BioEd Online

A woman who stopped dreaming after a stroke is helping researchers unravel the mysteries of sleep.

The 73-year-old patient was admitted to hospital after a stroke disrupted blood flow to an area at the back of her brain, called the occipital lobe. At first, her symptoms were not unusual - she lost some vision and was weak on one side of the body. But as the initial problems faded a few days later, a new symptom emerged: the woman had stopped dreaming. Her story is recorded in the Annals of Neurology¹.

She used to experience 3 to 4 dreams per week, says Claudio Bassetti, now of University Hospital Zurich in Switzerland, who studied the woman. After the stroke, she had no dreams for a whole year, yet her sleep and mental functions appeared otherwise unaffected.

People have been fascinated by dreams for centuries. Psychologist Sigmund Freud believed that dreams offer a release for repressed feelings. Others think they help us empty our minds at the end of a busy day, or solve problems as we sleep.

But the stroke study suggests that humans can live without dreams. "I don't think they have any real function," comments Jim Horne, who studies sleep at Loughborough University, UK.

"I think that dreams are the cinema of the mind," he continues. "They help to keep the brain entertained while we are asleep."

Bassetti, however, cautions against drawing firm conclusions from a single case. "How dreams are generated, and what purpose they might serve, are completely open questions at this point," he says.

Brainwave

To try to discover what was going on, Bassetti's team monitored the woman's brain waves as she slept. The researchers took 4 night-long recordings over 6 weeks.

The patient reported no dreams even when woken in the midst of rapid eye movement (REM) sleep, which is normally associated with dreaming. But to the researchers' surprise, her sleep pattern was perfectly normal.

This shows that REM sleep and dreaming do not always go hand in hand, says Bassetti. The occipital lobe, which was damaged by the woman's stroke, is likely to play an important role in dreaming. But different neural areas, such as the brain stem and midbrain, are thought to control REM sleep.

The study also backs up reports of patients who lost both their dreams and their REM sleep for up to a year after taking certain antidepressant drugs. "These people don't go mad," says Horne. They are completely normal and have no memory problems.

At present, the functions of REM sleep are as elusive as those of dreaming. Adults spend a quarter of their nightly slumber in REM sleep, scattered throughout the night. The remaining time is spent deeper in unconsciousness. So REM may simply bring the brain back from deep sleep periodically to help us wake up if we need to, says Horne.

But the function may be different in newborns, who typically spend around 8 hours per day in REM sleep. Here, the sleep pattern may be related to brain development.