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Whether you're cramming for an exam

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or trying to learn
a new musical instrument

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or even trying to perfect a new sport,

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sleep may actually be
your secret memory weapon.

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[Sleeping with Science]

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Studies have actually told us
that sleep is critical for memory

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in at least three different ways.

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First, we know that you need
sleep before learning

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to actually get your brain ready,

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almost like a dry sponge,

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ready to initially soak up
new information.

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And without sleep, the memory
circuits within the brain

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effectively become
waterlogged, as it were,

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and we can't absorb new information.

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

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

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because we also know
that you need sleep after learning

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to essentially hit the save button
on those new memories

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so that we don't forget.

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In fact, sleep will actually
future-proof that information

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within the brain,

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cementing those memories

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into the architecture
of those neural networks.

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And we've begun to discover

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exactly how sleep achieves
this memory-consolidation benefit.

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The first mechanism
is a file-transfer process.

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And here, we can speak about
two different structures

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within the brain.

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The first is called the hippocampus

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and the hippocampus
sits on the left and the right side

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of your brain.

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And you can think of the hippocampus

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almost like the informational
inbox of your brain.

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It's very good at receiving
new memory files

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and holding onto them.

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The second structure
that we can speak about

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is called the cortex.

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

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And during deep sleep,

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there is this file-transfer mechanism.

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Think of the hippocampus like a USB stick

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and your cortex like the hard drive.

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And during the day, we're going around

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and we're gathering lots of files,

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but then during deep sleep at night,

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because of that limited storage capacity,

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we have to transfer those files
from the hippocampus

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

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And that's exactly one of the mechanisms

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that deep sleep seems to provide.

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

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that helps cement
those memories into the brain.

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And it's called replay.

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Several years ago,

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scientists were looking
at how rats learned

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as they would run around a maze.

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

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And as the rat was running
around the maze,

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different brain cells would code
different parts of the maze.

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

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

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was the signature of that memory.

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So it would sound a little bit like ...

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(Bouncy piano music)

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It was this signature of learning
that we could hear.

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But then they did something clever.

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

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and what they heard was remarkable.

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The rat, as it was sleeping,

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started to replay
that same memory signature.

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But now it started to replay it
almost 10 times faster

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than it was doing when it was awake.

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So now instead you would start to hear ...

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(Fast bouncy piano music)

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That seems to be the second way

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in which sleep can actually
strengthen these memories.

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Sleep is actually replaying
and scoring those memories

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into a new circuit within the brain,

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strengthening that memory representation.

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The final way in which sleep
is beneficial for memory

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is integration and association.

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In fact, we're now learning that sleep

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is much more intelligent
than we ever imagined.

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Sleep doesn't just simply
strengthen individual memories,

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sleep will actually cleverly interconnect
new memories together.

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And as a consequence,

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you can wake up the next day

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with a revised mind-wide
web of associations,

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we can come up with solutions
to previously impenetrable problems.

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And this is probably the reason

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

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

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and that's exactly
what the science teaching us.