The Circuitry of Sensation Reality or Illusion
well
thank you folks for inviting me it’s a
pleasure to be here
it’s wonderful to interact with this
audience
uh yesterday with students from msu my
first visit here
um i’m a neuroscientist and i study the
brain
this marvelous computer in our heads
this marvelous organ because of which
we can see being here have the rich
experience
of life okay this is the privilege i
have
of studying this structure this is a
picture of
all of the nerve tracts in the human
brain look at it
these pathways are what give us all our
perceptions our feelings our functions
and these pathways can’t be wired up the
way you wire up a computer you can’t go
by the paths and then all sort of things
together
you have to grow them in place that’s
the subject of my research
but before i jump into that i would like
to challenge you folks a little bit
um but how confident we are about our
brain function how confident we are that
we
know the world around us okay humans are
great at this
we are so sure we are so
sure let’s challenge this today with a
little bit of
some experiments nothing bad will happen
at roms
okay the world is rich because of color
okay we see the world in glorious
technicolor
and this is supposed to change a slide
somewhere where do i point
yeah is seeing believing
is seeing believing you see these
glorious flowers i saw many flowers on
the way in
i don’t think people would argue too
much if i say okay the top one’s
purple and white the middle one’s yellow
the next one’s purple
yeah if you don’t see these colors come
and see me outside i’m a neuroscientist
okay but you know here’s our arrogance
the world is the way we see it you know
that we observe the world only in a
limited spectrum what we call the visual
spectrum
there’s so many wavelengths out there we
don’t see okay
there is so much information out there
that we just don’t see but we’re like oh
we can only sense this spectrum so
that’s how the world is
i mean how limited is that right
if only we could see an ultraviolet if
only we could see an ultraviolet
here are these same flowers photographed
with ultraviolet light
and i’m taking a chance here it went
away
okay am i doing it or are you
you’re doing it so i should just say
click click each time
okay here um ultraviolet
look how the flowers transform okay now
we can’t actually see ultraviolet so
these are color coded for us because our
limited eyes can only see
yeah but look how the bullseye patterns
show up in these flowers
there’s difference in the center
difference in the surround and the star
one down here has a nice bit of a
landing pad
who do you think the flowers were meant
for you and me so we can offer them to
the people we love
the flowers were meant for insects who
can see in ultraviolet
and look look at the patterns relevant
to the insect so the insect can find the
center of the flower
okay meant for a completely different
purpose we think we see
this there are many many more insects in
the world than
us and we have the hubris to claim this
flower is yellow and purple
okay threatens our sense of what we know
right okay now
i’m announcing happily that i see purple
and yellow and purple
and i’m so happy with the fact and most
of you are agreeing with me those that
don’t agree are too embarrassed to say
so
but even color that we think we know
even the color we think we know isn’t as
solid as we think it is
our brains can bamboozle us next please
this made waves on twitter okay
lots and lots of colored balls i’m not
going to ask you to count them or
anything
but most people can see at least three
types of colors in these balls right
okay let me show you i just went to
adobe photoshop and i cropped the balls
and placed them on the side one click
okay we still see three colors they are
just excerpts of the three balls on the
left if you just blow them to high mag
one more click
the colors begin to look not quite as
different
and now let’s block out the bars one
click
turns out that all of these balls were
actually identical in color
okay our eyes computed the color for
us because of the lines going through
them this is not magic it’s not wizardry
okay i’m just bringing out that
our circuits control our perceptions
okay it’s not wrong for our circuits to
control our perceptions what else is
going to control our perceptions
right but the way the circuits are wired
up
not only allow us to see and feel and
hear but they also place constraints on
what we can see and feel and hear
and most of the time we are blissfully
unaware of those constraints
we don’t even imagine how the world is
that we don’t that we are unable to
perceive
and we are so sure we know what it is
and i’m trying to tell you that there is
no
ease the world is as we perceive it and
that’s a completely different
uh frame of reference which most of us
don’t uh think about
right so as part of our fascination for
our brains we have to acknowledge
that what they’re doing is the best they
can our brains
and circuits the best they can with the
myriad signals they receive
and trying to make sense of the world
for us but
because the circuits are also limited
sometimes
they just do the best they can and
present us colors that aren’t even there
okay so essentially context is
everything
this was about colors
i’m now going to move to a different
modality sound
i am not going to play the veena
but my goodness what a magnificent
demonstration of sound
okay what is sound a physics physics
major will tell you
its vibrations of the air but my god
those vibrations can make you feel did
y’all not
feel did you feel the goosebumps didn’t
you feel
joy didn’t you feel emotion all of that
by vibrations
those vibrations hit our ear drums and
then circuitry kicked in
what our circuits did with those
perceptions
okay that’s the sound we hear outside of
our brains
sound is just vibrations okay so aren’t
we all glad we have our circuits
i’m going to now show you that sound
can also play games with us okay
next let’s have the first movie with
sound
would be so nice if we had sound on this
one can you stop it
and please with sound
once more the first movie
[Music]
this was not complicated baby sounds
if you didn’t hear baba
second movie please
okay what did you hear
far far far right i heard it too
no actually i didn’t no matter how many
times i do this experiment since i had
my back to the screen
i actually heard ba-ba-ba it’s gonna
knock your socks off when i tell you the
soundtrack was playing ba-ba-ba the
whole time but because the lips were
going
far far far okay our brains did this
what to do two two incoherent signals
coming and let’s just tell him he’s
hearing papa what’s he gonna know
i’ll prove it to you okay we’re going to
play the same soundtrack now and both
the visuals together
and in the middle of it close your eyes
and open look at whichever face you want
close your eyes and open and you’ll see
what i heard
[Music]
[Applause]
it’s not me it’s your brains that did it
for you
okay they allowed you to hear with your
eyes
okay now again this is not just a game
it’s trying to tell you that your
complex circuitry is doing the best it
can
in a very messy world right now
if usually you’re looking at the person
you see
who’s talking and you’re hearing sound
from all around you
but you’re going to focus on the person
whose lips are moving
in sync with what you’re hearing and
you’re going to assign the perception
that’s what the circuits do it’s not
magic or wizardry in fact
this way whatever moves you think that
the sound comes from it
i’m playing a monstrous auditory
illusion on you right now
my sound isn’t coming from my lips it’s
coming from the speakers
but you think it’s coming from me
because my lips are moving in sync
in sync okay
if i practiced hard enough i could
pursue it did it work
all right so
i guess i have brought you to question
your circuits even as much you
appreciate and admire them
we study how these circuits get wired up
next slide please
okay this is a picture of the circuits
in the human brain it looks like a wild
riotous
mess okay although it looks like a wild
riotous mess it’s almost like traffic
outside
you know everything else although the
traffic looks messy to an external
observer
each car in that traffic knows what it’s
doing
yeah i mean okay maybe some of you don’t
know what you’re doing when you’re
driving out there but
but there is a system of queues right
there are long range signals coming from
the gps
okay drive on whatever for four
kilometers
long range signals then as you approach
your destination
you no longer need the long range
signals because you recognize local
landmarks
there’s the temple the petrol pump the
restaurant the whatever
you recognize local landmarks then maybe
you enter your
building gate or something where there’s
a gatekeeper
who says okay does this car belong in
this colony
right much like that our nerve pathways
are guided in the brain
through a system of long range cues
local
signals and gatekeepers and we were
privileged to discover
a gene that acts as the gatekeeper
of sensory nerves coming in to the
cerebral cortex
how cool is that i’m going to show you
that in just a little bit but let me
first introduce how we do this
so this is like testing my balance here
let me
give you an idea of how we do this all
of our experiments are done on the mouse
because until date i have not found a
volunteer enthusiastic enough to give me
their brain
gosh of source so we work on the mouse
and we work on the mouse for
uh additional reason okay
so in green over there the thin line you
see
are green nerves entering the cerebral
cortex of the mouse
that’s an entire bundle of sensory
nerves entering the cerebral cortex
and that’s what they must do from where
they originate the green clump down
below
okay how do we find out
what genes or mechanisms are going to
control this very complex trajectory
for this we use a technology that knocks
out
genes of interest we can make a mouse in
which a particular gene has been knocked
out
now what’s that um let’s see
suppose an alarm clock landed into your
lap from the sky i bet your generation
has not seen a real alarm clock right
so good this will work imagine if an
alarm clock just landed
and it had an hour hand that moved
and a minute hand that moved and a
second hand that moved
and you opened it up and you saw a whole
bunch of gears and all inside
and you said hmm i’m going to knock out
this one gear
i’m going to knock it out and i’m going
to see how it affects the functioning of
the alarm clock
and you realize that the hour hand moves
and the minute hand moves but the second
hand is stuck
which allows you to conclude that that
gear might have something to do
with the functioning of the second hand
okay
it’s a bit of a crude technology because
it could have also affected the minute
hand which could have secondarily
affected the second hand
that’s why science is a long process but
this allows you to say okay this gear
has
something to do with the functioning of
the second hand and then you can go
further
so similarly we knocked out a particular
gene that we
thought might be important in this
pathway we knocked it out in the mouth
next slide
little mouse next click please
this is the normal mouse brain these are
sections and
those green blobs you can see are
actually where the sensory nerves came
into the cortex
and formed connections the picture on
that side is a high mag you can see the
beautiful
innervation the fibers each fiber knows
what it’s doing and it’s wired up
correctly
now what happens when we knock out this
single
gatekeeper gene next click
in the knockout mouse brain we don’t see
nice little blobs in the cortex
and look this giant fiber tract has come
in and is barely able to penetrate
okay it looks like we have found a
mechanism that controls the gate
of the entry of sensory nerves into the
cortex
this mouse has normal eyes normal ears
normal skin but it can neither see nor
hear nor feel
because the nerves carrying all of this
information have not entered the
cerebral cortex which is the first
station where they deliver the
information
into the cortex okay so this is where
our study is at
it’s unpublished science is not a done
package
thing to sell you know you stock it up
on shelves it’s all done
science is an ongoing process so i
wanted to tell you this process of
discovery
okay getting us this far took the phd
thesis of two students
and now we’re going to probe further and
ask hey how does it do it
okay how does it do it now
i’ve presented to you sensory circuitry
okay and broadly basic circuits
are similar in all of us next slide
please
okay our basic circuits are the same but
there are individual differences no
we’re not all clones of each other
in fact there are individual differences
in how we appreciate even the same piece
of music
right different people hear things
differently
and then in addition to individual
differences circuits can be shaped
click these they can be shaped by the
environment
which is the training and experience you
give them
okay so your differences may either be
because of your genes
or because of what you expose yourself
to and how hard you work at it
think of a piece of music the first time
you hear a piece of music
okay you hear it in a certain way if you
hear it over and over again the
20th time you hear that piece of music
it could be a pop song it could be
classical music anything
you’re hearing it differently because
you’re attending to different parts of
it
some parts of it you already know but
now you’re appreciating the detail
between some spaces and so on
okay so each time you actually hear
you’re doing it differently
you’re taking in the information you’re
focusing attention you’re processing it
differently
and all of this is based on a framework
that is different because of your innate
abilities
and then if you train very hard at
something you get better and better at
it okay
so i’m going to bring this out first i’m
going to persuade you that there
are genuine innate differences okay
and i’m going to do this as a
neuroscientist with an experiment
i’m going to have you hear a soundtrack
okay
and i’m do this with some trepidation
because this
always causes something of a ruckus
maybe some of you have heard this
soundtrack
which some people hear as yanny and some
people hear as
laurel it’s american accent yanny
and laurel let’s see what you hear
okay next slide please play the movie
with sound yanny
yanny
[Music]
okay i can’t dare to look but how many
heard yanny
okay look around you see all the hands
keep the hands up let everybody
sort of get a sense and how many heard
laurel
okay the brave few it’s okay it’s okay
there’s nothing wrong with you
okay there are innate differences right
each time i hear this i hear it
differently because it depends on the
sound system it’s coming from
and that’s sort of the key to these
different percepts
one click please yeah i just said one
yeah click click click yes wait wait
so just changing the sound equalizer
settings
for that same soundtrack is possibly
going to change the percept for some of
you
can you play the movie
laurel
[Music]
[Music]
okay how many’s perception switched
it’s okay raise it so people can see you
know so look a few people’s percept
switched
i’m not asking it with direction but
it’s switched and the rest of you the
percept stayed the same
okay one click we’ll now go to a
different sound equalizer
setting and now play the movie
laurel laurel laurel
laurel laurel laurel
okay how many perceptions switched
how many’s perception stayed the same
for one two and three
look just look look at how many
combinations we have okay
now you guys are a really kind and
tolerant audience i’ve had people come
to blows over this
in the middle of my talk i’ve had people
going how can you hear laura leave me
deaf or what
okay so i hope i persuaded you that our
innate setup is different okay how we’re
going to process sound is different
now add to this add to this training and
experience
okay there are some things that you
acquire only with training and
experience and this doesn’t only apply
to sensation
it applies to complex motor skills next
slide
okay how many people can make a roti
straight off the bat for the first time
we all know what wonderful maps of
gujarat we make
the first time we make a roti right if
you haven’t tried do it
okay it’s a complex skill and yet with
time you get
get it to perfection the same thing goes
to riding a bike
certainly playing a musical instrument
okay we have to thank our parents for
suffering through our initial attempts
at playing a musical instrument
it requires an act of great love and
tolerance but eventually some of us at
least
produce beautiful music and all of that
is those same circuits being exposed to
a lot of training
how is it possible if i say that all of
our behaviors and our
abilities come from circuits and then i
say we get better with training
that means the circuits have to change
you know there’s no other way
there is no other way there’s no like
magic masala you can sprinkle in your
head
to suddenly i wish there were but the
circuits have to change
i’m privileged that i work also on a
different part of the brain called the
hippocampus
okay not the hippopotamus okay that’s
different
hippocampus it’s the center
where learning is learning and memory
starts okay it’s the learning machine of
the brain
and in this hippocampus new
neurons get added throughout life
next slide please
here is a regular cage regular mice in
it
and click there is a
enriched cage where the mice are given
toys you know wheels to run on tunnels
and blocks and things
it’s a more interesting environment if
you look at the neurons in the
hippocampus
of these mice click please here you have
a regular neuron another click and the
mice in the enriched cage
get more neurons but also more branches
more sprouts
more connections okay so this is telling
you
that enriched experiences allow your
brain to form
more complex circuits and that’s the
substrate of new learning
now we’ve found an interesting genetic
mechanism
that controls how many neurons are made
in the hippocampus
next brains have stem cells
and these stem cells normally produce
two kinds of cells
next they’ll either produce neurons
if our particular gene is on next or
they’ll produce
a kind of support cell if our gene is
off
all right what my student lakshmi and
anandita discovered
is that if you make this gene
permanently on next
you can get large numbers of neurons
coming out from the stem cells
at the expense of glia you actually can
put
extra neurons into the hippocampus okay
i’ll show you a picture of this
this is an experiment done by my postdoc
archana this is a normal brain
next here’s a brain where every green
beautiful fiber next show on a time ag
here look at these lovely trees
okay all of these are neurons in which
this gene was forcibly turned on
and they formed into neurons instead of
support cells because of the functions
of this gene
now we’re asking are these neurons
actually good for hippocampal function
more neurons doesn’t mean everything
sometimes you need more support
right if you have too many neurons maybe
they mess up the original neurons that
are trying to do their job
we don’t know so look at the excitement
of science
it’s like yesterday we discovered this
gene that has this function
today we’ve done the experiment to make
a mouse with more neurons in its head
and tomorrow we’re going to test what do
these extra neurons do
isn’t that cool okay this is the ongoing
exciting nature of science that we live
in every day
now
these new extra connections extra
neurons
don’t just form
just because by themselves have to make
them happen
we have to take ourselves into enriched
environments
okay i mean right now hopefully
if you’re actually getting something
from this talk tick tick tick tick tick
new neurons are forming in your head
we have to take ourselves into spaces
that challenge us
right so every difficult task every
tough assignment
every impossible skill you’re trying to
learn all of that actually
challenges your brain to forming new
connections
and acquiring new abilities
and boy do these connections form are
these neurons alive
i’m going to show you a movie of a
neuron growing in a culture dish
to give you a sense of how alive a
neuron is these neurons
are practically dancing their way
through
through the brain okay in fact sometimes
it seems to me that they perform
bharatnatyam
i kid you not i’ll show you can you next
slide with the movie
so this is the neuron in a dish and it’s
going to put out many little fibers
okay can you play the movie
look
yeah and then one of those fibers says
i’m going to form the output wire the
axon
that’s my target that’s how i’m going to
grow now it’s kathak
okay i’m gonna grow there
there there
[Music]
i mean look at it if this neuron was a
neuron in the
spine of a giraffe look at what a long
way it would have to go to connect to
the muscle right
and look at it doing its job
reaching its target what are the cues
what are the signals that make all of
these grow these are the kinds of things
we study
in my developmental neuroscience lab
with my students and postdocs
these are the kinds of explorations we
do to study next slide
this amazing structure the brain that
gives us
all of our abilities next slide please
no please
please
ah all right it was actually just my
last slide of the fantastic complex
braid
let’s just let me just wrap up i hope
i’ve persuaded you
that our abilities are all because of
our circuits
our circuits control our perceptions
they control what we can do they control
our limitations as well
but then i’ve shown you that by taking
ourselves
to new experiences new challenges we can
actually grow and modify our circuits we
can acquire skills
that we didn’t have before and hey then
why not acquire new thoughts that we
didn’t have before
imagine if we have conversations
and hear points of views that are
completely different from ours
could we not perhaps grow circuits that
allow us to be more open
more accepting more tolerant could we
not actually
grow our circuits to making us better
human beings and a better society
it’s actually within our abilities to do
so okay
and within this lofty goal let me now
issue a challenge
to this audience and to our organizers
we opened with an environmental theme
right
let’s walk the talk every little plastic
bottle
on the table it’s on us every plastic
bottle we put in the trash is going to
outlive us by many many many lifetimes
insist on a glass that can be refilled
don’t add plastic bottles at least today
let’s walk the talk a new challenge a
new experience today
grow some circuits save the environment
thank you very much