Sleep quality can affect the mind

Good health requires plenty of sleep, but the quality of sleep is just as important as the quantity.

Unfortunately, many Americans wake frequently during the night and don't even know it. This type of sleep fragmentation can disrupt memory, impair learning and possibly set the stage for depression, according to research presented recently at the annual meeting of the Society for Neuroscience in Washington, D.C.

Sleep fragmentation is the most common sleep disorder, and it becomes more common as people age, according to Dennis McGinty, a sleep researcher at the University of California in Los Angeles. Even when people are not aware of waking many times a night, sleep fragmentation affects mental functioning.

In one recent experiment, McGinty monitored the brain waves of rats and woke them whenever they drifted off to sleep for more than 30 seconds. After 12 days he let them sleep normally for two weeks, and then subjected them to a test that involved learning the location of the correct escape hole among 22 possibilities in a maze. Normally rats move from hole to hole until they find the right one, and then they remember it. The sleep-deprived rats, however, failed to remember the right hole.

"This is similar to what happens when you park your car in a multilevel lot," McGinty said. "When you're young, you walk directly to it. You don't even have to think about where you parked. When you're older, or sleep-deprived, you can't remember automatically and you have to develop another strategy that involves noticing which floor you parked on, and which row. You can no longer rely on a cue-oriented strategy."

William Fishbein, a professor at the City University of New York, has a suggestion for offsetting at least some of the problems caused by sleep fragmentation: Take a nap.

"We perform studies in which people are shown words, and then they take a nap," Fishbein said. "Do they remember better? They do."

They also become better able to make logical associations and extract rules from what they learn. For example, when shown Chinese characters, subjects who took a nap during the testing process "did a better job of identifying the meanings," Fishbein said. "The role of sleep in memory formation is not passive. Rather, it actively fosters deeper processing of what we learn during wakefulness. The results of our study clearly indicate that a brief period of sleep serves a rather important role in memory. Not only do we need to remember to sleep, but most certainly, we sleep to remember."

Freelance writer Tom Valeo writes about medical and health issues.