Miranda Kelly, a 14-year-old from Sykesville, Md., says she's been sleepwalking since she was 6 or 7. The first time, she says, "I woke up on the couch on a school day. And I'd gone to bed in my bed."
Since that first episode, Kelly now sleepwalks every couple of months. "I wake up in weird places, randomly. I have once woken up in the kitchen, and on the floor of the bathroom wrapped in my sheet," she says.
Alon Avidan, director of the University of California, Los Angeles, Sleep Disorder Center, is a neurologist who studies sleepwalking. "We do not understand the reason why people sleepwalk," he says.
But at the basic level, sleepwalking is the brain's inability to fully wake up. "When you place electrodes on the sleeping brain, what you will see is a person going into very slow [brain wave] sleep," he says.
Slow brain waves are characteristic of a state called non-rapid eye movement (non-REM) sleep. It's the first stage of sleep as a person drifts off, and Avidan says this is when sleepwalking typically occurs. "As they experience the behavior, the sleepwalking, you'll start seeing the brain partially awakened, while the patient is still asleep," he says.
Though a sleepwalker's brain might be partially awake, most sleepwalkers have no memory of their episodes, and that's a key feature, says Russell Rosenberg, chairman of the National Sleep Foundation and CEO of Neural Trials Research in Atlanta. Some research suggests that the sleepwalker's frontal cortex — the brain's center for decision-making, judgment and short-term memory — is not fully online during sleepwalking.
Rosenberg says the fact that 10 percent to 20 percent of children occasionally sleepwalk shouldn't cause parents to worry. "It's a perfectly normal developmental phenomenon in which a child's brain has not fully developed or is immature, and the ability to arouse or awaken completely has not occurred just yet," he says. And usually, as their brains mature, kids will grow out of sleepwalking.
For some, though, sleepwalking continues into adulthood. This is the case for Steve Kelly, Miranda's dad.
Steve is now 52 years old and has been sleepwalking since his early teens. And it's not surprising that Miranda is a second-generation sleepwalker: Researchers say there is a strong genetic component driving sleepwalking. If one parent sleepwalks, a child has a 45 percent increased risk of being a sleepwalker, too. If both parents are sleepwalkers, a child has a 65 percent chance of being a sleepwalker.
There are also environmental triggers for sleepwalking, such as not getting enough sleep, drinking too much alcohol or a sleep apnea diagnosis. One of the most common triggers, stress, is what usually precipitates Steve Kelly's sleepwalking.
"When I was going to college for my master's degree, every semester around exams, I would start sleepwalking again," he says. Experts says this is probably because stress causes you to lose sleep, and sleep debt is another powerful trigger.
However, unlike Shakespeare's Lady Macbeth — who would sleepwalk from guilt and madness — sleepwalkers do not typically sleepwalk because of psychological problems. Sometimes, however, the medicines prescribed for anxiety or depression, or even for sleep itself, such as Ambien, can spur a sleepwalking episode.
Sleep experts advise that the best thing a spouse or parent can do for sleepwalkers is quietly, gently guide them back to bed and keep them safe.
Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.