Imagine a child who gets good grades in school, listens well to his teacher, and is commended for his good behavior in the classroom. Then slowly, his grades start to decline, he grows moodier, and his teacher reports that his attention often drifts in class. The parents are stumped – they can’t think of anything that has changed, except for the appearance of a snoring habit as the child sleeps at night. The parents wonder if their child may be showing signs of ADHD, but could the seemingly innocuous snoring be to blame?
That’s a story often heard in pediatric sleep clinics, said Leila K. Gozal, associate professor of Pediatrics and director of clinical research for the section of pediatric sleep medicine at the University of Chicago Medical Center. Over the past decade, many studies have shown that several behavioral symptoms commonly associated with ADHD – hyperactivity, mood swings, difficulty in school – have been linked in some children to obstructive sleep apnea, the disorder where sleep is frequently interrupted by episodes of blocked breathing.
Pediatric obstructive sleep apnea, or OSA, can have long-term, detrimental effects on a child’s cardiovascular and respiratory health. But it can also create neurocognitive effects, such as a reduced ability to learn and retain information, Gozal said. Previous research conducted by David Gozal, professor and chairman of pediatrics at the Medical Center, found that OSA can reduce a child’s IQ by as many as 10 points, while treatment in children with OSA can improve grades.
But many of these measurements of the neurocognitive effects of OSA on child require extensive testing and expert examiners, Leila Gozal said. So she wanted to develop a simpler test, one that could be used in any sleep clinic to directly test the effect of a sleep disorder upon a child’s memory.
“I wanted to come up with something fairly simple that can be easily done in any sleep center with almost no training or background in neuropsychology,” Gozal said. “The theory is if we come up with a simple test of pictorial memory – what you see and memorize – can we actually see any difference between kids who have OSA and kids who don’t have it?”
Using a $3.95 children’s picture book and a simple testing protocol, Gozal and her colleagues found a strong effect of OSA upon learning and memory. Published online earlier this year by the European Respiratory Journal, the study found that children with OSA were slower to learn the task, and retained less of the information the following morning when compared to normal children.
The children, spending a night at a sleep center to be tested for OSA, were tested before bedtime with a book called simply, “Animals,” containing photographs of cows, penguins, dogs, and 21 other well-known species. Children (ranging in age from 6 to 16) were shown each of the 25 photographs, then were asked to name as many as they could remember after the book was closed. The whole process was repeated four times, and then the children were given one final test 10 minutes after the final learning session. The following morning, after a night of sleep, the children were tested again.
“Based on our results, a child who has OSA needs to put in more effort to learn the same thing that a child without OSA can learn,” Gozal said. “Then the next morning, the child with sleep apnea remembers not even as well as he did the previous night, while the child who was normal remembered exactly what they learned.”
Dr. Gozal’s hypothesis is that these learning and memory deficits result from a decrease in sleep quality – even if the child appears to be getting enough sleep, they could be suffering interruptions from the breathing problems of OSA, as many as 30 times an hour in some kids.
“As an example, if a child’s sleep study results show an apnea hypopnea index [AHI] of 6, it’s similar to a person who gets phone calls every 10 minutes every hour the whole night,” Leila Gozal said. “Obviously that child the next day is not going to be listening to the teacher in the class, is going to be very grumpy, inattentive, hyper, moody, and agitated.”
(If regular ScienceLife readers are feeling a distinct deja vu, you may be remembering similar conclusions, in birds and humans, about the effect of sleep on learning and memory from the research of Daniel Margoliash and Howard Nusbaum – a nice example of clinical research and animal research moving converging.)
With these results published in the European Respiratory Journal, and a low-cost, simple test proven to work, Gozal said she will now move on to more finely-focused questions. Does treating a child’s OSA bring their memory skills back to normal? Are children more susceptible to the effects of OSA on memory at particular ages? Are boys and girls differently affected by low sleep quality? Do children with more severe sleep apnea exhibit more severe learning and memory deficits? Do children with sub-clinical sleep disturbances, below the criteria for an official diagnosis of OSA, still exhibit memory problems?
“Now that I know that it works, I am going to use it in every child I see in the pediatric sleep clinic here,” Leila Gozal said. “What is important is that by applying this simple test we can identify the children who are more susceptible. You can point out the children that are more at risk of memory function, and put them on a higher priority list of getting treated or referred to a sleep specialist.”
Kheirandish-Gozal, L., de Jong, M., Spruyt, K., Chamuleau, S., & Gozal, D. (2010). Obstructive sleep apnoea is associated with impaired pictorial memory task acquisition and retention in children European Respiratory Journal DOI: 10.1183/09031936.00114209