Matthew Walker: “Why We Sleep: The New Science of Sleep and Dreams” | Talks at Google

Matthew Walker: “Why We Sleep: The New Science of Sleep and Dreams” | Talks at Google

[MUSIC PLAYING] JOSH: Right. And thank you all for coming. This is a great crowd. And I want to welcome
Dr. Matthew Walker. He is professor of
neuroscience and psychology at the University of
California, Berkeley. And he’s the
founder and director of the Center for
Human Sleep Science, and he’s here today to
talk about his new book, “Why We Sleep.” So without further ado. MATTHEW WALKER: Thank
you very much, Josh. [APPLAUSE] Thank you. Well, it’s a delight and
privilege to be here. And I would like to
start with testicles. [LAUGHTER] Men who sleep five
hours a night have significantly smaller
testicles than those who sleep eight hours or more. In addition, men who routinely
sleep five to six hours a night will have a level
of testosterone which is that of someone
10 years their senior. So a lack of sleep
ages you by a decade in terms of that aspect, that
critical aspect of wellness and virility. And we see equivalent
impairments in female reproductive health
caused by a lack of sleep. This is the best news
that I have for you today. [LAUGHTER] From this point forward,
it’s only going to get worse. Rather than tell you about the
wonderfully good things that happen when you get
sleep, I’m going to tell you about the
alarmingly bad things that happen when you don’t get
enough both for the brain and for the body. Let me start with the brain
and the functions of learning and memory. What we’ve discovered over
the past 10 or so years is that you need sleep after
learning to essentially hit the Save button on
those new memories, so that you don’t forget. So sleep essentially
future-proofs those facts within the brain. But recently, we’ve discovered
that you not only need sleep after learning, you also need
sleep before learning, but now to actually prepare your
brain, almost like a dry sponge ready to initially soak
up new information. And without sleep, the
memory circuits of the brain effectively become
waterlogged, as it were, and you can’t absorb
new information. So here in this
study, we decided to test the hypothesis that
pulling the all-nighter was a good idea. How do you do that? Well, we took a group
of healthy adults and we assigned them to one of
two experimental conditions– a sleep group and a
sleep deprivation group. Now, the sleep
group, they’re going to get a full eight
hours of shuteye. But the deprivation
group, we’re going to keep them awake
in the laboratory under full supervision. There’s no naps,
there’s no caffeine. It’s miserable for everyone
included, us as well. And then the next
day, we’re going to place those participants
inside an MRI scanner, and we’re going to
have them try and learn a whole list of new facts
as we’re taking snapshots of brain activity. And then we’re
going to test them to see how effective
that learning has been. And that’s what you’re looking
at here on the vertical axis, the amount of learning. So the higher up you are,
the more that you learn. And when you put those
two groups head to head, what you find is a quite
significant 40% deficit in the ability of
the brain to make new memories without sleep. And I think this
should be frightening considering what we
know is happening to sleep in our education
populations right now. Just to frame this
in context, it would be the difference
between acing an exam and failing it miserably. And we’ve gone on
to discover what goes wrong within your brain to
produce these types of learning disabilities. There is a structure on
the left and the right side of your brain called
the hippocampus. And you can see it here in these
sort of orange-yellow colors. Think of the hippocampus
like the informational inbox of your brain. It’s very good at
receiving new memory files and holding on to them. And when we looked
at this structure in those people who’d had a full
night of sleep here in green, we saw lots of healthy
learning-related activity. Yet in those people who
were sleep deprived, we actually couldn’t find any
significant signal whatsoever. It’s almost as though
sleep deprivation had shut down the memory inbox
and any new incoming files, they were just being bounced. You couldn’t effectively commit
new experiences to memory. And parenthetically,
I should note if you would like
to know what life is like without a
functioning hippocampus, just watch the movie “Memento.” I suspect many of
you have seen this. But this gentleman
suffers brain damage. And from that point
forward, he can no longer make any new memories. He’s what we call
densely amnesic. The part of his brain that was
damaged was the hippocampus, and it is the very
same structure that sleep deprivation will
attack and block your brain’s capacity for new learning. So that’s the bad that happens
when you take sleep away. Let me just come back to that
control group for a second. Do you remember those
folks that got a full eight hours of sleep? Well, we can ask a very
different question here. What is it about the
physiological quality of sleep, when you do get it, that
actually enhances and restores your learning and memory
ability each and every day? And by recording sleep
with electrodes placed all over their head, we’ve
discovered that there are big, powerful brain waves
that happen during the very deepest stages of sleep that
have, riding on top of them, these spectacular bursts
of electrical activity called sleep spindles. And it’s the combined
quality of these deep sleep brainwaves at night that acts
like a file transfer mechanism. It takes memories from
a short-term, vulnerable reservoir and shifts
them to a more permanent, long-term storage
site within the brain called the cortex, this big,
wrinkled, massive tissue that sits atop of your brain. And it means that when you
wake up the next morning, there are two benefits. First, having shifted
memories of yesterday to that long-term, safe
storage haven in the brain, they are protected
so that you will remember rather than forget. The second benefit, however, is
that having shifted those files from that short-term reservoir,
almost like moving files from a USB stick,
you’ve cleared out all of that
memory-encoding capacity, so that when you
wake up the next day, you can start acquiring
new files all over again. You can start learning anew. So it’s this elegant, beautiful,
symbiotic system of memory that happens each and every night. And it’s important
that we understand what, during sleep, actually
transacts these memory benefits, because there are
real medical and societal implications. And let me just tell
you about two areas that we’ve moved
this work out into. I’ll begin clinically and
specifically the context of aging and dementia. Because I think many
of us have a sense or even know that
as we get older, our learning and memory
abilities start to fade. They begin to decline. But what we’ve also
known for many decades is that a physiological
signature of aging is that your sleep gets worse. And not just any type of sleep– especially that deep
quality of sleep that I was just describing. And only last year, we
finally published evidence that these two factors are
not simply co-occurring. They are significantly
interrelated. And it suggests that the
disruption of deep sleep is perhaps an underappreciated
factor that is contributing to what we call cognitive
decline, or memory decline, in aging, and most
recently, we’ve discovered, in Alzheimer’s
disease as well. Now, I know this is
remarkably depressing news. I understand. It’s in the mail. It’s coming at you. But there is a potential
silver lining here, because unlike many of the
other factors that we know are associated with
aging and dementia– for example, changes in
the physical structure of the brain or even changes in
the vasculature of the brain– those are fiendishly
difficult to treat right now. And we don’t have any
good wholesale approaches in medicine. But that sleep is a missing
piece in the explanatory puzzle of aging and
Alzheimer’s is exciting, because we may be able
to do something about it. And one way that
we are approaching this at my Sleep Center is
not by using sleeping pills, by the way. They are blunt
instruments that do not produce naturalistic
sleep, and they’ve been associated with a higher
risk of death and cancer. And I’m happy to speak about
that evidence during the Q&A, and it’s discussed
in the book as well. What we are actually doing
is developing a method based on this technology. It’s called direct-current
brain stimulation. It sounds like the stuff
of science fiction. It’s actually science fact. You apply electro
pads to the head, and you insert a small amount
of voltage into the brain, so small that you
tend not to feel it. But it has a measurable
impact on physiology. Now, if you apply this
stimulation during sleep, in young, healthy
adults, as if you’re sort of singing in time with
those deep sleep brain waves, not only can you
actually amplify the size of those deep sleep
brain waves, but in doing so, you can almost double the
amount of memory benefit that you get from sleep. The question now is
whether we can translate this same affordable,
potentially portable technology into older adults and
those with dementia. Can we restore back some
healthy quality of deep sleep? And in doing so, can we salvage
aspects of learning and memory function? That is my real hope now. That’s one of our moonshot
goals, as it were. I should note, by the
way, because I always get asked this question–
people will say, where can I buy one of those devices? I want one yesterday and
I want five more tomorrow. And they are not yet
FDA-approved for use in sleep. You can buy them
on the internet. I strongly advise against that. Just read around,
some horror stories. People have misaligned
the voltage, skin burns, they’ve lost their
eyesight for several days. Hang on. We are desperately
trying to bring this to fruition as soon as we can. So that’s sleep and memory
in a clinical context. But let me speak
about sleep and memory in society and specifically
here within education. Because if sleep really is
so important for learning and memory, then enhancing
sleep in a context where, arguably, it matters most
should prove transformative. And it has because there
are several counties throughout the
United States that have started to delay
their school start times and then measure the
academic consequence. Now, one of the earliest
test case examples happened in Edina in Minnesota. It’s a township that sits
just outside of Minneapolis. And they shifted their
school start times from 7:25 in the morning to
8:30 in the morning. By the way, what
are we doing trying to educate our next generation
at 7:25 in the morning? [LAUGHTER] To give you a sense of this,
buses for a 7:25 start time will often begin leaving
at 5:30 in the morning. That means that
some kids are having to wake up at 5:15, 5
o’clock, maybe even earlier. This is lunacy. But in Edina, it was the
beginnings of a movement. And the metric that they used to
assess the academic consequence was this– SAT scores. And they focused their analysis
on the top 10% performing students, arguably those
that have the least to gain in terms of any further
improvement by way of sleep. Now, in the year before
they made the time change, that top 10% performing
students got an average score of 1,288, which is a
very respectable score. The following year
when students were now going to school at
8:30 in the morning, the average SAT score was– AUDIENCE: Whoa. AUDIENCE: [WHISTLES] MATTHEW WALKER: –1,500. That is a 212-point increase,
which is non-trivial. That will change which tier of
university those school kids end up going to and
perhaps, as a consequence, their subsequent
life trajectories. Now, some people have questioned
aspects of the Edina study, and I think for
perhaps good reason. But in all of the subsequent
carefully controlled studies, the data is
unequivocal, I think. Academic grades increase,
behavioral problems decrease, truancy rates decrease, and
psychological and psychiatric issues also decrease. But something else actually
happened in this story of later school start times. And it was something that
we did not anticipate. The life expectancy of
students actually increased. And you think, I
don’t understand. How does that work? Does anybody know
what the leading cause of death in late-stage teenagers
is throughout most developed nations? AUDIENCE: Suicide. MATTHEW WALKER: Suicide
is actually second. It’s car crashes. And here sleep
matters enormously. Another example comes from
Teton County in Wyoming. They shifted their
school starts from 7:35 in the morning to
8:55 in the morning. And then they measured the
reduction in car crashes in this narrow age
of just 16 to 18. The only thing perhaps more
remarkable than the extra hour of sleep that those
students reported getting was the drop in
vehicle accidents. There was a 70% reduction. Just to sort of frame
that in context, the advent of ABS technology,
what we call anti-lock braking systems that prevent your
wheels from locking up into hard braking, so that
you can still safely maneuver a vehicle, that dropped
accident rates by 20% to 25%. And some deemed it
to be a revolution. But here is a
biological factor– sleep that will drop
accident rates by up to 70%. I think it’s time for us to
reconsider the importance of sleep in education. When sleep is abundant,
minds flourish. And if our goal
as educators truly is to educate and not
risk lives in the process, then I fear that we may
be failing our children in a significant manner
with this incessant model of early school start times. So that’s sleep for learning,
memory, aging, Alzheimer’s. What else is sleep good for? Let me tell you that sleep is
essential to help stabilize your emotional
and mental health. And without sleep, the
emotional circuits of your brain become hyperactive
and irrational. Allow me to demonstrate with
a sleep-deprived subject, because it turns out
that we do video diaries with our participants throughout
the deprivation night. And you go to meet one
under the pseudonym of Jeff. It’s 11:30 at night. Jeff has been awake
for about 16 hours. And I’m actually just going
to plug in the audio here to see if I can get you
some audio playing out. Jeff’s just entered the study. He’s been awake for
a normal 16 hours. And perhaps let’s
hear from Jeff what his sort of hopes
and aspirations are for the deprivation period. [VIDEO PLAYBACK] – Hey. It’s about 11:27 right now. I’ve been here for about an– I think about an hour now. Yeah, about an hour. So it’s the first hour. I’m writing my paper right
now, a 30-page paper. Hopefully I can get some of it
done before I get too sleepy. [PLAYBACK ENDS] MATTHEW WALKER: So that’s Jeff. Perfectly likable,
affable chap who’s hoping to get his 30-page
report complete in a night of sleep deprivation. [LAUGHTER] Classic delusional
under-graduate thinking, I have to say. I see it all of the
time in my students. So now let’s
fast-forward the clock. It’s now 5:30 the
following morning. Jeff has now been awake
for 22 hours straight. And instantly, you’ll notice
one of the hallmark features of sleep deprivation, which is
that you actually slide down in your chair. You can look around the room
right now, actually, and see. Jeff’s down about
six or seven inches. It’s about an inch
for every hour that you’ve been awake
beyond the standard 16 based on our highly
sophisticated machine-learning algorithms. But in all seriousness, notice
how emotionally different Jeff has become. Some people have, I
think perhaps unkindly, described him as becoming
a little bit emotionally unhinged. So let’s hear how that
30-page report has been going. And I do apologize ahead
of time for the profanity. [LAUGHTER] [VIDEO PLAYBACK] – Hello. I’m very angry
right now, because I didn’t get any fucking–
could I curse on this? Are they going to, like– whatever. [LAUGHS] They probably think I’m
crazy after all this. I’m very lucid, actually. [END PLAYBACK] [LAUGHTER] MATTHEW WALKER:
So did you notice how Jeff went from
being remarkably upset and annoyed
that he got none of his 30-page report
complete to then finding it almost hilarious? He was nearly sort
of punch-drunk giddy on sleep deprivation and
then came right back down to baseline again. That is a remarkably
abnormal emotional distance to travel within such
a short time period. And I think it emphasizes the
type of destabilizing influence that a lack of sleep has
on our emotional integrity. And we’ve since discovered
what actually changes within your brain to produce
this type of pendulum, emotional irrationality. There’s a structure very
deep within your brain called the amygdala. And you can see it here
in these red colors. Again, you have one on the
left side and one on the right. And the amygdala is one
of the centerpiece regions for the generation of
strong, emotional reactions, including negative reactions. And when we looked
at this structure in those people who’d had a full
night of sleep, here in green, we saw a nice, controlled,
modest degree of reactivity. Yet in those people who
were sleep deprived, we saw this amplified,
almost aggravated degree of reactivity. The amygdala was actually
60% more responsive under conditions
of a lack of sleep. And it’s almost as
though, without sleep, we become all sort of
emotional gas pedal and too little sort of
regulatory-control brake. But what is perhaps
more concerning, however, is that this represents
a neurological signature that is not dissimilar to numerous
psychiatric conditions. And we’re now finding
significant links between sleep disruption and conditions
such as depression; anxiety, including PTSD;
schizophrenia; and tragically, suicide as well. In fact, we cannot find a single
psychiatric condition in which sleep is normal. I think sleep has
a profound story to tell in our understanding,
in our treatment, and perhaps even may contribute
to our ultimate prevention of grave mental illness. So that’s sleep for the
brain, but sleep is just as essential for your body. And here I could have gone into
any one of the model systems and spoken about it in detail. We’ve already
spoken a little bit about sleep loss and
the reproductive system. I could tell you about sleep
loss and the metabolic system, that after one week
of short sleep, your blood sugar
levels are disrupted so significantly that your
doctor would classify you as being pre-diabetic. Or I could tell you
about sleep loss and the cardiovascular system,
that all it takes is one hour. Because there is a
global experiment that is performed on 1.6 billion
people across 70 countries twice a year, and it’s
called daylight savings time. Now, in the spring, when
we lose one hour of sleep, we see a subsequent 24%
increase in heart attacks. In the fall, when we
gain an hour of sleep, we see a 21% decrease
in heart attacks. That is how fragile your body
is to even just the smallest perturbations of sleep. I think many of us perhaps
don’t think anything of losing an hour of sleep. But as a deep dive,
I actually want to focus on this– sleep
and the immune system. And here I’ll introduce these
delightful blue elements in the image. They are called
natural killer cells. Think of natural killer
cells like the Secret Service agents of your immune system. They are very good
at identifying dangerous foreign elements
and eliminating them. In fact, what they’re
doing here in this image is embedding themselves into
a malignant, a cancerous tumor mass, and destroying it. And many of you may not
know, but today your body produced cancer cells. And it’s always doing this. What stops those cancer cells
from becoming the disease that we call cancer is, in part,
these natural killer cells. So what you want is a virile
set of these immune assassins at all times. And sadly, that’s exactly
what you don’t have if you’re not sleeping enough. So here in this study from my
wonderful colleague Mike Irwin, you’re not going to
have your sleep deprived for an entire night. You’re simply going to have
your sleep restricted to four hours for one single night. And then we’re
going to look to see what is the percent reduction
in immune cell activity that you suffer. And it’s not small. It’s not 10%, it’s not 30%. There was a 70% drop in
natural killer cell activity. That’s quite a concerning
state of immune deficiency. And it happens quickly,
essentially after just one bad night. Imagine the state of
your immune system after weeks, if not months,
of insufficient sleep. And it perhaps should
then come as no surprise to learn that we now
have significant links between short sleep and
numerous forms of cancer. Currently that list includes
cancer of the bowel, cancer of the prostate,
and cancer of the breast. In fact, the link between
a lack of sleep and cancer is now so strong that recently
the World Health Organization decided to classify any
form of nighttime shift work as a probable carcinogen. In other words,
jobs that may induce cancer because of a disruption
of your sleep-wake rhythms. So you may have heard
of that old maxim– oh, you can sleep
when you’re dead. Well, I’m being
absolutely serious. It is mortally unwise advice. Because if you adopt that
mindset, we know from the data that you will now
live a shorter life and the quality of
that shorter life will be significantly worse. Epidemiological
studies teaches this. Short sleep predicts
a shorter life. It predicts all-cause mortality. And the bad news, I’m
sorry, keeps coming. Because if you are fighting
a battle against cancer and not getting
sufficient sleep, that cancer may grow more
quickly and aggressively. So here I actually
want to feature work not from my own sleep center,
but by a scientist called David Gozal who works at
the University of Chicago. And he examines the relationship
between sleep loss and cancer in mice. Now, I know this
isn’t for everyone, so I will tell you when
to look away if you’d prefer not to see this. But in one of the
studies that he did, he inoculated some mice with
cancer cells on their back. And then he gave that cancer
a one-month period to grow. And at the end of that one
month, he resected the skin and measured the size
of that tumor mass. Half of the mice were
allowed to sleep normally during that one-month period. The other half had
their sleep disrupted. Not total deprivation. They just sort of played
with them a little bit more during the day and during the
night to restrict their sleep. So in a second, I’m going
to play a video with David illustrating the results. Now would be the
time to look away if you would prefer to do so. And here you can
see him pointing to a mouse on a monitor
with the skin resected, and you can clearly see
that tumor mass there. This is in one of the mice that
was allowed to sleep normally during that one month. I’ll play the video, and he will
reveal behind it another mouse. That mouse was in the
sleep restriction group, and you will see the
difference in the tumor mass. This is the difference. There was a 200%
increase in the speed and the size of that
cancerous growth linked to insufficient sleep. Worse still, the cancer
in those under-slept mice had actually metastasized. That’s just a
medical description meaning that it had
breached the original origin and started to
invade other areas– bone, other organs,
as well as brain. When cancer becomes
metastatic, that’s when we see mortality
rates escalate. So if you are fighting
a battle against cancer and not getting
sufficient sleep, it may be the equivalent
of placing gasoline on an already aggressive fire. Sleep loss is an accelerant. And we now know that it produces
a harmful biological fertilizer for the more rapid and
rampant growth of cancer. Now, if increasing your risk
of developing Alzheimer’s or cancer by way
of a lack of sleep were not sufficiently
disquieting, we have since discovered
that a lack of sleep will even erode the very
fabric of biological life itself, your DNA genetic code. So here in this study, they
took a group of healthy adults and limited them to six
hours of sleep for one week. And then they
measured the change in the gene activity
profile compared to when those same
individuals were getting eight hours of sleep for a week. And there were two
critical results here. First, a sizable and
significant 711 genes were distorted in terms
of their activity, caused by six hours of sleep. And that’s relevant, by the way. We know that almost one out
of every two American adults are trying to survive on
six hours of sleep or less during the week. The second result was that
about half of those genes were actually increased
in their activity. The other half were actually
decreased in their activity. Those genes that were
decreased by a lack of sleep were genes related to numerous
aspects of the immune system, which fits very well with
the evidence I was just discussing regarding cancer. Those genes that were actually
increased in their activity or what we call up-regulated
in their expression were genes related to
the promotion of tumors, genes that were related
to chronic inflammation within the body,
and also genes that were related to stress
and, as a consequence, cardiovascular disease. Now, I think many
individuals in society feel uncomfortable about
the idea of genetically modified embryos or even
genetically modified food. But by choosing to get
insufficient sleep, we may be forced
to accept that we are performing a similar
genetic modifying experiment on ourselves. And if we don’t let our
children get the sleep that they so desperately
need, then we may be inflicting a similar genetic
engineering experiment on them as well. There is simply no
aspect of your physiology that seems to be able to
retreat at the sign of sleep deprivation and
get away unscathed. It’s almost like a broken
water pipe in your home. Sleep loss will leak down
into every nook and cranny of your biology, even
tampering with the very DNA nucleic alphabet that
spells out your daily health narrative. So where does this leave us? What is the piece of
sort of mental furniture I would like to gift to
you as we finish the talk? Well, it would be this. Sleep is not an optional
lifestyle luxury. Sleep is a non-negotiable
biological necessity. It’s a life support system. And it is mother nature’s best
effort yet at contra-death. And the decimation of sleep
throughout industrialized nations is having a
catastrophic impact on our health, our
wellness, and the safety and the education
of our children. It’s a silent sleep
loss epidemic, and it is fast becoming one
of the greatest public health challenges that we now
face in the 21st century. I believe it is now time
for us to reclaim our right to a full night of sleep,
and without embarrassment and without that terrible
stigma of laziness. And in doing so, we
may finally remember what it feels like to
be awake during the day. And with that soapbox rant over,
I will simply say good night, good luck, and above all,
I do hope you sleep well. Thank you very much indeed. [APPLAUSE] I think we’ve got lots of
times for questions, I think. AUDIENCE: I don’t know
if you can hear me, but thank you so
much for the talk. It was actually
very informative. I have two questions for you. Number one, I have
a five-year-old and then there’s myself, right? So how much sleep
should we be getting? And number two, is there any
disadvantage of oversleeping? So let’s say if I sleep 10
hour, 15 hours in a day– MATTHEW WALKER: Yeah. AUDIENCE: Is there any
disadvantage to that? MATTHEW WALKER:
So great question. So firstly, recommendations
for sleep, you can find them on the
National Sleep Foundation website for all ages. For the average adult,
the recommendation, World Health
Organization– eight hours; range, seven to nine. Once the average
human being gets below seven hours
of sleep, we can measure objective impairments. So people who say, I can survive
on six hours of sleep, there’s a problem with
that, which is this. Your subjective
sense of how well you think you’re doing
without sufficient sleep is a miserable
predictor of objectively how you’re doing without
sufficient sleep. So it’s probably a little bit
like a drunk driver at a bar. They’ve had seven shots,
they pick up their car keys, and they say, I’m fine to drive. And your response is,
no, I know that you think you’re fine to drive, but
trust me, objectively, you’re not. The same is true
for a lack of sleep. Your second question
is fascinating. Can I sleep too much? Well, there are anecdotes
of something called a sleep hangover, where you
sort of oversleep and then you feel worse almost. When you oversleep,
it usually means that you’re trying to sleep
off a debt that you’ve lumbered yourself with. So if you could sleep past your
alarm, if it didn’t go off, then you’re under-slept, because
it’s physiologically impossible to sleep too much
if you’re healthy. Now, there is one
piece of evidence that suggests something called
hyper-somnia, excessive sleep. That principally expresses
itself in depression. But if you look at that data,
it’s actually very difficult to tell. Is it people just reporting
being in bed for longer rather than sleeping longer? So I think it’s
unclear right now. But let me just take it
to a theoretical realm. Could there be such a
thing as too much sleep? I think yes. But don’t forget. The same is true for the
other three essential factors of life– oxygen,
food, and water. Can you eat too much? Yes. Can you overhydrate? Yes. Can you increase blood pressure,
cause stroke and heart attack by excessive water intake? It happened in the 1990s
with the ecstasy craze, where people were dehydrating. Governments told
them, drink lots. They drank too much. Cardiac events. Can you actually become
hyper-oxygenated? So you get free radical
species, dangerous for cells. Yes, you can. Is there such a thing
as too much sleep? We haven’t found it yet,
but I suspect probably so. It’s a bell-shaped curve. It’s a U-shaped function in
terms of benefit, not linear. But on most people in danger
of getting too much sleep, au contraire. AUDIENCE: Thank you
for the great talk. MATTHEW WALKER: Thank you. AUDIENCE: Do you also
have any information on how quickly people
recover after they switch from kind of short sleep periods
to kind of more normal sleep periods? Because you only mentioned
kind of as a– one evidence was the DST change, or when we sleep
one hour more, kind of things get better in terms
of cardiac problems. But is it quick, the
recovery as well? As quick as the downhill
movement [INAUDIBLE]?? MATTHEW WALKER: Yeah. It’s a great question. So different aspects of
your brain and your body seem to come back online
to a status of health with recovery sleep. And those temporal
profiles are different based on– even within the
immune system, for example, some components take longer to
come back online than others. What I would note, however,
is that you can never get back all that you’ve lost. This is another one of
those myths with sleep. So sleep is not like the bank. You cannot accumulate a debt
and then pay it off at a later point in time, which is what
most of modern society does. Chronic short sleep
during the week, then you binge at the weekend. It’s what I call sleep bulimia. It’s what is otherwise
known as social jet lag. Now, if I were to take you and
deprive you of sleep for one single night, eight
hours of lost sleep, and then I give you
all of the sleep that you want for
however many nights and we keep recording
you, your brain never recovers all of
that lost eight hours. It will try to get
back some of it. It will never get
back all of it. Why is that the
case, we can ask? Why doesn’t your brain have
a credit system for sleep? Because there’s precedent
for this in biology. You have one for energy. It’s called a fat cell. You can actually store
up credit calorically and spend it when
you go into famine. Now, most of us aren’t
in that danger anymore. But during evolution,
we faced that challenge, so we came up with a solution
called the adipose cell. Where is the fat cell for sleep? Why isn’t it there? The reason is this. Human beings are
the only species that deliberately deprive
themselves of sleep for no apparent reason. [LAUGHTER] What that means is that
mother nature has never had to face the challenge
through evolution of coming up with a safety net
because of insufficient sleep. So there is no
mechanism of safety. There is no credit system. AUDIENCE: So similar to how
you can take supplements after exercising, have you done
any research about supplements that can help sleeping– well, without the device yet? And as a side note,
what about melatonin? MATTHEW WALKER: So no
drugs or supplements that we have currently
produce naturalistic sleep. Chemically, it’s an
incredibly complex job. Now, I don’t want to dismiss
people at drug companies. I’m not against medication. I’m not anti all medication. If medications work,
I’m all for them. It’s just that all
of the sleeping medications that we
have right now don’t produce naturalistic sleep. Most of them are a
class of drugs that we call the sedative hypnotics. Sedation is not sleep. All you’re doing is
knocking the cortex out. You’re not producing
naturalistic sleep. And as I said and I
mentioned in the book, they are also linked to
a higher risk of death– and it’s considerably higher– as well as cancer. What about melatonin? Well, melatonin turns out not
to be an effective sleep aid. And it shouldn’t surprise us
based on how melatonin works. Melatonin helps time
the onset of sleep, but it doesn’t help in the
creation of sleep itself. So the analogy would
be melatonin is like the starting official
in the 100-meter race at the Olympics. Melatonin gathers all of the
racers to the starting line and begins the race, but
that official themselves does not participate in the
great sleep race itself. That’s a whole different set of
brain mechanisms and chemicals. That’s why melatonin
is not efficacious once you’re stable
in a new time zone. Now, I will say this, however. If you’re taking melatonin
and you feel it’s beneficial, keep taking it, because
the placebo effect is one of the most reliable
effects in all of pharmacology. I mean, that tells you
something, by the way, something profound. There is such a thing
as mind over matter. And there is now a wonderful
science of the placebo effect. It’s very real. And we dismissed
it for a long time. I hope that answers
both your questions. AUDIENCE: Thank you. MATTHEW WALKER: Sure. AUDIENCE: I was wondering– again, thank you for the talk. MATTHEW WALKER: Sure. AUDIENCE: Does the time period
between when you wake up to when you start using
your brain for learning or whatever, also
play a difference? If a person had a full
eight hours of sleep but they don’t go to
school until evening when they have evening school,
do they learn worse than if they could have went
to a morning school and started learning
in the morning? MATTHEW WALKER: So it’s a
very interesting question. When on the clock face
is learning, let’s say, most sort of beneficial? Well, once you’re waking
at a reasonable time, it seems as though there
is some degree of stability of learning across the day. However, there does seem to
be a gradual deterioration. And we’ve done some
of these studies to basically map the
time course, sort of the Great Depression of
learning across the day. And we’ve inserted naps, and we
can actually restore learning. But I would like
to come on to naps. Someone should
ask me about that, because they’re a double-edged
sword with danger. But what we do know from
those school studies where they delayed the
school start times, where you get the greatest
grade-point increases is not in all classes across the
day, but it’s especially in those first morning classes. But I think that that’s
less about your brain being better at
learning in the morning than it was about when you
were starting so early, it was just so detrimental
to try and learn. So sort of you’d
lowered the floor rather than raise the ceiling. So yep. But to me, it makes
sense that learning is somewhat stable
across 16 hours, because if you were to design
a system of memory that could only learn in the last
couple of hours of wakefulness, then why are we awake
for the other 14? And we seem to have a system
of memory that gives us a capacity for about 16
hours of recording in humans before sleep is required. AUDIENCE: A quick
followup question. Do you do any study on
other brain activities like coding– well, not coding,
but more advanced [INAUDIBLE].. I try not to schedule
morning meetings, because everybody is asleep
and nobody’s making decisions. MATTHEW WALKER: Yes. So we’ve done lots of studies on
all aspects of brain cognition. We’ve done decision-making,
judgment making. We’ve done creativity,
emotional regulation. We’ve done visual
attention aspects. We’ve done motor skill learning. And it follows the same
profile, which is essentially when sleep is in high
volumes, all of those things are supported. Different operations
within the brain rely on different
stages of sleep at different times
of night, however. It’s not just one
stage of sleep that does it all for all of your
brain sort of mechanisms and apparatus features. And this is why there is no
single one stage of sleep that’s important. People will say, oh, how
can I get more REM sleep? And I would say, why do
you want more REM sleep? Or how can I get
more deep sleep? Mother nature took
about 3.6 million years to figure that out. Just let her do her job. She’ll see you well. AUDIENCE: Quick
question, basically. How do drugs, any kind of
drugs– medicine, alcohol, marijuana– how
would it basically affect the brain activity during
the night, during the sleep? MATTHEW WALKER: So how do
drugs, perhaps some legal, some non-legal, impact sleep? I’ll focus on
marijuana and alcohol since you mentioned them. Alcohol is perhaps the
most misunderstood drug when it comes to sleep. People say, you have a nightcap,
and I fall asleep better. Untrue. Alcohol is also a class of drugs
that we call the sedatives. And once again, that’s
not natural sleep. What you’re doing is simply
removing consciousness by way of alcohol. You’re not putting yourself
into natural sleep. Two more problems with alcohol. First, it will
fragment your sleep with awakenings
throughout the night. The problem is that they
are so brief that you tend not to remember them
and commit them to memory. So you wake up the next
morning feeling unrefreshed, but you don’t understand why– that it was the alcohol
fragmenting your sleep. Finally, alcohol is very
effective at blocking your REM sleep, at blocking
your dream sleep. So alcohol– misunderstood,
should be avoided. Marijuana– people
use it to try and help them get to sleep or relax. The problem is marijuana
also seems to fragment sleep. It also seems to block
rapid-eye movement sleep. Probably the other chemical
that deserves mention here is caffeine. Caffeine, most people
know, is an alerting drug. It’s actually a class
of drugs that we call the psychoactive stimulants. It’s the only legal stimulant
that we readily give to our children, by the way. Caffeine can obviously
keep you awake at night. But some people
will say, I’m one of those who can have a cup of
coffee, and I fall asleep fine. The problem there is that
even if you fall asleep, the depth of the deep
sleep that you have is not as deep as
if you were to have sleep that didn’t have
caffeine swilling around within the brain. So again, you wake up the next
morning feeling unrefreshed. You don’t remember waking up
or struggling to fall asleep, so you don’t think
it’s the caffeine. But now you need
two cups of coffee rather than one
the next morning. You build up this vicious
cycle, and it’s probably the reason that caffeine is the
second most traded commodity on the surface of
the planet after oil. I don’t think there’s probably
any other statistic that bares out how sleep
deprived we are throughout
industrialized nations. AUDIENCE: Cool. Thank you. One more quick question. How much of the sleep every
night is basically enough? It’s eight hours maybe? MATTHEW WALKER: As
I said, once you get below seven hours
of sleep, that’s when we can measure
objective impairments. Yup. AUDIENCE: Thank you. MATTHEW WALKER: But
that’s once we can measure objective impairments. It doesn’t mean that if we
had more sensitive tools, we would measure it at
seven hours and 15 minutes. AUDIENCE: I wondered
about blue light exposure, especially from devices. And back a couple
years ago, I got the blue light-blocking glasses. And it does seem to actually
give better sleep at night. I was curious what the
research is behind that. MATTHEW WALKER: Yeah, that
one is actually not a placebo effect, it turns out. So the studies are
very clear right now. As an industrialized
set of nations, we are a dark, deprived society. And we need darkness
because the way that darkness works
is that it actually removes the breaks from
the hormone melatonin that I described
that needs to rise to help time the normal
onset of healthy sleep. So if you’re bathed in
electrical light at night, even though it’s not as
powerful as daylight, it can keep the brake
pedal on melatonin. Now, they did some
fascinating studies where you read on
an iPad for one hour versus just reading a
normal book with dim light. And firstly, relative to
that one hour of dim light, normal book reading, the
one hour of iPad reading firstly delayed that
spike in melatonin by two to three hours. So here, if you’re reading
the iPad in Seattle, we’re almost all
the way to Hawaii in terms of our biological
melatonin rhythms. That’s how shifted
and delayed we are. Second, the sleep
was not as good. REM sleep was disrupted,
and people subjectively felt worse and less refreshed
the next morning. And it took a few
days before it washed itself away after they ceased. So I think the
recommendation right now is try to limit screen
time in the last hour. I know where I’m speaking
right now, which is at Google, and what that means. You can install software
that helps desaturate the most harmful wavelength of
light, which is the blue light. You can also put
those spectacles on. They seem to work as well. But overall, try to
decrease stimulation. Blackout curtains also great at
night during the night in bed. AUDIENCE: Yeah, a followup
on the blackout curtains. One of the things
I’ve found is it’s really hard to get
up in the morning if the room is all blacked out. Having that natural light
come in is important. And I wondered too– which is worse, to have
any of this light coming in during the
nighttime versus having to deal with an
unnatural alarm clock waking you up in the morning? MATTHEW WALKER: Yeah. I mean, it sounds as though
what you’re experiencing is sort of what we call
a sleep inertia, which is when you wake up. It usually means
that you’re sort of waking up at a
time that’s slightly offset from your natural
biological tendency. With that, you can use daylight
to perhaps try and help you. Some people actually
use eye masks in the first part of the night. And at some point, they
will take the eye mask off and then help with the
exposure to the daylight, because they’ve
kept their curtains non-blackout in that regard. But that’s a tricky
one to balance. Yeah. JOSH: I know there are
a lot more questions. It’s coming up on 2 o’clock,
so we’re going to cut it off. But Dr. Walker will stay,
and he’s going to sign books. We’re selling a
few of the copies. And so just everybody, let’s
give Dr. Walker our hands. MATTHEW WALKER: Thank
you very much indeed. [APPLAUSE] Thank you. Thank you so much. Thank you.


100 thoughts on “Matthew Walker: “Why We Sleep: The New Science of Sleep and Dreams” | Talks at Google”

  • 21:23 So this is why comedy shows seem so much funnier late at night. I remember wheezing out of breath watching late night adult swim shows like ATHF and Harvey Birdman, and then pondering the next day on why the jokes seemed so much more funny the night before.

  • That's all great knowledge and all…..but i kind of like doing things other than only working and sleeping. Sorry sleep! 4 hours it is.

  • Életem morzsái blog says:

    I always took seriously my sleeping. I sleep 7 hours regularly on weekdays and more on the weekend.
    A lot of people don't care too much. And there are people who advertise max 5-6 hours sleeping as the main key of success.

  • No need for odd devices. Water-only fasting is the very best and surest way to produce deep sleep. This has been known for a century, just nobody likes to do it.

  • The emotional roller coaster thing with Jeff was pretty bogus. He obviously just was giving a social reaction to cursing due to being miffed about not getting any work on his paper done.

  • When the one guy who inquired about using drugs before bed but really was asking obviously only about the marijuana proceeds to ask how much sleep you need in a night when Matthew had already stated in multiple times in the presentation….

  • Matthew Walker is amazing! Wish all my teachers was as enthusiastic and passionate in their fields as this guy is!

    Not about this topic, there is something I honestly don’t get. Like I’m not trying to be one of those guys and I do get weird looks all the time when I say this.. but when I go to bed at 12 am, I wake up by my self somewhere between 5 and 6 am, feeling completely refreshed…now since I had a girlfriend who absolutely hated it when I woke up around 5 in the morning, I tried pushing it until 7-10am. Around 7 am it’s really hard to wake up again, like when you try to wake up from deep sleep I assume. Waking up between 8-10am I get massive headaches and basically crippling myself for the rest of the day. I’m not joking and it’s really awe full, and it annoys me immense to have people tell me to go and sleep more… I will bring this up with my doctor next time I have an appointment.

  • Kids go to school early so parents can get to work for there ridiculous start'd think as society progressed and prospered we could work less hours of the day.. But no we always have to be pushing it.

  • Mathew is very knowledgeable, into his field, and a great communicator. Sleep always been a very interesting thing to me and it's awesome seeing someone like him studying and spreading information in this field.

  • Rob the lionheart Trindade says:


  • Matthew Walker is a genius! I made a video about his book Why We Sleep on my channel, here is the link if you fancy checking it out, the book is awesome 🙂

  • I've been working in a place for 3 years of constant sleep deprivation regularly doing 20 hr work marathons with half hour naps here and there, I've no excuse for that, but that's the time I started loosing hair on alarming scale, I was looking like a professional alcoholic, of course I was consuming lots of bread and sugar too, but sleep improved my health considerable after quitting the job and sleeping well for several months.

  • Absolutely the best lecture I have ever heard. I might be over 30 years too late. I have had chronic fatigue insomnia for over 25 years. I learned that sleep was an important factor amongst other things long time ago. I have been on sleep medications since then which still only gave me 5-6 hours sleep every night. I have been a caffeine addict because I felt that was the only thing that gave me noticeable amount of energy. After doing all kinds of diets supplements and exercises I realise sleep is the single most important thing above anything else. I have such a lot of memory problems, fatigue and loads of other symptoms. I don't know if I can reverse 30 years of damage, but If I can halt full blown dementia and other conditions, I will be happy. So my New Year resolution is to work on my sleep a top priority. Which means- exercise early , go in the sun, good diet, meditate, try to control stresses, no caffeine after 2 and try to wean off it. No blue light after 9. Go to bed by 10 and sleep in the dark. Try to wake up naturally and work on getting 8 hours sleep. Thank you so so much!

  • I lived in Argentina for four years as a kid. There you have the option to go to school in the morning or in the afternoon! Amazing! I went to the afternoon school and was never happier as a kid

  • Good talk, but the audio, multi billion dollar company, nobody knows how to setup the mans microphone/compressor. It's horrible. Jabbing away the sound every minute for seconds on end. Barely able to listen to it. In video terms, you are listening to 144p audio quality, on top of the wrong compressor settings. Really guys?

  • Fabulous presentation! Question: With sleep deprivation MRIs resembling those of all psychiatric illnesses, have any studies be done on the effects of inducing sleep in psychiatric patients for longer periods of time, say 10 hours or more per night while monitoring sleep cycles? Does induced sleep through the use of sleeping pills illicit the same effects as natural sleep? Can the effects of years of lost sleep be mitigated by adherence to an 8 hour sleep cycle? Thank you very much for making these lectures public!

  • You do understand Dr I lost my sleep completely when you said my body produces cancer
    Give me advice if I have a lifestyle where I work during the night and sleep during the day ?

  • I don't know why we dream
    But I've the answer of why we sleep….. it's not a ordinary same answer…… I just crack it yesterday night
    I hope it's caught Google attention

  • I need help. I have lost so much with insomnia. I’ve tried so much & given up hope of getting good sleep. Now I’m thinking if I don’t get help I’ll have full blown Alzheimer’s within a few short years.

  • daniel grisales says:

    I am a Muslim and surprisingly enough much of the things he is saying are Islamic teachings and prophetic practices as that of going to sleep early and giving the body it's right to proper sleep and rest and also morning time being efficient to learning activities.

  • I don't doubt the main points, but that thing about daylight savings time causing heart attacks seems to be mostly bogus. Have a look at this interpretation, for instance:

  • Oh that part about the placebo effect is most probably wrong. As I understand, modern research shows that placebo effect does not objectively improve anything, It is just an illusion of an improvement based on biased perception. In other words, it only affects subjective judgement of symptoms, not health.

  • Unfortunately I’m discovering this true too late. As an international airline pilot, I wish I knew this information 25 years ago. Don’t let you children to become a pilot for the sake of their health

  • Dang…. I was really curious about how naps factor into these cognitive changes especially in relation to these studies. If anyone has a lead on that information (hopefully from Matthew Walker) please let me know, thanks!

    Also curious about the effects of sleeping with audio and if different types of audio affect sleeping stages in particular ways.

  • Actually, sleep is necessary to resynchronize the mind, which is a temporal structure, with the body, which is a spatial structure. Study the Reciprocal System and prove it for yourself.

  • Richard Handler says:

    This did not feel like almost 55 minutes. Fantastically articulate and well structured speech. Some shocking findings in here!

  • Mohammed Esmael says:

    My body used to sleep 5-6 hours and i am getting up automatically in specific time, what shall i do to get back as i used to sleep 7 or 8 hours

  • multisomebodyelse notme says:

    Whhhaaaaat less accidents😲😲😲 insurance companies and government affiliates everywhere shitting it and protesting later starts for schools and make it 0533 start time lmfaoooooooo
    This is clearly going to be a rouse for THEM to fuck up our sleep.

  • multisomebodyelse notme says:

    They find out what is good for us then do the opposite….look at the food industry and water purity and public health lmfao. Gonna help us sleep my ass :/

  • multisomebodyelse notme says:

    Soon as they have it sussed theyll broadcast the frequency that ruins out sleep 🙁 its obvious to me now what the sleep illnes is ive seen in fit ppl gor over 5 years ppl who can never get rested….hmmmmmm 🤔🤔🤔🤔🤔🤔
    HARRP ???

  • OriginalIntentDoc says:

    Public schools that get kids up so early are guilty of child abuse and parents should withhold paying their property taxes until the abuse stops. See

  • Here's my review of Matthew Walker's book, Why We Sleep:

  • Zelda Pinwheel says:

    Schools start too early in some areas because the working class need to get to work, so the kids aren’t learning at 7:30 they are given breakfast and it’s basically a daycare situation. And so starts a lifetime of sleep deprivation which is tragically unavoidable for many. Adequate sleep has become a luxury. That’s why homeless people are insane. They are chronically sleep deprived. When they do get a bed to sleep in, they can’t relax, they are cramped in like sardines, and they are forced out too early.

  • Patrick Rutherford says:

    I work a swing shift. 3 different shifts and we change every single week. I sleep exactly 8 hours at the exact same time relative to each shift.

  • laurencefisher1 says:

    what a shame – the speaker mentioned evolution, which is dead and never was viable. otherwise an informative talk.

  • Ok, but have you examinated what were the results after sleeping too much? Ten hours is worse than eight? Moreover, this speaker use numerous logical mistakes and simplifications, for example you cannot shift experiments in mice to human, or he said that it had happened within a day so imagine what would happen for a week.

  • Memento is an amazing movie! Still not sure I can fully piece it together, even after wathing it 3 or 4 times. I don't sleep well, haven't since I was a teenager, now in my late 30s I honestly feel like my life is that movie. Just a feeling of being constantly confused, really poor executive memory, groggy when i wake up, sleepy during strange times of the day, constantly forgetful. I wonder if it's an acumulative effect of years of poor sleep. I wonder if that's one of the reasons why old people start to experience mental impairment too? You tend to sleep less and less as you age. Not sure why that is.

    On a completely unrelated note… Why did they put him behind a wall?

    Edit: Just got my answer about old people. I'm clearly a genuis! And that's despite my poor sleep. 😁

  • IcarUs uploads says:

    There are so many people who have done great things and sleep only 4 hours a day and are healthier than normal. Your sample size study is v small you are not taking into consideration lifestyles tge food they eat the type of weather the people live in the culture and practices of the study group how much exercise did the subject get any underlying genetic disease etc etc. This is quite unscientific when you just make such statements without taking into consideration so many other factors.

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