Matt Walker: A walk through the stages of sleep

Recorded atJuly 15, 2020
EventSleeping with Science
Duration (min:sec)04:47
Video TypeOriginal Content
Words per minute176.69 medium
Readability (FK)57.93 easy
SpeakerMatt Walker

Official TED page for this talk

Synopsis

Did you know you go on a journey every night after you close your eyes? Sleep scientist Matt Walker breaks down the difference between REM (Rapid-Eye Movement) and non-REM sleep, what occurs during each stage of sleep -- and why it's important to get enough of both.

Text Highlight (experimental)
     
100:00 Sleep is perhaps the single most effective thing
200:02 that we can do each and every day
300:05 to reset the health of our brain and our body.
400:08 And by understanding a little bit more about what sleep is,
500:12 perhaps we can get the chance to improve both the quantity and the quality
600:17 of our sleep.
700:18 [Sleeping with Science]
800:20 (Music)
900:23 So, exactly what is sleep?
1000:26 Well, sleep, at least in human beings,
1100:28 is subdivided into two main types.
1200:31 On the one hand, we have non-rapid eye movement sleep,
1300:35 or non-REM sleep for short.
1400:37 But on the other hand,
1500:38 we have rapid eye movement sleep, or REM sleep.
1600:42 And non-REM sleep has been further subdivided
1700:45 into four separate stages,
1800:47 unimaginatively called stages one through four,
1900:51 increasing in their depth of sleep.
2000:54 And as we go into those light stages of non-REM sleep,
2100:58 your heart rate starts to decrease,
2201:01 your body temperature starts to drop
2301:03 and your electrical brain wave activity starts to slow down.
2401:07 But as we move into deeper non-rapid eye movement sleep,
2501:11 stages three and four,
2601:13 now all of a sudden the brain erupts
2701:16 with these huge, big, powerful brain waves.
2801:20 The body is actually recharged in terms of its immune system.
2901:25 We also get this beautiful overhaul of our cardiovascular system.
3001:30 And, in fact, upstairs in the brain,
3101:32 deep non-REM sleep will help consolidate memories
3201:36 and fixate them into the neural architecture of the brain.
3301:39 So that's non-REM sleep.
3401:42 But let's come on to REM sleep,
3501:44 which is the other main type of sleep.
3601:46 And it's during REM sleep when we principally have the most vivid,
3701:51 the most hallucinogenic types of dreams.
3801:54 The brain wave activity actually starts to speed up again.
3901:58 It's during REM sleep that we receive almost a form of emotional first aid.
4002:04 And it's also during REM sleep where we get a boost for creativity,
4102:09 that it stitches information together
4202:12 so that we wake up with solutions
4302:14 to previously difficult problems that we were facing.
4402:18 Coming back to these two types of sleep,
4502:20 it turns out that non-REM and REM will play out
4602:24 in a battle for brain domination throughout the night,
4702:28 and that cerebral war is going to be won and lost
4802:33 every 90 minutes,
4902:34 and then it's going to be replayed every 90 minutes.
5002:38 And what this produces is a standard cycling architecture of human sleep,
5102:44 a standard 90-minute cycle.
5202:46 But what's different, however,
5302:48 is that the ratio of non-REM to REM within those 90-minute cycles
5402:54 changes as we move across the night,
5502:57 such that in the first half the night,
5602:59 the majority of those 90-minute cycles
5703:02 are comprised of lots of deep non-REM sleep,
5803:06 particularly stages three and four of non-REM sleep.
5903:09 But as we push through to the second half of the night,
6003:13 now that seesaw balance actually shifts over,
6103:17 and instead, most of those 90-minute cycles
6203:20 are comprised of a lot more rapid eye movement sleep, or dream sleep,
6303:25 as well as stage-two non-REM sleep,
6403:28 that lighter form of non-REM sleep.
6503:30 And it turns out that there are implications
6603:34 for understanding how sleep is structured in this way.
6703:38 Let's take someone who typically goes to bed at 10pm,
6803:42 and they wake up at 6am,
6903:44 so they have an eight-hour sleep window.
7003:47 But this morning, they have to wake up early
7103:50 for an early morning meeting,
7203:52 or they want to get a jump start on the day
7303:54 to get to the gym.
7403:55 And as a consequence, they have to wake up at 4am in the morning,
7503:59 rather than 6am in the morning.
7604:02 How much sleep have they actually lost?
7704:04 Two hours out of an eight-hour night of sleep
7804:07 means that they've lost 25 percent of their sleep.
7904:11 Well, yes and no.
8004:13 They have lost 25 percent of all of their sleep,
8104:17 but because REM sleep comes mostly in the second half of the night
8204:21 and particularly in those last few hours,
8304:23 they may have lost perhaps 50, 60, maybe even 70 percent
8404:28 of all of their REM sleep.
8504:30 So there are real consequences to understanding what sleep is
8604:36 and how sleep is structured.
8704:37 And we'll learn all about the benefits of these different stages of sleep
8804:42 and the detriments that happen when we don't get enough of them
8904:45 in subsequent episodes.
S M L