"This is paving new ground, scary new ground," said Dr. Ronald D. Chervin, the director of the University of Michigan Sleep Disorders Center, who was not associated with the study. "The fact that children with sleep apnea would score worse on neurocognitive testing than normal children is not new. The new part is actually showing evidence of neurochemical changes in the brain."

For the research, published in the Aug. 22 online issue of the journal Public Library of Science Medicine, Dr. Ann Halbower, medical director of the pediatric sleep disorders program at the Hopkins' Children's Center in Baltimore, and colleagues looked at 31 children between the ages of 6 and 16. Nineteen of them had untreated severe sleep apnea, a condition associated with repeated nighttime awakenings and daytime grogginess.

Using a special type of magnetic resonance imaging (MRI), the researchers found that those children with sleep apnea had significant changes in two brain regions associated with higher mental function: the hippocampus and the right frontal cortex. They also determined that the children had altered ratios of three brain chemicals -- N-aceytl aspartate, creatine and choline -- which are indicative of brain damage.

The kids with sleep apnea had lower mean IQ test scores than the healthy children (85 compared to 101) and performed significantly worse on standardized tests that measure executive functions such as verbal working memory and verbal fluency.

"Executive function is the ability to take an old memory and put it to use in a new situation," Halbower explained. "It's what makes smart people smart. The clinical implications are that doctors need to understand that sleep apnea is more of a problem that we thought it was. It's not just a disease of old people."

Because untreated sleep apnea appears to impair brain chemistry, its effects could be permanent, Halbower added.

"We can only assume that it could turn an otherwise smart kid into a mediocre kid, which could mark him for life," she said.

But it's also possible that these effects are reversible. Halbower's next study will try to determine whether sleep-apnea treatment can restore normal brain chemistry and cognitive function.

The standard treatment for sleep apnea in children is surgical removal of enlarged tonsils and adenoids, which can obstruct breathing. Other treatments include removal of excess tissue in the back of the throat or nose and the use of continuous positive airway pressure (CPAP) machines to maintain normal airflow during sleep.

Because untreated sleep apnea may have even more severe effects in children than in adults, the sooner it's detected, the better, Halbower said.

So parents should be aware that one of the most important symptoms of sleep apnea is frequent pauses in breathing that result in arousal from sleep and stirrings in bed. Other symptoms include snoring, labored or loud breathing, coughing, choking, gasping, excessive nighttime sweating and, sometimes, bedwetting by children older than 6.

"If you're looking at an infant or young child, they may sleep in odd positions," Chervin said. "They may sleep with their rear end up in the air and their head tilted back, which is probably an effort to open their airway."

Daytime signs of sleep apnea include sleepiness, an inability to concentrate and poor performance in school. "But it should be remembered that younger children with sleep apnea aren't just sleepy," Halbower pointed out. "They also show signs of hyperactivity and irritability."

Studies have also shown that some children with sleep apnea also have attention deficit hyperactivity disorder (ADHD).

"If you have a child who snores and has behavioral problems during the day associated with ADHD, conduct disorder or oppositional-defiant disorder, talk to your pediatrician about the possibility that there could be a relationship," Chervin said. " I don't think that sleep apnea explains a majority of ADHD, but it may explain a minority of ADHD."

While the prevalence of snoring in children is about 16 percent to 20 percent, the prevalence of true obstructive sleep apnea in children is only 2 percent to 3 percent, Halbower said.

But, like the adult version, children's sleep apnea is usually unrecognized, and it's often difficult for doctors to diagnose because its effects may not be evident during a typical examination.

However, Chervin cautioned that the Hopkins study, because of the small number of children studies, shouldn't be considered the last word on any possible link between sleep apnea and brain damage.

"I would describe it as preliminary news, because it opens up a whole area that needs further investigation," he said. "It'll be fascinating to see if the neurochemical changes that were present before treatment are still present after treatment."