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The structure and growth of a child's brain may be indirectly affected by their parents' income, a study in the US has claimed.

In research involving more than a thousand children and young people, scientists found that those with poorer parents were more likely to have smaller brain surface area in key regions linked with language and reading.

The effects of income, as well as parent's educational history, appeared to be independent of genetic factors, the researchers from nine American universities said.

Social and economic background has long been linked with variations in brain functioning, but the new research is thought to be the first to suggest these factors can even affect the structure of the brain itself.

A link between income and children's diet, healthcare, lack of access to good schools and play areas, and even exposure to polluted areas may lie behind the connection, neuroscientists said.

Not all children of poorer families had smaller brain surface areas and the authors of the study said their findings did not mean that a person's social status led to "an immutable trajectory of cognitive of brain development".

Nevertheless, the findings are a potent reminder of the long-term impact of health inequalities. Elizabeth Sowell, professor of paediatrics at the University of Southern California, said that the differences in brain structure could be linked to "wider access to resources likely afforded by the more affluent".

"Future research may address the question of whether changing a child's environment - for instance, through social policies aimed at reducing family poverty - could change the trajectory of brain development and cognition for the better," she said.

A wide variety of external factors can affect the growth of the brain during childhood and adolescence, when the regions of the brain responsible for the higher cognitive functions such as learning, reasoning and language develop rapidly.

Previous studies have shown that the brains of 10-year-olds who score better on intelligence tests have a greater surface area. During childhood and adolescence, the brain is at its most impressionable - known by scientists as 'experience-dependent plasticity'.

The study, which is published in the journal Nature Neuroscience, recruited 1,099 young people. Information on their background was collected through questionnaires sent to parents, and detailed pictures of the participants' brains were acquired through high resolution magnetic resonance imaging (MRI) scans.

A parent's educational background was also linked with their children's brain structure, with additional years at high school or college associated with greater surface area. The effect of parental income on brain structure was most pronounced among the poorest children, said the study's lead author Kimberley Noble, assistant professor of paediatrics at Columbia University Medical Center.

"Among children from the lowest income families, small differences in income were associated with relatively large differences in surface area in a number of regions of the brain associated with skills important for academic success," she said.

Dr Andrea Danese, a leading expert in developmental psychobiology at King's College London's Institute of Psychiatry, Psychology and Neuroscience, said the study showed "detectable differences" between disadvantaged young people and their better-off peers.

"The experience of socio-economic disadvantage could have caused changes in brain development among young people," he said. "Other adverse experiences associated with socio-economic disadvantage, such as child abuse, could have affected brain development.

However, he said that it could not be ruled out that some of the differences had been passed on in parents' genes.