Sleep pattern serves as harbinger of depression

THE SEARCH for the genetic roots of depression has led scientists to the bedroom, where they've discovered that people with a particular type of sleep pattern and a family history of depression are twice as likely to become depressed as relatives who don't sleep the same way. The link is true even in family members who have no history of the disease themselves and who feel absolutely fine.

The findings come from a team led by University of Rochester Medical Centre psychologist Donna Giles, who uses sleep as a window to study the origins of depression. Her latest work, builds on the link between sleep and depression to try and identify a specific brain chemical that may be at the root of depression for some patients.

Giles and her colleagues have found that the speed with which people fall into dream sleep can indicate people who are more prone to depression. In families where at least one person is depressed, people who enter dream sleep less than 60 minutes after falling asleep are more than twice as likely to become depressed than relatives who enter dream sleep in the more common 90-minute range. "This is the first physiological marker that predicts the onset of depression even in someone who has never had the illness," says Giles, in a news release issued by University Of Rochester.

Dream sleep, or rapid-eye-movement (REM) sleep, is the fifth of five stages of sleep that we cycle through several times each night. Our brain activity slows progressively throughout the first four stages, and then suddenly in REM sleep, our brains kick into high gear. "In REM sleep, brain activity looks just as it does when we're awake, but our muscles are inhibited," says Giles, professor of psychiatry. "It's also known as paradoxical sleep, because the brain behaves as if we're awake."

The sleep disturbances that many depressed people have, such as sleeping more than usual or having difficulty falling asleep, are apparent to patients and families. But falling into REM sleep quickly, a trait known as "short REM latency," isn't obvious in everyday life. It takes the technology of a sleep laboratory to find short REM latency. The brain activity, muscle activity, and eye movements of research subjects are monitored while they sleep for three nights. Since not all depressed people have short REM latency, and many healthy people do, the trait cannot be used to diagnose depression. But in families where depression has been identified, it might provide a way for some family members to find out if they are especially vulnerable.

"With this information, a person might be able to take some protective measures, such as becoming more educated about the first symptoms of depression," she says. Since it may not be practical to run all relatives of a depressed person through a sleep laboratory, Giles says an alternative would be to monitor the sleep patterns of a depressed person for two or three nights. If that person has short REM latency, his or her relatives are four times as likely to share the sleep pattern and the increased likelihood of depression.

In the latest phase of the current study, Giles and colleagues are testing whether Aricept, the same medicine used by patients with Alzheimer's disease to stave off problems with memory, can change sleep patterns. Aricept boosts the amount of the brain chemical acetylcholine, which triggers REM sleep and improves memory.

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