May 07, 2007
Magnetic Pulse Induces Slow Wave Sleep State

A University of Wisconsin scientist has found a way to induce the slow wave sleep state of the brain.

Now, Giulio Tononi, a professor of psychiatry at the University of Wisconsin-Madison School of Medicine and Public Health, has discovered how to stimulate brain waves that characterize the deepest stage of sleep. The discovery could open a new window into the role of sleep in keeping humans healthy, happy and able to learn.

Tononi figured out how to use transcranial magnetic stimulation above a particular spot to induce the slow wave state of sleeping.

During slow wave activity, which occupies about 80 percent of sleeping hours, waves of electrical activity wash across the brain, roughly once a second, 1,000 times a night. In a paper being published this week in the Early Edition of the scientific journal PNAS, Tononi and colleagues, including Marcello Massimini, also of the UW-Madison School of Medicine and Public Health, described the use of transcranial magnetic stimulation (TMS) to initiate slow waves in sleeping volunteers. The researchers recorded brain electrical activity with an electroencephalograph (EEG).

A TMS instrument sends a harmless magnetic signal through the scalp and skull and into the brain, where it activates electrical impulses. In response to each burst of magnetism, the subjects' brains immediately produced slow waves typical of deep sleep, Tononi says. "With a single pulse, we were able to induce a wave that looks identical to the waves the brain makes normally during sleep."

The researchers have learned to locate the TMS device above a specific part of the brain, where it causes slow waves that travel throughout the brain. "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," Tononi says.

Tononi is going to use this capability to investigate his hypothesis that the slow wave state allows the brain to weaken connections that formed from events experienced during the day. He sees sleep as something that weakens many unimportant memories so that our brains do not become burdened with too many memories.

Share |      Randall Parker, 2007 May 07 11:10 PM  Brain Sleep

Audacious Epigone said at May 9, 2007 12:14 AM:


I've seen other commenters opine that this may eventually mean that a full night's rest is attainable in an hour of sleep. But if slow wave comprises ~80% of standard sleeping, the math's throwing me off. Any reaction to those assertions?

Randall Parker said at May 9, 2007 6:50 PM:


I can see this thing helping people with some types of sleep disorders. But I do not think the ability to put normal people into slow wave state is going to help them any. I'm sure the time spent in the other sleep states serves some useful purpose.

Rob said at May 10, 2007 12:28 PM:

>During slow wave activity, which occupies about 80 percent of sleeping hours,
>waves of electrical activity wash across the brain, roughly once a second, 1,000 times a night.

Somebody got something wrong in there somewhere. 1,000 seconds is less than 17 minutes. Yet 80% of eight hours is more llike 23,000 seconds. Probably, the science write got a bit confused somewhere.

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