To Sleep, Perchance to Defrag: Stimulating Slow Waves

Human beings spend nearly a third of their lives asleep, and nearly 80 percent of our sleeping hours are occupied by "slow wave activity," when waves of electrical activity massage the brain once per second.

Slow wave activity is considered important to memory formation, mood and cognitive function, but it's been difficult to study. That may change: University of Washington psychiatrist Giulio Tononi has figured out how to stimulate the slow wave phase by sending a magnetic signal into a the brains of sleeping subjects.

Creating slow waves on demand could someday lead to treatments for insomnia, where slow waves may be reduced. Theoretically, it could also lead to a magnetically stimulated "power nap," which might confer the benefit of eight hours sleep in just a few hours.

Before that happens, however, Tononi must go further and prove that artificial slow waves have restorative benefits to the brain. Such an experiment would ask whether sleep with TMS leads to greater brain restoration than an equal amount of sleep without TMS.

Tononi thinks that slow wave activity acts like a defragmentation program for the brain, cleaning out unneeded fragments of daily experience and leaving the mind fresh to learn anew.

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."

Without this type of weakening, he says, we "would not be able to learn new things" because our brains would lack sufficient available energy, space and nutrients.

Deep Sleep: Researchers Discovery How To Simulate Slow Wave Activity [press release]

Image: N1NJ4