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