Wellness, Home & Lifestyle, Science & Tech

What Is Sleep?

Matthew Walker

Lesson time 10:32 min

Learn the basics of sleep, including what REM and NREM are, and what your brain is doing during these sleep periods.

Students give MasterClass an average rating of 4.7 out of 5 stars

Topics include: The Power of NREM Sleep • The Beauty of REM Sleep • Why Sleep


[MUSIC PLAYING] - When we look from an evolutionary perspective, what we found is that, in every species that we've carefully studied to date, sleep appears to be present or something very much like sleep. What that means is that sleep must be essential. Sleep in human beings has actually been subdivided into two separate types. We have known rapid eye movement sleep or what we call non-REM sleep for short. And then, on the other hand, we have rapid eye movement sleep, or REM sleep. And it turns out that these two types of sleep, non-REM and REM, will play out in a battle for brain domination throughout the night. So, as we play out this sort of a cerebral war of non-REM and REM, we can actually create a graph. It's actually called a hypnogram, so "Hypnos" from a Greek derivative for the God of Sleep and then "gram," simply meaning graph. And that sort of cerebral war is going to be won and lost every 90 minutes, and then it's going to be replayed every 90 minutes. And what that creates is a standard cycling architecture of human sleep across the night. What actually happens as we go in and out of these different stages of sleep? Well, l we first start to fall asleep, when we go into those light stages, stages 1 and 2 of non-REM sleep are respiration, and our heart rate just start to slow down. Our body temperature will start to drop. And the brain wave activity will begin to slow down a little bit. And then, as we go into the deeper stages of non-REM sleep, stages 3 and 4, all of a sudden, the brain erupts with these huge powerful big, slow brain waves. In fact, in the brain during deep sleep, for reasons that we still don't quite understand yet, hundreds of thousands of brain cells in your cortex, all of a sudden, decide to fire together, and then they all go silent together. It's this incredible physiological ballet of coordination. We have these sleep spindles that burst like fireworks on top of those deep brain waves. And there, those are synchronous short bursts of much faster brainwave activity, somewhere between 10 to 15 cycles per second. And, if you were to listen to the brain, the deep, slow brain waves are so rhythmical you could almost slow dance to them. Non-REM sleep serves a whole constellation of different nighttime benefits for your brain and also for your body. Upstairs in the brain, non-rapid eye movement sleep will actually help us strengthen and consolidate the information that you've been learning during the day. Sleep spindles in coordination with those big, powerful brain waves provide a file transfer mechanism at night from a more short-term vulnerable reservoir to a more permanent, long-term storage site within your brain. And so deep non-REM sleep is going to help the brain capture those memories and almost set them in amber, as it were, so you're far less likely to forget those memories. We also know that it's during non-REM sleep, and particularly the deeper stages of non-REM sleep, where ...

About the Instructor

As a professor of neuroscience and psychology at UC Berkeley and the director of the Center for Human Sleep Science, Matthew Walker is an expert on sleep. In this class, he will illuminate the science behind sleep and teach you how to increase the quality and quantity of your sleep. Learn how to prevent sleep debt, navigate the effects of alcohol and caffeine, and improve your health. Your best sleep starts tonight.

Featured Masterclass Instructor

Matthew Walker

Neuroscience professor Matthew Walker teaches you the science of sleep and how to optimize it to better your overall health.

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