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?