Hope for insomniacs as scientists unlock secrets of deep slumber

Scientists may have discovered a way of triggering deep sleep in people suffering from chronic insomnia.

A study has found a way of stimulating the brain so that sleep-deprived people can feel the full restorative powers of an eight-hour period of slumber.

The researchers have developed an electronic device that stimulates the brain with harmless magnetic pulses which cross into the nerves that control a type of deep sleep called "slow-wave activity".

Giulio Tononi, professor of psychiatry at the University of Wisconsin-Madison, said that about 80 per cent of sleeping hours are composed of slow-wave activity. In response to each burst of magnetism used in the study, the brain produced the typical slow waves of deep sleep, he said.

"With a single pulse, we were able to induce a wave that looks identical to the waves the brain makes normally during sleep," Professor Tononi said.

There are two broad categories of sleep. One is when the brain starts to dream and the eyes moves rapidly from side to side under the closed eyelids. The other type of sleep is when slow waves wash over the brain at a rate of about one a second 1,000 times a night.

The scientists have shown that by stimulating a particular part of the brain of sleeping volunteers with harmless magnetic pulses they were able to induce slow waves to move across the entire brain - just like they do in deep sleep.

"We don't know why, but this is a very good place to evoke big waves that clearly travel through every part of the brain," Professor Tononi said.

One of the aims of the research is to understand the nature of sleep and to find a way of helping people suffering from chronic insomnia which may result from an inability to carry out slow-wave activity.

"We have reasons to think that slow waves are not just something that happens, but that they may be important in sleep's restorative powers," Professor Tononi said.

The importance of slow waves can be seen from the fact that when sleep-deprived people are allowed to sleep they produce larger and more numerous slow waves, which become weaker as sleep progresses.

It may be possible to produce an electronic device that stimulates a deep-sleep power nap that mimics a full eight-hour period of rest in a fraction of the time, the scientists said.

Another possibility is that the magnetic stimulator might be used to aid the retention of memories that are normally formed during the day and consolidated at night, Professor Tononi said.

One theory is that during the day the brain is having to cope with masses of new information which is constantly stimulating the connections between the brain's nerve cells. The function of slow-wave sleep may be to weaken these connections so that they do not overload the brain, he said.

"During the slow waves, all the connections, step by step, are becoming a little weaker. By morning, the total connection strength is back to the way it was the morning before," Professor Tononi said. "The trick is to downscale all the connections by the same percentage so the ones that were stronger are still stronger. That way you don't lose the memory," he said.

The latest research is published in the journal Proceedings of the National Academy of Sciences.