Growing up poor may have an effect on brain size, a new study suggests.
Researchers wrote in a study published in JAMA Pediatrics on Oct. 28 that children who grew up in impoverished environments had smaller white and cortical gray matter volumes in the brain, in addition to a smaller hippocampal and amygdala volume.
"We've known for many years from behavioral studies that exposure to poverty is one of the most powerful predictors of poor developmental outcomes for children," lead author Dr. Joan L. Luby, a professor of child psychiatry at Washington University, in St. Louis, said in a press release. "A growing number of neuroscience and brain-imaging studies recently have shown that poverty also has a negative effect on brain development."
"What's new is that our research shows the effects of poverty on the developing brain, particularly in the hippocampus, are strongly influenced by parenting and life stresses that the children experience," she added.
Grey matter has been linked to intelligence, and white matter is the portion of the central nervous system that is responsible for transmitting signals in the brain. In addition, the hippocampus is the location of the brain responsible for consolidating short and long-term memory. The amygdala deals with processing memories and emotional responses.
The researchers looked at data from a study on depression that had been completed on 145 children around the St. Louis area. The children had been followed since preschool, and had their brains scanned using magnetic resonance imaging (MRI). The kids also had stress tests completed.
Poverty was assessed by the "income-to-needs ratio," which looks at the family's size in relation to their annual income.
The impact of poverty on the brain was more pronounced in children with stressful home environments whose parents lacked good nurturing skills, researchers found.
To evaluate parental nurturing in the study, researchers asked the children to wait eight minutes before opening a present. Their parents were also in the room, and were instructed to fill out questionnaires during this time. The purpose of the activity was to observe the child-parent interaction. Parents were judged to be poor nurturers if they were visibly more stressed and impatient towards their children during the task.
The poor children had smaller gray, white, hippocampal and amygdala brain volumes regardless of the parental style.
In addition, poor children were linked to smaller hippocampal volumes in the left and right hemispheres if they had less parental nurturing. More stress in the children's lives was linked to smaller hippocampal volume in the left hemisphere alone.
The study did not look at the children's behavior or cognitive abilities, so no conclusions could be drawn about whether brain size was linked to any of these problems.
Ludy said to the Press Association that she herself was surprised by the study's finding.
"Initially, we thought we would have to control for the effects of poverty, but as we attempted to control for it, we realized that poverty was really driving some of the outcomes of interest, and that caused us to change our focus to poverty, which was not the initial aim of this study," she pointed out.
But in an accompanying editorial, Charles Nelson, Ph.D., a professor of pediatrics at Harvard Medical School and Boston Children's Hospital, said the results might ring true for children regardless of their economic background, if their parents weren't nurturing.
"It's not as if those affluent families are protected from these same [parenting] issues," Nelson told Reuters.
"The reason it's probably more common in poorer families is that they're lacking in resources and trying to make ends meet. There is a level of background stress... that may keep them from being the parent they want to be," Nelson added.
Dr. Charles Gay, medical director of Texas Children's Hospital neurology clinics and an associate professor in the department of pediatrics at Baylor College of Medicine, told CBSNews.com the findings are interesting, but cautioned that the study did not prove that poor children were more likely to have behavioral or cognitive problems.
Gay, who was not involved in the study, explained that research has shown that brains two standard deviations from the optimal brain size have been associated with an increased risk of cognitive problems. However, if the brain is smaller but still within the normal range, it doesn't necessarily mean the person is at a higher risk for developmental problems.
Animal models have shown that certain kinds of social interaction deprivation and high levels of stress have led to differences in brain volume.
"If that leads to behavioral -- or phenotypic -- differences, and if that translates to humans, that would be concerning," he said. "We're still waiting on that."
He also pointed out that studies have shown that growing up in a low income environment can have a negative effect on child development, especially through poor cognitive outcomes, poor school performance and a higher risk of behavioral problems. He called for more studies to see what the potential behavioral or cognitive implications of smaller brains might be.
"This could raise important questions that really need to be looked at more carefully," he said. "How do we approach the children and the families if there are differences?"