The study says that the more stress a child has the more it effects the short term memory, which is needed for classroom studies. The research was led by Professor Gary Evens of Cornell University.
From the Washington Post, reporter Rob Stien explains how the research was carried out.
"We know low-socioeconomic-status families are under a lot of stress -- all kinds of stress. When you are poor, when it rains it pours. You may have housing problems. You may have more conflict in the family. There's a lot more pressure in paying the bills. You'll probably end up moving more often. There's a lot more demands on low-income families. We know that produces stress in families, including on the children," Evans said.
For the new study, Evans and a colleague rated the level of stress each child experienced using a scale known as "allostatic load." The score was based on the results of tests the children were given when they were ages 9 and 13 to measure their levels of the stress hormones cortisol, epinephrine and norepinephrine, as well as their blood pressure and body mass index.
"These are all physiological indicators of stress," said Evans, whose findings were published online last week by the Proceedings of the National Academy of Sciences. "The basic idea is this allows you to look at dysregulation resulting from stress across multiple physiological systems."
The subjects also underwent tests at age 17 to measure their working memory, which is the ability to remember information in the short term. Working memory is crucial for everyday activities as well as for forming long-term memories.
"It's critical for learning," Evans said. "If you don't have good working memory, you can't do things like hold a phone number in your head or develop a vocabulary."
When the researchers analyzed the relationships among how long the children lived in poverty, their allostatic load and their later working memory, they found a clear relationship: The longer they lived in poverty, the higher their allostatic load and the lower they tended to score on working-memory tests. Those who spent their entire childhood in poverty scored about 20 percent lower on working memory than those who were never poor, Evans said.
"The greater proportion of your childhood that your family spent in poverty, the poorer your working memory, and that link is largely explained by this chronic physiologic stress," Evans said. "We put these things together and can say the reason we get this link between poverty and deficits in working memory is this chronic elevated stress."
McEwen said the findings are consistent with earlier research in animals and brain imaging studies in people indicating that the body's response to stress, such as chronically elevated levels of cortisol, can adversely affect the brain, including the regions involved in working memory.