Last month, psychiatrists at Stanford University announced that sleepwalking is on the rise. More than 8.4 million adult Americans—3.6 percent of the population over 18—are prone to sleepwalking. That’s up from a 2 percent prevalence the same authors found a decade ago. And as the latest issue of Scientific American Mind notes, a subset of these nighttime wanderers may be at risk for a disturbing and dangerous phenomenon: sleep violence. Aggressive somnambulance in the general population hovers at or below 2 percent in surveys conducted in North America and Europe. But not all sleepwalkers exhibit violent behavior and what causes the violence remains a puzzle to researchers.
In fact, three separate disorders are associated with sleep violence. In arousal disorders—discussed in-depth in this month’s feature—an individual operates in a mental state between wakefulness and sleep, carrying out complex behaviors with no evident conscious awareness. In comparison, people with nocturnal frontal lobe epilepsy experience brief, repetitive and inadvertently violent actions, such as running or kicking, that precede a seizure. A third condition, rapid eye movement (REM) sleep behavior disorder, occurs when movement centers in the brainstem—which create paralysis during deep sleep—deteriorate, often due to a disease of the nervous system such as Parkinson’s. Without this paralysis, the body is free to move around and act out dreams during REM sleep, often causing accidental harm to the sleeper and bedmate. In 2000, the Mayo Sleep Disorder Center’s Eric Olson reviewed the records of 93 patients with REM sleep behavior disorder and found that 64 percent had assaulted their spouses and 32 percent had injured themselves during sleep.
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