NEIL DEGRASSE TYSON: Hello. I'm Neil deGrasse Tyson, your host for NOVA scienceNOW.
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
NEIL DEGRASSE TYSON: But sometimes, she has a strange way of showing that affectionóespecially,
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
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
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
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 TetrisÆ...
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...
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
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
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
MIT researcher Matt Wilson says he can read rats' minds, including their dreams, with
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 wiresópainlessly implanted in the rat's brain, and held there by a kind of hatócarry
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
That's right, Wilson eavesdrops on his rats' dreams. And they aren't about cheese, they're
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
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
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
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
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.