May 14, 2012 at 4:03 PM ET
This, finally, may explain our cultural obsession with zombies: Long after dark, millions of Americans basically become one.
Without warning, they suddenly rise from their silent, supine states then roam aimlessly, eyes open and mouths sputtering gibberish.
About 8.5 million U.S. adults -- or 3.6 percent of the grownup population -- have taken at least one sleepwalking jaunt during the past year, according to research released today by the Stanford University School of Medicine. That figure, calculated via a survey of nearly 20,000 people, means there are far more nocturnal wanderers than scientists previously suspected.
“It’s something, we were thinking, that was not frequent among the general population. And here, big surprise, it is,” said Dr. Maurice Ohayon, professor of psychiatry and behavioral sciences at Stanford and lead author of the paper. A previous report done a decade ago in European adults showed that 2 percent of that population were sleepwalkers. “It’s astonishing.”
The finding offers American doctors their first, solid sleepwalking benchmark, Ohayon said. Earlier speculation on how often the phenomenon occurred were based on anecdotal clinical reports as well as court cases and media tales of people who had gone sleep-driving, sleep-shopping or sleep-eating. Typically, those more sensational examples were linked to Ambien use.
But Ohayon and his colleagues found no significant link between prescription sleeping pills and increased sleepwalking. What they did discover: Folks who take certain anti-depressants (selective serotonin reuptake inhibitors, or SSRIs) are three times more likely to also take a snoozy stroll than the general population, and people who swallow over-the-counter sleeping pills have a higher likelihood of experiencing sleepwalking episodes at least twice a month month.
Brand names for anti-depressants in the SSRI category include Prozac, Zoloft, Paxil, Lexapro and Celexa. Non-prescription sleep aids linked to increased sleepwalking by the Stanford team contained diphenhydramine. Products laced with that chemical include 40 Winks, Simply Sleep, Sleep-Eze, Sominex, Unisom Sleep, Advil PM, and Tylenol PM, according to the National Institutes of Health.
Chronic sleepwalking also runs (rambles?) within certain families, Ohayon learned: Nearly one-third of individuals who often do it can point to parents, grandparents, uncles, aunts or siblings who have a history of shuffling while slumbering.
To assess the sleepwalking rate in America, Ohayon and his Stanford colleagues used phone interviews conducted with 19,136 randomly selected individuals from 15 states. The participants offered baseline information on their mental health, medical histories and use of medications. They were quizzed on the frequency of any sleepwalking episodes as well as whether they had ever suffered any inappropriate or possibly perilous behaviors while asleep.
What's more, participants were asked if they'd sleepwalked when they were kids and if any family members were known to take unintended, nighttime strolls. In addition to the more more than 3 percent of the U.S. population who sleepwalk chronically, the researchers found that 29.2 percent of the test sample had gone sleepwalking at least once during their lives.
Personal trainer Robert Budd figures he sleepwalks about once a month. When he gathers with his kin, sleepwalking lore is a common topic: while seemingly in dreamland, his grandfather once urinated in a friend’s drawer, his uncle often meandered the decks of navy boats, and his dad dismantled tents and ceiling fans.
“All the boys in the family do it,” said Budd, who operates a gym called PHYZYKS in Encinitas, Calif. “I've done it since I was a kid. I would walk out the door and my parents had to grab me and get be back inside. The commonality with my family and myself is it seems to happen when we’re really tired, really drained. When you really need sleep, that’s when you get up and sleepwalk.”
Budd has sleepwalked out of a tent at the Grand Canyon (on the floor, not near the rim). His friends spotted him heading off alone -- apparently wide awake -- but he remembered nothing the next day. While dozing, he once packed for a vacation, even remembering his toothbrush. And there was the night he tried to climb out a second-floor window only to be stopped by the woman who is now his ex-wife.
Was that intended exit possibly symbolic, even for a sleeping man? “It might have been,” Budd said with a laugh.
“It drives my girlfriend drives nuts because sometimes we have conversations and she doesn’t know if I’m awake. Like, I can’t be accountable in the middle of the night.”
Sleepwalkers typically have their eyes open and may speak, making detection tricky. But Ohayon isn’t certain, he said, if they are actually seeing what’s in front of them or if sleepwalkers’ brains have simply mapped out their homes in their minds, allowing them not to bump into walls or furniture. He is sure they’re not dreaming, though, because sleepwalking coincides with a period of “slow-wave sleep” or SWS when brain activity is diminished.
During another sleep phase called REM (rapid eye movement), brain neurons are firing as if a person is awake. This is when you dream. A mechanism within the brain blocks stirring and shifting when you’re in REM sleep, Ohayon said.
“During slow wave sleep, you can move,” he added. “This is an old function of our brain, (possibly a evolutionary leftover). You know, when birds fly, they can sleep with one half of their brain, while the other half is analyzing the flight.
“That is why you see the bird going for thousand of kilometers without any problem. They sleep when they fly.”