The Science of Sleep
Over the past decade, researchers have learned much about the science of sleep, says Mark W. Mahowald, MD, a neurologist and director of the Minnesota Regional Sleep Disorders Center in Rochester.
There are nearly 100 identified sleep/wake disorders, Mahowald says. In a recent issue of the journal Nature, Mahowald outlined the latest scientific findings on these two familiar patterns:
Hypersomnia: This is sleep deprivation, or excessive daytime sleepiness without an obvious cause. This pattern "should be taken very seriously," Mahowald writes. The result is sleepiness, which results in impaired sustained attention, with adverse, occasionally disastrous consequences in the classroom, workplace, or the highways. It is likely that more than 100,000 crashes occur annually in the U.S. due to driving while drowsy, he adds.
The most common cause of hypersomnia is voluntary sleep deprivation done for social or economic reasons - like work or surfing the Internet, he notes. "We get 20% less sleep than previous generations, yet there is no evidence that earlier generations required more sleep - or that ours needs less," he writes.
Insomnia: This is the most common sleep complaint, says Mahowald. It is not defined by total sleep time but by trouble falling or staying asleep. It is the inability to obtain sleep that is sufficiently long or "good enough" to result in feeling rested or restored the following day. Depression has been linked as a cause of insomnia; however, for many people, untreated insomnia may be a risk factor for depression, he tells WebMD.
Many insomniacs may have a condition called hyperarousal - essentially, they're always on alert, which means they rarely can sleep, Mahowald explains. "There is overwhelming evidence that many who have insomnia have a constitutional predisposition to be hyperaroused 24 hours a day. They have trouble sleeping, then feel miserable during the day, fatigued, washed out, have trouble concentrating. But they are not sleepy. They never take naps, because the same thing happens - they can't sleep during the day."
Neurological scans show differences between the brains of insomniacs and non-insomniacs. There seems to be a genetic component to both hyperarousal and insomnia, Mahowald tells WebMD.
"They typically have a family history of insomnia. Many people have had it as long as they can remember, since childhood. It takes very little for them to get insomnia - a test the next day, an upcoming trip. They can get insomnia for what seems like very trivial reasons, but it's probably constitutional. They are very fragile sleepers because they are predisposed to developing insomnia."