Translator: Tanya Cushman Reviewer: Queenie Lee
You know, for a sleep scientist,
I actually don't sleep very well.
Any little chink of light in the room, and I'm awake all night.
And my eye-mask is just as important to me as my laptop.
But really, I take sleep very seriously,
and I'm hoping this talk will be a sort of wake-up call to all of you
to make some of you feel the same about it.
Now, what I'm not going to do
is preach to you about how you should get more sleep.
We all know that.
We all know we live in a sleep-deprived society.
Instead, I'm going to talk about something which I think is much more interesting.
This is how we can manipulate the sleep that we do get
in order to get the most out of it,
in order to improve our quality of life.
And I call this "the new science of sleep engineering."
But let's start from the beginning.
As humans, we spend roughly a third of our lives asleep,
eight hours a day.
That's more time than we spend doing anything else;
that's a huge amount of time.
And just the pure fact of that time investment
suggests that sleep must be doing something incredibly important.
But what is this?
Well, it turns out that sleep is all about the brain.
Contrary to popular opinion,
the brain doesn't just switch off when we go to sleep;
instead, it goes through a series
of highly specific, different types of activities.
We can measure these by putting electrodes all over the scalp, like this.
This, by the way, is a sleep scientist's idea of a selfie.
(Laughter)
With these electrodes, we can measure the electrical activity of the brain.
And during wake, it looks something like this - just a wiggly line,
with time going from left to right.
And what that tells us is the brain is active - good -
and that the activity is not particularly synchronized,
so things aren't summing up in any particular way.
But as we fall asleep, the pattern changes a little bit.
It slows down a little bit,
and the amplitude of those brainwaves gets a little bit higher,
showing a bit more synchrony.
And we also start to see occasional bursts of high-frequency activity
that we call "sleep spindles."
These spindles don't occur across the whole brain;
they just occur in localized areas at any one time.
I'm going to come back to them several times during the talk,
so try to remember what those look like.
Now, as we go deeper into sleep, the activity slows down still more,
and we start to see these high-amplitude, slow oscillations
that we call "slow waves."
And this shows a high degree of synchrony in the firing across the cortex.
So many neurons are all firing together, then pausing, then firing together.
It's very different than the kind of activity that we see during wake.
And if we go still deeper,
we go into a sleep stage that I'm sure you've all heard about -
rapid eye movement sleep.
This is famous for the way the eyes dart around under closed lids,
and it actually looks very similar to the brain activity
that we see during wake,
probably because of the dreaming that's happening,
not much cortical synchrony there.
So why do we do this?
Why do our brains spend a third of our life
going through these highly precise different types of activity
in a cycle from one stage to another?
Well, there are two main answers to this.
One of them relates to sleep's role in maintaining a healthy brain,
and the other to its role in learning and memory.
And I'm going to start by talking about the healthy brain.
Sleep plays a sort of housekeeping role:
it cleans our brains, it helps us to remove toxins.
And some of the most interesting studies of this
have shown that the spaces between brain cells
expand during that slow-wave sleep that I showed you
by as much as about 60%.
This allows cerebrospinal fluid, the fluid in the brain,
to flush through and efficiently clear away toxins that build up during wake.
One of these toxins that's particularly interesting
is something you might have heard about - beta amyloid.
This is a protein that can build up
not only during wake but actually across a lifetime.
And buildups of beta amyloid are linked to a formation of plaques in the brain
that are predictive of cognitive impairment,
particularly problems with memory.
If it gets bad, it's also linked to dementia and Alzheimer's Disease.
Beta amyloid is also linked to cell death in the brain
and a gradual degeneration of some parts of the cortex
that can happen with aging,
again, in dementia and Alzheimer's Disease.
So it's obvious it's important for us to flush this out of the brain if we can.
Now, interestingly, as we age, our sleep patterns also change.
Our sleep becomes more fragmented,
and those high-amplitude, slow oscillations that I told you about
gradually stretch and flatten out,
and after the age of 65 or so,
it's quite common not to get any more slow-wave sleep at all.
Problem, right?
Furthermore, this gradual decline in slow-wave across the lifecycle
has been shown to predict
the extent to which the cortex actually atrophies and shrinks,
so [for] some of the prefrontal regions of the cortex
that shrinkage is predicted by the decrease in slow-wave sleep.
So wouldn't it be great
if there was a way that we could maintain those slow-waves as we got older,
and not have that decline?
And this is where we come to sleep engineering.
Very recent research has suggested a way that we can do this.
If we play sounds to people -
just click, simple click sounds -
while they're in slow-wave sleep,
and if we place those sounds
near the peaks of those high-amplitude, slow oscillations,
it turns out that can enhance them.
Let me show you what this looks like.
(Clicking)
So the clicks occurring just near the peaks boost the amplitude,
and they've also been shown to improve memory the next day.
That works very well in healthy young people.
And I've got several quite sleep-deprived graduate students
who are working hard on taking this to the older population.
Right now, our results are very promising,
so we're hoping that in not too many years
we might be able to offer a sort of preventative treatment
that could help people to maintain their slow-wave sleep as they get older,
and possibly might slow down some of this decline -
cortical and cognitive -
that happens.
So, let me move on now to talk about learning and memory.
[Why Sleep?]
In his famous book "One Hundred Years of Solitude,"
Gabriel Garcia Marquez
wrote about a plague of insomnia that swept across a land.
People just couldn't sleep.
At first, they didn't mind that at all.
But eventually, negative symptoms started to manifest.
And these symptoms were the fact that they lost their memories,
they couldn't learn new things,
and they started to forget what objects were.
They had to cover things with notes, saying things like
"This is a cow, it gives milk. Pull here."
(Laughter)
Given that this book was published in 1967,
when we knew almost nothing about sleep's role in memory,
it's really quite remarkable that Garcia Marquez had insight into this.
But subsequent research has shown that he was absolutely right.
Sleep is very important for forming new memories
and also integrating those memories with what we know already,
also strengthening memories.
Let me give you an example.
I want you all to hold up your left hand,
and we're numbering your fingers from one - pinky, to four - index finger,
and now I want you to press your fingers on your thumb in this pattern:
4, 1, 3, 2, 4;
4, 1, 3, 2, 4.
Okay, I think you all got it.
This was the task
that was used in the experiment I want to tell you about.
People were asked to press "4-1-3-2-4 sequences" like this
as quickly as they could
for about two hours.
(Laughter)
They were pretty bored,
but they also stopped getting faster, as the experimenters wanted,
and when they got to that point, they were given a test.
30 seconds. Press as many 4-1-3-2-4 sequences as you can.
And this all happened around about 10 AM,
and people did just fine - they pressed about 21 sequences.
And then, they were told to go away, come back 12 hours later, and do it again.
And their performance didn't change much.
Now, here's the interesting bit:
they went away a second time, and they slept overnight,
and they came back and did this a third time.
And now their performance improved dramatically,
about 20% improvement.
Furthermore, the extent to which they improved
was predicted by the sleep spindles -
remember those high-frequency oscillations I told you about -
that occurred over the bit of their brain,
the motor cortex,
that's particularly associated with hand movement.
So, this is the kind of data
that suggested sleep is doing something really important for memory.
It's helping us to strengthen up memories.
But it turns out it doesn't just help us to strengthen memory.
Sleep also helps us to integrate memories
and to make connections between things
that we might not otherwise have realized were connected.
And this is critical for solving some kinds of problems.
It's critical for creativity and forms of innovation,
and I bet everyone here has experienced this:
you've woken up in the morning
with a solution to something that you hadn't been able to solve the day before.
So, in fact, our history is peppered with examples of this.
(Music: The Devil's Trill Sonata - Giuseppe Tartini)
So this sonata by Tartini is an example.
This was inspired by a dream
that he had of the Devil playing violin on his bed.
A more scientific example comes from Friedrich Kekulé,
who won the Nobel Prize
for discovering the chemical structure of benzene is cyclical
rather than acyclical, more linear.
And again, this was inspired by a dream
in which he saw a serpent biting its own tail.
Interestingly, this type of associative problem-solving
is linked to REM sleep rather than spindles, or slow-wave, sleep.
So, what you might be wondering is what's going on in sleep.
How does sleep allow us to do these things?
And the answer seems to be linked to the fact
that memories are spontaneously replayed during sleep.
So the neural activity associated with something that you've done
replays spontaneously when you're asleep.
Let me explain to you an experiment which shows this.
This is a maze
which participants were asked to navigate around in a video game.
And while they were doing this, their brain activity was measured,
and unsurprisingly, the hippocampus - amongst other areas -
which is associated with spatial memory and navigation,
was active while they did this.
Then, the same participants stayed in the scanner,
and they were asked to sleep.
And during slow-wave sleep, those high-amplitude, slow oscillations
I told you about,
the same structure was active again.
And the extent to which it was active
actually predicted how much better they got at navigating around the town
when they were tested again the next day.
Furthermore, the sleep spindles that I told you about
are thought to be a marker of this type of reactivation.
So not only is this experiment a nice example
of how reactivation happens during sleep and is linked to strengthening memories
but also that finger-tapping experiment -
this explains why the spindles of the motor cortex were greater
because, actually,
that people were probably reactivating those memories as well.
So, what has this got to do with sleep engineering?
Well, what's exciting about it is now that we know
reactivation during sleep is important for strengthening memories,
we've also learned how to manipulate it.
So we don't have to sit and wait for reactivation to happen spontaneously,
but instead, we can control it.
Let me show you how this works.
If I show you a cat (meow) in this part of the screen
and a dog (bark) in this part of the screen,
and then tonight, when you're asleep and you enter slow-wave sleep,
I'm watching,
and I play (meow).
Then the next day when I test you,
you'll be much more likely to remember where the cat was on the screen
than the dog.
And that's because that sound cue
will have triggered reactivation of the memory and strengthened it.
So this doesn't end with just simply strengthening memories.
It's been shown that if we trigger some kinds of problems
while people are asleep,
then they can be better at solving those the next day as well.
So reactivation can also help with association
and potentially with creativity and innovation as well.
But as we all know, we don't want to remember everything always.
So I'm sure some of you have had a traumatic experience
at some point in your life.
You may have been mugged,
you may have been in a car crash,
maybe other things that happened to you that you'd really -
you might not mind remembering the details,
but you really don't want to be as upset about it every time you remember it
as you were right after it happened.
We were interested in this
and how reactivation during sleep might help with it.
It turns out that if we show people upsetting pictures or videos
and then play them the associated sounds when they're in slow-wave sleep,
(Chattering)
(Gunshots)
(Screaming)
then ask them the next day how upsetting that was,
the things that have been replayed to them during slow-wave sleep
will be less upsetting.
So it looks as though triggering replay of memories
can actually help to disassociate the emotional response from them as well.
We live in a time when we are hyper-aware of our bodies.
We're all very aware of how important exercise is and how important diet is.
We have gadgets to measure every calorie that we take in
and every calorie that we expend.
We even have gadgets to measure our sleep.
But I'd like to finish here
by suggesting that we could be taking this to the next level.
Instead of just measuring our sleep,
we could be using the information that we now have about sleep
to manipulate it
in order to enhance things like reducing our aging,
improving aspects of our memory,
enhancing our creativity,
and also potentially controlling aspects of our emotional responses.
So, as a sleep scientist,
my hope is that in not too many years,
when your boss walks into your office
and gives you a very difficult problem to work on,
you'll feel like the most appropriate response to make
to show her you're taking this seriously
is to pull out a pillow
(Laughter)
and tell her you'll sleep on it.
Thank you very much.
(Applause)