1
00:00:06,643 --> 00:00:08,412
In the third millenium BCE,

2
00:00:08,412 --> 00:00:13,806
Mesopotamian kings recorded and
interpreted their dreams on wax tablets.

3
00:00:13,806 --> 00:00:15,146
A thousand years later,

4
00:00:15,146 --> 00:00:17,248
Ancient Egyptians wrote a dream book

5
00:00:17,248 --> 00:00:20,654
listing over a hundred common dreams
and their meanings.

6
00:00:20,654 --> 00:00:21,863
And in the years since,

7
00:00:21,863 --> 00:00:25,650
we haven't paused in our quest
to understand why we dream.

8
00:00:25,650 --> 00:00:28,121
So, after a great deal
of scientific research,

9
00:00:28,121 --> 00:00:29,787
technological advancement,

10
00:00:29,787 --> 00:00:31,005
and persistence,

11
00:00:31,005 --> 00:00:36,443
we still don't have any definite answers,
but we have some interesting theories.

12
00:00:36,443 --> 00:00:40,937
We dream to fulfill our wishes.

13
00:00:40,937 --> 00:00:42,494
In the early 1900s,

14
00:00:42,494 --> 00:00:46,512
Sigmund Freud proposed that while all
of our dreams, including our nightmares,

15
00:00:46,512 --> 00:00:49,851
are a collection of images
from our daily conscious lives,

16
00:00:49,851 --> 00:00:51,901
they also have symbolic meanings,

17
00:00:51,901 --> 00:00:55,464
which relate to the fulfillment
of our subconscious wishes.

18
00:00:55,464 --> 00:00:59,154
Freud theorized that everything 
we remember when we wake up from a dream

19
00:00:59,154 --> 00:01:01,050
is a symbolic representation

20
00:01:01,050 --> 00:01:05,535
of our unconscious primitive thoughts,
urges, and desires.

21
00:01:05,535 --> 00:01:08,489
Freud believed that by analyzing
those remembered elements,

22
00:01:08,489 --> 00:01:12,182
the unconscious content would be revealed
to our conscious mind,

23
00:01:12,182 --> 00:01:14,747
and psychological issues stemming
from its repression

24
00:01:14,747 --> 00:01:17,615
could be addressed and resolved.

25
00:01:17,615 --> 00:01:20,789
We dream to remember.

26
00:01:20,789 --> 00:01:23,192
To increase performance 
on certain mental tasks,

27
00:01:23,192 --> 00:01:24,535
sleep is good,

28
00:01:24,535 --> 00:01:27,107
but dreaming while sleeping is better.

29
00:01:27,107 --> 00:01:28,781
In 2010, researchers found

30
00:01:28,781 --> 00:01:32,767
that subjects were much better 
at getting through a complex 3-D maze

31
00:01:32,767 --> 00:01:37,476
if they had napped and dreamed
of the maze prior to their second attempt.

32
00:01:37,476 --> 00:01:39,973
In fact, they were up to 
ten times better at it

33
00:01:39,973 --> 00:01:44,211
than those who only thought of the maze
while awake between attempts,

34
00:01:44,211 --> 00:01:48,739
and those who napped but did not dream
about the maze.

35
00:01:48,739 --> 00:01:51,269
Researchers theorize that certain
memory processes

36
00:01:51,269 --> 00:01:53,401
can happen only when we are asleep,

37
00:01:53,401 --> 00:01:58,202
and our dreams are a signal
that these processes are taking place.

38
00:01:58,202 --> 00:02:02,544
We dream to forget.

39
00:02:02,544 --> 00:02:05,053
There are about 10,000 trillion 
neural connections

40
00:02:05,053 --> 00:02:07,615
within the architecture of your brain.

41
00:02:07,615 --> 00:02:11,510
They are created by everything you think
and everything you do.

42
00:02:11,510 --> 00:02:15,869
A 1983 neurobiological theory of dreaming,
called reverse learning,

43
00:02:15,869 --> 00:02:19,490
holds that while sleeping,
and mainly during REM sleep cycles,

44
00:02:19,490 --> 00:02:22,765
your neocortex reviews 
these neural connections

45
00:02:22,765 --> 00:02:25,329
and dumps the unnecessary ones.

46
00:02:25,329 --> 00:02:27,095
Without this unlearning process,

47
00:02:27,095 --> 00:02:28,924
which results in your dreams,

48
00:02:28,924 --> 00:02:31,623
your brain could be overrun 
by useless connections

49
00:02:31,623 --> 00:02:34,962
and parasitic thoughts could disrupt
the necessary thinking

50
00:02:34,962 --> 00:02:37,303
you need to do while you're awake.

51
00:02:37,303 --> 00:02:42,815
We dream to keep our brains working.

52
00:02:42,815 --> 00:02:46,257
The continual activation theory proposes
that your dreams result

53
00:02:46,257 --> 00:02:51,551
from your brain's need to constantly
consolidate and create long-term memories

54
00:02:51,551 --> 00:02:53,294
in order to function properly.

55
00:02:53,294 --> 00:02:55,792
So when external input falls
below a certain level,

56
00:02:55,792 --> 00:02:57,331
like when you're asleep,

57
00:02:57,331 --> 00:02:58,914
your brain automatically triggers

58
00:02:58,914 --> 00:03:01,588
the generation of data 
from its memory storages,

59
00:03:01,588 --> 00:03:04,458
which appear to you in the form of
the thoughts and feelings

60
00:03:04,458 --> 00:03:06,848
you experience in your dreams.

61
00:03:06,848 --> 00:03:07,724
In other words,

62
00:03:07,724 --> 00:03:10,966
your dreams might be
a random screen saver your brain turns on

63
00:03:10,966 --> 00:03:14,200
so it doesn't completely shut down.

64
00:03:14,200 --> 00:03:18,145
We dream to rehearse.

65
00:03:18,145 --> 00:03:21,994
Dreams involving dangerous and threatening
situations are very common,

66
00:03:21,994 --> 00:03:24,072
and the primitive instinct 
rehearsal theory

67
00:03:24,072 --> 00:03:27,790
holds that the content of a dream
is significant to its purpose.

68
00:03:27,790 --> 00:03:31,650
Whether it's an anxiety-filled night of
being chased through the woods by a bear

69
00:03:31,650 --> 00:03:34,188
or fighting off a ninja in a dark alley,

70
00:03:34,188 --> 00:03:37,657
these dreams allow you to practice
your fight or flight instincts

71
00:03:37,657 --> 00:03:41,720
and keep them sharp and dependable
in case you'll need them in real life.

72
00:03:41,720 --> 00:03:43,947
But it doesn't always have 
to be unpleasant.

73
00:03:43,947 --> 00:03:46,388
For instance, dreams 
about your attractive neighbor

74
00:03:46,388 --> 00:03:50,571
could actually give your reproductive
instinct some practice, too.

75
00:03:50,571 --> 00:03:54,512
We dream to heal.

76
00:03:54,512 --> 00:03:57,786
Stress neurotransmitters in the brain
are much less active

77
00:03:57,786 --> 00:03:59,839
during the REM stage of sleep,

78
00:03:59,839 --> 00:04:02,428
even during dreams 
of traumatic experiences,

79
00:04:02,428 --> 00:04:04,174
leading some researchers to theorize

80
00:04:04,174 --> 00:04:08,632
that one purpose of dreaming is to take
the edge off painful experiences

81
00:04:08,632 --> 00:04:10,881
to allow for psychological healing.

82
00:04:10,881 --> 00:04:13,998
Reviewing traumatic events
in your dreams with less mental stress

83
00:04:13,998 --> 00:04:16,070
may grant you a clearer perspective

84
00:04:16,070 --> 00:04:20,140
and enhanced ability to process them
in psychologically healthy ways.

85
00:04:20,140 --> 00:04:25,279
People with certain mood disorders
and PTSD often have difficulty sleeping,

86
00:04:25,279 --> 00:04:28,199
leading some scientists to believe
that lack of dreaming

87
00:04:28,199 --> 00:04:32,689
may be a contributing factor
to their illnesses.

88
00:04:32,689 --> 00:04:37,364
We dream to solve problems.

89
00:04:37,364 --> 00:04:40,263
Unconstrained by reality
and the rules of conventional logic,

90
00:04:40,263 --> 00:04:43,269
in your dreams, your mind can create
limitless scenarios

91
00:04:43,269 --> 00:04:45,256
to help you grasp problems

92
00:04:45,256 --> 00:04:49,295
and formulate solutions
that you may not consider while awake.

93
00:04:49,295 --> 00:04:51,527
John Steinbeck called it 
the committee of sleep,

94
00:04:51,527 --> 00:04:53,024
and research has demonstrated

95
00:04:53,024 --> 00:04:56,612
the effectiveness of dreaming 
on problem solving.

96
00:04:56,612 --> 00:04:58,958
It's also how renowned chemist 
August Kekule

97
00:04:58,958 --> 00:05:01,879
discovered the structure 
of the benzene molecule,

98
00:05:01,879 --> 00:05:05,180
and it's the reason that sometimes 
the best solution for a problem

99
00:05:05,180 --> 00:05:06,920
is to sleep on it.

100
00:05:06,920 --> 00:05:10,293
And those are just a few of the more
prominent theories.

101
00:05:10,293 --> 00:05:13,856
As technology increases our capability
for understanding the brain,

102
00:05:13,856 --> 00:05:15,497
it's possible that one day

103
00:05:15,497 --> 00:05:18,059
we will discover 
the definitive reason for them.

104
00:05:18,059 --> 00:05:21,942
But until that time arrives,
we'll just have to keep on dreaming.