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The man hasn't recalled any dreams for 26 years, but his sleep is unquiet. Sometimes he speaks in French and Spanish or starts swearing; he has also been known to point and kick and punch. Once, his movements propelled him right out of bed. Though the fall woke him and he needed stitches, the man could not remember any dream.

But just because he couldn't recall any dreams doesn't mean that he isn't having them, indicates a study of this man and others. People like him, who have a rare sleep disorder and do not lie still when asleep, are giving researchers a rare window into the dreaming mind.

In general, adults recall 1 to 3 dreams per week on average. If they are awakened right after the REM stage of sleep, in which most dreaming occurs, they can remember their dreams up to 90 percent of the time. Studies suggest that some people are more likely to recall their dreams than others (including women, those who are open-minded and sensitive, and people who have the ability to become highly absorbed in an imagined or aesthetic experience). But some people go years without remembering any dreams, and a few have no recollection of ever dreaming.

Researchers in France wanted to find out whether these people are actually not dreaming at all, or simply not recalling it. So they turned to people with a rare sleep condition called rapid eye movement (REM) sleep behavior disorder or RBD, which causes them to act out their dreams. Most of us are temporarily paralyzed while we dream, but in people with RBD, "the network that blocks movements during sleep is affected in the brainstem and not always functional, so talking and moving is possible," says Isabelle Arnulf, a neurologist at the Pitié-Salpêtrière University Hospital in Paris. "These patients are referred mostly because they injure themselves or their spouses by boxing and kicking during the night."

When awakened after making a movement, most of these people will recall a dream that fits their behavior. "I have been surprised by the numerous behaviors exhibited by asleep people," says Arnulf; these have included singing, fighting and smoking invisible cigarettes. "I realized there were mental images made visible for external observers."

Most dream studies have been restricted to recollections the dreamer reports after they have awakened, she says. "With RBD we can see the event at the present, at the very moment dream occurs."


Video: a person with REM behavior disorder (RBD) acting out dreams while sleeping in a clinic so that he can be monitored by doctors.

Arnulf and her colleagues interviewed 289 people with RBD. Among them, eight people said they recalled no dreams for at least 10 years. Four of these people had no memories of ever dreaming in their entire life (which is similar to the incidence of non-recollection in the general population). These non-recallers—plus 17 of the other interviewees who did recall dreams—were videotaped while they slept, underwent EEG scans and had their breathing, heart rate, muscle tone and eye movements measured.

Despite their inability to remember any dreams, the non-recallers all acted out behaviors (including gesturing, speaking and cursing) indicating that they were dreaming. On all the other measures Arnulf and her colleagues took, these people were no different from the others who could remember the dreams they'd enacted.

The findings add more evidence to the idea that dreaming is universal, even though the ability to recall one's nocturnal adventures varies.

People with RBD are in a unique situation. "There are no other conditions in which one may know at the place of others what they are thinking," wrote Arnulf and her colleagues, who published the findings August 25 in the Journal of Sleep Research. In future, she wants to further investigate these people's nighttime behaviors to understand what's on their minds. "The final idea is to find why we dream," she says.