Name: Sleep
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<div class="rich-text">(This video is no longer available for streaming.) We spend about one-third of our lives sleeping. Why? Believe it or not, scientists don't know for sure. But evidence is building that sleep may play a crucial role in strengthening memories and facilitating learning, not just in humans but in most animals.
NOVA scienceNOW visits research labs at the University of Pennsylvania and MIT, where scientists are peering into the brains of dozing flies and rats to understand the connection between sleep and memory. At Harvard Medical School, host Neil deGrasse Tyson tests his powers of learning on a virtual ski machine and a speed typing exercise, and then catches some z's. He discovers that it's not practice that makes perfect, but practice plus a good night's sleep.
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Why do we need sleep? Part of the answer may be to strengthen memories.

<div class="rich-text">Why do we need sleep? Part of the answer may be to strengthen memories.</div>

Sleep

Body & Brain

<div class="rich-text"><h3>
 SLEEP
</h3>

 PBS Airdate: July 10, 2007



 NEIL
DEGRASSE TYSON:
 
 Hello. I'm
Neil deGrasse Tyson, your host for
 <cite>
 NOVA scienceNOW
 </cite>
 .


 We
all know that dreams can be, dreams can be a little weird, sometimes filled
with bizarre events that would never happen in real life. Nobody really knows
why we dream. In fact, nobody really knows why we sleep.


 Here
are some folks who are trying to figure it out.


 Amita
Sehgal likes her flies, fruit flies, to be precise.



 AMITA
SEHGAL
 
 (University of Pennsylvania and
Howard Hughes Medical Institute)
 
 :
 
 I do have a genuine affection for them.



 NEIL
DEGRASSE TYSON:
 
 But sometimes, she
has a strange way of showing that affection—especially, when she puts
them into this thing.



 AMITA
SEHGAL:
 
 We use
this piece of equipment we call "The Deprivator."



 NEIL
DEGRASSE TYSON:
 
 The Deprivator?
It's like riding a roller coaster during an earthquake.


 What's
interesting to Sehgal is what the flies do after spending a whole night in
here. The flies on the left were undisturbed last night, and they look fine.
But the flies on the right, they were jostled all night long in the Deprivator.
Now, some of them look dead, but they're not. According to Sehgal,
they're catching up on lost sleep.



 AMITA
SEHGAL:
 
 If we keep
flies awake at night, they need to make up for the sleep they have lost, and so
will sleep in the morning, at a time when they're normally active.



 NEIL
DEGRASSE TYSON:
 
 But why would flies
need to sleep? Could it be for the same reason we need to sleep? Maybe. But if
you ask an expert what exactly that reason is...



 MATTHEW
P. WALKER
 
 (Harvard Medical School)
 
 :
 
 We actually know very little about what sleep is
doing for the brain.



 AMITA
SEHGAL:
 
 We spend a
third of our lives sleeping. If you don't sleep, you die.



 MATT
WILSON:
 
 Sleep
is an enigma. What is its purpose? That's something that we do not
understand.



 NEIL
DEGRASSE TYSON:
 
 Looks like a waste
of time. But then why would so many creatures do it?



 MATT
WILSON:
 
 Sleep
is something that, the more we look at it, the more we see that it is
fundamental. It's fundamental to essentially all organisms.



 NEIL
DEGRASSE TYSON:
 
 Including, it
seems, organisms like fruit flies. When they're not being knocked around
all night, Amita Sehgal's flies follow a pretty familiar schedule.



 AMITA
SEHGAL:
 
 They're
active during the day and they sleep at night, for the most part, although
there is an afternoon siesta as well, especially in males.



 NEIL
DEGRASSE TYSON:
 
 Trying to pinpoint
the reason for a fly to snooze up to 12 hours a night, Sehgal's lab
studies the fruit fly's brain.



 AMITA
SEHGAL:
 
 What we
were doing was trying to figure out which part of the fly brain was important
for sleep.



 NEIL
DEGRASSE TYSON:
 
 Sehgal's
experiments pointed to the mushroom body, a part of the brain found in
creatures like insects and spiders, but not in humans. Biologists have known
about the mushroom body for years, but they associated it, not with sleep, but
with something else entirely, an insect's memory.



 AMITA
SEHGAL:
 
 There is,
then, this structure in the fly brain, which we already knew was required for
memory, and we now find that it controls sleep.



 NEIL
DEGRASSE TYSON:
 
 The finding's
intriguing because, for a long time now, sleep researchers have been debating a
possible connection between sleep and memory.


 Bob
Stickgold has been looking into this possibility, sometimes in unconventional
ways. For him, video games are research tools that can help reveal how our
brains learn.



 ROBERT
STICKGOLD:
 
 Do you remember when you first
started playing Tetris
 
 ®
 
 ...



 NEIL
DEGRASSE TYSON:
 
 Oh, yeah.



 ROBERT
STICKGOLD:
 
 ...that you went to bed at
night, and you lay in bed, and you closed your eyes, and you saw little Tetris
pieces floating around in front of your eyes?



 NEIL
DEGRASSE TYSON:
 
 How did you know
that? How did you know that...



 ROBERT
STICKGOLD:
 
 Because...



 NEIL
DEGRASSE TYSON:
 
 ...I dreamed
Tetris shapes?



 ROBERT
STICKGOLD:
 
 ...because everybody does.



 NEIL
DEGRASSE TYSON:
 
 After taking a few
rides on a ski machine, Stickgold's research subjects fall asleep, and
then he promptly wakes them up.



 ROBERT
STICKGOLD:
 
 If we wake you up just two or
three minutes after you fall asleep and ask you, "Neil, what's
going through your mind?" You'll say, "Seeing those suckers
somersaulting down when I crash."



 NEIL
DEGRASSE TYSON:
 
 And why would I
dream of this embarrassing moment?


 Stickgold
is convinced that while you sleep, your brain is reviewing what you've
learned and strengthening your memories.



 ROBERT
STICKGOLD:
 
 The brain is being modified
while we sleep, so that when we wake up in the morning, in some way, we have a
different brain. And it's a brain that functions better.



 NEIL
DEGRASSE TYSON:
 
 At least it seems
to function better on some kinds of memory tasks. Recent studies show that
after a single night's sleep, sometimes even after a nap, we can do a
better job recognizing visual patterns and even solving some math puzzles.



 MATTHEW
WALKER:
 
 What we're going to have you
do is try and type out a short, five-digit sequence.



 NEIL
DEGRASSE TYSON:
 
 I saw it first hand
when I took a simple typing test, typing a string of five numbers over and over
again as fast as I could.


 After
a night's sleep, I could suddenly type the numbers faster and more
accurately. And research backs this up. Most people improved their typing by
about 20 percent after sleep.



 MATTHEW
WALKER:
 
 Practice doesn't make
perfect. It seems to be practice with a night of sleep that makes perfect.
Sleep is enhancing that memory so that when you come back the next day
you're even better than where you were the day before.



 NEIL
DEGRASSE TYSON:
 
 But exactly how
could sleep enhance your memory? We don't know. But possible clues have
been showing up, not just in the brains of flies, but in the dreams of rats.


 MIT
researcher Matt Wilson says he can read rats' minds, including their
dreams, with tiny electric probes.



 MATT
WILSON:
 
 What
it means is that we're able to, at any time, plug in our electronics,
and...



 NEIL
DEGRASSE TYSON:
 
 Figure out what
they're thinking.



 MATT
WILSON:
 
 ...read
their, read their mind.



 NEIL
DEGRASSE TYSON:
 
 Wilson's
mind-readers are actually thin wires, about a tenth of the width of a human
hair, that pick up the electrical signals among dozens of brain cells.


 The
wires—painlessly implanted in the rat's brain, and held there by a
kind of hat—carry the signals right into Wilson's computers.


 That
information comes up back through these connectors into your computer, and
you're sitting there watching a map of the thoughts of this rat?



 MATT
WILSON:
 
 Exactly.
That's exactly right.



 NEIL
DEGRASSE TYSON:
 
 It's
remarkable.


 Wilson
is most interested in mapping the rat's thoughts in a part of its brain
called the hippocampus. Like the fruit fly's mushroom body, the
hippocampus of a rat or a human plays an important role in memory, including
our sense of space and location.


 Wilson
uses a specially designed rat maze. If the rat follows the right route,
he's rewarded with some chocolate syrup. And as he moves through each
different spot in the maze in search of his goal, a unique pattern of cells
fires in his brain.



 MATT
WILSON:
 
 So
we can tell where the animal is, simply based upon which cells in the
hippocampus are active. That pattern will be unique for a given location in a
given environment.



 NEIL
DEGRASSE TYSON:
 
 What's
amazing is that the same patterns turn up again, even after the rat drifts off
to sleep.


 That's
right, Wilson eavesdrops on his rats' dreams. And they aren't about
cheese, they're about running the maze.



 MATT
WILSON:
 
 So
when the animals would go to sleep, we would see these patterns of brain
activity that were expressed while the animals were running on the maze, being
replayed, in the same sequence, the same order in which they had been
experienced.



 NEIL
DEGRASSE TYSON:
 
 But the replay
wasn't exactly the same as when the rat ran the maze. Sometimes it was
like an extreme fast-forward; quick flashes of the experience.



 MATT
WILSON:
 
 Now,
at the time, you never know what is going to be important and what is not
important. So you may re-evaluate or edit those memories to identify the things
that were important.



 NEIL
DEGRASSE TYSON:
 
 And this fragmented
replay wasn't just happening in the hippocampus. Wilson also detected it
in the visual cortex, meaning the rats were likely seeing the maze in their
sleep.


 What's
more, the visual cortex is part of the larger neocortex, which, in humans, is
responsible for, among other things, long-term memory.



 MATTHEW
WALKER:
 
 The hippocampus is replaying the
events of the day. The hippocampus is almost, sort of, reactivating the
memories at night and playing them out to the neocortex. It's almost as
though the hippocampus is having a therapy session with the, with the
neocortex. And it's almost saying, "Okay, here's what we
learned during the day."



 MATT
WILSON:
 
 What
are rats and what are people doing during sleep? They are processing memory.
They are replaying memory. Now, we could ask, "Is this about
learning?" And I believe that's exactly what it is about, that
animals are, and humans are trying to learn from past experience.



 NEIL
DEGRASSE TYSON:
 
 So, the idea here
is that the sleeping brain might be reviewing and strengthening new memories it
wants to hold on to for the long-term. And it might identify certain goals we
want to work towards. Some believe the sleeping brain could lead us to real
insights.



 ROBERT
STICKGOLD:
 
 We all know about
"sleeping on a problem." And sleeping on a problem is when you have
a lot of new information and don't know what to do with it, and you
can't decide how to interpret it. And so you say, "Let me sleep on
it." And, with remarkable success rates, you can wake up the next morning
and have an answer to a problem that you couldn't find the answer to the
night before. And that's all about processing information, processing
memories in the brain.



 NEIL
DEGRASSE TYSON:
 
 So could it be that
sleeping on it isn't just an old saying but a biological process that
consolidates and organizes important information?



 MATT
WILSON:
 
 These
are pretty big concepts. And they certainly are controversial. The function of
sleep, as it relates to learning and memory, that's something that, at
this point, remains speculation. We're making a leap.



 NEIL
DEGRASSE TYSON:
 
 Not everybody is
leaping into bed with this idea. And researchers have a long way to go before
they know what sleep is really doing for our brains. But if the speculation
turns out to be true, then you'd have to wonder, "What is our 24/7
culture doing to our ability to think straight?"



 MATTHEW
WALKER:
 
 Sleep is not just something that
we can choose to sort of dabble in every now and again. It's not a
luxury; it's a biological necessity.



 MATT
WILSON:
 
 My
sense is that disruption of sleep is much deeper than simply, you know, robbing
us of rest. My guess would be that we lose the opportunity to gain
understanding, a deep understanding of our past experience, that what we
sacrifice, in a sense, is wisdom.
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