A pair of new studies sheds light on toddler sleep

In the basement of a building on the University of Colorado Boulder’s east campus, sleep researchers have been busy trying to explain one of the biggest mysteries of parenting: Why won’t my child just go to sleep?

The Sleep and Development Lab, headed up by integrative physiology Assistant Professor Monique LeBourgeois, specializes in early childhood sleep: why it’s important, what happens when there isn’t enough of it and why sometimes it seems so hard to come by.

This fall, researchers at the lab published two new studies, one of which explains why some toddlers take so long to drift off. The problem, according to the study published in the journal Mind, Brain and Education, may be that the child’s bedtime doesn’t coincide with his or her biological clock.

The researchers recorded the time in the evening when the hormone melatonin increased, signaling the start of the biological night, in 14 toddlers. They found that toddlers who were put to bed before their melatonin increased took longer to actually fall asleep.

“There is relatively little research out there on how the physiology of toddlers may contribute to the emergence of sleep problems,” said LeBourgeois. “Sleeping at the wrong ‘biological clock’ time leads to sleep difficulties, like insomnia, in adults.”

While adults get to choose their own bedtime, toddlers rarely have this option. “This study is the first to show that a poor fit between bedtimes selected by the parents of toddlers and the rise in their evening melatonin production increases their likelihood of nighttime settling difficulties,” said LeBourgeois.

The findings are important because about 25 percent of toddlers and preschoolers have problems settling after bedtime, said LeBourgeois.  Evening sleep disturbance can include difficulties falling asleep, bedtime resistance, tantrums, and episodes known as “curtain calls” that manifest themselves as calling out from bed or coming out of the bedroom, often repeatedly, for another story, glass of water or bathroom trip.

Getting enough sleep as a toddler may be critical to the maturing of the child’s brain, according to the second study published this fall, this one led by Salome Kurth, a postdoctoral researcher in the Sleep and Development Lab.

Kurth used electroencephalograms, or EEGs, to measure the brain activity of eight sleeping children multiple times at the ages of 2, 3 and 5 years for the study published in the journal Brain Sciences. “Interestingly, during a night of sleep, connections weakened within hemispheres but strengthened between hemispheres,” Kurth said.

Scientists have known that the brain changes drastically during early childhood: New connections are formed, others are removed and a fatty layer called “myelin” forms around nerve fibers in the brain. The growth of myelin strengthens the connections by speeding up the transfer of information.

Maturation of nerve fibers leads to improvement in skills such as language, attention and impulse control. But it is still not clear what role sleep plays in the development of such brain connections—or how sleep disruption during childhood may affect brain development and behavior, though the lab is already involved in studies that they hope will shed light on those questions.

“I believe inadequate sleep in childhood may affect the maturation of the brain related to the emergence of developmental or mood disorders,” Kurth said.

Read more about toddler sleep and the biological clock.

Read more about toddler sleep and brain connections.

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