Essentials: The Science & Practice of Perfecting Your Sleep

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health and performance. And now my discussion with Dr. Matt Walker. Let's start off very basic. What is sleep?

**Matt Walker** (0:18)
Sleep is probably the single most effective thing you can do to reset your brain and body health. Sleep as a process though, is an incredibly complex physiological ballet. Sleep is broadly separated into these two main types. And we've got non-rapid eye movement sleep on the one hand, and then we've got rapid eye movement sleep on the other. When you go into REM sleep, you are completely paralyzed. You are locked into a physical incarceration of your own body.

**Andrew Huberman** (0:50)
Amazing.

**Matt Walker** (0:50)
The brain paralyzes the body so that the mind can dream safely. Because think about how quickly we would have all been popped out of the gene pool. You know, if I think I'm one of the best skydivers who can just simply fly, and I get up on my apartment window and I leap out, you're done. You're done. Now, of course, the involuntary muscles thankfully aren't paralyzed. So you keep breathing, your heart keeps beating. You go through these bizarre, what we call, autonomic storms. There are only two voluntary muscle groups that are spurred from the paralysis. Bizarre. One, your extraocular muscles, because if they were paralyzed, you wouldn't be able to have rapid eye movements. And the other that we later discovered was the inner ear muscle. Some people have argued that the reason the eyeballs are spurred from the paralysis is because if your eyeballs are left for long periods of time inactive, you may get things such as oxygen sort of issues in the aqueous or vitreous humor. And so the eyeballs have to keep moving in some way.

**Andrew Huberman** (1:56)
The drainage systems of the anterior eye are made to require movement.

**Matt Walker** (1:59)
Exactly.

**Andrew Huberman** (2:00)
People with glaucoma have deficits in drainage through the anterior chamber. So maybe take me through the arc of a night.

**Matt Walker** (2:06)
When I first fall asleep, I'll go into the light stages of non-REM sleep, stages one and two of non-REM. And then I'll start to descend down into the deeper stages of non-REM sleep. So after about maybe 20 minutes, I'm starting to head down into stage three non-REM and then into stage four non-REM sleep. And as I'm starting to fall asleep, as I've cast off from the usually with me murky waters of wakefulness, and I'm in the shallows of sleep, stages one and two, my heart rate starts to drop a little bit. And then my brain wave pattern activity starts to slow down. Normally, when I'm awake, it's going up and down maybe 20, 30, 40, 50 times a second. As I'm going into light non-REM sleep, it will slow down to maybe 15, 20, and then really starts to slow down, down to about sort of 10 or 8 cycles per second, 8 cycle waves per second.
Then, as I'm starting to move into stages 3 and 4 non-REM sleep, several remarkable things happen. All of a sudden, my heart rate really does start to drop. Hundreds of thousands of cells in my cortex all decide to fire together, and then they all go silent together. And it's this remarkable physiological coordination of the likes that we just don't see during any other brain state. I will then stay there for about another 20 or 30 minutes. So now I'm maybe 60 or 70 minutes into my first sleep cycle. And then I'll start to rise back up, back up into stage 2 non-REM sleep. And then after about 80 or so minutes, I'll pop up and I'll have a short REM sleep period. And then back down I go again, down into non-REM, up into REM. And you do that reliably, repeatedly, and I will be doing that every 90 minutes. At least that's the average for most adults. In the first half of the night, the majority of those 90 minute cycles are comprised of lots of deep non-REM sleep. That's when I get my stage 3 and 4 of deep non-REM sleep. Once I push through to the second half of the night, now that seesaw balance changes, and instead the majority of those 90 minute cycles are comprised either of this lighter form of non-REM sleep, stage 2 non-REM sleep, and much more and increasingly more rapid eye movement sleep.

**Andrew Huberman** (4:35)
And who suffers more, those that lack the early phase or those that lack the later phase of the night?

**Matt Walker** (4:41)