Slow wave magentic pulses simulate deep sleep and prune synapses

TMS - Transcranial Magnetic StimulationEarlier this month an interesting study surfaced from the Psychiatry department at the University of Wisconsin-Madison.

Professor Giulio Tononi, who directed the research, analyzed the use of slow, rhythmic magnetic pulses to induce brain activity similar to that seen in deep, restorative sleep.

It is being touted as a possible cure for insomnia, and a clue into why all animals need so much sleep.

“We have reasons to think the slow waves are not just something that happens, but that they may be important” in sleep’s restorative powers. For example, a sleep-deprived person has larger and more numerous slow waves once asleep. And as sleep proceeds, Tononi adds, the slow waves weaken, which may signal that the need for sleep is partially satisfied.  

While awake, we “observe and learn much more than you think,” he observes. “Tons of things are leaving traces, changing the synapses, mainly by making them stronger. It is wonderful that you can have all these synaptic traces in the brain, but they come at a price. Synapses require proteins, fats, space and energy. At the end of a waking day, you have all these traces of memories left behind.

“During the slow waves, all the connections, step by step, are becoming a little weaker,” Tononi adds. “By morning, the total connection strength is back to the way it was the morning before. 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.” 

Although the explanation is still a hypothesis, Tononi hopes that the ability to artificially stimulate slow waves will allow him and other researchers to test the notion that sleep restores the brain by damping connectivity between neurons.

Slow waves, he suspects, “Clear out the noise to make sure your brain does not become too much of an energy hog, a space hog. By morning, you have a brain that is energy efficient, space efficient and ready to learn again.”

So, according to Tononi’s hypothesis, slow-wave activity during sleep acts as a kind of mental pruning, or the brain’s version of emptying the recycling bin. 


The technology used in this experiment is called Transcranial Magnetic Stimulation, or TMS. The interesting part is that they found a particular place on the skull to position the TMS device that resulted in more effective stimulation.

“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.

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

I wish the article had gone a bit more in depth as to how TMS was applied in this case – I couldn’t find any specifics on where the TMS device was positioned, or any further information on its use in this research. The technical aspects of this are what I’m really interested in. But then, I’m a big geek with this stuff.


Some are also claiming this type of stimulation could be used to reduce sleep hours from 8 to 2, though I haven’t heard anything from Tononi on this particular point.


Here’s the Science Daily article on it:

Also, here is an interesting take on sleep in general by Tononi:


One Comment to “Slow wave magentic pulses simulate deep sleep and prune synapses”

  1. Adam 18 May 2007 at 2:15 pm #

    Update! I found the full study, here:

    It goes much further into the technical details.


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