By ANDY DOLAN

Last updated at 11:53 02 May 2007

For anyone who struggles to get a good night's rest, it could be a dream come true.

Scientists have invented a technique which they say could help trigger deep sleep in the most chronic insomniac.

Using medical equipment, they stimulated the brain with harmless magnetic pulses.

These penetrate the nerves that control a type of deep sleep called "slow-wave activity" and made their brains produce these waves.

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Researchers believe the same principles could be used to create a machine which can electronically stimulate a deep-sleep power nap. This mimics the restorative benefits of eight hours of rest.

Professor Giulio Tononi led the research at the University of Wisconsin-Madison in the U.S.

He sent the magnetic signal through the skull into a specific part of the brain.

There, it activated electrical impulses. In response to each burst of magnetism, the sleeping volunteers' brains produced slow waves typical of deep sleep. "We don't know why, but this was a very good place (in the brain) to evoke big waves that clearly travel through every part of the brain.

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

There are two broad categories of sleep. In REM (rapid eye movement), the brain starts to dream and the eyes move rapidly from side to side under the closed eyelids.

In the other phase, slow waves wash over the brain at a rate of about one a second, 1,000 times a night. Slow-wave activity occupies about 20 per cent of sleeping hours.

For the study, the researchers used an electroencephalograph machine, which records brain activity, and a transcranial magnetic stimulation machine to deliver the electronic pulse.

They aim to find a way of helping those with chronic insomnia. It is not known what causes the condition. But it is believed it may result from an inability to carry out slowwave activity, which occurs at the start of a night's sleep.

Studies have shown that when the sleep-deprived are allowed to rest, they produce larger and more numerous slow waves, which become weaker as sleep progresses. This, Professor Tononi said, may signal that the need for sleep is partially satisfied.

Creating slow waves on demand raises the potential of similar treatments for insomnia. Theoretically, it could also lead to a magnetically-triggered "power nap".

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

But other sleep experts reacted with scepticism. Dr Joan Harthan, a sleep expert from the University of Nottingham, said: "We know that people go through five or six sleep cycles which alternate between slow-wave sleep and REM sleep, but we don't know exactly how each type of sleep benefits the body.

"As a result I don't think it would be beneficial to have eight hours of solid slow-wave sleep. But I think this device could have potential to trigger short 'power naps'."

Dr Neil Stanley, a sleep expert at Norfolk and Norwich University Hospital, said: "This research doesn't actually prove anything. The problem insomniacs have is getting to sleep in the first place, not drifting into a deep sleep where this short-wave activity occurs."