imagine you’re walking up a flight of
stairs you slip and you fall and you’re
trying to catch your fall with your arm
only to realize your arm isn’t really
there it’s an illusion
that happened to a patient that was
talking to first study he had lost his
arm years ago in an accident but still
everyday all the time it fell to him as
if the arm was still there so what we
call a phantom limb now as he was
falling you would think that his brain
would alert him to the fact that
something is wrong and would tell him
you know do something else this isn’t
working but instead his brain tried to
maintain this idea of an phantom arm and
try to reconcile it with reality and so
he had this very clear image in his mind
off his arm going through the stairs as
if they were water and he fell flat on
his face these phantom limbs the feeling
that a limb is still there they’re
fairly common after amputation but still
not everybody feels them a lot of the
people who do report them as being very
painful we’ve known about this
phenomenon for quite some time the first
public figure to talk about it was
British Admiral Lord Nelson in the 18th
century he had lost his arm in in a
battle and to him his view was that his
phantom sensations were providing him
with direct evidence for the existence
of an immortal human soul because
otherwise how could the body still leave
an impression after its destruction
other people thought it was merely a
psychological thing like we cannot
accept what has happened to our body and
so we fantasize about the limb being
back again so we had all these theories
but only in the last 25 years did we
develop a piece of technology that
allows us to look into the brain in a
way that makes phantom limbs visible I’m
talking about functional magnetic
resonance imaging or fMRI but if I’m
gonna call it the brain scan from now on
how does this work I’m gonna ask you for
example to come down to our lab be in
the brain scanner and do a simple hand
movement like this if you do that the
scanner allows me to pinpoint exactly
where in your brain
this movement is controlled and
initiated so it’s going to light up as
as an area as an active area on my
screen
so I do that and then I ask somebody
else into the scanner somebody who has
lost their arm and perceives a phantom
hand and I ask them to do the exact same
thing
but with their phantom hand so they’re
in the scanner they’re moving their
phantom hand and keep in mind there’s no
real movement going on the person is
lying perfectly still and yet the brain
scans that I took from you and from them
will look very similar in both cases
there will be clearly discernible
activation in the area that controls
hand movement now crucially if I ask
somebody in the scanner who’s been
amputated but who does not perceive a
phantom hand this activation will not be
there so that means this activation is
our first-ever proof that phantom limbs
exist think of it this way you all know
the story about the tree falling in the
forest and the question of whether or
not it makes a sound even there’s no you
know even though there’s nobody around
to hear it that question actually has
sort of an answer that tree is certainly
gonna cause pressure waves in the air
which I would usually convey sound to us
but without the brain around to
interpret them there’s not going to be
the experience of sound in this example
the phantom limb is like these pressure
waves intangible until and unless it’s
interpreted by a brain and the scanner
becomes like placing a recording device
in the forest so suddenly we can collect
a record an objective proof and we can
talk about this and we can investigate
it but how does it work in the brain
like how can the brain experience
something feel something that just
doesn’t exist well spoiler alert
the full story is not in yet we’re still
debating about the details but I can
still I can already talk to you about a
fair bit that we do know so let’s go
back to the idea of who was it you lying
in the scanner and doing the the hand
movement so the area that controls this
hand movement is right around here it’s
one spot a cluster of cells more or less
right below your skull on the surface of
your brain right next to that is the
spot that controls mouse movement so
that’s going to be active for me right
now because I’m talking to you and then
there’s you know the area for leg
movement around and so forth so
basically what I could do is I could put
you in the scanner we could do all these
movements and afterwards I could
basically
you know take you out open up your skull
take a pen and I’m not gonna do that
it’s just I’m I’m trying to make a point
you know everybody’s like what exactly
did I sign up for here but what I could
do is I could draw a little hand over
the hand region the mouth over the mouth
region of your brain and I would end up
with a complete drawing of a small
person on the surface of your brain
because every part of your body that you
can move is represented in your brain
now this person this drawing would look
a bit odd because again the mouth is
right next to to the hand and the
proportions are off but it’s going to be
an entire map of your body and in fact
it’s not the only map of your body that
you have in your brain you have a couple
of them for example there’s a whole
other one just to process touch so the
question now becomes what happens to all
of these maps all of these
representations if the shape of your
body drastically changes for example
after amputation first of all there’s
going to be a number of brain cells with
nothing to do because they’re waiting
for signals that will never come from
limbs that don’t exist anymore brain
cells hate this kind of boredom so you
know they might sit around they might
look around with the neighbors are doing
and one of those cells represented used
to represent your hand might look at the
neighbor who represents the lip and so
might start doing whatever they are
doing and as a result these maps might
shift around as cells are being
reassigned new tasks so here’s the thing
using fMRI brain imaging we can measure
the degree of this shift the degree of
this organization and in fact it was my
PhD mentor back in Germany who found out
that the amount of this shift directly
relates to the severity of phantom limb
pain which means the more your brain
reorganizes itself after amputation the
more painful your phantom limb will be
but even if we accept that phantom limbs
exist isn’t it you know even weirder
that they can hurt like how can that be
because usually we would think of pain
as something that’s just an automatic
reaction to injury right like switching
on the light but phantom limb pain tells
us that there can be pain without injury
we also know that there can be injury
without pain we know stories from
soldiers on the battlefields
I’m sustained severe injuries and
sometimes don’t feel any pain presumably
because their brain has something more
important to do at the time so pain is
not objective the same injury can cause
different degrees of pain depending on
the context depending on whether you’re
on the battlefield you’re in a good mood
you’re in love all kinds of stuff that’s
also the reason why there will never be
an objective pain scale like a bee sting
hurts as much as two slaps in the face
or something like that it has been tried
but it’s never going to be successful
because it’s not objective because our
our brain doesn’t just report back
what’s happening it has to interpret
what’s going on and only what’s real to
our brain is what is real for us the
same thing is true for other topics as
well the taste of food for example
changes depending on context that’s why
it’s so hard to recreate that great meal
from your last trip to Italy because
even if you recreate the meal perfectly
down to its last the last molecule if
it’s commissioned it might not have the
same taste because there’s other stuff
coming into it you know you’re at home
you’re not in Italy you didn’t just
spend the great day hiking you don’t
have the same life music all of that can
influence the taste of your food in a
similar way the same story the same
experience will be remembered
differently depending on whether you
were hungry or scared or angry as it
occurred that’s why it’s so vitally
important to take any eyewitness
accounts in court with a grain of salt
so here’s the amazing thing that ties
all of these strands together if I were
to do a brain scan in any of these
situations in any in any situation where
there is a divide between objective
reality and your subjective experience
the activation in your brain will always
side with the subjective experience not
with objective reality because only
what’s real to your brain is what is
real to you now if that sounds a bit
abstract I have a I have an example for
you there is a body illusion called the
cutaneous rabbit illusion and it works
like this I’m going to tap your skin two
times like this and if I do it just
right in terms of location in terms of
the timing it’s gonna feel like three
taps to you
it’s an illusion that’s based on the way
our nerves interpret what’s going on in
the skin this has been done in the
scanner as well and what you see if you
do that
three distinct locations of activation
so for our brain this third tap exists
on the skin it does not so where does
that leave us
in terms of the question of what’s real
and what’s not real is that third tap
real not really right it’s an illusion I
don’t care if it’s you know pops up on
the brain scan it’s still an illusion
but if that’s true then the phantom limb
is also just an illusion and I mean if
it’s an illusion it’s a pretty powerful
one we can feel it we can we can measure
it we can use it in pain therapy which
is what I did as a study when I talked
to that page in the beginning it’s it’s
real to us it’s real as it happens it’s
pain real of course pain is real
everybody knows that I mean sure it’s
generated by your brain and as it
interprets reality but that doesn’t mean
that we can ignore it or change it or
forget about it and in fact that this is
too a misconception that we have if we
say oh something’s you know that’s all
in your head or that’s just in your mind
that’s all way of saying it’s not real
you can ignore it and that’s a very bad
misconception that’s a misconception
that hurts people
because there are people out there
there’s chronic pain patients out there
who are physically completely healthy
but their brain registers pain all the
time and they have trouble being taken
seriously by society they have trouble
getting the right diagnosis because we
have this myth in our minds that our
brain just sits back and reports to us
whatever is going on in reality but
phantom limb pain tells us that that’s
not the case
phantom limb research tells us that our
brain needs to interpret what’s going on
in reality it might do so you know
imperfectly and we have to rely on this
interpretation of reality flawed as it
may be because it becomes our new
reality but then where do we go from
here what can we do about this
I can give you three pieces of not even
advice but of a take-home message of
consequences out of this that I think
are important first of all we should
always question our own beliefs our own
perceptions regardless you know of the
context whether it’s a taste of food or
you know whatever because
it might be flawed it might not be what
what reality is second of all wherever
we can we should try to use critical
thinking and the scientific method to
find out what’s actually going on in
reality that’s what we developed science
for to kind of overcome this flawed
perception of reality and the third one
is the most important one I think if
it’s true that each of us has their own
reality about all kinds of things about
things as basic as whether something is
hurtful about as meanness things as
basic as the shape of our body and all
of us each of us has this you know
specific reality for our own and they
are all equally flawed then I think
that’s a great reason to go out there
and approach people with as much
understanding and openness and tolerance
as we can because something that is
absolutely a hundred percent real for us
might something that’s not real for them
thank you for your time
[Applause]
you
stairs you slip and you fall and you’re
trying to catch your fall with your arm
only to realize your arm isn’t really
there it’s an illusion
that happened to a patient that was
talking to first study he had lost his
arm years ago in an accident but still
everyday all the time it fell to him as
if the arm was still there so what we
call a phantom limb now as he was
falling you would think that his brain
would alert him to the fact that
something is wrong and would tell him
you know do something else this isn’t
working but instead his brain tried to
maintain this idea of an phantom arm and
try to reconcile it with reality and so
he had this very clear image in his mind
off his arm going through the stairs as
if they were water and he fell flat on
his face these phantom limbs the feeling
that a limb is still there they’re
fairly common after amputation but still
not everybody feels them a lot of the
people who do report them as being very
painful we’ve known about this
phenomenon for quite some time the first
public figure to talk about it was
British Admiral Lord Nelson in the 18th
century he had lost his arm in in a
battle and to him his view was that his
phantom sensations were providing him
with direct evidence for the existence
of an immortal human soul because
otherwise how could the body still leave
an impression after its destruction
other people thought it was merely a
psychological thing like we cannot
accept what has happened to our body and
so we fantasize about the limb being
back again so we had all these theories
but only in the last 25 years did we
develop a piece of technology that
allows us to look into the brain in a
way that makes phantom limbs visible I’m
talking about functional magnetic
resonance imaging or fMRI but if I’m
gonna call it the brain scan from now on
how does this work I’m gonna ask you for
example to come down to our lab be in
the brain scanner and do a simple hand
movement like this if you do that the
scanner allows me to pinpoint exactly
where in your brain
this movement is controlled and
initiated so it’s going to light up as
as an area as an active area on my
screen
so I do that and then I ask somebody
else into the scanner somebody who has
lost their arm and perceives a phantom
hand and I ask them to do the exact same
thing
but with their phantom hand so they’re
in the scanner they’re moving their
phantom hand and keep in mind there’s no
real movement going on the person is
lying perfectly still and yet the brain
scans that I took from you and from them
will look very similar in both cases
there will be clearly discernible
activation in the area that controls
hand movement now crucially if I ask
somebody in the scanner who’s been
amputated but who does not perceive a
phantom hand this activation will not be
there so that means this activation is
our first-ever proof that phantom limbs
exist think of it this way you all know
the story about the tree falling in the
forest and the question of whether or
not it makes a sound even there’s no you
know even though there’s nobody around
to hear it that question actually has
sort of an answer that tree is certainly
gonna cause pressure waves in the air
which I would usually convey sound to us
but without the brain around to
interpret them there’s not going to be
the experience of sound in this example
the phantom limb is like these pressure
waves intangible until and unless it’s
interpreted by a brain and the scanner
becomes like placing a recording device
in the forest so suddenly we can collect
a record an objective proof and we can
talk about this and we can investigate
it but how does it work in the brain
like how can the brain experience
something feel something that just
doesn’t exist well spoiler alert
the full story is not in yet we’re still
debating about the details but I can
still I can already talk to you about a
fair bit that we do know so let’s go
back to the idea of who was it you lying
in the scanner and doing the the hand
movement so the area that controls this
hand movement is right around here it’s
one spot a cluster of cells more or less
right below your skull on the surface of
your brain right next to that is the
spot that controls mouse movement so
that’s going to be active for me right
now because I’m talking to you and then
there’s you know the area for leg
movement around and so forth so
basically what I could do is I could put
you in the scanner we could do all these
movements and afterwards I could
basically
you know take you out open up your skull
take a pen and I’m not gonna do that
it’s just I’m I’m trying to make a point
you know everybody’s like what exactly
did I sign up for here but what I could
do is I could draw a little hand over
the hand region the mouth over the mouth
region of your brain and I would end up
with a complete drawing of a small
person on the surface of your brain
because every part of your body that you
can move is represented in your brain
now this person this drawing would look
a bit odd because again the mouth is
right next to to the hand and the
proportions are off but it’s going to be
an entire map of your body and in fact
it’s not the only map of your body that
you have in your brain you have a couple
of them for example there’s a whole
other one just to process touch so the
question now becomes what happens to all
of these maps all of these
representations if the shape of your
body drastically changes for example
after amputation first of all there’s
going to be a number of brain cells with
nothing to do because they’re waiting
for signals that will never come from
limbs that don’t exist anymore brain
cells hate this kind of boredom so you
know they might sit around they might
look around with the neighbors are doing
and one of those cells represented used
to represent your hand might look at the
neighbor who represents the lip and so
might start doing whatever they are
doing and as a result these maps might
shift around as cells are being
reassigned new tasks so here’s the thing
using fMRI brain imaging we can measure
the degree of this shift the degree of
this organization and in fact it was my
PhD mentor back in Germany who found out
that the amount of this shift directly
relates to the severity of phantom limb
pain which means the more your brain
reorganizes itself after amputation the
more painful your phantom limb will be
but even if we accept that phantom limbs
exist isn’t it you know even weirder
that they can hurt like how can that be
because usually we would think of pain
as something that’s just an automatic
reaction to injury right like switching
on the light but phantom limb pain tells
us that there can be pain without injury
we also know that there can be injury
without pain we know stories from
soldiers on the battlefields
I’m sustained severe injuries and
sometimes don’t feel any pain presumably
because their brain has something more
important to do at the time so pain is
not objective the same injury can cause
different degrees of pain depending on
the context depending on whether you’re
on the battlefield you’re in a good mood
you’re in love all kinds of stuff that’s
also the reason why there will never be
an objective pain scale like a bee sting
hurts as much as two slaps in the face
or something like that it has been tried
but it’s never going to be successful
because it’s not objective because our
our brain doesn’t just report back
what’s happening it has to interpret
what’s going on and only what’s real to
our brain is what is real for us the
same thing is true for other topics as
well the taste of food for example
changes depending on context that’s why
it’s so hard to recreate that great meal
from your last trip to Italy because
even if you recreate the meal perfectly
down to its last the last molecule if
it’s commissioned it might not have the
same taste because there’s other stuff
coming into it you know you’re at home
you’re not in Italy you didn’t just
spend the great day hiking you don’t
have the same life music all of that can
influence the taste of your food in a
similar way the same story the same
experience will be remembered
differently depending on whether you
were hungry or scared or angry as it
occurred that’s why it’s so vitally
important to take any eyewitness
accounts in court with a grain of salt
so here’s the amazing thing that ties
all of these strands together if I were
to do a brain scan in any of these
situations in any in any situation where
there is a divide between objective
reality and your subjective experience
the activation in your brain will always
side with the subjective experience not
with objective reality because only
what’s real to your brain is what is
real to you now if that sounds a bit
abstract I have a I have an example for
you there is a body illusion called the
cutaneous rabbit illusion and it works
like this I’m going to tap your skin two
times like this and if I do it just
right in terms of location in terms of
the timing it’s gonna feel like three
taps to you
it’s an illusion that’s based on the way
our nerves interpret what’s going on in
the skin this has been done in the
scanner as well and what you see if you
do that
three distinct locations of activation
so for our brain this third tap exists
on the skin it does not so where does
that leave us
in terms of the question of what’s real
and what’s not real is that third tap
real not really right it’s an illusion I
don’t care if it’s you know pops up on
the brain scan it’s still an illusion
but if that’s true then the phantom limb
is also just an illusion and I mean if
it’s an illusion it’s a pretty powerful
one we can feel it we can we can measure
it we can use it in pain therapy which
is what I did as a study when I talked
to that page in the beginning it’s it’s
real to us it’s real as it happens it’s
pain real of course pain is real
everybody knows that I mean sure it’s
generated by your brain and as it
interprets reality but that doesn’t mean
that we can ignore it or change it or
forget about it and in fact that this is
too a misconception that we have if we
say oh something’s you know that’s all
in your head or that’s just in your mind
that’s all way of saying it’s not real
you can ignore it and that’s a very bad
misconception that’s a misconception
that hurts people
because there are people out there
there’s chronic pain patients out there
who are physically completely healthy
but their brain registers pain all the
time and they have trouble being taken
seriously by society they have trouble
getting the right diagnosis because we
have this myth in our minds that our
brain just sits back and reports to us
whatever is going on in reality but
phantom limb pain tells us that that’s
not the case
phantom limb research tells us that our
brain needs to interpret what’s going on
in reality it might do so you know
imperfectly and we have to rely on this
interpretation of reality flawed as it
may be because it becomes our new
reality but then where do we go from
here what can we do about this
I can give you three pieces of not even
advice but of a take-home message of
consequences out of this that I think
are important first of all we should
always question our own beliefs our own
perceptions regardless you know of the
context whether it’s a taste of food or
you know whatever because
it might be flawed it might not be what
what reality is second of all wherever
we can we should try to use critical
thinking and the scientific method to
find out what’s actually going on in
reality that’s what we developed science
for to kind of overcome this flawed
perception of reality and the third one
is the most important one I think if
it’s true that each of us has their own
reality about all kinds of things about
things as basic as whether something is
hurtful about as meanness things as
basic as the shape of our body and all
of us each of us has this you know
specific reality for our own and they
are all equally flawed then I think
that’s a great reason to go out there
and approach people with as much
understanding and openness and tolerance
as we can because something that is
absolutely a hundred percent real for us
might something that’s not real for them
thank you for your time
[Applause]
you
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