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