YT YouTube2Text

YouTube2Text → Transcripts → Why We Sleep: Science of Sleep & Dreams | Matthew Walker | Talks at Google

Why We Sleep: Science of Sleep & Dreams | Matthew Walker | Talks at Google — Transcript

by Talks at Google · 7,624 words · 1,125 segments · language en · Watch on YouTube

Open in transcriber Summarize with AI Download SRT/VTT

Full transcript

0:00[Music]
0:04and thank you all for coming this a
0:06great crowd in order welcome dr. Matthew
0:09Walker he is professor of neuroscience
0:11and psychology at the University of
0:12California Berkeley and he is the
0:14founder and director of the Center for
0:16human sleep science and he's here today
0:18to talk about his new book why we sleep
0:20so it's that further adieu thank you
0:22very much Josh thank you well it's a
0:27it's a delight and privilege to be here
0:30and I would like to start with testicles
0:37men who sleep five hours a night have
0:40significantly smaller testicles than
0:43those who sleep eight hours or more in
0:47addition men who routinely sleep five to
0:51six hours a night will have a level of
0:54testosterone which is that of someone
0:56ten years their senior so a lack of
1:01sleep ages you by a decade in terms of
1:04that aspect that critical aspect of
1:07wellness and virility and we see
1:11equivalent impairments in female
1:13reproductive health caused by a lack of
1:16sleep this is the best news that I have
1:21for you today
1:24from this point forward it's only going
1:27to get worse rather than tell you about
1:30the wonderfully good things that happen
1:32when you get sleep I'm going to tell you
1:34about the alarmingly bad things that
1:36happen when you don't get enough both
1:38for the brain and for the body and let
1:42me start with the brain and the
1:43functions of learning and memory what
1:46we've discovered over the past 10 or so
1:49years is that you need sleep after
1:52learning to essentially hit the Save
1:54button on those new memories so that you
1:57don't forget so sleep essentially future
2:01proofs those facts within the brain but
2:05recently we've discovered that you not
2:07only need to sleep after learning you
2:09also need to sleep before learning but
2:13now to actually prepare your brain I'm
2:15almost like a dry sponge ready to
2:18initially soak up new information and
2:21without sleep the memory circuits of the
2:24brain effectively become waterlogged as
2:27it were and you can't absorb new
2:30information so here in the study we
2:33decided to test the hypothesis that
2:36pulling the all nighter was a good idea
2:39how do you do that well we took a group
2:42of healthy adults and we assign them to
2:45one of two experimental conditions a
2:47sleep group and a sleep deprivation
2:49group now the sleep group they're going
2:52to get a full eight hours of shut-eye
2:55but the deprivation group we're going to
2:57keep them awake in the laboratory under
2:59full supervision
3:01there's no naps there's no caffeine it's
3:05miserable for everyone included as well
3:07and then the next day we're going to
3:10place those participants inside an MRI
3:13scanner and we're going to have them try
3:16and learn a whole list of new facts as
3:19we're taking snapshots of brain activity
3:22and then we're going to test them to see
3:26how effective that learning has been and
3:29that's what you're looking at here on
3:31the vertical axis the amount of learning
3:33so the higher up you are the more that
3:36you learn
3:37and when you put those two groups
3:39head-to-head what you find is a quite
3:41significant 40 percent deficit in the
3:45ability of the brain to make new
3:47memories without sleep and I think this
3:52should be frightening considering what
3:54we know is happening to sleep in our
3:56education populations right now just a
4:00frameless in context it would be the
4:02difference between acing an exam and
4:04failing it miserably and we've gone on
4:10to discover what goes wrong within your
4:13brain to produce these types of learning
4:16disabilities there is a structure on the
4:19left and the right side of your brain
4:21called the hippocampus and you can see
4:24it here in these sort of orange yellow
4:26colors think of the hippocampus like the
4:29informational inbox of your brain it's
4:33very good at receiving new memory files
4:36and holding on to them and when we
4:40looked at this structure in those people
4:41who'd had a full night of sleep here in
4:44green we saw lots of healthy learning
4:47related activity yet in those people who
4:51were sleep deprived we actually couldn't
4:53find any significant signal whatsoever
4:58it's almost as though
5:00sleep deprivation had shut down the
5:03memory inbox and any new incoming files
5:07they were just being bounced you
5:10couldn't effectively commit new
5:12experiences to memory and
5:16parenthetically I should note if you
5:18would like to know what life is like
5:20without a functioning hippocampus and
5:22just watch the movie memento I suspect
5:25many of you who have seen this but this
5:27gentleman suffers brain damage and from
5:30that point forward he can no longer make
5:33any new memories he's what we call
5:35densely amnesic the part of his brain
5:40that was damaged was the hippocampus and
5:43it is the very same structure that sleep
5:46deprivation will attack and block your
5:49brains kapow
5:50thirty-four new learning so that's the
5:55bad that happens when you take sleep
5:57away let me just come back to that
5:59control group for a second
6:01remember those folks that got a full
6:04eight hours of sleep well we can ask a
6:07very different question here what is it
6:10about the physiological quality of sleep
6:13when you do get it that actually
6:16enhances and restores your learning and
6:19memory ability each and every day and by
6:23recording sleep with electrodes placed
6:25all over the head we've discovered that
6:28there are big powerful brain waves that
6:31happen
6:31during the very deepest stages of sleep
6:34that have riding on top of them
6:37these spectacular bursts of electrical
6:39activity called sleep spindles and it's
6:44the combined quality of these deep sleep
6:47brain waves at night that acts like a
6:50file transfer mechanism it takes
6:54memories from a short-term vulnerable
6:56reservoir and shifts them to a more
6:59permanent long-term storage site within
7:02the brain called the cortex this big
7:04wrinkled massive tissue that sits the
7:07top of your brain and it means that when
7:10you wake up the next morning there are
7:12two benefits first having shifted
7:16memories of yesterday to that long-term
7:18safe storage Haven in the brain they are
7:22protected so that you will remember
7:25rather than forget the second benefit
7:29however is that having shifted those
7:32files from that short-term reservoir
7:34almost like moving files from a USB
7:37stick you've cleared out all of that
7:39memory encoding capacity so that when
7:42you wake up the next day you can start
7:44acquiring new files all over again you
7:47can start learning and new so its this
7:52elegant beautiful symbiotic system of
7:56memory that happens each and every night
7:58and it's important that we understand
8:01what during sleep at
8:04transacts these memory benefits because
8:07there are real medical and societal
8:10implications and let me just tell you
8:12about two areas that we've moved this
8:14work out into I'll begin clinically and
8:17specifically the context of Aging and
8:20dementia because I think many of us have
8:24a sense or even know that as we get
8:27older our learning and memory abilities
8:30start to fade they begin to decline but
8:33what we've also known for many decades
8:35is that a physiological signature of
8:38aging is that your sleep gets worse and
8:43not just any type of sleep especially
8:46that deep quality of sleep that I was
8:50just describing and only last year we
8:54finally published evidence that these
8:56two factors are not simply co-occurring
8:59they are significantly interrelated and
9:04it suggests that the disruption of deep
9:07sleep is perhaps an underappreciated
9:10factor that is contributing to what we
9:13call cognitive decline or memory decline
9:15in aging and most recently we've
9:19discovered in Alzheimer's disease as
9:21well now I know this is remarkably
9:28depressing news I understand it's in the
9:31mail it's it's coming at you but there
9:34is a potential silver lining here
9:37because unlike many of the other factors
9:40that we know are associated with aging
9:42and dementia and for example changes in
9:45the physical structure of the brain or
9:48even changes in the vasculature of the
9:50brain those are fiendishly difficult to
9:53treat right now and we don't have any
9:56good wholesale approaches in medicine
9:59but that sleep is a missing piece in the
10:03explanatory puzzle of aging and
10:06Alzheimer's is exciting because we may
10:09be able to do something about it and one
10:13way that we are approaching this at my
10:15sleep center is not by using sleeping
10:17pills by the way
10:18they are blunt instruments that do not
10:21produce naturalistic sleep and they have
10:23been associated with a higher risk of
10:25death and cancer and I'm happy to speak
10:29about that evidence during the Q&A and
10:31it's discussed in the book as well what
10:34we are actually doing is developing a
10:36method based on this technology it's
10:38called direct current brain stimulation
10:41it sounds like the stuff of science
10:43fiction it's actually science fact you
10:45apply electro pads to the head and you
10:47insert a small amount of voltage into
10:50the brain so small that you tend not to
10:52feel it but it has a measurable impact
10:54on physiology now if you apply this
10:59stimulation during sleep in young
11:03healthy adults as if you're sort of
11:05singing in time with those deep sleep
11:09brainwaves not only can you actually
11:12amplify the size of those deep sleep
11:15brainwaves but in doing so you can
11:18almost double the amount of memory
11:21benefit that you get from sleep the
11:26question now is whether we can translate
11:29the same affordable potentially portable
11:32technology into older adults and those
11:35with dementia can we restore back some
11:39healthy quality of deep sleep and in
11:42doing so can we salvage aspects of
11:46learning and memory function that is my
11:50real hope now that's one of our moonshot
11:53goals as it were I should note by the
11:58way because I always get asked this
11:59question people will say where can i buy
12:01one of those devices
12:03I want one yesterday and I want five
12:06more tomorrow and they are not yet FDA
12:09approved for use in sleep you can buy
12:12them on the Internet
12:13I strongly advise against that just read
12:18around some horror stories people have
12:20misaligned the voltage skin burns
12:22they've lost their eyesight for several
12:24days and hang on we are desperately
12:27trying to bring this to fruition as soon
12:30as we can
12:31so that's sleep and memory in a clinical
12:35context but let me speak about sleep and
12:37memory in society and specifically here
12:41within education because if sleep really
12:44is so important for learning in memory
12:47then enhancing sleep in a context where
12:50arguably it matters most should prove
12:53transformative and it has because there
12:59are several counties throughout the
13:01United States that have started to delay
13:03the school start times and then measure
13:06the academic consequence now one of the
13:10earliest test case examples happened in
13:13Edina in Minnesota
13:16it's a Township that sits just outside
13:18of Minneapolis and they shifted their
13:21school start times from 7:25 in the
13:24morning to 8:30 in the morning by the
13:29way what are we doing trying to educate
13:32our next generation at 7:25 in the
13:37morning to give you a sense of this
13:41buses for a 7:25 start time will often
13:45begin leaving at 5:30 in the morning
13:48that means that some kids are having to
13:50wake up at 5:15 5 o'clock maybe even
13:53earlier this is lunacy but in a döner it
14:02was the beginnings of a movement and the
14:05metric that they used to assess the
14:08academic consequence was this SAT scores
14:11and they focused their analysis on the
14:14top 10% performing students arguably
14:18those that have the least to gain in
14:20terms of any further improvement by way
14:23of sleep now in the year before they
14:26made the time change that top 10%
14:29performing students got an average score
14:32of 1288 which is a very respectable
14:36score the following year when students
14:41were now going to school at 8:30 in the
14:43more
14:44the average SAT score was 1500 that is a
14:55212 point increase which is non-trivial
15:00that will change which tier of
15:03university those school kids end up
15:05going to and perhaps as a consequence
15:08their subsequent life trajectories now
15:14some people have questioned aspects of
15:16the Adina study and I think for perhaps
15:18good reason but in all of the subsequent
15:21carefully controlled studies the data is
15:25unequivocal I think academic grades
15:28increase behavioral problems decrease
15:33truancy rates decrease and psychological
15:37and psychiatric issues also decrease but
15:44something else actually happened in this
15:47story of later school start times and it
15:52was something that we did not anticipate
15:56the life expectancy of students actually
15:59increased and you think I don't
16:04understand how does that work does
16:06anybody know what the leading cause of
16:08death in late stage teenagers is
16:11throughout most developed nations
16:13suicide is actually second it's car
16:16crashes and here sleep matters enormous
16:19Lee another example comes from Teton
16:23County in Wyoming they shifted their
16:26school starts from seven thirty five in
16:28the morning to eight fifty five in the
16:30morning and then they measured the
16:32reduction in car crashes in this narrow
16:35age of just 16 to 18 the only thing
16:40perhaps more remarkable than the extra
16:42hour of sleep that those students
16:44reported getting was the drop in vehicle
16:48accidents
16:53there was a 70% reduction just to sort
16:59of frame that in context the advent of
17:02ABS technology what we call anti-lock
17:04braking systems that prevent your wheels
17:06from locking up and a hard braking so
17:08that you can still safely maneuver a
17:10vehicle that dropped accident rates by
17:13twenty to twenty five percent and some
17:15deemed it to be a revolution but here is
17:20a biological factor sleep that will drop
17:25accident rates by up to 70% I think it's
17:33time for us to reconsider the importance
17:38of sleep in education when sleep is
17:43abundant Minds flourish and if our goal
17:48as educators truly is to educate and not
17:53risk lives in the process then I fear
17:56that we meet that we may be failing our
17:59children in a significant manner with
18:03this incessant model of early school
18:06start times
18:08so that's sleep for learning memory
18:12aging Alzheimer's what else is sleep
18:16good for let me tell you that sleep is
18:19essential to help stabilize your
18:21emotional and mental health and without
18:25sleep the emotional circuits of your
18:27brain become hyperactive and irrational
18:31allow me to demonstrate with a
18:34sleep-deprived subject because it turns
18:37out that we do video diaries with our
18:40participants throughout the deprivation
18:42night and you go to meet one under the
18:45pseudonym of Jeff it's 11:30 at night
18:49jeff has been awake for about 16 hours
18:53and I'm actually just going to plug in
18:55the audio here to see if I can get you
18:59some audio playing out Jeff's just
19:01entered the study he's been awake for
19:04for a normal 16 hours
19:06perhaps let's hear from Jeff what his
19:09sort of hopes and aspirations are for
19:12the deprivation period I've been here
19:20for about and I think about an hour No
19:25yeah about an hour so it's the first
19:27hour I'm reading my paper right now 30
19:32page paper hopefully I can get some of
19:33it done before I get to say so that's
19:37Jeff perfectly likable affable chap
19:40who's hoping to get his 30 page report
19:43complete in a night of sleep deprivation
19:50classic delusional undergraduate
19:53thinking I have to say I see it all of
19:55the time in my students so now let's
19:58fast-forward the clock it's now at 5:30
20:01the following morning Jeff is now been
20:04awake for 22 hours straight and
20:06instantly you'll notice one of the
20:08hallmark features of sleep deprivation
20:11which is that you actually slide down in
20:14your chair you can just you can look
20:17around the room right now actually and
20:18see Jeff's down about about 6 or 7
20:22inches it's about an inch for every hour
20:25that you've been awake beyond the
20:27standard 16 based on our highly
20:31sophisticated machine learning
20:32algorithms so but in all seriousness
20:37notice how emotionally different Jeff
20:41has become some people have I think
20:44perhaps unkindly described him as
20:46becoming a little bit emotionally
20:48unhinged so and let's hear how that 30
20:51page report has been going and I do
20:54apologize ahead of time for the
20:56profanity
21:02[Applause]
21:03I'm very angry right now because I
21:07didn't get me more but I curse
21:08on this and you know like
21:13[Laughter]
21:15they really have crazy addresses and
21:18very loose erection so did you notice
21:24how Jeff went from being remarkably
21:26upset and annoyed that he got none of
21:28his 30 page report complete - then
21:30finding it almost hilarious he was
21:33nearly sort of punch-drunk giddy on
21:35sleep deprivation and then came right
21:37back down to baseline again that is a
21:40remarkably abnormal emotional distance
21:44to travel with in such a short time
21:46period and I think it emphasizes the
21:50type of destabilizing influence that a
21:53lack of sleep has on our emotional
21:56integrity and we've since discovered
22:00what actually changes within your brain
22:03to produce this type of pendulum
22:06emotional irrationality there's a
22:09structure very deep within your brain
22:11called the amygdala and you can see it
22:14here in these red colors again you have
22:16one on the left side and one on the
22:17right and the amygdala is one of the
22:20centerpiece regions for the generation
22:23of strong emotional reactions including
22:27negative reactions and when we looked at
22:31this structure in those people who'd had
22:33a full night of sleep here in green we
22:36saw a nice controlled modest degree of
22:39reactivity yet in those people who are
22:43sleep deprived we saw this amplified
22:45almost aggravated degree of reactivity
22:49the amygdala was actually 60% more
22:52responsive under conditions of a lack of
22:55sleep and it's almost as though without
22:59sleep we've become all sort of emotional
23:01gas pedal and too little sort of
23:04regulatory control break but what is
23:08perhaps more concerning however is that
23:11this represents a neurological signature
23:14that is not dissimilar to numerous
23:17psychiatric conditions and we're now
23:21finding significant links between sleep
23:25disruption and
23:26conditions such as depression anxiety
23:29including PTSD schizophrenia and
23:33tragically suicide as well in fact we
23:41cannot find a single psychiatric
23:44condition in which sleep is normal
23:47I think sleep has a profound story to
23:54tell in our understanding in our
23:57treatment and perhaps even may
23:59contribute to our ultimate prevention of
24:02grave mental illness so that's sleep for
24:09the brain but sleep is just as essential
24:12for your body and here I could have gone
24:16into any one of the model systems and
24:19spoken about it in detail we've already
24:21spoken a little bit about sleep loss and
24:24the reproductive system I could tell you
24:27about sleep loss and the metabolic
24:29system that after one week of short
24:32sleep your blood sugar levels are
24:35disrupted so significantly that your
24:37doctor would classify you as being
24:39pre-diabetic or I could tell you about
24:44sleep loss and the cardiovascular system
24:47that all it takes is one hour because
24:51there is a global experiment that is
24:53performed on 1.6 billion people across
24:5770 countries twice a year and it's
25:01called daylight savings time now in the
25:04spring when we lose one hour of sleep we
25:08see a subsequent 24 percent increase in
25:11heart attacks in the fall when we gain
25:16an hour of sleep we see a 21 percent
25:19decrease in heart attacks that is how
25:24fragile your body is to even just the
25:27smallest perturbations of sleep I think
25:31many of us props don't think anything of
25:33losing an hour of sleep but as a deep
25:37dive I actually want to focus on this
25:40in the immune system and here I'll
25:42introduce these delightful blue elements
25:45in the image they are called natural
25:47killer cells think of natural killer
25:50cells like The Secret Service agents of
25:54your immune system they are very good at
25:57identifying dangerous foreign elements
26:00and eliminating them
26:01in fact what they're doing here in this
26:04image is embedding themselves into a
26:05malignant a cancerous tumor mass and
26:08destroying it and many of you may not
26:12know but today your body produced cancer
26:16cells and it's always doing this what
26:20stops those cancer cells from becoming
26:23the disease that we call cancer is in
26:26part these natural killer cells so what
26:30you want is a veeraiah set of these
26:34immune assassins at all times and sadly
26:39that's exactly what you don't have if
26:41you're not sleeping enough so here in
26:45this study from my wonderful colleague
26:47Mike Erwin you're not going to have your
26:49sleep deprived for an entire night
26:51you're simply going to have your sleep
26:53restricted to four hours for one single
26:57night and then we're going to look to
26:59see what is the percent reduction in
27:01immune cell activity that you suffer and
27:05it's not small it's not ten percent it's
27:09not thirty percent there was a 70
27:13percent drop in natural killer cell
27:16activity that's quite a concerning state
27:21of an immune deficiency and it happens
27:25quickly essentially after just one bad
27:28night imagine the state of your immune
27:32system after weeks if not months of
27:35insufficient sleep and it perhaps should
27:39then come as no surprise to learn that
27:41we now have significant links between
27:44short sleep and numerous forms of cancer
27:48currently that list includes cancer of
27:51the bowel cancer of the prostate
27:53and cancer of the breast in fact the
27:58link between a lack of sleep and cancer
28:01is now so strong that recently the World
28:05Health Organization decided to classify
28:08any form of nighttime shift work as a
28:11probable carcinogen in other words jobs
28:16that may induce cancer because of a
28:18disruption of your sleep wake rhythms so
28:24you may have heard of that old maxim you
28:26know you can sleep when you're dead
28:28well I'm being absolutely serious it is
28:31mortally unwise advice because if you
28:36adopt that mindset we know from the data
28:38that you will now live a shorter life
28:42and the quality of that shorter life
28:45will be significantly worse
28:48epidemiological studies teaches this
28:51short sleep predicts a shorter life it
28:54predicts all cause mortality and the bad
29:01news I'm sorry keeps coming because if
29:04you are fighting a battle against cancer
29:06and not getting sufficient sleep that
29:09cancer may grow more quickly and
29:11aggressively so here I actually want to
29:15feature work not from my own
29:17sleep center but by a scientist called
29:20David goes out who works at the
29:22University of Chicago and he examines
29:25the relationship between sleep loss and
29:27cancer in mice now I know this isn't for
29:31everyone so I will tell you when to look
29:33away if you prefer not to see this but
29:36in one of the studies that he did he
29:38inoculated some mice with cancer cells
29:41on their back and then he gave that
29:43cancer a one-month period to grow and at
29:47the end of that one month he resected
29:49the skin and measured the size of that
29:51tumor mass half of the mice were allowed
29:55to sleep normally during that one-month
29:58period the other half had their sleep
30:01disrupted not total deprivation they
30:04just sort of played with them a little
30:07bit more
30:07the day in during the night to restrict
30:09their sleep so in a second I'm going to
30:13play a video with David illustrating the
30:15results and now would be the time to
30:17look away if you would prefer to do so
30:19and here you can see him pointing to a
30:23mouse on a monitor with the skin
30:26resected and you can clearly see that
30:28tumor master this is in one of the mice
30:31that was allowed to sleep normally
30:33during that one month I'll play the
30:36video and he'll reveal behind it another
30:39mouse that mouse was in the sleep
30:42restriction group and you will see the
30:45difference in the tumor mass this is the
30:48difference there was a 200% increase in
30:59the speed and the size of that cancerous
31:03growth linked to insufficient sleep were
31:08still the cancer in those underslept
31:11mice had actually metastasized that's
31:15just a medical description meaning that
31:17it had breached the original origin and
31:19started to invade other areas bone other
31:22organs as well as brain when cancer
31:27becomes metastatic that's when we see
31:30mortality rates escalate so if you are
31:36fighting a battle against cancer and not
31:39getting sufficient sleep it may be the
31:42equivalent of placing gasoline on an
31:45already aggressive fire sleep loss is an
31:48accelerant and we now know that it
31:51produces a harmful biological fertilizer
31:54for the more rapid and rampant growth of
31:58cancer
32:04now if increasing your risk of
32:06developing Alzheimer's or cancer by way
32:10of a lack of sleep were not sufficiently
32:12disquieting we have since discovered
32:16that a lack of sleep will even erode the
32:19very fabric of biological life itself
32:24your DNA genetic code so here in this
32:30study they took a group of healthy
32:32adults and limited them to six hours of
32:35sleep for one week and then they
32:38measured the chain and change sorry in
32:40the gene activity profile compared to
32:44when those same individuals were getting
32:46eight hours of sleep for a week and
32:49there were two critical results here
32:52first a sizable and significant 711
32:58genes were distorted in terms of their
33:02activity caused by six hours of sleep
33:05and that's relevant by the way we know
33:08that almost one out of every two
33:10American adults are trying to survive on
33:13six hours of sleep or less during the
33:16week the second result was that about
33:21half of those genes were actually
33:23increased in their activity the other
33:25half were actually decreased in their
33:27activity those genes that were decreased
33:31by a lack of sleep were genes related to
33:34numerous aspects of the immune system
33:37which fits very well with the evidence I
33:40was just discussing regarding cancer
33:42those genes that were actually increased
33:45in their activity or what we call up
33:47regulated in their expression were genes
33:50related to the promotion of tumors genes
33:54that were related to chronic
33:56inflammation within the body and also
33:59genes that were related to stress and as
34:02a consequence cardiovascular disease now
34:09I think many individuals in society feel
34:13uncomfortable about the idea of
34:16genetically modified embryo
34:18or even genetically modified food but by
34:22choosing to get insufficient sleep we
34:26may be forced to accept that we are
34:28performing a similar genetic modifying
34:31experiment on ourselves and if we don't
34:37let our children get the sleep that they
34:39so desperately need then we may be
34:42inflicting a similar genetic engineering
34:45experiment on them as well there is
34:50simply no aspect of your physiology that
34:54seems to be able to retreat at the sign
34:58of sleep deprivation and get away
35:01unscathed it's almost like a broken
35:06water pipe in your home sleep loss will
35:09leak down into every nook and cranny of
35:13your biology even tampering with the
35:18very DNA nucleic alphabet that spells
35:22out your daily health narrative so where
35:29does this leave us what is the piece of
35:32sort of mental furniture I would like to
35:35gift to you as we finish the talk well
35:40it would be this sleep is not an
35:45optional lifestyle luxury leave is a
35:50non-negotiable biological necessity it's
35:55a life support system and it is mother
35:59nature's best effort yet at contra death
36:04and the decimation of sleep throughout
36:09industrialized nations is having a
36:11catastrophic impact on our health or
36:14wellness and the safety and the
36:17education of our children it's a silent
36:20sleep loss epidemic and it is fast
36:24becoming one of the greatest public
36:26health challenges that we now face in
36:28the 21st century
36:31I believe it is now time for us to
36:37reclaim our right to a full night of
36:41sleep and without embarrassment and
36:46without that terrible and stigma of
36:49laziness and in doing so we may finally
36:55remember what it feels like to be awake
36:59during the day and with that soap box
37:05rant over I will simply say good night
37:08good luck and above all I do hope you
37:12sleep well thank you very much indeed I
37:15[Applause]
37:19think we've got lots of times for
37:22questions I think thank you so much for
37:27the target was actually very informative
37:28I have two questions for you number one
37:31I have a five year old and then there's
37:33myself right so how much sleep should we
37:35be getting and number two is there any
37:39disadvantage of over sleeping so let's
37:40say if I sleep 10 or 15 hours day in the
37:42day yeah that's a so great questions so
37:46first the recommendations for sleep you
37:48can find them on the National Sleep
37:49Foundation website for all ages for the
37:53average adult the recommendation World
37:55Health Organization eight hours range
37:58seven to nine once human beings the
38:03average human being gets below seven
38:05hours of sleep we can measure objective
38:07empowerment's so people who say I can
38:09survive on six hours of sleep there's a
38:11problem with that which is this your
38:13subjective sense of how well you think
38:15you're doing without sufficient sleep is
38:17a miserable predictor of objectively how
38:20you're doing without sufficient sleep so
38:22it's it's probably a little bit like a
38:24drunk driver at a bar you know they've
38:26had seven shots they pick up the car
38:27keys and they say I'm fine to drive and
38:29your response is now I know that you
38:31think you're fine to drive but trust me
38:33objectively you're not the same is true
38:36for a lack of sleep your second question
38:39is fascinating
38:40can I sleep too much well there are
38:44anecdotes of some
38:45called a sleep hangover where you said
38:47of oversleep and then you feel worse
38:49almost when you oversleep it usually
38:52means that you're trying to sleep off a
38:54debt that you've lumbered yourself with
38:56so if you could sleep past your alarm if
38:59it didn't go off then your underslept
39:02because it's physiologically impossible
39:04to sleep too much if you're healthy now
39:08there is one piece of evidence that
39:11suggests something called hypersomnia
39:13excessive sleep that principally
39:16expresses itself in depression but if
39:19you look at that data it's actually very
39:20difficult to tell is it people just
39:22reporting being in bed for longer rather
39:25than sleeping longer so I think it's
39:26unclear right now but let me just take
39:28it to a theoretical realm could there be
39:31such a thing as too much sleep I think
39:33yes but don't forget the same is true
39:36for the other three essential factors of
39:38life oxygen food and water can you eat
39:41too much yes
39:42can you over hydrate yes can you
39:45increase blood pressure cause stroke and
39:47heart attack by excessive water intake
39:50it happened in the 1990s with the
39:52ecstasy craze where people were
39:53dehydrating governments told them drink
39:55lots they drank too much cardiac events
39:58can you actually become hyper oxygenated
40:02so you get free radical species
40:03dangerous for cells yes you can is there
40:06such a thing as too much sleep we
40:09haven't found it yet but I suspect
40:10probably so it's a bell-shaped curve
40:13it's a u-shaped function in terms of
40:14benefit not linear but on most people in
40:18danger of getting too much sleep Oh
40:20contraire thank you for the great talk
40:24do you also have any information on how
40:27quickly people recover after they switch
40:29from a kind of short sleep periods to
40:32kind of a more normal sleep periods
40:35because we only mentioned kind of as one
40:37of those was the d'Este change or when
40:39we'd sleep one or more kind of things
40:41get better in terms of cardiac province
40:43yeah kind of is it quick to recover as
40:47well as quick as the yeah it's a great
40:52question so different aspects of your
40:54brain in your body seemed
40:57to come back online to a status of
40:59health with recovery sleep and those
41:02temporal profiles are different based on
41:05even within the immune system for
41:07example some components take longer to
41:09come back online than others what I
41:11would note however is that you can never
41:13get back all that you've lost this is
41:16another one of those myths with sleep so
41:18sleep is not like the bank
41:21you cannot accumulate a debt and then
41:23pay it off at a later point in time
41:25which is what most of modern society
41:27does chronic short sleep during the week
41:30then you binge at the weekend it's what
41:32I call sleep bulimia it's what is
41:34otherwise known as social jetlag now if
41:37I were to take you and deprive you of
41:39sleep for one single night eight hours
41:41of lost sleep and then I give you all of
41:43the sleep that you want for however many
41:45nights and we keep recording you your
41:47brain never recovers all of that lost
41:49eight hours it will try to get back some
41:52of it it will never get back all of it
41:54why is that the case we can ask why
41:58doesn't your brain have a credit system
41:59for sleep because there's precedent for
42:02this in biology you have one for energy
42:04it's called a fat cell you can actually
42:08store up credit calorically and spend it
42:13when you go into famine now most of us
42:15are in that danger anymore but during
42:17evolution we face that challenge so we
42:19came up with a solution called the
42:21adipose cell where is the fat self
42:24asleep why isn't it there the reason is
42:28this human beings are the only species
42:30that deliberately deprived themselves of
42:32sleep for no apparent reason
42:35what that means is that Mother Nature
42:37has never had to face the challenge
42:40through evolution of coming up with a
42:42safety net because of insufficient sleep
42:44so there is no mechanism of safety there
42:47is no credit system have you done any
42:56research about supplements that can help
42:58sleeping well without the device yet so
43:07no drugs or supplements that we have
43:10currently produced naturalistic sleep
43:13chemically it's an incredibly complex
43:15job now I don't want to dismiss people
43:19at drug companies I'm not against
43:21medication I'm not anti all medication
43:23for medications work I'm all for them
43:25it's just that all of the sleeping
43:27medications that we have right now don't
43:29produce naturalistic sleep most of them
43:31are a class of drugs that we call the
43:33sedative hypnotics
43:34sedation is not sleep all you're doing
43:36is knocking the cortex out you're not
43:38producing naturalistic sleep and and as
43:41I said mentioned in the book they are
43:44also linked to a higher risk of death
43:47and considerably higher as well as
43:49cancer what about melatonin
43:52well melatonin turns out not to be an
43:55effective sleep aid and it shouldn't
43:58surprise us based on how melatonin works
44:00melatonin helps time the onset of sleep
44:04but it doesn't help in the creation of
44:07sleep itself so the analogy would be
44:10melatonin is like the starting official
44:13in the hundred meter race at the
44:15Olympics melatonin gathers all of the
44:17races to the starting line and begins
44:19the race but that official themselves
44:22does not participate in the great sleep
44:24race itself that's a whole different set
44:26of brain mechanisms and chemicals that's
44:29why melatonin is not efficacious once
44:31you're stable in a new time zone now I
44:35will say this however if you're taking
44:38melatonin and you feel it's beneficial
44:40keep taking it because the placebo
44:43effect is one of the most reliable
44:45effects in all of pharmacology
44:49and and this I mean that tells you
44:52something by the way something profound
44:54there is such a thing as mind over
44:56matter and there is now a wonderful
44:58science of the placebo effect
45:00it's very real and we dismissed it for a
45:03long time I hope that answers both your
45:05question ain't it sure does like the
45:13time period between when you wake up to
45:16when you start using your brain like for
45:19learning or whatever also play a
45:22difference like if a person had a full
45:248-hour sleep but they don't go to school
45:26until evening when they have evening
45:27school do they learn worse than if they
45:30could have went to a morning school and
45:33so it's a very interesting question sort
45:36of you know when on the clock face is is
45:38learning let's say most sort of
45:41beneficial well once you're waking at a
45:47reasonable time it seems as though there
45:49is some degree of stability of learning
45:52across the day however that does seem to
45:54be a gradual deterioration and we've
45:56done some of these studies to basically
45:57map the time cost the sort of the Great
46:00Depression of learning you know across
46:03the day and we've inserted naps and we
46:06can actually restore learning and but I
46:07would like to come on to nap someone
46:09should ask me about that because there
46:10are a double-edged sword with danger but
46:14what we do know from those school
46:16studies were they delayed the school
46:17start times where you get the greatest
46:20grade point increases is not in all
46:23classes across the day but it's
46:25especially in those first morning
46:28classes but I think that that's less
46:30about your brain being better at
46:33learning in the morning than it was
46:35about when you were starting so early it
46:37was just so detrimental to try and learn
46:39so sort of you lowered the floor rather
46:42than raise the ceiling so yeah but to me
46:46it makes sense that learning is somewhat
46:48stable across 16 hours because if you
46:50were to design a system of memory that
46:52could only learn in the last couple of
46:54hours of wakefulness then why are we
46:56awake for the other 14 and we seem to
46:58have a system of memory that gives us a
47:00capacity for about a
47:02about 16 hours of recording in humans
47:05before sleep is required a quick
47:07question there you're doing a study on
47:09all their brain activities like code it
47:13well I'm not coding but you know more
47:14advanced out like should I try not to
47:16schedule morning meetings because
47:17everybody is asleep but nobody's making
47:18decisions yes so we've done lots of
47:21studies on all aspects of brain
47:23cognition we've done at decision making
47:26judgment making we've done creativity
47:29emotional regulation we've done visual
47:32attention aspects we've done motor skill
47:34learning and it follows the same profile
47:37which is essentially when sleep is in
47:39high volumes all of those things are
47:42supported different operations within
47:45the brain rely on different stages of
47:48sleep at different times of night
47:50however it's not just one stage of sleep
47:53that does it all for all of your brain
47:55sort of mechanisms and apparatus
47:58features and this is why there is no
48:00single one stage of sleep that's
48:02important people will say oh how can I
48:04get more REM sleep and I would say why
48:06do you want more REM sleep well how can
48:08I get more deep sleep mother nature took
48:10about 3.6 million years to figure that
48:12out just let her do a job she'll see you
48:15well quick question basically how do
48:20drugs from any kind of drugs medicine
48:23alcohol marijuana how would it be simply
48:26at the brain activity during the my
48:28doing so how do you drugs perhaps some
48:33legal some non legal impact sleep I'll
48:36focus on marijuana and alcohol since you
48:39mentioned them alcohol is perhaps the
48:41most misunderstood drug when it comes to
48:43sleep people say you have a nightcap and
48:46I fall asleep better untrue alcohol is
48:49also a class of drugs that we call the
48:51sedatives and once again that's not
48:54natural sleep what you're doing is
48:55simply removing consciousness by way of
48:58alcohol you're not putting yourself into
49:00natural sleep to more problems with
49:02alcohol first it will fragment your
49:05sleep with awakenings throughout the
49:06night the problem is that they are so
49:09brief that you tend not to remember them
49:11and commit them to memory so you wake up
49:13the next morning feeling unrefreshed
49:15but you
49:15don't understand why that it was the
49:17alcohol fragmenting your sleep
49:19finally alcohol is very effective at
49:22blocking your REM sleep or blocking your
49:24dream sleep so alcohol misunderstood
49:28should be avoided and marijuana people
49:31use it to try and help them get to sleep
49:33or relax the problem is marijuana also
49:36seems to fragment sleep it also seems to
49:39block rapid eye movement sleep probably
49:42the other chemical that deserves mention
49:45here is caffeine caffeine most people
49:49know is an alerting drug it's actually a
49:51class of drugs that we call the
49:53psychoactive stimulants it's the only
49:55legal stimulant that we readily give to
49:57our children
49:58by the way caffeine can obviously keep
50:02you awake at night but some people will
50:04say I'm one of those who can have a cup
50:05of coffee and I fall asleep fine
50:07the problem there is that even if you
50:09fall asleep the depth of the deep sleep
50:12that you have is not as deep as if you
50:15were to have sleep that didn't have
50:17caffeine swirling around within the
50:19brain so again you wake up the next
50:21morning feeling unrefreshed
50:23you don't remember waking up or
50:24struggling to fall asleep so you don't
50:26think it's the caffeine but now you need
50:28two cups of coffee rather than one the
50:30next morning you build up this vicious
50:32cycle and it's probably the reason that
50:34caffeine is the second most traded
50:35commodity on the surface of the planet
50:37after oil I don't think there's probably
50:39any other Cystic that Burres out how
50:41sleep-deprived we are throughout
50:43industrialized nations quick question
50:48how much of this deep every night is
50:50basically enough um
50:52zero hours maybe uh once you as I said
50:55once you get below seven hours of sleep
50:57that's when we can measure objective
50:59impairments yeah yep but that's once we
51:04can measure objective impairments
51:06doesn't mean that if we had more
51:07sensitive tools we would measure it at
51:09you know 7 hours and 50 minutes I
51:12wondered about blue light exposure
51:14especially from devices and I couple
51:18years ago I got the blue light walking
51:20glasses and it does seem actually
51:22giving better sleep and I know spirits
51:23what the researchers behind that yeah
51:25that one is actually not a placebo
51:27effect it turns out so the studies are
51:30very clear right now we are as as an
51:35industrialized set of Nations we are a
51:38dark deprived society and we need
51:42darkness because the way that darkness
51:44works is that it actually removes the
51:48breaks from the hormone melatonin that I
51:51described that needs to rise to help
51:54time the normal onset of healthy sleep
51:56so if you're bathed in electrical light
51:59at night even though it's not as
52:01powerful as daylight it can keep the
52:04brake pedal on melatonin now they did
52:07some fascinating studies were you read
52:10on an iPad for one hour versus just
52:12reading a normal buck with dim light and
52:15firstly relative to that one hour of dim
52:17light normal book reading the one hour
52:19of iPad reading firstly delayed that
52:22spike in melatonin by two to three hours
52:25so here if we are reading the iPad in
52:28Seattle were almost all the way to
52:30Hawaii in terms of our biological
52:32melatonin rhythms
52:34that's how shifted and delayed we are
52:36second the sleep was not as good REM
52:39sleep was disrupted and people
52:41subjectively felt worse and less
52:43refreshed the next morning and it took a
52:46few days before it washed itself away
52:48after they ceased so I think you know
52:52the recommendation right now is try to
52:54limit screen time in the last hour I
52:57know where I'm speaking right now which
52:59is at Google and what that means you can
53:02install software that helps desaturate
53:04the most harmful wavelength of light
53:06which is the blue light you can also put
53:09those spectacles on they seem to work as
53:11well but overall try to decrease
53:13stimulation blackout curtains also great
53:16at night during the night in bed you
53:19know follow up on the blackout curtains
53:21so one of the things I found is this
53:24really hard to get up in the morning if
53:25the room is all blocked out of having
53:27that
53:28and as is important and I wanted to
53:31which is worse to have any of this light
53:34coming in during the nighttime versus
53:36having to deal with an unnatural alarm
53:40clock waking up in the morning yeah if
53:42you do have to I mean it sounds as
53:44though what you're experiencing is sort
53:45of a groggy what we call a sleep inertia
53:47which is when you wake up it usually
53:49means that you're sort of waking up at a
53:51time that slightly offset from your
53:53natural biological tendency with that
53:56you can use daylight to perhaps try and
53:59help you some people actually use eye
54:00masks in the first part of the night and
54:02at some point they will take the eye
54:04mask off and then help with the exposure
54:07to the daylight because they've kept
54:08their curtains you know non-black out in
54:11that regard but that's a tricky one to
54:12balance yep I know there are a lot of
54:15more questions it's coming up on two
54:17o'clock so we're gonna cut it off but
54:18dr. Walker will stay and he's gonna sign
54:20books we're selling a few of the copies
54:21and so just everybody let's give dr.
54:23Walker our hands thank you very much
54:24indeed thank you thank you so much thank
54:30you
54:40you

About this transcript

This page contains the full transcript of Why We Sleep: Science of Sleep & Dreams | Matthew Walker | Talks at Google by Talks at Google, generated from the public captions YouTube serves with the video. The transcript has 7,624 words across 1,125 segments, with the original timestamps preserved so you can click any line to jump to that moment in the embedded player.

What you can do with it

Use the transcript to take notes, quote the speaker, build a study guide, generate a summary with ChatGPT or Claude via the YouTube Summary tool, or export it as a timed subtitle file with YouTube to SRT. You can also re-open it in the transcriber to translate the transcript into 100+ languages.

Free YouTube transcript tool

YouTube2Text is a free YouTube transcript generator — no signup, no daily limit. Paste any YouTube link and get the full transcript instantly, with timestamps, click-to-jump, translation to 100+ languages, AI prompts for ChatGPT, Claude, and Gemini, and exports to TXT, SRT, VTT, or Markdown.