Poverty Saps the Brain's Mental Reserves

financial stress
Money woes can strain the brain, making it harder to perform mental tasks. (Image credit: Financial Stress Image via <a href="http://www.shutterstock.com">Shutterstock</a>)

The mere circumstance of being poor can reduce a person's cognitive abilities by consuming precious mental resources, a study finds.

Researchers gave intelligence tests to two very different groups, demographically speaking — shoppers at a New Jersey mall and farmers in rural India — and found that mental performance decreased markedly when financial pressures were weighing on them. The findings suggest money woes leave the poor less brainpower for other tasks.

"We're not saying the poor are dumber," said study researcher Sendhil Mullainathan, an economist at Harvard University. "It's as if being poor is like pulling an all-nighter, every night," Mullainathan told LiveScience. [10 Ways to Keep Your Mind Sharp ]

Money on the mind

Mullainathan compared doing mental tasks while being poor with surfing the Web while a movie is downloading in the background. "It's going to be much slower," he said.

Some studies have shown people who are poor are less productive workers, less attentive parents and worse money managers. Explanations for poverty often focus on people's lack of effort or a rigged social system, but Mullainathan and his colleagues wondered whether mental resources played a role.

In the New Jersey mall study, the researchers gave an intelligence test similar to an IQ test to about 400 shoppers with a median annual household income of $70,000 and lowest income of $20,000; the incomes were normalized to the number of individuals in a household and then the researchers divided that group in half to represent the "rich" and the "poor."

In one experiment, participants earned real money for correct answers. 

Before the tests, the researchers primed some of the participants to think about their financial woes by asking them questions such as how they would deal with an inexpensive car repair compared with a costly one.

When the repair cost was low, the rich and poor performed equally on the IQ tests that followed. But when the repair cost was high, triggering financial worries, the poor shoppers scored as badly on the tests as if they had stayed up all night, researchers reported online today (Aug. 29) in the journal Science.

Next, the researchers studied the effect of poverty on cognition in a very different setting, in rural Tamil Nadu, India. Sugarcane farmers in India are only paid once a year, after their harvest, so the researchers gave about 460 farmers a numerical intelligence test twice, once before the harvest (when they were "poor") and once afterward (when they were "rich").

The farmers performed almost as much worse on the test before the harvest compared with after the harvest as losing a full night's sleep, the results showed. Across both the mall study and the farmer study, the state of being poor caused an equivalent drop of 9 to 13 IQ points.

Poverty to blame?

The researchers ruled out other factors that could explain the improvement in the farmers' cognitive performance, suggesting the difference had to do with the amount of money the participants possessed.  For instance, the improvement was not due to having more time available, better nutrition or better work ethic, they found.

Nor was mental performance linked to stress — at least not by biological measures. Farmers were more stressed, as measured by heart rate and blood pressure, before the harvest, but this did not account for their lower performance on the tests. In fact, stress has been shown to heighten cognitive ability in some studies.

"I thought it was a very interesting study," said Kimberly Noble, an assistant professor of pediatrics at Columbia University, New York, who was not involved with the research, adding, "I liked how they combined both a laboratory setting and much more realistic setting."

Prudence Carter, a sociologist at Stanford University, questioned whether age or sex differences between the rich and poor shoppers in the mall study may have affected their performance on the intelligence tests. But she found the results convincing. "What's important is they show that both the poor and the rich [perform] the same when there's no pressure on them," Carter told LiveScience. "It's only when the poor were subjected to more strenuous economic conditions that they performed less well than the rich," she said, adding that the notion could explain why poorer children often do worse in school.

The notion that being poor is mentally taxing has implications for how society addresses poverty. For example, a child care program for low-income families could not only free up time for parents to pursue other responsibilities, but could actually provide a cognitive benefit.

The mental effects of poverty apply to scarcity more broadly, whether it's money, time or food, Mullainathan said. "When you experience scarcity, your mind focuses on that one thing."

Follow Tanya Lewis on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Tanya Lewis
Staff Writer
Tanya was a staff writer for Live Science from 2013 to 2015, covering a wide array of topics, ranging from neuroscience to robotics to strange/cute animals. She received a graduate certificate in science communication from the University of California, Santa Cruz, and a bachelor of science in biomedical engineering from Brown University. She has previously written for Science News, Wired, The Santa Cruz Sentinel, the radio show Big Picture Science and other places. Tanya has lived on a tropical island, witnessed volcanic eruptions and flown in zero gravity (without losing her lunch!). To find out what her latest project is, you can visit her website.