Dreaming
is so basic to human existence, it’s astonishing we don’t understand it
better. It consumes years of our lives, and no other single activity
exerts such a powerful pull on our imaginations. Yet central as
dreaming is, we still have no idea why we dream. Freud saw dreams as
convoluted pathways toward fulfilling forbidden aggressive and sexual
wishes; frightening dreams were wishes in disguise—wishes so scary, he
believed, they had to transmute themselves into fear and masquerade as
nightmares.

Later came the idea that dreams
are the cognitive echoes of our efforts to work out conflicting
emotions. More recently, dreams have been viewed as mere
"epiphenomena"—excrescences of the brain with no function at all, the
mind’s attempt to make sense of random neural firing while the body
restores itself during sleep. As Harvard sleep researcher Allan Hobson
puts it, dreams are "the noise the brain makes while it’s doing its
homework."

"There’s nothing closer to a
consensus on the purpose and function of dreaming than there’s ever
been," says Deirdre Barrett, a Harvard psychologist and editor of the
forthcoming The New Science of Dreaming. Indeed, no theory has been able to reconcile the findings of various subdisciplines of dream science. Until now.

Finnish
psychologist Antti Revonsuo believes the marooned rats lost their
ability to defend themselves not because they were exhausted but
because they were robbed of their dreams. Dreams, he contends, are a
training ground in which animals and people alike go over the behaviors
that are key to their survival. Prevented from dreaming, the rats were
unable to rehearse their survival behaviors. In other words, they were
defenseless because they were out of practice.

Say
you’re in a fight and somebody wraps his arms around you from the
front, pinning your arms to your sides—a bear hug. Most people
reflexively stiffen their body. But this is actually the worst thing to
do; making your body rigid makes you easier to lift—and lets your
assailant pick you up and drop you on your head, or worse, haul you off
somewhere.

Better to bend your knees and
lower your center of gravity so you’re harder to lift. You’re then free
to punch your aggressor’s testicles, claw the skin on his back, kick
out his knee, stomp his foot, even bite his neck—unappetizing options,
but effective against even the biggest thug.

The
difference between the typical and optimal response could save your
life. But making such a reaction swift and automatic takes practice.
It’s the reason martial arts students drill their movements over and
over. Frequent rehearsal prepares them for that one decisive moment,
ensuring that their response in an actual life-or-death situation is
the one they practiced.

Dreams may do the
same thing. A dream researcher at the University of Turku, in Finland,
Revonsuo believes that dreams are a sort of nighttime theater in which
our brains screen realistic scenarios. This virtual reality simulates
emergency situations and provides an arena for safe training. As
Revonsuo puts it, "The primary function of negative dreams is rehearsal
for similar real events, so that threat recognition and avoidance
happens faster and more automatically in comparable real situations."

Faced
with actual life-or-death situations—traffic accidents, terrorist
attacks, street assaults—some people report entering a mode of calm,
rapid response, reacting automatically, almost without thinking.
Afterward, they often say the episode felt unreal, as if it were all a
dream. Threat simulation, Revonsuo believes, is why.

As
a grad student in psychology in the early 1990s, Revonsuo often had bad
dreams. What struck him the most was how lifelike they were. "I would
say to myself, in my dream, ‘Oh shit! I’ve dreamt of this before, but
now this is really happening!’ " he recalls.

"Credible
world analogs" are what cognitive psychologist David Foulkes calls
dreams. Although we tend to dwell on the bizarreness of dreams, most
dreams are quite mundane, Foulkes notes. You move around, talk, run,
interact with others, experience emotions, and feel the passage of
time, just as in everyday life.

When
Revonsuo began studying dreams, he asked his students to start keeping
logs of their own nocturnal escapades. He noticed something striking.
The dreams were filled with dangerous events, negative emotions,
monsters, chases, escapes, fights, and near-death experiences. The
dream world was a hellscape of danger, teeming with threatening events
far more sinister than in waking life.

These
weren’t the misfirings of diseased brains. Threat dreams were the norm,
accounting for a staggering two-thirds of all dreams. Revonsuo
discovered that we grossly underestimate the number of nightmares we
have. As it turns out, we have 300 to 1,000 threat dreams per year—one
to four per night. Just under half are aggressive encounters: physical
aggression such as fistfights, and nonphysical aggression such as
verbal arguments. The rest are about car crashes, falling and drowning,
missing a meeting or a test, being lost or trapped, and being naked in
public. The whole dream world seemed to have a negative bias: more
negative emotions than positive ones, more misfortune than good
fortune, more nightmares than fantasy.

In
the ancestral environment, Revonsuo reasoned, our dreams served to
protect us, teaching us how to respond when a wild animal was chasing
us or when we got lost in the forest. That was why the dream world was
so filled with peril: to simulate the potential threats and prepare us
to react quickly. But how could dreams help us select the optimal
response, given that dream recall is so fragile? After all, we remember
only a few of our dreams, and even those fade fast in the tumult of the
day.

Revonsuo believes that by providing
rehearsal, dreaming helps us recognize dangers more quickly and respond
more efficiently. We don’t need to be aware of this rehearsal, just as
you don’t have to recall exactly where you practiced your tennis serve
in order to reap the rewards.

The idea
that dreams are a dojo for perfecting waking activities fits well with
what is already known about practice. Mental rehearsal through
visualization improves skills, enhances learning, and changes the
brain, polishing performance in almost any domain, from sports to piano
playing.

The single most pervasive theme
in dreaming is that of being chased or attacked. Just as athletes in
training repeat parts of their performance, we may, in our nightmares,
be attacked and chased over and over again, not to solve a particular
problem but to actually practice efficient escape behavior.

Saber-toothed
tigers no longer stalk our villages, but Stone Age themes still rule
our dreams. "Nowadays, the evolutionary footprint is clearest in the
dreams of children, who often dream about being chased by monsters,
much the same way we were once chased by predators," says Revonsuo. As
life has evolved, so have the threats we rehearse. "You insert a modern
danger into that ancestral key and get a bizarre combination," says
Revonsuo. "We dream of being chased, shot, or robbed, getting into
traffic accidents, a burglar in our house, or perhaps smaller mishaps
such as losing our wallets—and that prepares us for our waking life."

The
dreaming brain, explains Revonsuo, scans emotional memories. When it
detects a memory trace with a strong negative emotion, it constructs a
nightmare around that theme. The more traumatic the event, the more
intense the nightmare. The brain’s system for detecting threats is
sensitive and flexible: Anything the brain tags with a strong negative
charge gets thrown into the threat bin and dredged up at night.

Sometimes
this system works well: Dreaming about a boy running in front of our
car better prepares us should that danger crop up in real life. But
sometimes the modern world throws the threat-detection mechanism out of
whack: Watching horror movies can trigger nightmares about vampires,
ghosts, aliens, or zombies. Such "nonsense nightmares" don’t rehearse
any useful threats; they’re like an allergic reaction, says Revonsuo.
Just as our immune system can mistake pollen for a pathogen and mount a
defensive campaign, the threat-detection system misperceives horror
movies and deploys its defenses by generating a nightmare.

In
the jungles of the amazon lives a tribe called the Mehinaku. The
Mehinaku lead the traditional life of hunter-gatherers. They spend
their days fishing and gathering roots. Since they believe that dreams
predict the future, they are scrupulous about remembering them and
sharing them with others. That makes them perfect for an ethnographic
study of dreams. In 1981, anthropologist Thomas Gregor surveyed their
dreams and analyzed the content.

As it turns
out, the Mehinaku dream profusely about the dangers in their everyday
lives: being attacked by wild pigs; chased by jaguars; bitten by
snakes; stung by wasps, ants, or bees—all potentially lethal. "Their
dreams simulate over and over again what to do and how to do it quickly
when they spot these animals in the wild," reports Revonsuo. Across a
tribesman’s lifespan, a single failure to react efficiently could be
fatal. If threat simulation even marginally increases the likelihood
that such fatal failures won’t occur, it would prove adaptive.

If
the threat-simulation theory is correct, dreams should focus on the
self, and when confronted with a threat, the dream self should react
realistically to ensure its own survival and that of its loved ones.
And so it is. We are the heroes of our own dreams. We don’t dream about
other people’s adventures or about fictional superheroes battling
monsters. We dream about ourselves.

If
dreams evolved to simulate the threats in our environment, then being
exposed to more dangers in real life should activate the nightmare
function, overstuffing our dreams with threats. This is precisely what
happens. Even a single exposure to a life-threatening situation can
plunge a person into an inferno of post-traumatic nightmares, dreams in
which the threatening event—the attack, the rape, the war—is repeated
over and over in every possible variation.

Studies
of traumatized Iraqi and Palestinian children who grew up in extremely
violent environments, some of whom witnessed their parents’ deaths,
show that their dreams are phantasmagoric carnivals of threatening
events. People who watched more television on September 11, 2001, and
saw threatening images were more likely to dream about the events of
that day; people who merely talked about it with others were less
likely to dream about it.

Traumatic dreams
do seem to rehearse relevant threats. Just four weeks into the first
Gulf War, as Scud missiles were raining down on Tel Aviv and Haifa, the
war was already encroaching on the dreams of Israeli college students,
according to a study. The most prominent topic: gas masks.

But
not all our dreams contain threats. That’s not surprising, says
Revonuso. There’s no reason a biological system has to express its
function at all times. Many bodily systems spring into action only in
critical situations. Take sperm cells. The average man ejaculates over
100 million sperm at a time, yet over the course of his life, only a
few will ever accomplish their biological mission of fertilizing an
egg. Every day, millions of sperm are wasted—and while this may, as
Monty Python sings, make God quite irate, it doesn’t mean that sperm
cells have some function other than fertilizing eggs and competing with
other sperm.

Intriguing
as Revonsuo’s theory is, not everyone is sold on the idea that dreams
are primarily a theater of threat rehearsal. Dream researchers have
known for centuries that dreaming helps problem solving, for
example—but they still do not know why.

Some
researchers argue that dreams are designed specifically to help us come
up with creative solutions. But if that’s the case, it’s infuriatingly
inconsistent—and complicated by the fact that we rarely remember our
dreams.

Those who awake with brilliant
solutions to scientific or artistic problems are the exception. German
chemist Friedrich August Kekulé struggled to find the molecular
structure of benzene until he dreamed about a snake devouring its own
tail and realized benzene was a closed circle—a ring. The self-taught
Indian mathematician Srinivasa Ramanujan came up with every one of his
proofs in dreams. Paul McCartney dreamed "Yesterday," woke up, and
wrote it down.

Problem solving may be a
side effect of the simulation system. The mere fact of running
scenarios over and over may inevitably generate new solutions. That’s
why when we have an important decision to make, we like to "sleep on
it" first, why, according to a study by University of Maryland
psychologist Clara Hill, couples who dream about their relationship are
more likely to resolve their conflicts than couples who don’t.

It’s
also known that we get better at tasks just by dreaming about them.
Robert Stickgold, a sleep researcher at Harvard Medical School, has
found that if you time people as they tap out the sequence 4-1-3-2-4
with their fingers, then ask them to do it again later that day, they
are no better.

But let them sleep in
between and their performance improves—literally overnight. The
implication seems obvious: Sleep provides practice. People given
brainteasers before bed dream about the answers. Math students are all
too familiar with dreams about algebra problems. Anyone who’s ever
played too much Tetris knows you can start having Tetris dreams.

Stickgold
holds that dreaming is much more complex than rehearsal. He points, for
example, to the ability of sleep to allow us to integrate and
consolidate knowledge. During sleep, our brains are making sense of the
world, discovering new associations among existing memories, looking
for patterns, formulating rules. "That’s how we create meaning," says
Stickgold. "Our brain puts things together."

Dreams
do have a certain edge over conscious thought. Neuroimaging work has
shown a distinct pattern of activation and inhibition in the dreaming
brain. Visual and emotional centers are abnormally activated, while
censoring mechanisms are deactivated. When we try to visualize during
the day, imagery is thin and insubstantial, less real than the real
world. But studies suggest that vivid hallucinations during dreaming
rival the clarity and detail of vision itself.

"Dreaming
is a sensitive system that tries to pay much attention to the
threatening cues in our environment," Revonsuo concludes. "Their
function is to protect and prepare us."

"Yes,"
says Harvard’s Barrett, "dreams are worrying about disasters. But
they’re also planning for nice things and they’re fantasizing and
they’re problem solving."

She contends that
the purpose of dreaming is "as broad as all waking thought. That’s why
I say dreams are really just thinking in a different biochemical state."

Via Psychology Today