"Children may fail to develop adequate reading skills because of their environment, abnormal brain structure, or both," says lead study author Mark A. Eckert, Ph.D., of the McKnight Brain Institute of the University of Florida.
The researchers found that reading skill and verbal ability were predicted by asymmetry of the temporal plane, a brain area that processes auditory information. Poorly performing children had more symmetrical temporal planes, compared with a left-weighted asymmetry which is more commonly seen.
Eckert and colleagues also found that although children from low-income families performed more poorly on the reading tests, brain asymmetry had similar effects across income levels.
They also found that parents in low-income families, identified through their participation in a government subsidized school lunch program, spent significantly less time helping their children with homework than wealthier parents. Children with both weak asymmetry and low income demonstrated the weakest language mastery.
"I think it's important to note that there were no anatomical differences in children from different socioeconomic environments. But if a child has a less asymmetrical brain, improving the literacy environment becomes especially important", says Christiana M. Leonard, Ph.D., a co-author of the study.
The study is published in the August issue of the journal Child Development.
Magnetic resonance imaging was used to examine the brains of 39 sixth grade children who were representative of the public school population in Alachua County, Florida.
The researchers gave the study participants verbal tests, including tests of their ability to pronounce unfamiliar words, to determine missing words in a paragraph and to reorder nonsense syllables into words.
The researchers aren't sure why brain symmetry interferes with the development of reading skills. "One possibility is that larger right hemisphere structures might interfere with left hemisphere dominance of language processing," suggests Linda Lombardino, Ph.D., another co-author at the Institute.
The researchers note that the correlation between reading ability and brain asymmetry only applied to right-handed participants. In most right-handed people, the left hemisphere dominates language processing, while language dominance is unpredictable in non-right-handed individuals.
Current studies are testing whether reading intervention programs should be tailored to children's anatomy. An understanding of how home environment and brain structure affect reading skill may lead to more effective reading intervention programs, says Eckert.
These findings emphasize the importance of a rich early linguistic environment, especially for children with less asymmetrical brains.
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