Why Does My Brain Sleep?


MATTHEW WALKER: It’s a
pleasure to be here. And I want to start with a
standard disclaimer, which is that when most speakers look to
their audience and they see people who are falling asleep
or nodding off, it can be profoundly disheartening. However, based on the topic of
today’s presentation, I’m almost going to actively
encourage that kind of behavior from you. In fact, knowing what I know
particularly about the relationship between sleep and
memory, it’s actually the greatest form of flattery for me
to see people like you not being able to resist the urge to
strengthen what I’m telling you by falling asleep. So feel free just to sort of
ebb and flow in and out of consciousness throughout
the entire talk. I’ll take absolutely
no offense. And the talk itself is really
going to come in at four main acts, so to speak. Firstly, I want to spend some
time telling you about what sleep actually is, the
different types, it’s characteristics,
its structure. And then after that, I’ll tell
you about the variety of different functions, plural,
that we’re starting to understand that sleep serves. So I’ll tell you about the role
of sleep in promoting learning and also memory. But I’ll also then tell you how
sleep can go beyond simply manipulating individual
memories. Sleep seems to be intelligent in
that it can cross-link new pieces of information together
so you can come up with creative, novel insights
the next day. And then finally, I’ll describe
a role of sleep beyond information processing
into your mental health and how sleep seems to be critical
for emotional regulation, preparing specific brain
circuits for next day social and emotional interactions. So that’s the basic overview. Coming on to what sleep is, and
I do love this picture. You can just kind of get a sense
of the quality and the depth of sleep that’s
happening there. If we’re going on that whole
savanna grasslands kind of side street by the way,
I just want to come onto this, the giraffe. Firstly, what a strange
morphology for a creature. Have you ever wondered
how something that looks like that sleeps? Would you like to know
how a giraffe sleeps? That’s how a giraffe sleeps. Isn’t that remarkable. And it tells us at
least two things. Firstly, despite such bizarre
anatomy, sleep will still find a way to be obtained
by the brain. Second, and more generally, in
every species that we’ve studied to date, sleep, or
something that looks very much like it, has been observed. What that means is that sleep
has fought its way through vehemently every step along
the evolutionary pathway. If that’s true, sleep must be
essential at some of the most basic of biological levels. And that’s exactly what we’re
starting to discover. And sleep in terms of mammalian
species at least has been broadly separated into
two main types, as some of you may know. On the one hand, we have
non-rapid eye movement sleep or non-REM sleep for short. And non-REM sleep has been
further subdivided into four separate stages, unimaginatively
called stages 1 through 4– increasing in their
depth of sleep– or a creative bunch of
sleep researchers. So increasing in the depth of
sleep, stages 3 and 4 are those really deep stages
of dreamless sleep. And they’re often grouped
together under the term slow-wave sleep. Why? Because of these slow, lazy
brain waves that happen during the stage of sleep that
we measure with electrodes on the head. But don’t be fooled. That’s not that your brain is
dormant by any stretch of the imagination. What it means is that vast
portions of your brain, hundreds of thousands of
neurons, have all decided to synchronize together and
sing together in time. It’s a phenomena like no other
brain state that we know of. It doesn’t happen whilst
you’re awake. It’s a strange phenomena and
we still don’t truly understand why. On the other hand, we have rapid
eye movement sleep or REM sleep named, not after the
popular Michael Stipe pop band, but because of these
bizarre, horizontal, shuttling eye movements that occur during
this stage of sleep. And again, we don’t truly
understand why your eyes move during that stage of sleep. And it turns out that these two
types of sleep, REM and non-REM, will play out in a
battle for brain domination throughout the night. And that sort of cerebral war
is going to be won and lost every 90 minutes and replayed
every 90 minutes. And what that creates is a
standard architecture of sleep, what we call
a sleep cycle. So I’ll just unpack
this for you here. We’ve got the different stages
of sleep on the vertical axis. And then time of night along
the horizontal axis. And I’ll speed this
up for you. But what you can see is that
upon falling asleep, your brain goes on this delightful
roller coaster ride in and out of these different
stages of sleep. So you’ll quickly descend down
into the deep stages of non-REM sleep, 3 and 4. And you’ll stay there
for a while. And then after about 70 or 80
minutes, you’ll start to rise back up and you’ll pop up and
have a short REM sleep period, here in red. And then back down you go again,
down into non-REM sleep and then up into REM. As I said, this cycle is 90
minutes, non-REM through REM. And that’s stable across
the night. However, what changes is the
ratio of non-REM to REM within that 90-minute window as you
move across the night, such that in the first half of the
night the majority of those 90-minute cycles are comprised
of deep non-REM sleep, slow-wave sleep. Whereas as you push through to
the second half of the night, now that ratio balance
shifts across. And instead, they’re dominated
much more by rapid eye movement sleep, as well as
that lighter form of non-dreaming sleep, stage
2 non-REM sleep. And just to come back to REM
sleep, REM sleep is the principal stage during which
your brain dreams. And REM sleep is a case of
essentially how your brain goes completely out
of its mind. Because every one here, as long
as you slept last night, you became flagrantly
psychotic. Now before you reject my
diagnosis of a nightly psychosis, let me give you
five good reasons. Because last night when you were
in REM sleep and you were dreaming, you started to see
things which were not there. So you were hallucinating. Secondly, you believed
things that couldn’t possibly be true. So you were delusional. Third, you became confused about
time, place, and person. So you’re suffering from
disorientation. Fourth, you had wildly
fluctuating emotions. Something that psychiatrists
call being affectively labile. And then how wonderful, you woke
up this morning and you forgot most, if not all, of
that dream experience. So you’re suffering
from amnesia. If you were to experience any
one of those five symptoms whilst you’re awake,
you would be seeking psychiatric treatment. Yet for reasons again that we
don’t fully understand, it seems to be both a normal
biological and psychological process. One of the other fascinating
features of REM sleep is this, paralysis. All of you, when you
went into REM sleep last night, were paralyzed. It turns out that there’s
mechanism deep down here in your brain stem– so here we
have the brain, which as Woody Allen suggested, was his
second most favorite organ of the body. And so here’s the front of the
brain, back of the brain, brain stem down here. Now, this war of REM and non-REM
sleep essentially plays out down here. And then is beamed up to the top
of the wrinkled mass, atop of the brain, called
the cortex. But there’s also another signal
that goes south, down into the spinal cord. And this signal during REM
sleep that goes south essentially inhibits what we
call the alpha motor neurons in your spinal cord. They control all of your
voluntary skeletal muscles. So ensuring REM sleep, your
brain paralyzes your body so your mind can dream safely. It’s a bad evolutionary design
when you’re not perceiving your outside world to
start acting out all of those dream commands. And there are plenty of them. Just as a quick aside on this
process note by the way, sometimes this persists
despite you waking up. Some of you may have experienced
this, this persistence of sleep paralysis
on awakening. It’s quite unusual– well, it’s not unusual
proportional wise. About 25% of the population
will experience this. It’s about as common
as hiccups. And what seems to happen is that
your brain starts to wake up, but the paralysis isn’t
released from the body. So you start to become aware. But you can’t lift your eyelids,
voluntary muscles. You can’t move. You can’t say anything. It is often associated with a
sense of sort of anxiety, a sense of someone else being
there in the room. It turns out that this sleep
paralysis, this persistence, accurately explains most,
if not all, of so-called alien adoptions. I mean when was the last time
you ever heard of someone being abducted during the day,
in the middle of a meeting? You know. I mean– whoosh, what was that? Well I believe Jimmy just
got abducted by aliens. No, it never happens
like that. It’s usually at night,
when you’re in bed. People describe a sense of a
presence in the room, that you were paralyzed by these
other agents. You couldn’t move. You couldn’t fight back. You couldn’t talk. It’s a strange interesting
feature. That’s a little bit about
what sleep is, together with some odd sides. I don’t quite know I threw
that in there. But anyway, let’s now come
onto what sleep is doing. And it is serving a whole broad
array of functions. Firstly, let me tell you why
it’s essential to sleep before learning, to prepare your
brain, almost like a dry sponge, ready to soak up new
information the next day. And to sort of test this
question, we’re going to run an experiment. Essentially, is pulling the
all-nighter a good idea? Here’s how you do this. You take two groups
of participants. You assign them to a
sleep group or a sleep deprivation group. Both are awake across
the first day. But then across the following
night, those in the deprivation group, we keep them
awake in the laboratory under full supervision. They can’t fall asleep. The sleep group they get
a full eight hours. Both of them are awake across
the second day. And then we have them try and
cram a whole bunch of facts into their brain. And then we’re going to test
them to see how efficient that learning has been. But instead of testing them
immediately after learning, we actually wait until two full
recovery nights of sleep before we test them. So that any measure of memory
that we get is not confounded by them simply being too sleepy
or inattentive to recollect what they’ve
learned. And that’s what you’re looking
at here on the vertical axis, the efficiency of learning. So the higher up you are,
the better you are. And if you put those two groups
head to head, what you find is that under conditions of
sleep deprivation, there is a quite profound 40% deficit in
the capacity of your brain to make new memories, to
be able to create new experiences. And this should perhaps be
little concerning considering what we know is happening to
sleep in our educational populations. If you want to put this in
context, it’s simply the difference between acing the
exam and failing it miserably. Now, of course these are
just performance data. We don’t know what’s going
on inside the brain. So to answer that question,
we’ve repeated these experiments. But now, during that attempted
learning, subjects are actually inside an MRI scanner
as we’re taking snapshots of brain activity to see which
parts of the brain are switching on or not
switching on. So you get these attempted maps
of learning in the sleep group and in the sleep
deprivation group. And then you simply subtract one
from the other to see what the difference is. And when you do that
subtraction, you find a highly selective, but highly
significant impairment in this part of the brain here. It’s a structure called the
hippocampus that I’m circling for you. So just to orient you for those
not familiar with MRI images, it’s as if I’ve
sliced through the brain from ear to ear. And you’re looking in from the
front, top of the brain, bottom of the brain, left
and right side. And I’m circling for you
the hippocampus here. You have one on the left
and one on the right. And these cool, blue blobs
demonstrate that this part of the brain was significantly
impaired in those people who were sleep deprived compared
to a nice, strong signal coming from that part of the
brain in those people who had had a good night of sleep. Why is this important? Well, it turns out that this
structure, the hippocampus, is the quintessential reservoir for
where your brain creates new memories. In fact if you want to know what
life is like without a functioning hippocampus, just
watch the movie “Memento.” I’m sure many of you have
seen this film. If you haven’t, watch it,
it’s a great film. And I won’t spoil it for you. But essentially, this gentleman has some brain damage. And from that point forward,
he can no longer make any new memories. He is densely amnesic. The part of his brain was
damaged was this structure, the hippocampus. It is the very same structure
that sleep deprivation seems to selectively attack and block
your brain’s capacity for efficient learning. Let me just go back to these
data because there’s an unresolved question here. That was the bad that happens
when you don’t get sleep. What’s going on in those people
who are getting sleep? In other words, what is it about
the sleep that they’re getting, the physiology of their
sleep, that seems to be promoting the restoration
of memory? And what we’ve been finding
is that there are specific electrical brainwave patterns
that are promoting this memory restoration. And they’re coming from
non-rapid eye movement sleep. And they’re these delightful
little chaps. They’re called sleep spindles. These are short, synchronous
bursts of electrical activity in the EEG, the
electroencephalogram. They last for about one
second of time. So you’re going along,
brrrrrrr, that’s the burst of activity. Your brain doesn’t make
that sound, of course. That would just be strange. But they’re these sort of
champagne cork, synchronous bursts of activity. And we believe that they form
part of a broad network that promotes the transformation or
the translocation of memories from one location in the
brain to another. And you can think of the USB,
since I’m at Google, in a crass analogy, like a USB
hippocampus stick. It’s very good grabbing
information somewhat quickly, but it has a limited
storage capacity. And we believe that these
spindles are helping promote the transfer from that
hippocampus USB stick, up into that folded mass, the cortex,
essentially, in terms of the analogy, the hard drive,
the mass storage capacity of the system. And by promoting that real
estate transaction, that shifting of geography of
information within the brain, not only do you take previous
memories and make them safe, put them onto the hard drive,
you clear out the USB stick in terms of its memory capacity. So when you wake up the next
day, you’re freely able to start loading up new
information again. Because what we find is that
the more of these sleep spindles that you have, the
greater the degree of restoration of your learning
capacity the next day. So each of these dots represents
an individual participant. The more of those spindles that
you have, the greater the degree of memory return in terms
of capacity for learning that you get the next day. So we’re starting to understand
not just the bad, when you don’t get sleep, but
exactly what it is in terms of the good, when you do get sleep,
that promotes these cognitive benefits. It turns out that it’s not just
sufficient for you to sleep before learning. You also need to sleep after
learning to essentially cement that new information into the
neural architecture of the brain and make it less
vulnerable to being forgotten. So it’s essentially like hitting
the save button. It just takes a lot longer
organically within the brain to do that. And there’s now good evidence
that following that type of a learning scenario, you do need
sleep to hit that save button so that you get that improved
recollection the following day. And for fact-based memories,
what you would think of as textbook-like memory, that seems
to require, in terms of sleep, deep sleep, stages 3 and
4, or that slow-wave sleep that I described. So there’s lots of good evidence
of the past sort of 15 or 20 years that
this is the case, correlational evidence. But of course, what you tend to
want in science is a causal demonstration. So the question is if you can
increase the amount or the quality of your deep slow-wave
sleep, presumably you could boost the amount of memory
benefit that that sleep is providing. The question of course becomes
how do you boost the quality of your slow-wave sleep? Well, there are a variety
of different ways. But of course, your favorite and
my favorite that would be this, direct current
brain stimulation. Have you seen those adverts late
night on television where they say don’t try
this at home? This is one of those. This is not car battery and a
couple of electrodes, OK. Although that would be an
interesting experiment. Just imagine– I’m just picturing someone
tucking themselves into bed at night, with a bed partner. Good night, honey. And you’re playing
these electrodes. She says, what are you doing? Don’t worry about me. I’m just boosting my sleep. So you can inject essentially
a small amount of voltage. And I’ll just show you. They’re clinically approved. This is what it looks like. You inject a small amount of
voltage into the brain. Now, it’s so small that you
don’t even feel it. That’s how tiny it is. But it is physiologically
efficacious. And the idea here is that you’ve
going to try and pulse in time with the brain during
those slow brain waves, OK. And you’re going to try and
boost the amplitude, the size of those slow waves, on the sea
of your brain’s cortex. And by boosting that quality
of that deep sleep, what happens to memory? So you’re going to be applying
it during that deep, slow-wave sleep. You’ve sort of singing in
time with the brain. And there are two groups
in this experiment. Both groups get all
of the equipment applied to their head. One of them doesn’t get
any stimulation during sleep, however. The other does get simulation. And here’s how the
experiment works. Here’s the mock stimulation
group, so the placebo as it were. They’re going to study
a whole list of facts before going to bed. Then you can briefly test
them to see what their retention is like. Then after a night of sleep, the
next morning you test them again to see how well their
brain has retained the information following sleep. In the other group, the
experimental group, this is where we’re going to stimulate
the brain activity. We’re going to juice it
up and see if you can sort of enhance it. This is great study done by a
German group a few years ago. The question is what
happens in terms of the memory benefit? Well, if you look at the group
that slept but didn’t get simulation, we see the nice,
normal memory retention benefit across sleep,
replicating what we’ve seen many times before. In the group that gets the
stimulation, you almost double the amount of memory benefit
that you get by way of sleep, a causal demonstration that
when you manipulate sleep, your manipulate memory. One of the depressing things,
however, unfortunately, is some evidence that we recently
published just a few months ago, looking at the interaction
between sleep and memory as you’re
getting older. Which for me, seems to
be rather rapid. And what we know certainly, and
of course everyone knows, is that as you get older, your
capacity for learning and memory starts to deteriorate. But one of the quintessential
physiological hallmarks of aging is that your sleep
starts to deteriorate. And it’s not all types of
sleep homogeneously. Some types of sleep get hit by
the aging process far more severely than others. The type that gets hit most
severely is that deep, slow-wave sleep. And so the question was whether
or not these factors are simply co-occuring or
actually closely related? In fact, we demonstrated that
they are significantly interrelated. And this pernicious drop in deep
sleep by over about 70% accurately accounts for about
50% of the forgetting that happens with age. These are huge numbers. So there’s a suggestion here
that disrupted sleep is an underappreciated factor that
may contribute to what we called cognitive decline
in aging. The exciting silver lining part
to that cloud, however, is that it’s a potentially
treatable target. So we’re now trying to see if
we can use these types of methods to restore some quality
of sleep in aging and see if as a consequence,
we can give back some memory function. As it happens, it’s not just
sleep after learning to strengthen individual
memories. Because we’ve been recently
finding that sleep can go far beyond individual memories. Sleep can actually seemingly
cross-link vast sets of information, and from that
abstract understanding, and even develop creative insights
and ideas from that information processing
en mass. Let me show you an
example of this. Here, in this study, you’re
going to be, as the subject, performing what’s called the
numeric number reduction task. It’s the type of test that
psychologists love to administer and participants
hate to perform. What you’re going to do is
see lots and lots of these number strings. And you’re going to have to work
through them to come up with a final end solution. Now, one way that you can work
through these problems is by using some rules that
I’ll give you. The first thing you can see is
that there are only three numbers here that make up this
string, 1, 4, and 9. And this is common. Thought that the numbers
are the same. But this notion that there’s
only ever three numbers in a string set. That’s common. And here’s what you’re
going to do. You’re going to take the first
number, compare it to the next number, and the first
rule is this. If this number is the same as
the next number, write down the very same number, which
it is in this case, a 1, Now, you’ve got the 1. Compare it to the next
number in the line. Is it the same number? If it is, write down
the same number. Well, it’s not. And here’s the second rule. If it’s a different number,
write down the only other remaining number in the string,
which would be a 9. So let’s repeat that again. You can take the 9,
compare it to a 4. Same or different? It’s different. Write down the only other
remaining number, a 1. 1 to a 9, different. Write down 4. 4 to 4, it’s the same number. So write down the same
number, 4 to a 9, 1. 1 to a 9. Oh, my goodness, is it
boring and laborious. Now it turns out, and this is
exactly how the experiment works, if you paid attention to
what I said, I told you one way to solve these problems
is by using those rules. Because it turns out there’s
another way. There is a hidden rule. There is a shortcut. There’s a cheat. And if you figure it out, you
can blow through many more of these problems. And here’s the cheat. The second number that you
produce in the string is always the final answer. And so whilst this is different
across all the problems in terms of the number,
the overarching rule, the commonality across this informational set, is the same. So here’s what we’re
going to do. We’re going to expose a whole
collection of participants to these problems. Then 12 hours later, you’re
going to bring them back and expose them to some
more problems. And at that 12 hour delay point,
you’re then going to see what proportion of those
participants have developed insight into that hidden rule. Half of those participants
are going to remain awake across the day. Expose them to problems
in the morning, reexpose them in the evening. The other half, they’re exposed
in the evening. They reexpose in the morning
to the problems. And therefore, they’ve had a
full eight-hour night of sleep in between. So the brain has had equal
amounts of opportunity time to distill that informational
set and see if it can find out the solution. The only difference is that
one group has had sleep. The other hasn’t. And we’re going to put sort of
wake and sleep, head to head in this Coke-Pepsi challenge
to see which one wins out. And so here’s our outcome
metric, the proportion of participants in each of those
two groups that gained that knowledge, that creative
insight. In the group that remained awake
across the day, less than 25% of those participants
developed that hidden insight knowledge. What about the sleep group,
worse, the same, better? Well, of course they
were better. But what was shocking
was how much better. This was how much better
after sleep. Over 60% of participants,
having slept, developed insight into that hidden rule. And what we’ve been finding– what I should say is it’s almost
as though sleep, there is an algorithm in sleep that
takes vast informational sets and starts to try and understand
the statistical regularities and the rules
of those mass data sets. It’s a huge distillation. It’s a collision of information,
creative information processing. And we’re finding that some,
not all, but some of these types of associative memory
processing occurs during rapid eye movement sleep,
dreaming sleep. And I believe that it’s probably
not a coincidence that this is the stage
from which we dream. If dreaming is a reflection
of whatever information processing is going on with the
brain, then it may be this hypersensitive, hypercreative
creative, hyperassociative processing that’s going
on, that leads to these creative insights. As an aside, many people, when
I present this evidence to them, will say well, aren’t
there those sort of creative genius types in history
who were supposed not to sleep very much? One of them that’s often quoted to me is this gentleman. Does anybody know who this is? AUDIENCE: Edison. MATTHEW WALKER: Edison,
exactly. What he’s holding is a
bit of a giveaway. A brilliant man of
course, supposed to be a short sleeper. Now, of course, we’ll never
truly know if he was a short sleeper or not. But even if he was a short
sleeper, it turns out that Thomas Edison was a habitual
napper during the day. Here he is after a pretty good
garden party it looks like. Here he is on his inventor’s
bench taking a nap. In fact, Edison understood the
creative brilliance of sleep and he used it as a tool. Here’s what he would do. He would take a metal saucepan, like this behind him. He would turn it upside down
and rest it underneath the armrest of his chair. Then he would take two steel
ball bearings in his hand, rest the back of his
arm on the chair. Take a pad of paper and
a pencil, put it next to him on his desk. And then slowly relax back
and fall asleep. And so he didn’t
sleep too long. What would happen is that his
muscle tone would relax. He would release the steel
ball bearings. They would crash on the
saucepan underneath him, wake him up. And then he would write down all
of the ideas that he was having from his sleep. Isn’t that brilliant? What a guy. So no wonder you’re never told
you should really stay awake on a problem. Nobody tells you that. Instead that they tell you
to sleep on a problem. And we’re starting to find
scientific evidence that rigorously backs that up. It turns out, and a friend and a
colleague told me this, that this phrase of “sleeping on a
problem” seems to be common in most all languages that
he’s explored to date. What that means is that this
phenomenon seems to transcend cultural boundaries. And I should also note that it
probably says a lot about the difference between me as a
British gentleman and our arch rivals, the French. Because the French translation
it turns out of this, essentially is not sleeping
on a problem. It’s that you sleep
with a problem. British, you sleep
on a problem. French you sleep
with a problem. And it turns out that the
politics, the people in politics, reflect this. If you look at the past
president Mr. Sarkozy and Mrs. Sarkozy, these are
the press release pictures that they offer. She’s draped on a bed. He’s looking forlorn at her. Whereas the people in British
politics, who did we have? Well, we had Margaret
Thatcher. We had sort of Tony Blair. You sleep with a problem. You sleep on a problem. I’ll say no more. Before– I’m probably never going to be
able to go back to the UK now after that. Beyond information processing,
of which now there is good evidence for in terms of sleep
dependency, we’re now starting to realize there’s another
brain function of sleep. And that is in preparing the
emotional circuits of the brain, offering you stable
mental health. Now, I think many of us have a
sense that these two factors of sleep and emotion
interact in some meaningful kind of way. An example would be a parent
holding a child, the child is crying. And they look at you and they
say well, you just didn’t sleep well last night. As if there’s some universal
parental knowledge that bad sleep the night before equals
bad mood and emotion reactivity the next day. We also know clinically that
these factors interact in that nearly all psychiatric mood
disorders display co-occurring abnormalities of sleep. In fact, these sleep
abnormalities are so prominent they form part of the diagnostic
criteria for those psychiatric disorders. But despite that suggested
interplay, we’ve known remarkably little about the
basic brain dynamics of this relationship. And that’s something that
we’ve also been testing. When you think you’ve got two
factors that are interacting, one way to test that interaction
is to manipulate one of the factors and
then observe what happens to the other. So here we’re going to
manipulate sleep and dial it down again and block it with
deprivation and see if as a consequence, we can trigger an
amplified emotional brain reaction as a consequence. So a very similar design to
one I showed you before, a sleep group and a deprivation
group. The deprivation group,
we keep awake. But then the next day, we put
them inside the MRI scanner and we perform an emotional
challenge task with them. And here we’re going to show
them a series of standardized psychological picture slides
that range in a gradient from being emotionally neutral to
increasingly negative and unpleasant. And I’m just showing you
some examples here. They get far worse than
this, by the way. They get pretty gruesome. I don’t show them. There’s probably reactive
vomiting of lunch in the front row. But you get the idea. What we can then do is ask a
very simple question from our experiments. What in the brain shows
increasing reactivity in response to increasing
emotional negativity? And the structure that we were
focusing on here was this structure in the brain,
here in red. It’s a structure called
the amygdala. It’s very deep within
your brain. You have one on the left
and the right. And it’s one of the centerpiece
anatomical features for emotion processing
and reactivity. And when we looked at this part
of the brain in those people who’d had a good night
of sleep, there was a modest degree of reaction in response
to those negative experiences. So again, a similar view that
I described previously. You’re looking into the brain
from the front, top and bottom, left and right. I’m circling the amygdala
for you here. And these hot spots demonstrate
a modest reaction. That’s what you would want. You don’t want no reaction. You don’t want too much. In the group who were sleep
deprived, rather than seeing impaired brain activity, which
is what we’d seen with learning and memory, when it
comes to emotion you see exactly the opposite. In fact, here is the emotional
brain was 60% more reactive in response to those negative
experiences compared to when you’d had a good
night of sleep. And you can see that
more clearly if you just focus in here. For us, the much more
interesting question though was why? Why was your emotional brain
so reactive without sleep? And we performed some
additional analyses. And what we found is that in
those people who had had a good night of sleep, this part
of the brain here in green, it’s a part that we call the
frontal cortex and the middle part of your frontal cortex. The frontal cortex you can
think of in terms of the brain, it’s like the
CEO of the brain. It’s very good at making
high-level executive decisions, top-down control. By the way, this view,
it’s as if now you’re looking from the side. So this is the front of the
brain, the back of the brain, top and base. And when a night of sleep,
this part of the frontal cortex was strongly connected
to the amygdala, believed to send inhibitory, regulatory
control. So with a night of sleep, you
had this nice, balanced mix between the emotional gas
pedal and the brake. Without sleep, unfortunately,
what we found is that connection had been severed. And as a consequence, you’ve
got this amplified, almost Neanderthal-like emotional
reaction as a consequence. So now without sleep, it’s
as though you’re all gas pedal and brake. You’re all amygdala and too
little frontal lobe control as it were. Now, I could go on and show you
more bar graphs and MRI images to illustrate
these effects. But I’m actually going to let
a sleep deprived subject do that for me. Because it turns out that we
do video diaries with our sleep deprived participants
throughout the period. And I think at this point, we
may want to just close down the have video feeds just to not
present particular people. It’s fine for the
audience here. So in summary then in terms of
the talk and answer to the question why does my brain
sleep, well it sleeps for a whole constellation of different
functions, plural. It seems to promote emotional
regulation, learning, memory, creativity. And I should also say that
I didn’t mention anything about the body. But sleep has huge impacts
on body systems. It’s essential for metabolic
control, cardiovascular health, for your immunity. In fact, there is not one single
tissue that we have yet to find that isn’t beneficiary
affected by sleep. So I think my advice would be
that the single most effective thing that you can do each and
every day to reset your brain and body health is sleep. And I should finish there. I should thank all of
my lab members. I actually don’t do
any hard work. I just drink tea. I write lots of emails. They do all of the hard work. And then I come and give talks
like this and pretend that the data is my own. It’s not at all. And I’m immensely grateful for
all of their dedicated hard work and brilliance. And finally, I noticed
some of you stayed awake during this talk. So tonight, after all
of this information. I hope you sleep well. Thanks very much indeed. CHRIS: All right. Matt has agreed to take
some questions. I think we don’t have
a microphone up. MATTHEW WALKER: I’ll repeat
the questions. CHRIS: You have to repeat it. Or we actually have– I’d like to welcome
back, Sina. Come on up. Sina, from SWAN Solutions. For those of you who where at
the Sleep-posium a few months ago now, Sina was the
MC back then. And we’re going to welcome him
back to MC again today. MATTHEW WALKER: Hello. SINA NADER: It’s good
to meet you. MATTHEW WALKER: Good to
you meet you, too. SINA NADER: Thank you, Chris. And thank you all
for joining us. So we’d like to open
it up to questions. Yes, please go ahead? So I’ll just repeat the question
real quick, about bimodal sleep and maybe
polyphasic sleep and any kind of information on that? So Dr. Walker. MATTHEW WALKER: Yes. So it’s an interesting
question. There is sort of this first
sleep and second sleep. The evidence for that I don’t
think yet is robust. The idea, however, that
we should be sleeping biphasically, rather than
monophasically, what I mean by that is right now most of us
sleep monophasically, one large bout during the night. If you look at some cultures
that are not touched by electricity, by some of the
devices of Edison, what you see is that some of them will
sleep biphasically. They’ll sleep about 6 and 1/2
hours at night and then have that siesta-like
afternoon nap. And it turns out that if you
look at people’s physiology and their alertness physiology,
in the afternoons, right around this time now,
there is a physiologically measurable dip in
your arousal. It’s that sort of afternoon
meeting around the table and everyone sort of doing
those head– those really ugly things. They’re not listening
to good music. It’s that they’re
falling asleep. And it’s because of this drop. Suggesting that in fact we may
be biologically preprogrammed to have this sort of
dip into that. So I think right now,
it’s unclear. What I can tell you is that
we have also found a whole collection of brain benefits
by way of naps as well. Sometimes naps can give
as much benefit as a whole night of sleep. And it’s not entirely
clear why. SINA NADER: Next question. Yes, please? So caffeine and sleeping
pills, Dr. Walker? MATTHEW WALKER: So caffeine can
certainly mask some of the effects of sleepiness. The way caffeine works is that
during the day whilst you’re awake, a chemical builds
up in your brain. That chemical is called
adenosine. Adenosine is there to tell your
brain how long you’ve been awake. And when it gets up to a
critical mass, you start to feel sleepy. That’s how it works. Caffeine comes in and blocks the
receptors of adenosine and fools your brain into thinking
there is not as much adenosine around anymore. So you start to become alert. However, caffeine can get you
around some of the very rudimentary impacts of
insufficiency, like reaction times for example. You can speed back up with
caffeine to a degree. For these much more complex
processes of brain plasticity and emotional regulation, there
caffeine doesn’t seem to be a sufficient substitute. You can’t get over
it with caffeine. In terms of sleep medications,
it’s a great question. The older sleep medications,
what we used to call the sedative hypnotics, certainly
you weren’t awake when you took those medications. That’s for sure. That you were asleep is actually
very difficult to argue based on the physiology
of the brain wave patterns. Essentially, they just
sedated you. So the naturalistic sleep was
I think highly arguable. The more recent new-to-market
medications are producing what some have argued is more
naturalistic sleep. But it’s still not necessarily
purely naturalistic. Some of those sleep medications,
the common ones, and I won’t describe a
particular target, particular brand names, but the common ones
that are prescribe right now, they can impact the ratio
and the quality of your non-REM sleep. So, for example, that you
may not get the depth of that deep sleep. And you’ve seen the benefit of
that depth of deep sleep. It can change the quality
and when your REM sleep seems to arrive. So again, I think thinking about
those medications as yes, I slept eight hours and
yes, I don’t remember waking up so I must have had a good
night of sleep, that may be a fool’s gold. MALE VOICE: Question from VC. SINA NADER: What’s that? Oh, OK. Go ahead. MALE VOICE: Do you have any data
on the amount of sleep needed to have these constantly
good or optimal? To little sleep, too much
sleep, what it is the boundaries? MATTHEW WALKER: Yes. So it’s a good question about
what is the optimal sweet spot for sleep? The answer to that question is
a little difficult because it will be different for
every individual. It’s just like giving a calorie
recommendation. I can tell you that 2,000
calories a day is about the right prescription for
most individuals. But for different people’s
physiology and their metabolic demand, some people will
need more or less. And it’s the same with sleep. But what we’ve been finding is
that once you start to get less than seven hours of
sleep, you can observe measurable impairments. One of the other dangers of that
is that your subjective opinion of how you’re doing with
insufficient sleep is a miserable predictor of
objectively how you actually are doing when you’ve had
insufficient sleep. So people will say no, I can
survive fine on six hours. We said no, I know that you
think you can survive fine. But you can measure
those changes. You can see those impairments. And they happen quite quickly. One of the other interesting
question is too much sleep. And there has been some evidence
in the literature that once you start to get past
nine or 10, things like mortality and morbidity actually
start to go back up again in a way. So it’s sort of like this
U-shaped function, that there’s a sweet spot in the
middle around eight. Anything to either side of
that, maybe that’s bad. It’s difficult because if you
look at some of that data, firstly it’s not clear that it’s
just people staying in bed longer from those surveys,
rather than sleeping longer. Secondly, one of the other
theories is that sleep is so essential for your body health,
that if you look, those people who are sleeping
longer may actually be people who are sick. And the reason that they’re
sleeping longer is the body is desperately trying to do what it
does very well to get them better, which is to sleep. So I think some of that evidence
about what’s called hypersomnia, sleeping too
much, is still unclear. It’s not to say that too much
sleep can be a bad thing. I think it possibly could
be, just like too much weight is a bad thing. It’s about a natural balance
between the two. And it’s about 1/3 to 2/3 in
terms of the 24-hour period. It’s about eight hours is
a good, sweet spot. SINA NADER: All the way in
the back there, please? So the question was about the
sleep spindle experiment and the not so light exposure? MATTHEW WALKER: Yes. So for that stimulation
experiment where they were injecting the voltage, yes, you
saw both an increase in the quality of the deep sleep,
and you can measure that quality electrically. And there was also an increase
in the amount of spindles that went along with it. There weren’t correlations
reported between those two. But both of those things, the
deep sleep and the spindles, where ratcheted up by
that stimulation. Light pulse frequency, I don’t
know if anyone’s tried it yet. But there was a recent report
that used auditory stimulation, rather than
electrical stimulation. And they were even able to use
a subthreshold awakening auditory stimulation to kind
of almost entrain the brain into greater rhythmic activity
and increase the slow-wave sleep and as a consequence
increase the memory performance too. And there’s other ways that
you can do that too. During learning when you’re
awake, you can pair the specific material with certain
perceptual cues like sound or smells, like a rose odor. If you puff back up the nose
during deep sleep that same rose odor, whilst they’re
sleeping, you reactivate the memories and you boost
the amount of consolidation that you get. There lots of ways you
could manipulate it. So I mean if you want to burn
your incense whilst you’re learning, and then at night
blaze a few more up, maybe that would– fire hazard actually. That’s probably a very– don’t do that, sorry. That’s a stupid idea–
but anyway. SINA NADER: Fascinating stuff. Next question, right
here please? Cognitive function, exercise,
and sleep? MATTHEW WALKER: So the
interaction triad that you’re speaking about there, I don’t
know of any evidence that people have done that particular
experiment. But certainly the first two
factors is well known. That exercise will improve the
quality of your sleep. It can increase the depth
of that deep sleep. So the argument would be that
it should produce causal memory benefits. You have to be a little
bit careful. There’s some argument that
exercising too close to bedtime stops you efficiently
going to sleep. The reason is because for you to
initiate sleep, your brain and your body have to drop by
about 1 degree Celsius in terms of core temperature
to initiate that sleep. That’s why it’s always easier
to fall asleep in a room that’s too cold than
that’s too hot. And because of that core
increase due to the metabolic expenditure from exercise, you
can maintain that heat and you don’t fall asleep as well. It’s the reason by the way that
baths, a warm bath works. And it’s for the exact opposite
reasons that you think it works. You have a bath. You feel oh, that’s sort of
nice, warm, and cozy, I’ll get into bed. And you fall asleep
more easily. What happens is that when you
come out of the bath, because you’ve have what’s called mass
vasodilation dilation, all of your capillaries have sort of
expanded to try and get the heat out of your body. Then when you get out, you lose
a massive amount of heat. You get far more heat
expenditure. That heat expenditure helps
you with that initiation, dropping your core
body temperature. That’s why you fall
asleep easier. SINA NADER: Questions? Yes, please? That’s a wonderful question. The question was is yawning
contagious? MATTHEW WALKER: Yes, yawning
is contagious. And you can even see
cross-contagion, cross-species contagion. I’m not kidding you. People have– I don’t if they’ve empirically
studied But there’s good evidence that you can
be staring at your dog and you can yawn. And then what happens
is that your dog starts to yawn in addition. So that does seem to be. And that seems to
be perhaps not necessarily related to sleep. But there’s something
called a mirror system within the brain. That the brain seems to have
this capacity to understand and even mirror what’s going
on in other people. It’s that same reason that if
you see someone closing a door and their fingers are going to
get trapped in the door, you instantly go– hsst. Why did you do that? Your hand is not going to
get trapped in the door. It’s because you have
this mirror system. It’s a very clever system
in the brain. It allows you almost this
insight into how other people are. And that same system can
create these types of contagions and yawning
is one of them. SINA NADER: Next question? Yes, please? So the question was about
marijuana and sleep? MATTHEW WALKER: Yeah, it’s
a good question. I’ve got no idea obviously
why you’re asking that. And I don’t know of good
evidence right now to examine the systematic changes on sleep
and how it influences things like learning and
memory and cognition. It certainly does
seem to disrupt some features of sleep. There are some reports of
alterations in rapid eye movement sleep. What I can speak to much more so
though is alcohol, which is far more frequently used. Alcohol, you’re absolutely
right, it is a potent suppressor of REM sleep. And it’s one of the reasons that
people will describe to you, saying well, I’ve had a bit
too much to drink and then I was having these
really strange dreams the next morning. Here’s how it works. It’s actually not alcohol. It’s the metabolic byproduct of
alcohol, the aldehydes and the ketones. And they will suppress
REM sleep. So you’re going throughout the
night and you’ve got all of this drink in you system. And your liver and your kidneys
are desperately trying to metabolize it, get it
out of the system. And what’s happening is that
you’re not getting any REM sleep because of
the impairment. But your brain is clever. It keeps a clock count
of how much REM sleep you should have had. And then when the alcohol is
finally washed out of the system, not only do you then
have the REM sleep that you were going to have, you also
have that plus it tries to get back some of the REM sleep
that you missed. Its called the REM sleep
rebound effect. And as a consequence, you get
this really intense REM sleep late morning. With REM intense sleep, you
get intense dreaming. That seems to explain why. SINA NADER: Next question? Yes, please? So a follow-up question on the
electrostimulation question and different effects
it might have? MATTHEW WALKER: Yes. So I don’t know yet of the
electrical brain stimulation and benefits downstairs, sort
of south in the body. But I can tell you the inverse
of that question, which is if you selectively deprive people
of deep sleep, what are the body consequences? And they are significant. You can manipulate. And the way that you do this is
whilst people are sleeping, you play them just sort of
tones, annoying tones. Now, the tones aren’t enough
to make them fully wake up because you dial the
volume around. But it keeps them out of
deep sleep and keep them in shallow sleep. So you can remove the anxiety
of waking them up. You don’t have to shake
them or anything. So it’s a very clever
manipulation where you can selectively excise deep sleep. As a consequence, you can
disrupt metabolic regulation profoundly. In fact after a couple of nights
of this, your capacity to regulate your basic body
glucose look so severe that you’d be classified
as prediabetic. And you can do that even just
with basic sleep disruption. If I take you for five days and
I let you only sleep for five hours or four hours a night
for five days, the same metabolic profile of sort of diabetic-like impairment happens. You can see the same
with immunity. If I do the same thing, if I
short-sleep you for five days, your body’s capacity to create
an immune reaction to something like the influenza
A virus, the flu jab, is dropped by 50%. Your body’s immunity is at half
its capacity to mount a response after short sleeping. So there are profound impacts,
not just on the brain, but deep within the body by way of
insufficient sleep or even selective sleep disruption. SINA NADER: Other questions? Yes, please? So the correlation between
timing of sleep and learning? MATTHEW WALKER: Yeah. It’s a very good question. What we found for the most part
is that as long as you sleep that evening sometimes,
even learning earlier during the day will still be
retained and saved. And in some ways that make sense
because you wouldn’t want to create a system of
memory where only that which you learned just in a few hours
before sleep was going to be retained by sleep. The sleep system seems to have
a capacity to absorb about 16 hours of the day’s duration. However, if you don’t sleep
that night after learning, then I don’t test you
the next day. I give you a recovery night of
sleep on the next night and even another recovery night of
sleep and then test you, there is no evidence of a memory
consolidation benefit. In other words, if you don’t
sleep in the first 24 hours after learning, you
lose the chance to consolidate those memories. So it is a time-sensitive
feature. But within the natural
boundaries of how we normally should be waking and sleeping,
that seems to be fine. SINA NADER: Right here. Yes, please? So I guess the timing
of sleep onset? MATTHEW WALKER: Yeah. So that’s a fantastic
question. I only know of one
study out there. We didn’t do this. But they looked at how regular
or irregular your sleep was in terms of onset and offset,
which is just what you’re describing there. And they found that, perhaps
even more strongly or as strongly as amount of sleep,
was the instability of that sleep predicted worse
memory retention. I believe it was actually in a
very prominent university and one of the hardest exams for
that university, which is organic chemistry. And they found that less so than
the lecture or the great lecture notes, your sleep
stability was a very statistically strong predictor
of how you were going to do on that exam. SINA NADER: I wish I
would have known that when I was taking– OK. Yes, please? The question is about what state
of sleep you wake up in, and alarm clocks, and health? MATTHEW WALKER: Yeah. Again, I don’t know of any
systematic studies that have tried to look at forced
awakening by way of an alarm clock versus naturalistic. The alarm clock, from sort
of an anthropological perspective, is a fascinating
thing. Again, if you go to cultures
that are not touched by sort of electrical means, the notion
of ratcheting your brain out of sleep non-naturally
is a very strange one. And it came by way of
the factory whistle. I mean that was the first
alarm clock in a sense. So you got standardized,
mass people movement. So certainly, I don’t think it’s
necessarily a good thing to be setting an alarm clock
if you can do it naturalistically. Your body has a pretty
good clock counter of what it needs. And it will wake up
when it’s time. But I don’t know of any good
evidence that tries to look at those sort of clever clocks
that seem to essentially monitor your brain, figure out
when the optimal sweet spot is, base it on the light time. I haven’t seen many ambulatory
devices like those that are actually accurate for
sleep staging. SINA NADER: Next question? Let’s go with you please. The question was about naps
and studies about them? MATTHEW WALKER: Yeah. We just shout at them,
go to sleep. No. It turns out that we time them
to co-occur with that– it’s called the post-prandial
dip, that drop in your physiological alertness right
surround now in the afternoon. So you give them a meal. You put them to bed
around this time. And for most young, healthy
people, even though we’ve standardized their sleep
schedule, for five days before we’ve made sure that they’ve
been getting eight hours of sleep or between 7 and 1/2 and
eight hours of sleep a night. They still seem to be able
to initiate a nap. It takes them about 10 to 15
minutes to go into that nap, but once they’re there. These are young,
healthy people. By the way, I should
say 18 to about 35. It seems to be harder with
age to do those things. But you can seem to
initiate that sleep during the afternoon. It’s obviously a lot harder if
you place the nap earlier in the morning. They haven’t built up enough
sleep pressure yet to go back into sleep. In other words, they haven’t
accumulated enough adenosine in their brain to force
them to go into sleep. Around 6:00 PM, you start to
rise back up again in your alertness after that
afternoon dip. So it’s actually quite hard,
despite it being later in the day, to get people
to nap then too. So if you understand the
biology, you can place the nap window of opportunity time right
where it sits and you can get about an 85% hit
rate in terms of people falling asleep. SINA NADER: Other questions? So coffee in the morning? MATTHEW WALKER: Yep. So it’s actually just
a habit based– I mean your body doesn’t
need caffeine. People who are drinking caffeine
before about midday, you’re simply self-medicating
your lack of sufficient sleep. So after while it becomes a psychologically habituating effect. If you start to have
decaffeinated and people don’t tell you, apart from the
headaches, based on the physiology that’s built up– you
know the notion of a warm drink can do it for you. It tells you have it
habit-based, rather than a physiological need. So it’s a misnomer that
you need that. If you do need that, you should
probably be getting more sleep. SINA NADER: A question
here, please? So I guess light sleepers and
perception versus reality? MATTHEW WALKER: So what we know
is that some of those other electrical features of the
brain, including the sleep spindles, are not just
important for memory processing. Sometimes they seem to respond
to external stimuli in your environments. And some people have argued that
some of those spindles, they are slower frequency
spindles. The faster frequency
ones are the ones that relate to memory. The slower frequency
ones seem to be relating to external noise. And the argument is that there
is physiological mechanisms in place that try to
keep you asleep. But it turns out that depending
on the spindle quality that you have, you may
be more or less susceptible to being woken up by
external noises. And it seems to be that that
physiology can determine whether or not you’re a quote,
unquote “light sleeper” versus a “deep sleeper.” So we haven’t fully understood
and characterized that yet. But there are a few reports out
there demonstrating that electrical features of the
sleeping brain can determine how vulnerable or resilient
you are to the sort of alerting, waking up cues is of
external sounds and stimuli. So we can understand better. SINA NADER: We had one
question over here. Yes, please? So the question was about
duration of sleep and– MATTHEW WALKER: No. I would always recommend getting
as much sleep as you can possibly get. It’s not clear exactly how
those 90-minute cycles interact with each other to
accumulate and accommodate all of the different brain and body
demands that are going on, since we don’t understand
that algorithm right now. But what we certainly do
understand is that getting less than sufficient sleep can
cause impairments, it would be far better just to sleep as
long as you possibly can. Yeah. I mean you have to remember that
human beings are one of the few species that have
decided to deliberately deprive themselves of sleep. The rest of the organismic
kingdom seems to be far smarter than we are in terms of
our understanding of sleep. So I would definitely recommend
get as much as you possibly can. AUDIENCE: How much
do you sleep? MATTHEW WALKER: It’s
a good question. I usually say I sleep about
eight hours whenever I can, which is never. No. I will routinely get between
about seven and a half to eight hours of sleep. If I get less than seven
hours, I know it. When you’re this type of a
researcher you become sort of like the Woody Allen neurotic
of the sleep world, both by way of I know I can observe all
of the impairments because I’m acutely aware of them. And worse still, when I’m in
bed, let’s say I’ve kind of crossed time zones and I’ve
got all of those problems. I’m lying in bed and I know all
about the biology of what should happen to
initiate sleep. So I’m thinking my god, my
core body temperature is probably half a degree off. I’m not shutting down my dorsolateral prefrontal cortex. The histamine in my brain– and at that point, you’re
dead in the water. In the next hour, you’re
going to ruminate. So I wouldn’t recommend– stay with whatever job
you’re in as long as it’s not sleep research. SINA NADER: Well said. How much time do
we have, Chris? CHRIS: You can go longer. SINA NADER: Keep going, OK. Over here, please. Yes? So the question was how to deal
with daytime fatigue? MATTHEW WALKER: Yeah. I think the most obvious
question is start to get sufficient sleep, if that’s
routinely happening. If it’s that one-off
circumstance, certainly you can have countermeasures. So things like caffeine can be
somewhat effective in terms of driving, sort of if you
start to feel drowsy. But drowsy driving, for the most
part the recommendation is just get off the road. Because what you can have during
fatigue is what we call microsleeps. And they can happen for just a
few seconds, even less, where you just kind of zone out
and you come back. And it turns out that at 65
miles an hour, you only need one of these microsleeps to go
two lanes in the opposite, left or right, direction. So that may be the last
microsleep that you ever have. So caffeine can work to an
extent if it’s a one-off. Certainly, if you can
take sleep, have a short sleep period. You have to be a little bit
careful after a nap though because what happens upon waking
up from a nap or a normal night of sleep is that
you have something called sleep inertia. Which is that it’s just
like the car engine. It takes a little bit
of time to warm up. Now, it’s not oil that needs
to warm up in terms of your brain of course. Some parts of your brain
come back online more slowly than others. The frontal lobe in particular
seems to take a longer duration of time. So in other words, if you do
have a counteractive nap to overcome that tiredness, don’t
necessarily jump right back in the car, wake up and start
driving again. Go grab a coffee. And then sort of give yourself
15 or 20 minutes to wake up. Then start doing those
types of activities. SINA NADER: Question? Let’s go with the back
there, please? The question was what’s a
good length for a nap? MATTHEW WALKER: The answer
really depends on what you want out of it. If you want to just restore your
basic level of alertness, 15, 20 minutes, that can have
potential benefits. For things like learning and
memory, it seems as though you need to go longer, depending on
what type of learning and memory information that you’re
trying to get a benefit from. For emotional brain regulation,
what we’re finding there is that rapid eye movement
sleep again comes into play, dream sleep. And we’ve been finding that for
those emotional regulation benefits from a nap, you need
to go long to get that REM sleep, which comes at the
end of the cycle. So it’s not a simple answer. It really depends on what you’re
trying to self-medicate in terms of a functional
benefit from that nap. SINA NADER: Question
right here, please? So melatonin and sleep? MATTHEW WALKER: So I think the
evidence right out there now suggests that melatonin doesn’t
necessarily affect the duration of your sleep, nor
the quality of your sleep. What melatonin does is help
with the regulation of initiation of sleep. So the timing of sleep,
not the duration or the quality of sleep. Melatonin is a naturally
released hormone within the body. It’s called the “hormone of
darkness,” not because it looks just great and bad-assed
sort of thing. It’s because it’s released
at night time. And it tells your brain
that it is night time. It tells the brain and
the body that this is the time to sleep. So that’s why it’s efficacious
when you travel through time zones because now there’s
a mismatch between your biological clock and
the time zone. And so whilst your biological
clock is still saying it’s 4:00 in the afternoon, in the
new time zone it’s midnight. And so if you take melatonin a
little bit before sleep onset, then your brain is fooled into
no longer thinking it’s sort of 4:00 PM in the afternoon. But it’s oh, my goodness,
it must now be midnight. And that can help the
initiation of sleep. But I think the evidence is
pretty robust now, not the duration or the quality. SINA NADER: Let’s go with
somebody we haven’t had yet. Yes, please? So the question was about
elderly people and sleep and kind of what can be done to
remedy or address it? MATTHEW WALKER: Yes. So certainly electrical brain
stimulation is one of those that we’re starting to try
and implement now. Obviously, it’s probably not a
population-wise therapeutic device sort of more generally. I think firstly, we need to
demonstrate that by restoring that sleep we can get
the memory benefit. If we can, then I think there’s
lots of other ways that you can do it. Exercise is one of them. One of the types of sleep that
exercise will enhance when you do get it, as long as the
exercise isn’t too close, is deep slow-wave sleep. There is pharmacology
of course. Although you have to be a bit
careful with pharmacology because it tends to be systemic
and it tends to have variety of other effects. But there are drugs out there
on the market that seem to increase what looks like the
depth of that deep sleep. So I think there are a variety
of pharmacological, electrical, behavioral
techniques that you can use. And some combination or all of
those may be useful long term, depending on how the
technology could be distributed at a population
level. SINA NADER: A question over
here please, yes? So the question was sort of
about the pattern of maybe the sleep/wake cycle, if
I can summarize it. MATTHEW WALKER: So it’s a
fascinating, still within the field, philosophical rather than
sort of scientifically addressed question right now,
which is why would you lose consciousness? It’s not the energy savings. So it turns out that if you
were to just lie on your couch, couch-potato like, even
with your eyelids closed but remain awake, the caloric
difference between sort of that and falling asleep is only
about the calorie savings of a slice of brown bread. My point being is that that
seems to be a totally inefficient benefit for losing
consciousness and falling prey to all of the dangers that
happen like that. Why wouldn’t you just go out and
club another seal and have more food and save back that–
sort of get back that energy and not have to lose
consciousness by way of this thing that we call sleep
in terms of a process that evolved. So clearly what seems to be
essential, or one of the things that seems to be
essential, is disengaging with the outside information
or perceptual world. Don’t forget though that the
perceptual information processing world does reoccur
during sleep, during this thing that we call REM sleep,
which is dreaming. But one of the potential
benefits of going offline is that the processing cognitively
of information that happens either when you’re
awake with your eyes shut versus the nonconscious
state of the deep non-REM sleep, that may be required
for this type of offline information processing. Because otherwise, you get
information interference. You get cross-wiring of those
combating information streams. And you can’t effectively
do what the sleeping brain seems to do. That’s one possibility. I still think it’s a huge
mystery though as to why. It seems so counterintuitive. You’re not finding a mate. You’re not socially
interacting. You’re not getting food. All of these things would
suggest sleep is a bad idea. Yet it’s universal, it seems. SINA NADER: It reminds me of a
quote I heard you mention in another talk. If sleep wasn’t– if it wasn’t necessary, it was
the greatest mistake of evolution, something
to that effect. Another question? Yes, please? Go ahead. So naps and interfering
with regular– restless sleep? MATTHEW WALKER: Yes. So when it comes back to naps,
we come back to the adenosine story again. So as I described to you,
adenosine starts to build up in this time-dependent
fashion in the day. When you sleep, what happens–
it’s like a pressure cooker building up with steam. When you sleep, you dissipate
that pressure. You remove the adenosine. So you come back down to your
baseline level again. That’s why if you’ve had enough
sleep, you wake up feeling alert or
you should be. What happens with the naps, and
naps can be a double-edge sword, if you sleep too long or
you have them too late in the day, is that you’re building
up that adenosine pressure that will make
you go to sleep in a healthy manner at night. You have a nap and
the nap removed– opens the valve. And you dissipate some of that
sleep pressure, some of it, not all of it, but some of it. And now, you wake up and you
feel more alert again. And it takes you longer to get
back to that point of feeling sleepy again that evening than
it would have if you had not taken the nap. So in other words, you then
start to think well, it’s 11:00, midnight. Well, I’m not sleepy. I normally am. And the reason is because
you haven’t taken a nap during the day. But because you have just
recently, that has removed some of that sleep pressure. So you’re no longer as sleepy
anymore at that time of day. So you have to be a bit careful
with naps because they will take away some of
that urge to sleep. And that’s presumably
why exactly that happens that you described. AUDIENCE: [INAUDIBLE]? MATTHEW WALKER: No,
I think the idea would be that if you’re– the question was would you sort
of habituate to the naps? The idea would be if you’re
taking those naps, essentially you can think of it like
absorbing some of the eight-hour quota that
you’re having. And so it may be that you would
then be going to bed later, but you would sleep
a shorter amount and wake up the next day. And it depends on the evidence
that look at. But there’s some argument that
as long getting that eight hours, to a degree that’s
not too bad in that biphasic manner. I think highly polyphasic
sleep, however, that is somewhat of a trend now and sort
of sleeping 90 minutes, being awake then another two
hours, and all of this stuff, that doesn’t seem to be the
way that the biology is programmed within
adult humans. It was the way in which you were
programmed when you were a small infant though. Infants are highly polyphasic
in their sleep. They will be asleep for short
periods, then awake, sleep. And parents know this, unfortunately, to their detriment. But once you get into adulthood,
the pattern stabilizes, certainly into a
biphasic, perhaps monophasic. So, yup. SINA NADER: Other questions? Yes, please? So the question was about new
parents and sleep deprivation? MATTHEW WALKER: Yeah. I hear that a lot. I did survive. And if that’s your basal level
of success, it says so much. There is no good knowledge right
now that human beings have any kind of learned ability
to overcome sleep deprivation. You hear this a lot in some
of these sort of heroic professions. Medicine is a good one. Sort of that old boys’ network
notion that well, it takes a special person, one who can
learn to deal with sleep deprivation. You have to realize that, again,
the few sort of set of species that do go into sleep
deprivation, there’s no way that within a short lifetime of
an individual you can learn to adopt to millions of years
of evolution that put this thing in place called sleep. And it’s never faced the
evolutionary challenge of having to deal with
a lack of sleep. Because it’s not common. And so this idea, this misplaced
idea, that you can sort of learn to cope with it or
that there is a biological safety net that you can invoke
at certain times, that doesn’t seem to be necessarily true. However, there are
some exceptions. There are some interesting
scenarios where some species for a certain duration of their
cycle will undergo sleep deprivation, one of which
is migrating birds. And there is a particular
migrating bird that during that period of migration, seems
to be somewhat resistant to the effects of insufficient
sleep. Yet out of that phrase of the
migration, it is susceptible to the sleep deprivation. And that’s fascinating. Because it tells us that maybe
there are some biological mechanisms that can offer
some resilience for a short period of time. It turns out the military
were fascinated by it. They were very interested in
finding that work to figure out– obviously, you know,
a 24-hour soldier. But for the most part,
there isn’t good evidence that people– or there’s anything like sort of
breastfeeding or nursing or any circumstance that seems to
co-opt and invoke resilience to the impact of sleep
deprivation. SINA NADER: Question
in the back? So the question was about
gadgets, including the Zeo? And then also about sort of
self-treatment or maybe autotitration, that
type of thing? MATTHEW WALKER: So since I’m
not a clinician, an M.D., I can’t really give too many
recommendations about the apnea stuff. But certainly in terms of Zeo,
there have been some empirical data put out there that suggests
that it may have a somewhat good degree of
correlation between the gold standard of in-lab electrodes,
validated sleep staging relative to its algorithm
of sleep staging. It tends to be able to simply
quantify light sleep and deep sleep and then arguably dream
sleep, REM sleep. However if you look around,
for example if you just go onto to Amazon and you look at
the user reviews, some people are saying well, right now,
I am looking at my Zeo. And I’m awake and I’m looking
at the clock and it’s saying I’m in REM sleep. What’s going on? And I don’t believe that they’re
having a hallucination whilst their dreaming. I think that’s probably real. So I think those algorithms have
got a way to go before they reach that. And I don’t think they’re valid
yet as a strong, at least a experimental tool. And I think Zeo has actually,
unfortunately, just gone out of business. SINA NADER: Other questions? Yes, over here please? That’s a great question. I have the same question
myself. The question was about kind of
upcoming research and things that might be on the horizon? MATTHEW WALKER: Yeah. Well, not wanting to give away
too many of our research goals and secrets. But I think certainly one of the
areas is in this area of sleep and the lifespan. So firstly, you’re looking at
the aging issue, not just in aging, but now into dementias. We know that the pathology of
things like Alzheimer’s disease hits very perniciously
the sensors in the brain that regulate and generate
that deep sleep. So starting to really understand
translationing, what all of this basic science
means for things like clinical disorders such as Alzheimer’s
disease I think is going to be critical. Also that role of sleep in
emotional brain regulation I think is going to just explode
in terms of a field. And its core relevance will
be in this selection of psychiatric disorders that
suffer co-occurring impairments of sleep. I think sleep has a huge story
to tell in psychiatry. And I think that story right
now has not been told. In part, because people like me
haven’t been doing enough basic research. I think we’re starting to get
to the stage where we’ve understood it enough where
we can make that translational leap. I think psychiatry has often
thought that sleep disruption was simply a side product of
the psychiatric disorder. You could flip that question
around and ask is the sleep disruption contributing
or causing the psychiatric disorder? That’s a tenable hypothesis. Ultimately, I think it’s going
to be neither one of those. Biology tends to never
be unidirectional. It tends to be bidirectional. Is the flow of traffic going
more strongly one way up the street than another? That’s possible. So I think the whole translation
of this basic understanding of what sleep is
doing is going to be big in terms of clinical
medicine soon. Also reversing the time clock
back into development. Some of the greatest changes in
our sleep happen within the first two years of life and then
after that, right into adolescence. If sleep is regulating all of
these functions, they’re also functions that show demonstrable
changes in those developmental phases, learning,
memory, plasticity. Babies starting to understand
what the rules of this thing that we call the world
that we live in are. It turns out that if you give
infants naps, they can start to abstract rules, even
before they can speak. You can see it in their
behavior, sleep-promoting creativity. So I think that understanding. Because developmental changes
and developmental disorders also co-occur with some
sleep abnormalities. So I think there’s a lot. I think other interactions
are also going to be with genetics. I think we’re starting to
understand that different genetic compositions have a
lot to tell us about the impact of sleep and
sleep deprivation. Being one genetic flavor, does
that mean that you’re resilient versus another that
means that you’re vulnerable? What does that mean ethically
for professions if we’ve got a number of professions that
we know of where sleep deprivation is rife, should we
be interviewing them and then doing a genetic test if we find
that type of evidence? So I think there’s fascinating
possibilities. But I think the cool one is that
this is one of the last, great scientific mysteries
of why we sleep. You spend a third of
you life doing it. And people like me, doctors and
scientists, I can’t give you a satisfying, consensus
answer. I mean that just
blows my mind. Despite all of the advances in
molecular biology, we don’t have an answer. And imagine that. When as a parent, you first
child is born and the doctor walks in and says,
congratulations, everything looks great. It’s a healthy boy or a girl. All the tests look good. And they smiling in that
reassuring way and they start to walk away. And before they get to
the door they say, there is just one thing. Routinely from this point
forward and for the rest of your child’s life, they will
lapse into a state that looks like nonconsciousness. In fact, it looks not
dissimilar to death. But don’t worry, it’s
reversible. And they will do that,
fulfilling approximately one third of their entire life. They will have hallucinogenic,
bizarre experiences. And I don’t know why. Good luck. And at that point, you’d say,
no, no, that can’t be true. I’m sorry. That’s silly. That’s what sleep is. So beyond all of the translation
or big picture stuff, I think we still have to
come back to answering that question, why do we sleep?

27 thoughts on “Why Does My Brain Sleep?

  1. sleep serves the 4th dimensional energy …hence the reason for strange dreams; when the body is still the easier it is to infiltrate it

  2. i would just like to say that after regularly not sleeping for periods up to 118 hours I am still able to remember everything just fine which contradicts the 24 hour memory consolidation rule about deletion. excellent talk though.

  3. At 50:30 Dr. Walker mentions a study which found that irregularity of sleep times was a significant factor predicting poor performance in university exams. Can anyone tell me where to find this study?

  4. These tech talks used to be in high definition with good production quality regarding the camera cutting to slides. To the organizer: this format is not nearly as good; it's like going back 5 years and getting a worse camera besides!

  5. Great talk. Lots of good information that one can even apply to day to day life. Regarding the format the black out pauses are annoying, sometimes one thinks that the net connection went down: suggest at least quick fade in/out.

  6. well he said that capacity of memory decreases, and abilities of memory is individual.
    another very important thing is emotional factor, in some cases it can take positive effect on memory and brain functional abilities.

    sleep and brain functions is a very huge research topic.

  7. 56:56
    I probably have some sleep disorder, 'cause I can sleep over 18h without waking up.
    clock is the only thing that keeps me away from sleeping so much.

  8. Dr. William Dement has studies in his book of people trying to sleep as much as they can and they weren't able to oversleep. When their sleep debt was paid (by sleeping as much as they can for a week or so), they just woke up and lay in a bed in a dark room, despite the fact that there was nothing to do there but to sleep. But they felt amazing. There are not that many people who are not constantly sleep deprived.
    I'm surprised he didn't mentioned those studies. But at least he mentioned that if you sleep a lot it's most likely a symptom not a problem. People can't oversleep. If their sleep debt is paid, they wake up and they won't be able to go back to sleep no matter how hard they try. But when they are sick or have some health issues their body has to sleep more. Another reason for sleeping more might be bad sleep quality, which can be caused by some sleep disorder like sleep apnea. In any case, you can't reduce the number of hours you need to sleep by sleeping less. IF you're sleeping a lot, you should address your health or sleep quality, not try to reduce sleep time, which will just cause in more problems.

  9. Subjectively, I feel  overwhelmingly fatigue and drowsy in the evening(setting sun with decrease sunlight).
    Good lecture.   

  10. nice video I just found method to stop insomnia from Banfan Instant Sleeping Miracle fantastic idea

  11. The most likely reason for sleep has nothing to do with the brain directly – but is first based on finishing the daily digestive system – it came first. Look to the ENS, enteric nervous system or gut brain.  Sleep stops eating, finishes digestion, prepares hormones and retrieves needed water, for the next day's digestion, and prepares waste out.
    Evolving out of that is waste out of the brain.  See the Univ. of Rochester study.
    That further suggests that the cleansing of the brain, may carry over to not only the blood brain barrier area, but all the blood barrier areas, including testes, spine, and parts of the eyes and ears etc.
    Notice also the connection between NREM and parasympathetic, and REM and sympathetic. These points are important too.

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