What makes a child nap? Most parents cherish toddlers’ naps as moments of respite and recharging, for parent and child alike; we are all familiar with the increased crankiness that comes when a nap is unduly delayed or evaded. But napping behavior has been somewhat taken for granted, even by sleep scientists, and napping problems have often been treated by pediatricians as parents’ “limit-setting” problems.

Now, researchers are learning that it is not so simple: napping in children actually is a complex behavior, a mix of individual biology, including neurologic and hormonal development, cultural expectations and family dynamics.

What parents usually want to know is simply how long a child should nap. That concern dates back a little over a hundred years: In the first decade of the 20th century, European experts published the original studies measuring the sleep patterns of children and promptly began worrying they were not getting enough sleep.

Today, researchers believe that very young children take naps because so-called sleep pressure builds rapidly in their brains — that is, the need for sleep accumulates so quickly during waking hours that a nap becomes a biological necessity. It is not just a question of how much total sleep that children need in 24 hours. Possibly because of the intense synaptic activity that goes on in their highly active, highly connected brains, young children are less able to tolerate long periods of time awake.

In the early 1980s, Dr. Alexander A. Borbély, a professor of pharmacology at the University of Zurich, Switzerland, posited a “two-process model of sleep regulation.”

The “circadian process,” which has been localized to a specific place in the brain, works a little like a clock, tying our sleep to schedules and to cycles of light and dark, regardless of how much we have or have not slept. This interacts with the “homeostatic process” which works differently, pushing us harder toward sleep the longer we stay awake and building up sleep pressure, which can be measured via EEG recordings.

Napping happens “because children have a much faster sleep homeostasis — they build up sleep pressure more quickly, they are not so tolerant toward longer waking periods,” said Dr. Oskar Jenni, a pediatrician who is director of the child development project at the University Children’s Hospital Zurich.

Generally, new infants sleep between feedings in short periods both days and nights. As they grow, babies sleep at night (more or less), waking to be active in the early morning and taking morning naps; they wake again for play and food, followed by afternoon naps.

Sometime after the first birthday, the two naps are consolidated into one, usually in the late morning or early afternoon. “The rationale for having your afternoon nap over by 3 p.m. is to build up enough sleep drive so you can fall asleep at night,” said Dr. Judith Owens, a pediatrician who is director of sleep medicine at Children’s National Medical Center in Washington.

As they grow toward school age, most children begin to fight against that remaining nap or just leave it behind. But there is a great deal of individual variation, and many parents struggle with a child who seems too eager to do without a nap.

Sometimes problems arise because relinquishing the nap conflicts with a parent’s daily program or a day care center’s routine. Sometimes the parent sees the tantrums and whining and general negativity that come with fatigue, a sign that the child is not really ready to do without a nap.

“By age 5, about 80 percent of kids have given up a nap — that means one in five still napping,” Dr. Owens said.

Dr. Jenni was one of the authors of a large study, published in 2003 in the journal Pediatrics, which measured sleep duration across childhood. He and his colleagues documented the decrease in daytime napping and the consolidation of nighttime sleep as a group of Swiss children grew up. They also found that individual children’s sleep needs and sleep patterns tended to be consistent through age 10. In other words, children who slept less than their peers as infants grew into older children seemed to need less sleep.

A 2005 study of American children ages 3 to 8 showed distinct differences between black and white children, too. While total sleep duration for the two groups was similar, black children napped more and tended to be older when they gave up their naps.

Despite the intriguing findings, the study of napping patterns is still in its infancy — or perhaps toddlerhood. Experts are just beginning to understand the biological underpinnings.

Dr. Monique LeBourgeois, a sleep scientist at the University of Colorado at Boulder, and her colleagues recently conducted the first study on how napping affects the cortisol awakening response, a burst of hormone secretion known to take place shortly after morning awakening. They showed that children produce this response after short naps in the morning and afternoon, though not in the evening, and it may be adaptive in helping children respond to the stresses of the day.

By experimentally restricting sleep in young children, and then analyzing their behavior in putting puzzles together, Dr. LeBourgeois’ group also is quantifying how napping — or the lack of it — affects the ways that children respond to situations. “Sleepy children are not able to cope with day-to-day challenges in their worlds,” she said. When children skip even a single nap, “We get less positivity, more negativity and decreased cognitive engagement.”

But for parents and scientists alike, there are many unanswered questions: When is it too early to give up a nap? Too late to hold on to a nap? How do domestic patterns and cultural norms affect the circadian and homeostatic processes?

“I think there’s a dire need for adults in general to be in tune with individual children’s physiology,” Dr. LeBourgeois said. “What are the capabilities, and what are the limits?”

This everyday childhood behavior, commonly a source of family struggle, is the product of cultural and familial expectations as well as complicated biology, which changes as the child grows.

“If the child is stopping the napping, that represents a process of neurological maturation,” Dr. Jenni said. “The ability to tolerate wakefulness is an indication that the brain is maturing.”

Source: New York Times – http://goo.gl/wS5OP