You may have heard about the 31-year-old Idaho woman who last week woke up after “sleep swimming” in the Snake River. She was found, suffering from hypothermia, along the shore. It was the second time she’d done it this summer.

Sounds ridiculous, right? Sure, we’ve all heard of bizarre cases of “sleep driving” and “sleep eating” and even “sleep sex,” but sleep swimming? In a cold river? (I’ve been in the Snake River in Idaho, and I can tell you, it’s cold.) Surely, even if you could walk to the river in your sleep, that first splash of icy water would wake you.

Not necessarily. 

The problem with that popular notion, explained Dr. Mark Mahowald, visiting professor at Stanford University’s parasomnia clinic (parasomnia refers to sleep disorders involving behavior), is that “sleep” doesn’t have to be an all-or-nothing affair.

Parts of your brain can be “asleep” while other parts are “awake.” Brain regions, mainly the frontal cortex, responsible for self-control, reasoning and laying down memories can be happily snoozing while parts of the deep brain, like the stem, can be “awake.”

Because deep brain regions have been equipped with what Mahowald calls “central pattern generators,” patterns of physical acts, something like one of those dance steps instructors lay down on a floor, “you can have somebody who is sleepwalking, and be capable of performing extremely complex behaviors.”

He likens it to a chicken that goes under the hatchet and then starts running around, headless, through the barnyard. The chicken doesn’t have any brain at all, and yet, because its spinal cord has complex pattern generators in it, the chicken runs.

“In humans,” he explained, “there is good evidence that complex behaviors like running, screaming, shouting, sex acts, are all pre-packaged central pattern generators,” either learned or instinctive, that are let loose while the rational brain is sleeping.

You’d have to know how to swim in order to swim in your sleep, of course -- you can’t just start playing Chopin in your sleep if you don’t already know how -- but this explains why people can drive, sometimes long distances, and not recall ever doing it.

People have actually committed murder while sleeping, as documented on a website run by Mahowald and colleagues.

The cold water of a river wouldn’t necessarily wake the sleeper because sleep is like being in a state of anesthesia. We tend not to feel pain or discomfort while sleeping, only after the event is over.

“We had a case in Minnesota where a guy sleep walked outside, at 20 below zero, and sustained incredible frostbite on his feet,” Mahowald recalled. “He wasn’t aware until he woke up and saw the blisters.” 

The causes of sleep walking vary, but may have a genetic component, explained Dr. Steven Poceta, a neurologist affiliated with the Scripps Clinic Sleep Center in San Diego who has documented cases of sleep eating, driving, and cooking among other behaviors.

While science hasn’t figured out why many children sleep walk, but outgrow it, it does appear that the habit can return during times of stress. “That’s a very common scenario,” Poceta said.

Sleep deprivation caused by apnea, or restless leg syndrome, can lead to sleepwalking. So can drugs like zolpidem (Ambien), which became infamous for leading to sleep eating. As for how often that happens, Poceta said, “we think it is more common than is fully appreciated.”    

Brian Alexander (www.BrianRAlexander.com) is co-author, with Larry Young PhD., of "The Chemistry Between Us: Love, Sex and the Science of Attraction," (www.TheChemistryBetweenUs.com) to be published Sept. 13.

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Wake up, folks: There is no health risk in rousing a sleepwalker from their somnambulistic stroll. Well, no risk to them, anyway. You, on the other hand, might suffer a swift, roundhouse kick to the dome.

Long-repeated medical myths have held that if you forcibly snap a sleepwalker back to a wakeful state it will A) induce a state of shock or possibly even insanity, B) give them “lockjaw,” and, C), our personal favorite, cause their soul to become trapped outside their body. The truth matters now more than ever: On Monday, the Stanford University School of Medicine released new research estimating that 8.5 million U.S. adults (3.6 percent of the grownup population) went sleepwalking during the past year -- a far higher rate of nocturnal wanderers than previously thought by doctors. 

“It’s not dangerous for the sleepwalker to wake him up,” said Dr. Mark R. Pressman, a psychologist and sleep specialist at Lankenau Hospital in Wynnewood, Pa. “You’re not going to do them any harm.”

But there are two potential pitfalls in attempting to yank them back to the conscious world. First, sleepwalkers take their short journeys with eyes open yet without turning on a key part of their brain -- the frontal lobe, a portion that controls social interaction. They are momentarily trapped in an altered, gray state that falls between alertness and full sleep, making them quite difficult to bring back to the real world, Pressman said.

“You just can’t talk to them and say ‘Hey!” and have them wake up,” Pressman said. “I’m not even sure where that myth began that you shouldn’t wake them. But the more you dig back (to try research that legend), the more you’ll find that sleepwalking once was thought to be mixed in with spirits and demonic possessions.”

Most sleepwalking episodes last only seconds or a few minutes, ending with the person either sitting or lying on the floor and returning sleep or eventually trudging back to bed.

“It’s very likely to go away on its own while the family is watching,” Pressman said.

You can try to verbally redirect a sleepwalker -- especially a child -- by standing a short distance away and speaking to them in short, easy commands: “Stop, turn around, go back to bed.” But don’t expect them to answer or even to recognize you, Pressman said. Those particular neurons are still snoozing. “Hopefully they turn around and go the other way.

“There’s really no reason to dive in and stop it unless the sleepwalker is about to climb out a window or fall down some stairs. If that’s the case, the family member doesn’t really have much choice,” he added.

If you do approach a sleepwalker -- especially if you physically block or grab one -- they may flash some "defensive aggressiveness,” Pressman said. “This is a very primitive response to what they see as a potential attacker. They may become violent.

“The first thing, obviously, is you have to protect them anyway you can. That’s the bottom line: safety. So you may have to be prepared to take a punch or kick.”

Just don’t expect your zombified loved one or housemate to offer an apology. 

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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. 

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Robert Budd, a personal trainer from Southern California, takes sleeping strolls about once a month, as do almost all the men in his family.

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.”

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