[MUSIC PLAYING]
MATTHEW WALKER: Thank you.
Well, it's a delight and privilege to be here.
And I would like to start with testicles.
Men who sleep five hours a night have
significantly smaller testicles than those
who sleep eight hours or more.
In addition, men who routinely sleep five to six hours a night
will have a level of testosterone,
which is that of someone 10 years their senior.
So a lack of sleep ages you by a decade
in terms of that aspect, that critical aspect of wellness
and virility.
And we see equivalent impairments
in female reproductive health caused by a lack of sleep.
This is the best news that I have for you today.
From this point forward, it's only going to get worse.
Rather than tell you about the wonderfully good things that
happen when you get sleep, I'm going
to tell you about the alarmingly bad things that
happen when you don't get enough, both for the brain
and for the body.
Let me start with the brain and the functions of learning
and memory.
What we've discovered over the past 10 or so years
is that you need sleep after learning to essentially hit
the save button on those new memories
so that you don't forget.
So sleep essentially future-proofs
those facts within the brain.
But recently we've discovered that you not only
need sleep after learning, you also
need sleep before learning.
But now to actually prepare your brain,
and almost like a dry sponge ready to initially soak up
new information.
And without sleep, the memory circuits of the brain
effectively become waterlogged, as it were,
and you can't absorb new information.
So here in this study we decided to test the hypothesis
that pulling the all-nighter was a good idea.
How do you do that?
Well, we took a group of healthy adults
and we assigned them to one of two experimental conditions,
a sleep group and a sleep-deprivation group.
Now the sleep group, they're going
to get a full eight hours of shuteye.
But the deprivation group we're going
to keep them awake in the laboratory
under full supervision.
There's no naps, there's no caffeine.
It's miserable for everyone included, us as well.
And then the next day we're going
to place those participants inside an MRI scanner.
And we're going to have them try and learn
a whole list of new facts as we're taking snapshots
of brain activity.
And then we're going to test them
to see how effective that learning has been.
And that's what you're looking at here on the vertical axis,
the amount of learning.
So the higher up you are, the more that you learned.
And when you put those two groups head to head,
what you find is a quite significant 40% deficit
in the ability of the brain to make
new memories without sleep.
And I think this should be frightening
considering what we know is happening
to sleep in our education populations right now.
Just to frame this in context, it
would be the difference between acing an exam
and failing it miserably.
And we've gone on to discover what
goes wrong within your brain to produce these types of learning
disabilities.
There is a structure on the left and the right side
of your brain called the hippocampus.
And you can see it here in these sort of orange-yellow colors.
Think of the hippocampus like the informational inbox
of your brain.
It's very good at receiving new memory files
and holding onto them.
And when we looked at this structure
in those people who'd had a full night of sleep here in green,
we saw lots of healthy learning-related activity.
Yet in those people who were sleep deprived,
we actually couldn't find any significant signal whatsoever.
It's almost as though sleep deprivation had
shut down the memory inbox, and any new incoming files,
they were just being bounced.
You couldn't effectively commit new experiences to memory.
AUDIENCE: Thank you so much for the talk.
It was actually very informative.
I have two questions for you.
Number one, I have a five-year-old
and then there's myself.
How much sleep should we be getting?
And number two, is there any disadvantage of oversleeping?
So let's say if I sleep 10 or 15 hours in a day,
is there any disadvantage to that?
MATTHEW WALKER: That's a great question.
So first thing recommendations for sleep.
You can find them on the National Sleep Foundation
website for all ages.
For the average adult, the recommendation
World Health Organization eight hours, range seven to nine.
Once human beings, the average human being,
gets below seven hours of sleep, we
can measure objective impairments.
So people who say, I can survive on six hours of sleep, there's
a problem with that which is this.
Your subjective sense of how well
you think you're doing without sufficient sleep
is a miserable predictor of objectively
how you're doing without sufficient sleep.
So it's probably a little bit like a drunk driver at a bar.
They've had seven shots.
They pick up their car keys and they say, I'm fine to drive.
And your response is, no, I know that you
think you're fine to drive, but trust me,
objectively you're not.
The same is true for a lack of sleep.
Your second question is fascinating.
Can I sleep too much?
Well, there are anecdotes of something called a sleep
hangover, where you sort of oversleep
and then you feel worse almost.
When you oversleep, it usually means
that you're trying to sleep off a debt that you've
lumbered yourself with.
So if you could sleep past your alarm, if it didn't go off,
then you're under slept, because it's physiologically impossible
to sleep too much if you're healthy.
AUDIENCE: Thank you for the great talk.
Do you also have any information on how quickly people recover
after they switch from short sleep periods
to more normal sleep periods?
Because you only mentioned what happens with the DST change,
when we sleep one hour more, things get better
in terms of cardiac problems.
But is it quick, the recovery as well,
as quick as the downhill movement?
MATTHEW WALKER: Yeah, it's a great question.
So different aspects of your brain and your body
seem to come back online to a status of health
with recovery sleep.
And those temporal profiles are different based on--
Even within the immune system, for example, some components
take longer to come back online than others.
What I would note, however, is that you can never
get back all that you've lost.
This is another one of those myths with sleep.
So sleep is not like the bank.
You cannot accumulate a debt and then pay it off at a later
point in time, which is what most of modern society does.
Chronic short sleep during the week,
then you binge at the weekend, it's what I call sleep bulimia.
It's what is otherwise known as social jet lag.
If I were to take you and deprive you of sleep for one
single night, eight hours of lost sleep,
and then I give you all of the sleep
that you want for however many nights
and we keep recording you, your brain
never recovers all of that lost eight hours.
It will try to get back some of it.
It will never get back all of it.
Thank you very much indeed.
[APPLAUSE]
Thank you.
Thank you so much.
Thank you.