for National Geographic News
Adults spend nearly a third of their lives asleep. Infants sleep twice that much or even moreyet scientists don't completely understand the processes of sleep and why the state is so essential.
"We do know a lot today about the importance of sleep and the consequences of not getting enough sleepor enough quality sleep," said Carl E. Hunt, director of the National Institutes of Health's National Center on Sleep Disorders Research in Bethesda, Maryland. "What we don't know is why the body was designed that way. We don't know why sleep is so critical. Clearly we know it's a fundamental requirement of the brain in order to continue to function at its bestyet we don't know why," Hunt said.
But new research on rats has added a piece to this puzzle by revealing that infant and adult sleep are strikingly similar.
Mark Blumberg, of the Department of Psychology at the University of Iowa, and colleagues have reported that the neural (nerve) mechanisms in the active sleep of week-old rats are similar to the sleep mechanisms of adult rats.
The results suggest that the basic components of sleep are present soon after birth and develop in more or less a straight line throughout life.
"Fundamentally there are many more similarities than differences between rat and human sleep. Most of the basic phenomenaphysical twitching, changes in cortical activity, REM movements, and many others are similar. Infant rats are also similar to human babies in the way that they rapidly cycle in and out of sleep. In both species, these cycles become longer as we age," Blumberg said.
"Every parent is aware of their infant's tendencies to rapidly go back and forth between sleep and wakefulness or to sleep all day. That's what we see in rats. So why does sleep change developmentally and become more scheduled and regulated so that we sleep through the night? What's changing here? [We're trying] to understand the basic features of the brain that regulate sleep, and then understand how sleeping cycles change with age," he said.
Led by fellow University of Iowa researcher Karl Karlsson, Blumberg and colleagues published their findings this week in the journal PLoS Biology.
Tracking Brain Changes
In 1953 University of Chicago researchers discovered rapid eye movement (REM) sleep, the sleep most closely associated with dreaming. Before then, the conventional wisdom was that the brain simply "shut down" during sleep.
In fact, while the body rests, the brain itself cycles through periods of rest and activity. "You have intriguing changes going on in the brain [during sleep], and we don't know what they are for, what they represent functionally," Blumberg explained.
Tracking these neural functions in infants proved a challenge.
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