids from families reporting more than $150,000 in annual earnings. The gap was especially pronounced in areas involved in language, reading, executive functions, and spatial skills. And as parental income dropped, so did kids’ performance on cognitive tests.
“Past work has suggested that greater surface area tends to be associated with intelligence,” says Noble. “By age 10, more intelligent children tend to have greater brain surface area than less intelligent children.” But, she adds, this is true only on average, at a population level. “You couldn’t show me a brain surface area and I could tell you what that kid’s IQ would be.”
It's not clear what, specifically, about poverty takes a toll on brain development, but there are dozens of potential culprits, likely working together. For instance, Hanson says, housing in low-income neighborhoods tends to be noisy, crowded, and built with substandard, potentially neurotoxic materials like lead; low-income areas also tend to have more air pollution than more affluent neighborhoods, and poor nutrition is common. All of this can hinder proper physiological development.
Living in resource-poor neighborhoods also exposes young children to the stressors of violence and crime, as well as unstable parental relationships. Over time, the constant stress “starts to affect our body and behavior pretty strongly,” says Hanson. Too much stress can, for example, cause the adrenal glands to flood the body with the fight-or-flight "stress hormone," cortisol, which in large amounts can cause systemic inflammation. Excess levels of cortisol in pregnancy can even potentially harm fetal cognitive development.
Healthy brain development is also linked to how much cognitive stimulation a child receives in those early years, says Noble. Parents in low-income households may be working multiple jobs with unpredictable hours, returning home physically and emotionally drained. As a result, they’re less likely to speak at length to and around their kids, and when they do, they use less complex words. They’re also less likely to read to their children and can’t afford as many toys and books, not to mention educationally enriching extracurricular hobbies and activities. All of this can stunt the development of cognitive capacities like language, logic, and memory.
Scarcity Takes a Behavioral Toll
Poverty also alters human behavior in dramatic ways. In a series of experiments, Sendhil Mullainathan, Ph.D., a professor of economics at Harvard, and Eldar Shafir, Ph.D., a professor of psychology and public affairs at Princeton, found that adults who find themselves in situations of scarcity begin to lose their cognitive capacities. Quite literally, scarcity saps IQ points.
In one study, published in Science in 2013, Mullainathan and Shafir polled a random group of shoppers at a New Jersey mall. They gave one group of participants the following scenario:
"Imagine you’ve got car trouble and repairs cost $300. Your auto insurance will cover half the cost. You need to decide whether to go ahead and get the car fixed, or take a chance and hope that it lasts for a while longer. How would you make this decision? Financially, would this be easier or hard?"
Afterwards, they administered IQ tests to the participants. The subjects all performed about the same, regardless of self-reported level of income.
Then, the researchers changed the dollar amount in the scenario to $3,000. Suddenly, test scores dropped by 14 points among participants with the lowest incomes — a difference comparable to the cognitive gap between chronic alcoholics and healthy adults, or the equivalent of being sleep-deprived for 24 hours.
Put simply, Shafir says, human cognitive bandwidth is finite. “When we attend to one thing, we attend much less to something else.” If you’re thinking about one problem — say, the burst pipe in your kitchen that will cost $200 to repair — that means there are scores of other issues — like the overdue car payment — that aren’t on your mind.
When people encounter severe scarcity day-in, day-out, they’re basically paralyzed by their competing concerns, Mullainathan and Shafir write in their book Scarcity: Why Having Too Little Means So Much. And that’s hardly conducive to making rational, clear-headed decisions. Take overborrowing and predatory, high-interest payday loans, for instance. “You are extremely stressed for money. You need something urgently, so you take a little bit of money,” says Shafir. “But the next month you’re just a little bit poorer than you were this month, and the only way to manage it is to take another payday loan. At some point, each loan just becomes a way to pay off the previous one.”
Plus, the constant taxing of cognitive capacity leaves little mental energy left over for resource-poor people to think about the big picture: pursuing an advanced degree, looking for a better-paying job, or moving to a neighborhood that’s safer for children (to say nothing of the racial or institutional barriers to achieving these goals). “When you find yourself heavily preoccupied by poverty-related concerns — it could be food, rent, medicine — you neglect other things in your life, even stuff you otherwise know is important,” says Shafir.
Inattention, impulsivity, and irrational decisions may therefore not be character traits inherent to the poor, but rather a byproduct of poverty: the consequence of an overextended mind. Take away some of the stress, the researchers propose, and you’ll free up a reservoir of mental energy that can be applied to pursuing an education, a job, and a better life for the family.
“When we talk about the poor, there’s a temptation to have this image of somebody homeless living under a bridge,” Shafir adds. “But in the study in the Jersey mall, these were not people in abject poverty. These were essentially people with budget constraints. When you look at their income levels, we’re talking 100, 150 million Americans, not some exotic group.”
Loosening Poverty's Grip
Combined, the behavioral and developmental research suggest that social programs that seek to alleviate the psychological, environmental, and financial stressors of poverty could reverse some of the toll on brain development and behavior, ultimately improving outcomes for those living below the poverty line.
The science hasn’t progressed to the point where researchers can confidently prescribe solutions to the neurodevelopmental deficits caused by growing up poor, but they have seen evidence that the brain’s ability to adapt and change over time — its plasticity — can be harnessed, with the proper stimulus, to fill some of the gaps in brain development.
In his research, for instance, Charles A. Nelson III, Ph.D., a professor of education at Harvard and a professor of pediatrics and neuroscience at Harvard Medical School, has studied groups of children who grew up institutionalized in Romania, where human contact and care was minimal. Being reared in conditions of extreme neglect left these children with lower brain gray and white matter volumes compared with kids who had never been institutionalized. But when these developmentally disadvantaged kids, aged 18 to 24 months, were moved from an institution to a high-quality foster care program, their white matter volumes rebounded, catching up with those of their non-institutionalized peers.
“Those kids showed more developmental recovery and healthier development generally,” Nelson says. “This argues that there is a sensitive period where the brain can recover from having grown up initially in an adverse environment.”
But what about people who are past that critical period, like older children or adults? At least in terms of brain imaging studies, Nelson says, “no one has done that research yet.”
Still, social programs aimed at improving outcomes for low-income kids and teens seem to make a difference from a behavioral standpoint, Wolfe says. In 1994 through 2010, for instance, a US Department of Housing and Urban Development-sponsored program called Moving to Opportunity helped move families living in public housing into public-market housing in more prosperous neighborhoods with lower crime rates. During the 10 to 15 year follow-up period, researchers found that physical and mental health improved among adults who moved to these neighborhoods, compared with those who remained in public housing. Young women who were children when the study began had lower rates of mood disorders, panic attacks, and other emotional and behavioral problems, and arrests for violent crime decreased among young men and women. However, this study did not find any changes in educational or economic achievement.
"Poverty is not deterministic. People do move out of it, and many people succeed in amazing ways," says Hanson. "But what our work and many other people’s work shows is that poverty stacks the odds against them."
From the behavioral economists’ point of view, social programs designed to benefit the poor, such as job-training courses, vaccine programs, and financial education, need to become more flexible in order to accommodate the needs of the people they’re serving. For example, because many people living below the poverty line work multiple low-wage jobs with unpredictable schedules, job training or continuing education courses should offer the same classes at different times and be less punitive when it comes to lateness or absenteeism, Mullainathan argues in a Harvard Magazine article.
Even small changes could have an outsize impact, Shafir says. “There are many working poor who are juggling child care, for example. If you work shifts at McDonald’s, they often don’t tell you your schedule much ahead of time. You find out a day or two before that you’re working on Wednesday, and now you have to run and find someone to be with your child that day. If McDonald’s gave you your schedule a week or a month in advance, even that could make a big difference to someone who is trying to arrange child care two days from now.”
It’s just a drop in the bucket, to be sure, but it's one that stands to liberate some of those precious — and finite — cognitive resources, Shafir argues. And the more social policies are guided by data and research, the more we stand to even the playing field for those who enter the game with stacked odds.