Whether you're cramming for an exam

or trying to learn
a new musical instrument

or even trying to perfect a new sport,

sleep may actually be
your secret memory weapon.

[Sleeping with Science]

Studies have actually told us
that sleep is critical for memory

in at least three different ways.

First, we know that you need
sleep before learning

to actually get your brain ready,

almost like a dry sponge,

ready to initially soak up
new information.

And without sleep, the memory
circuits within the brain

effectively become
waterlogged, as it were,

and we can't absorb new information.

We can't effectively lay down
those new memory traces.

But it's not only important
that you sleep before learning,

because we also know
that you need sleep after learning

to essentially hit the save button
on those new memories

so that we don't forget.

In fact, sleep will actually
future-proof that information

within the brain,

cementing those memories

into the architecture
of those neural networks.

And we've begun to discover

exactly how sleep achieves
this memory-consolidation benefit.

The first mechanism
is a file-transfer process.

And here, we can speak about
two different structures

within the brain.

The first is called the hippocampus

and the hippocampus
sits on the left and the right side

of your brain.

And you can think of the hippocampus

almost like the informational
inbox of your brain.

It's very good at receiving
new memory files

and holding onto them.

The second structure
that we can speak about

is called the cortex.

This wrinkled massive tissue
that sits on top of your brain.

And during deep sleep,

there is this file-transfer mechanism.

Think of the hippocampus like a USB stick

and your cortex like the hard drive.

And during the day, we're going around

and we're gathering lots of files,

but then during deep sleep at night,

because of that limited storage capacity,

we have to transfer those files
from the hippocampus

over to the hard drive
of the brain, the cortex.

And that's exactly one of the mechanisms

that deep sleep seems to provide.

But there's another mechanism
that we've become aware of

that helps cement
those memories into the brain.

And it's called replay.

Several years ago,

scientists were looking
at how rats learned

as they would run around a maze.

And they were recording the activity
in the memory centers of these rats.

And as the rat was running
around the maze,

different brain cells would code
different parts of the maze.

And so if you added a tone
to each one of the brain cells

what you would hear
as the rat was starting to learn the maze

was the signature of that memory.

So it would sound a little bit like ...

(Bouncy piano music)

It was this signature of learning
that we could hear.

But then they did something clever.

They kept listening to the brain
as these rats fell asleep,

and what they heard was remarkable.

The rat, as it was sleeping,

started to replay
that same memory signature.

But now it started to replay it
almost 10 times faster

than it was doing when it was awake.

So now instead you would start to hear ...

(Fast bouncy piano music)

That seems to be the second way

in which sleep can actually
strengthen these memories.

Sleep is actually replaying
and scoring those memories

into a new circuit within the brain,

strengthening that memory representation.

The final way in which sleep
is beneficial for memory

is integration and association.

In fact, we're now learning that sleep

is much more intelligent
than we ever imagined.

Sleep doesn't just simply
strengthen individual memories,

sleep will actually cleverly interconnect
new memories together.

And as a consequence,

you can wake up the next day

with a revised mind-wide
web of associations,

we can come up with solutions
to previously impenetrable problems.

And this is probably the reason

that you've never been told
to stay awake on a problem.

Instead, you're told
to sleep on a problem,

and that's exactly
what the science teaching us.