Dr. Matt Walker

Auditory.

So acoustic stimulation.

In a very similar way to...

electrical stimulation, where you're trying to target that deep sleep and see if you... A better analogy is probably a metronome.

And you're trying to see if you can kind of force the metronome further over and back and forth with these types of technologies.

But auditory stimulation came on the map again.

I think probably Jan Born's group in Germany was some of the first to do this.

They initially started with the same generalized approach where they would take acoustic tones and they would first assess what is your level of awakening threshold.

So you'd be asleep and they would just have these tones, very light tones, like a sort of a

And they would gradually increase the volume up and they would look to see what is the point where that volume of the tone wakes you up.

And then they understood your specific threshold, what's called an awakening threshold.

And they would set the volume to a sub awakening threshold.

Great.

So you've got that locked in place.

And now you...

start and they did this within the first 90 minutes of people falling asleep they started to play these sub awakening level volume levels of tones but they were playing them at this very slow frequency as if again they're trying to sync and match the slow dancing rhythm of the slow brain waves and

And sure enough, in that first study, and it was indiscriminate, meaning they just set the tones, like a metronome, set the tone, and then, sorry, set the volume, and then set the cadence of the volume, the speed, the frequency of those tones to just a little bit less than one hertz, a little bit less than one cycle per second.

And then off you drifted to sleep, and they played it for the first 90 minutes, because that's the rich phase of deep sleep.

And they were able to increase the amount of deep sleep significantly.

The problem in that first study was that they also did a memory test.