WEBVTT

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In the third millenium BCE,

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Mesopotamian kings recorded and
interpreted their dreams on wax tablets.

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A thousand years later,

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Ancient Egyptians wrote a dream book

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listing over a hundred common dreams
and their meanings.

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And in the years since,

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we haven't paused in our quest
to understand why we dream.

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So, after a great deal
of scientific research,

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technological advancement,

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and persistence,

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we still don't have any definite answers,
but we have some interesting theories.

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We dream to fulfill our wishes.

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In the early 1900s,

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Sigmund Freud proposed that while all
of our dreams, including our nightmares,

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are a collection of images
from our daily conscious lives,

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they also have symbolic meanings,

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which relate to the fulfillment
of our subconscious wishes.

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Freud theorized that everything 
we remember when we wake up from a dream

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is a symbolic representation

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of our unconscious primitive thoughts,
urges, and desires.

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Freud believed that by analyzing
those remembered elements,

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the unconscious content would be revealed
to our conscious mind,

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and psychological issues stemming
from its repression

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could be addressed and resolved.

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We dream to remember.

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To increase performance 
on certain mental tasks,

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sleep is good,

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but dreaming while sleeping is better.

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In 2010, researchers found

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that subjects were much better 
at getting through a complex 3-D maze

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if they had napped and dreamed
of the maze prior to their second attempt.

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In fact, they were up to 
ten times better at it

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than those who only thought of the maze
while awake between attempts,

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and those who napped but did not dream
about the maze.

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Researchers theorize that certain
memory processes

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can happen only when we are asleep,

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and our dreams are a signal
that these processes are taking place.

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We dream to forget.

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There are about 10,000 trillion 
neural connections

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within the architecture of your brain.

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They are created by everything you think
and everything you do.

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A 1983 neurobiological theory of dreaming,
called reverse learning,

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holds that while sleeping,
and mainly during REM sleep cycles,

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your neocortex reviews 
these neural connections

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and dumps the unnecessary ones.

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Without this unlearning process,

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which results in your dreams,

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your brain could be overrun 
by useless connections

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and parasitic thoughts could disrupt
the necessary thinking

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you need to do while you're awake.

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We dream to keep our brains working.

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The continual activation theory proposes
that your dreams result

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from your brain's need to constantly
consolidate and create long-term memories

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in order to function properly.

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So when external input falls
below a certain level,

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like when you're asleep,

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your brain automatically triggers

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the generation of data 
from its memory storages,

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which appear to you in the form of
the thoughts and feelings

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you experience in your dreams.

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In other words,

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your dreams might be
a random screen saver your brain turns on

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so it doesn't completely shut down.

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We dream to rehearse.

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Dreams involving dangerous and threatening
situations are very common,

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and the primitive instinct 
rehearsal theory

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holds that the content of a dream
is significant to its purpose.

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Whether it's an anxiety-filled night of
being chased through the woods by a bear

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or fighting off a ninja in a dark alley,

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these dreams allow you to practice
your fight or flight instincts

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and keep them sharp and dependable
in case you'll need them in real life.

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But it doesn't always have 
to be unpleasant.

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For instance, dreams 
about your attractive neighbor

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could actually give your reproductive
instinct some practice, too.

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We dream to heal.

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Stress neurotransmitters in the brain
are much less active

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during the REM stage of sleep,

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even during dreams 
of traumatic experiences,

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leading some researchers to theorize

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that one purpose of dreaming is to take
the edge off painful experiences

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to allow for psychological healing.

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Reviewing traumatic events
in your dreams with less mental stress

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may grant you a clearer perspective

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and enhanced ability to process them
in psychologically healthy ways.

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People with certain mood disorders
and PTSD often have difficulty sleeping,

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leading some scientists to believe
that lack of dreaming

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may be a contributing factor
to their illnesses.

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We dream to solve problems.

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Unconstrained by reality
and the rules of conventional logic,

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in your dreams, your mind can create
limitless scenarios

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to help you grasp problems

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and formulate solutions
that you may not consider while awake.

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John Steinbeck called it 
the committee of sleep,

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and research has demonstrated

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the effectiveness of dreaming 
on problem solving.

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It's also how renowned chemist 
August Kekule

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discovered the structure 
of the benzene molecule,

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and it's the reason that sometimes 
the best solution for a problem

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is to sleep on it.

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And those are just a few of the more
prominent theories.

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As technology increases our capability
for understanding the brain,

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it's possible that one day

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we will discover 
the definitive reason for them.

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But until that time arrives,
we'll just have to keep on dreaming.