Why Do We Dream
[Music]
[Applause]
several years ago my friend barbara told
me a dream she had had the night before
this is something of an occupational
hazard for me
for the past 25 years at harvard medical
school
i’ve made the study of sleep memory and
dreams
my life work but if i go to a party and
someone asks me what i do
i only mention sleep and memory because
if i mention
dreams the next seven words out of their
mouth without exception
are oh i had the most amazing
dream and they then proceeded to tell me
a totally boring dream
followed by the question what do you
think it means
i always give the same answer i shake my
head and i say you
are one sick cookie
then as their expression starts to
crumble i laugh and i say
actually i have no idea what your dream
means
and i’m not even sure it does have a
meaning
but barbara’s dream was different
in it she told me i was on the street
where stuart her fiance
lived and i was trying to find his
apartment
because i wanted to settle or not seeing
each other anymore
and i couldn’t remember why we weren’t
seeing each other
whenever i thought i was at his
apartment
it’d be somewhere else and i have to go
looking for him again
i kept wondering whatever happened to
stuart
in the seconds after waking up barbara
asked again
whatever happened to stuart and then she
remembered
two weeks earlier stewart had had a
massive heart attack in her living room
and fallen dead in front of her
barbara didn’t ask me what her dream
meant but she asked me what i think is
the second most common question
why did i have that dream
on one level the answer was clear
i knew that dreams had a preference for
including
recent emotional events which this
definitely had been
but at a deeper level i couldn’t tell
her why the brain’s algorithms
showed this preference for emotional
memories
and i had no idea what the brain was
actually
trying to accomplish despite what freud
had said 110 years
earlier dreams are not about playing out
our repressed desires
nor as alan hopson and bob mccarley had
suggested just 35 years earlier
our dream is just the product of the
random firing of neurons in our
brainstem
but what was the brain trying to do
i knew what it didn’t do it didn’t show
barbara the memory
of stuart’s collapse and it didn’t let
her know even that stewart was dead
all that had let her know was that she
wasn’t seeing stuart anymore
and then shown her that without stewart
she was lost it was
almost as if the brain wanted to see how
barbara the dreaming barber in the dream
how she would react to this situation
what she would do with the knowledge
that she was lost
without steward
and it turns out that is exactly
what the brain was trying to do
my daughter jessie when she was two
years old
received from her grandpa irv an amazing
present
a duck marionette he made it dance and
even
fly up kissing her on the cheek jesse
loved it when she went to bed that night
we had to hang ducky on the wall across
from her crib
later that night i heard jesse scream
i ran into her bedroom and found her
standing her crib up on her tiptoes arms
outstretched towards me
in terror as i picked her up
she spun around stared down into her
crib and screamed
there’s a duck in my bed clearly
while jessie slept her brain recalled
grandpa herb and the dancing duck
and identified it as an emotionally
significant event
but then did what turned it into a real
duck and plunked it down
in her crib what was thinking
well just that it didn’t really
understand why that duck was so
important to jesse just like barbara’s
brain
didn’t understand the ultimate
significance of stewart’s death
to her and so
both brains dreamed
not to deliver messages not to give
answers
but just to explore the significance of
these events
because that’s what brains do when they
dream
they sift through in neural networks
that encode
all of our memories all of our ideas
it’s use of 15 billion nerve cells
and the 125 trillion connections between
them
that’s a thousand times more connections
than there are stars in the milky way
and it goes through these looking for
memories even weekly related to these
events
searching for those that might help us
understand them better
they engage in what we call network
exploration
to understand possibilities or
next up for short why do we dream
because it’s the only mechanism our
brain has
for sorting through all the myriad
associations it discovers and deciding
which ones are potentially
of value are worth strengthening and
maintaining
it’s the same as when we’re awake my
wife debbie
comes to me and says what do you think
of taking the bowls and plates out of
that cabinet and
moving them over there and taking the
pasta and the spices and moving them
where the plates were
i don’t know so i imagine it first i
imagine the hassle
of taking everything out of the one
cabin and moving it to the other and
vice versa
but i also imagine grabbing a bowl
for breakfast which is now right next to
the cereal
i imagine cooking dinner and having the
spices near at hand
and i react i like the idea or i don’t
like the idea
and those feelings give me the answer to
her question
it’s the same when we’re dreaming
the brain creates an imagined world
out of the associations that it has
discovered
and plunks you down in the middle of it
forcing you to react to the ongoing
story
and it looks at those reactions to
determine whether the associations
that it has built into the story
are worth keeping and if they are
right then and there it strengthens the
physical connections
between the events of the day and the
new associations it has discovered
now when brains dream they have extra
tools extra tricks
at its disposal that help but find
weaker associations more creative ones
we can see these most clearly when we
look at the brain in rem sleep
when we have our most vivid emotional
bizarre dreams first your brain shuts
off
output from the hippocampus a region of
your brain required for the detailed
recall of recent memories
so you can’t replay actual memories in
your dreams
next it shuts off its release of the
neuromodulator noradrenaline
which leads to a bias for finding weaker
associations
it then almost completely shuts down
regions of your forebrain responsible
for logical reasoning
and impulse control regions that
otherwise might prevent these
unlikely dream scenarios from ever
getting imagined
and finally it cranks up your limbic
system
increasing the intensity of your
emotional responses
taken as a whole these tricks allow our
brains
to explore identify and strengthen
previously unnoticed associations
that can help us better understand both
what has happened to us
in the past and what might happen to us
in the future let me end with a dream of
my own
hopefully not a boring one
when jesse was five years old i was
hired as an assistant professor in the
department of physiology
the university of massachusetts medical
center
one of my responsibilities was to
co-teach
the introductory physiology course along
with its
lab component one lab
was notoriously known as the dog lab
when students arrived they found
anesthetized dogs
on benches and were assigned to one of
the dogs
where they would spend the next couple
of hours injecting drugs
monitoring heart rate monitoring blood
pressure
and doing other only slightly invasive
experiments on the dogs
but then they would get to the final
portion of the lab
where they had to take a small buzz saw
and cut through the rib cage
and open the chest so they could apply
drugs and do recordings directly from
the heart it was a gruesome process and
frankly i couldn’t cope with it i would
always turn my
group over to one of the other faculty
members to supervise them as they opened
the chest
the night after i first taught the lab i
had a dream
we had just cut open the chest of the
dog when i looked down
and saw not in horror
but in confusion over how it had
happened
that it was jesse and not a dog
and then as i watched the edges of the
incision came back together and healed
without any scar at all
when i woke up and told my wife she said
well that makes sense the lab
obviously brought up issues of mortality
and where are you most fearful
about mortality except for jesse
this made sense to me but it didn’t
match my own
gut feeling to me it seemed that the
dream was saying
if this is okay to do to a dog why isn’t
it okay
to do to jesse
well we now know that neither of these
was the meaning of the dream
my brain had identified the event as
extremely
emotional and had sought out
memories related to it
and found another small helpless
creature
jesse and then put them together in the
dream
to explore possibilities maybe finding
something about the fragility
or the sanctity of life
and that’s all my brain was doing
exploring
possibilities strengthening those
connections
and leaving that newly found association
available for my use
in the future that’s all brains do
when they dream years later my son
adam was born with a congenital heart
defect
and so at four months of age he
underwent open-heart surgery to patch a
hole
in his heart they cut through his chest
wall
repaired his heart and then sewed him
back together
today he’s a vibrant athletic pain in
the ass 16 year old
with almost no scar at all
it was so tempting to believe that my
dreaming brain
had looked forward into the future to
warn me of what was to come
but no i’m convinced that’s not what
happened it was in fact just one of
those coincidences that we all have that
are
so hard to shake especially
when they occur in a dream when we dream
our brain is in a unique
neurophysiological and neurochemical
state
that not only facilitates the discovery
of weak associations
but also biases that brain towards
finding significance importance in those
associations
an importance that carries over for at
least a few minutes
after we wake up giving us that sense
of great meaning
so now what’s next up i think we
finally know the function
of dreaming we know why we dream
the dreaming brain serves as a mechanism
to identify explore
and evaluate unexpected associations
within our memory systems that might
help us better understand what has
happened to us
and what is going to happen with us but
for
all that science has and will
discover about the meaning
and function of dreams
their magic their mystery their wonder
will remain thank you