By age 15, those who had unsatisfactory relationships with their parents were likely to have a larger hippocampus, an area of the brain associated with memory formation, said Martha Farah, the director of the Centre for Cognitive Neuroscience at the University of Pennsylvania, who conducted the study.
Professor Farah said the change in brain development might be a consequence of high blood levels of stress hormones such as cortisol. She also found differences in the prefrontal cortex area, which governs working memory and attention.
"Parental behaviour is important because it buffers against the effects of stress. We come into the world not able to dampen the stress response ourselves. If it doesn't get damped for you [by being comforted] you have these circulating stress hormones which are [toxic to the brain]," said Professor Farah, who presented the findings to the American Association for the Advancement of Science annual meeting in Boston on Friday.
She said children who lived in poverty were likely to suffer more adverse consequences of stress, because struggling parents were preoccupied and less able to attend to them. "Poverty [is] not about money," she said. "It's about neighbourhoods in which you don't trust your neighbours, exposure to horrible violence and so on."
The research is the first to follow a group of children from infancy, matching measures of their social circumstances during the early school years against psychological tests and brain scans taken in high school.
The study, of 118 African-American children from low- and middle-income Philadelphia families, included home visits by researchers when the children were aged four and eight years. They recorded whether the parent introduced them to the child, hung the child's artwork on the wall, or smacked the child - as indicators of the relationship quality. They looked for the presence of books and musical instruments to gauge the degree of mental stimulation.
Children who had a poor relationship with their parents at four were most likely to display the hippocampus changes later. Language skills were also dramatically impaired.
Jack Shonkoff, director of the Centre on the Developing Child at Harvard University, said: "This isn't just a hocus-pocus black box. It literally disrupts brain architecture, and we can see it happening."