How sound can hack your memory while you sleep

Can you cram for a test while you sleep? Our intrepid neuroscientists attempt to enhance memory by running experiments on subjects while they sleep. You'll be surprised by the results.

Greg Gage: Who wouldn't love
acing a geography exam,

remembering all the locations
of the countries on a map

or avoiding embarrassing situations
of suddenly forgetting the person's name

standing right in front of you.

It turns out that memory,
like other muscles in the body,

can be strengthened and enhanced.

But instead of practicing
with flash cards,

there may be an interesting way

that we can hack our memory
while we sleep.

(Music)

Why do we sleep?

This has been a question asked
since the early days of civilization.

And while we may not know
the exact answer,

there are a number of really
good theories about why we need it.

Sleep is when the brain transfers
short-term memories

experienced throughout the day

into long-term memories.

This process is called
memory consolidation,

and it's the memory consolidation theory
that has scientists wondering

if we can enhance
certain memories over others.

There was a paper recently
in the journal "Science"

by Ken Paller and his colleagues
at Northwestern

that seemed to show that this may be true,

and that piqued our curiosity.

Joud has been working
on a DIY version of this task

to see if we can improve memories
through the use of sound in sleep.

So Joud, how do you test if we can
improve our memories with sleep?

Joud Mar’i: We need a human subject.

[Step 1: Play a game]

We have a memory game
that we have on an iPad,

and then we make our subject
play this game

and remember the images
and where they appear on the screen.

GG: So this is like a memory game
you used to play as a child,

which picture was where.

And we tie each picture
with a sound that represents it.

JM: So, if you can see
a picture of a car, for example,

and you would hear the car engine.

(Car engine starting)

GG: Just before you go to sleep
we're going to test you.

We're going to see how well
you remember where the pictures are.

Every time you see the picture,
you're going to hear the sound.

And now comes the experiment.

You're going to go take a nap.

[Step 2: Take a nap]

And while you're sleeping,
we're going to be recording your EEG.

JM: And then we wait for them to go
into what's called the slow-wave sleep,

which is the deepest phase of your sleep
where it's really hard for you to wake up.

GG: OK, pause.

So, here's some information on sleep.

There are four stages:
we have lighter stages of sleep and REM,

but what we're interested in
is called slow-wave sleep.

And it gets its name
from the electrical signals

called Delta waves
that we record from the brain.

This is the part of sleep
where scientists believe

that memory consolidation can happen.

In this deep period of sleep,

we're going to do something
that you don't know we're going to do.

JM: Here's where the tricky part comes,
and we start playing our cues.

(Car engine starting)

GG: Do you play all the cues?

JM: No. We only want to play half of them
to see if there's a difference.

GG: So your hypothesis is

the one that they were listening to
while they're sleeping

they're going to do better at.

JM: Yes, exactly.

GG: When you wake back up
and play the game again,

do you do better or worse
than before a nap?

What we found is that if we played you
a cue during your sleep,

for example, a car --

You would remember
the position of that car

when you woke back up again.

But if we didn't play you the cue
during the sleep,

for example, a guitar,

you'd be less likely to remember
that guitar when you woke up.

The memories that were cued
they remembered better

than the ones they weren't,

even though they don't remember
hearing those sounds?

JM: Yes, we ask them.

GG: We know they're sleeping,
they can't hear it, they wake up,

they do better on those
than the ones you didn't play.

GG: That's amazing.
JM: It's like magic.

GG: Joud ran this experiment on 12 people
and the results were significant.

It's not that you remember things better;
it's that you forget them less.

I was a huge skeptic when I first heard
that you could do better at a memory test

just by playing sounds during sleep.

But we replicated these experiments.

The facts and memories we collect
throughout the day are very fragile,

and they are easily lost and forgotten.

But by reactivating them during sleep,
even without us being aware,

it seems like we could make them
more stable and less prone to forgetting.

That's pretty incredible.

Our brains are still active
even when we're not.

So if you're like me and a bit forgetful,

perhaps a solution is a pair
of headphones and a soft couch.