One school of thought contends that, while we sleep, our brains work at processing information into a form we can understand.
Another states that when we sleep, basically, so do our brains.
Sleepers perform better
Robert Stickgold of the Department of Psychiatry at Harvard Medical School says his study shows that sleep allows the brain to understand new information.
"Understanding the complexity of the world is one of our brain's most difficult tasks," he said. "It needs more than our hours of awake time to get the job done."
In his experiment, two groups of people were given complex problems to solve and their scores were recorded over several days.
One group was allowed to deep sleep, or REM sleep, during those days. The other was kept awake.
Stickgold says that the group that was allowed to sleep improved more at solving their problems than the sleepless group did.
He attributes that improvement to their brains' being able to process information while they slept.
No evidence for sleeping brain theory
Jerome Siegel, a professor at the University of California at Los Angeles and researcher at the Center for Sleep Research of the Department of Veterans Affairs, has another explanation for Stickgold's results.
"There is a great deal of stress involved in depriving someone of REM sleep," he said. "That stress can make someone perform worse."
Siegel's research involved analysing previous studies on sleep and dreams. He says he found no evidence that the brain does anything of importance while we sleep.
He says studies on a class of drugs called MAO inhibitors, which stop REM sleep, show that people who take these drugs don't have impaired memory. In fact, some show improved memory.
As well, Siegel points to studies that show that highly intelligent animals, such as dolphins, barely achieve REM sleep at all.
On the other hand, comparatively dim animals, such as the duck-billed platypus, have eight hours of REM sleep a night, he says, compared to a human's two hours.
Both studies appear in Friday's issue of Science.
