Why Do People Sleepwalk?

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It's a strange and sometimes extremely dangerous condition experienced by one-quarter of children and 3 percent of adults. Somnambulism, the sleep disorder otherwise known as sleepwalking, causes its sufferers to arise from non-REM sleep — the dreamless, deep-sleep stage — and perform activities that are usually done during a state of full consciousness. Sleepwalkers have been known to cook, drive, write letters, have sex with strangers , and even commit murder. They perform these acts with a creepy, blank expression locked on their faces, and, later, often have little to no memory of what they've done.

For hundreds of years, doctors have sought an answer to the question: What causes people to sleepwalk?

Scientists haven't yet turned up a satisfying answer, but they might very soon: They are just beginning to uncover the root cause of somnambulism.

"We have not yet found the gene that is responsible for sleepwalking, though we have strong evidence that one exists on chromosome 20," Christina Gurnett, a neurologist at the Washington University School of Medicine, told Life's Little Mysteries.

Gurnett and her colleagues found that families of sleepwalkers tend to share a particular genetic code variant on the 20th chromosome, which they believe to be linked to the strange sleep disorder. Their finding is relatively new — it was published in the January issue of the journal Neurology — and at this point they can only speculate as to how such a gene would produce a tendency to somnambulate.

"We suspect that the gene(s) responsible for sleepwalking will be important for brain activity," Gurnett wrote in an email. For example, the genetic defect could exist in the gene that is normally responsible for switching off a sleeping person's motor function, she explained. A faulty off-switch could allow sleepwalkers to physically act out their subconscious impulses, sometimes accomplishing complex tasks despite being asleep. Alternatively, "the pathways that are responsible for differentiating sleep and wakefulness may be altered."

"However, there is also data linking sleepwalking to partial arousals from sleep," she wrote. One common trigger of sleepwalking is sleep apnea — a disorder in which sleepers momentarily stop breathing. If sleepwalking and sleep apnea are related, Gurnett explained, "the [variant] gene may play a role in respiratory function."

Further research will determine which hypothesis is correct, but whichever it is, the defective gene doesn't get sleepers walking all by itself. "[The] occurrence of sleepwalking requires genetic predisposition, priming factors such as severe sleep deprivation or stress, and, in addition, a proximal trigger factor such as noise or touch. These factors form the background for a 'perfect storm,' all of which must occur before a sleepwalking episode will occur," neurologist Okan Dogu of the Mersin University School of Medicine in Turkey wrote in an editorial in the peer-reviewed journal Neurology.

To ensure an uneventful night's sleep, somnambulists should reduce their stress level as much as possible, get enough sleep, and avoid noise and physical contact during the night.

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