MONDAY, June 21, 2004 (HealthDayNews) -- Normal but slowed brain development and the onset of puberty may be important factors in learning disorders such as dyslexia, a new study reports.
The study, which appears in the June 21-25 online edition of the Proceedings of the National Academy of Sciences, suggests that children with learning disabilities may have immature brains that simply didn't have the time needed to develop properly.
The researchers from Northwestern University found that children with dyslexia showed brain development that was about two to four years younger than their chronological age. And while they found that these children's brains could catch up somewhat, the onset of puberty seemed to halt any further improvements in performance.
"Kids with impairments behave essentially normally, just as if they're three years younger," said one of the study's authors, Beverly Wright, an associate professor of communication sciences and disorders at Northwestern University. "Kids with impairments also get better as they get older, but when they start they're about two to four years behind."
And "where they don't catch up is where the brain is developing on into adolescence," added Wright, because the authors believe the onset of puberty may actually stop further brain development in children with learning impairments.
For this study, Wright and her colleague, Steven Zecker, tested the hearing ability of 115 volunteers who ranged in age from 6 to adulthood. Fifty-four of the volunteers were known to have a learning disability, such as dyslexia, specific language impairment, or central auditory processing disorder. The other 61 participants had no known learning problems.
Wright and Zecker led each study participant through five different hearing tests that required them to hear a specific tone even though there was background noise present.
Children with impairments performed the same as children without learning problems but were two to four years younger. And, the researchers found, if a task was one where brain development was expected to be complete by age 10, the children with impairments were able to catch up in performance to the children without impairments.
But if a hearing task involved something where brain development continued into adolescence, the children with impairments never caught up, suggesting that puberty's onset halted further brain development in this area, said the authors.
For example, one test played a brief tone before noise. The group without any learning disabilities could hear the tone at an average of 35 decibels, according to Wright. Those with learning problems, however, couldn't hear it until the tone was played at an average of 58 decibels.
"What we're showing is that they do catch up on some tasks, but they don't catch up on others," said Wright. Normally, according to the study, children's brains would continue to develop and performance on these tests would improve.
Wright added that these findings strongly support the need for early intervention for children with learning disorders.
"If you can identify these children early, maybe you can force-feed them what would be extracted naturally," said Wright.
Dr. Renee Reymond, a general pediatrician at Ochsner Clinic Foundation Hospital in New Orleans, said this study's findings "certainly support the idea of early intervention."
"The brain is plastic, and the earlier we do things, such as cochlear implants or correcting vision problems, the better children do," said Reymond.
The challenge, she said, is identifying children who might have learning problems as early as possible. Wright said that children with impairments are already behind in brain development by the age of 2.
Reymond said at that age it's often difficult to know if a child is developmentally delayed because there is such a wide range of what's normal.
A good guideline, she said, is to talk with your doctor if your 2-year-old can't use two-word sentences, or if a younger child -- about 12 or 15 months -- isn't using specific words other than "Mommy" and "Daddy." Later, schools are generally very good at picking up reading problems and other learning disorders, Reymond added.
For more information on learning disabilities, visit the National Dissemination Center for Children with Disabilities.