But this perception is off-base, he added; sleepwalkers are functioning at a very low level, with the parts of their brains responsible for planning and socialization out of commission. "Legal cases in which the defendant supposedly went somewhere and sought out the victim are not likely to be true cases of sleepwalking," said Pressman, who has acted as an expert witness in such cases.

He undertook his review, published in the journal Sleep, to test the hypothesis that sleepwalkers may harm people who touch them or are close by, but they don't spontaneously attack other people. For centuries, he noted, there have been reports of violent acts by sleepwalkers, and even cases of people acquitted of murder because they claimed to have been asleep when they committed the act.

He divided the cases into three categories: sleepwalking; confusional arousal, a state identical to sleepwalking but the sleeper doesn't leave the bed; and sleep terrors, or sudden partial awakening due to a frightening stimulus, followed by sleepwalking.

In all of the confusional arousal cases, the victim of violence had been close to or touching the attacker, the researcher found, and the same was true in 81 percent of sleep terror cases and 40 to 90 percent of the sleepwalking cases. "Often the provocation was quite minor and the response greatly exaggerated," he noted.

Sleepwalking appears to occur when something "goes bump in the night," but a person doesn't wake up fully in response, Pressman explained. "There's something that interferes with waking up fully from sleep," he added.

Genetics appear to be involved, as sleepwalking often runs in families. Up to 15 percent of children sleepwalk, but the majority grows out of it; only 1 to 4 percent of adults sleepwalk.

The old advice that people shouldn't wake a sleepwalker is misguided, Pressman noted, because it's actually quite difficult to do so. The best way to cope with sleepwalkers, he added, is to speak to them in a clear voice -- using very simple language -- and attempt to steer them away from dangerous situations and back into bed.

And touch and approach them with care, he added. "There certainly is a possibility if you have a sleepwalker who is big enough to inflict damage and you grab them and you block them they may not respond as you expect, probably because they don't even recognize who you are," Pressman said.

SOURCE: Sleep, August 1, 2007.

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