Don't think that while you're asleep, your brain's cortex function is stopped!

While you're dreaming, it is full of electrical activity, suspected of solidifying your memories formed during the day. For the first time, scientists have proved that electrically stimulating the brain during sleep can increase memorizing capacity.

Previous studies had showed that waking people up during the slowly oscillating wave activity of brain during sleeping makes them perform poorly on tasks that imply remembering recently memorized facts. Neuroscientists at the University of Lübeck, Germany tested the reverse: what happens when these waves are enhanced ?

Subjects were put to learn some tasks before settling down for the night: to study pairs of words and pairs of figures, to tap a sequence of keys on a keyboard, and to practice drawing figures while looking at a mirror. They were fitted with electrodes that recorded their brain waves and stimulated their brains through their scalps.

When the subjects entered into slow wave sleep, the scientists switched on the stimulating electrodes for about half an hour. "The idea was to provide low frequency stimulation that enhanced the brain's natural slow waves," said Jan Born, one of the researchers.

The subjects' performances after stimulated sleep were compared with those after normal non stimulated sleep. Although the subjects did not perceive the stimulation, memory tests pointed a difference. Stimulation added a modest but consistent improvement on the word pair and figure pair tests compared to non stimulated sleep. However, typing and drawing performance weren't affected by stimulation. "The research adds to growing evidence that different types of memory gel during different stages of sleep at different times of night," says Robert Stickgold, a neurobiologist at Harvard University.

Even so, probably people won't use brain stimulators because "evolution has already done a pretty good job of optimizing brain activity during sleep. Tweaking it further isn't going to do all that much good for you," added Stickgold.