This heightened activity was observed during the brief but active stage known as rapid-eye movement, or REM, sleep. The study was published in the August issue of Nature Neuroscience and was led by Pierre Maquet of the University of Liege in Belgium. Animal studies had shown similar results. Rats that ran new routes through mazes showed increased activity in the same portions of their brains when they slept afterward. But the human brain is more complex.
Humans spend one-third of their lives asleep, but sleep's purpose is poorly understood.
Among other things, scientists believe dreaming may help sort out emotions, impressions and other ideas. During the test, the activity in several regions of their brains was monitored by PET scans, which reveal how the brain is functioning by watching its use of glucose and oxygen, the fuels of brain cells. Groups of volunteers were tested in several ways. Those who took the computer test for several hours, slept and retook the test when they woke up scored the highest, with even faster reaction times after they slept. PET scans showed that during REM sleep their brain activity and blood flow were similar to when they were taking the test.