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How Does a Child's Brain Develop? | Susan Y. Bookheimer PhD | UCLAMDChat



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hello welcome to today's UCLA health

webinar my name is dr. Susan book heimer

I am a professor of psychiatry and bio

behavioral sciences here at UCLA and I

do research in brain imaging today's

topic is going to be how does a child's

brain develop during this talk you can

ask questions on Twitter at UCLA MD chat

or go ahead and just ask a question on

Facebook we'll save them for the end

today what I'm going to be focusing on

are first how brain development is

designed to form connections which

together we call the human connectome

I'll also talk about how these

connections relate to brain function and

I'll talk about the adolescent brain the

teen brain and why that teen brain is so

let's say difficult I'll also talk about

a few things that can go wrong in brain

development because of these abnormal

connecting connections that can develop

and then I'll mention some studies that

were going on at UCLA now that you could

consider participating in one of the

first things that we need to know about

brain development is that it's really

not about size the brain in fact does

get bigger but that's not really what's

important what's important is what's

happening inside brain development is

all about forming connections we are

actually born with a lot more brain

cells than we're going to use and in two

critical periods of development at about

age two and then again at adolescence we

actually lose a lot of neurons during

this period of time however our brains

are forming connections the good ones

the ones that we are using are going to

be maintained and the rest are going to

be pruned away just like we would cut

off an old branch that is no longer

useful so we use the phrase use it or

lose it when we think about brain

development in this way there's a very

important relationship between our

environments and our brains what our

brains are exposed to what we do what we

see and experience will all help

determine which of those connections are

going to stay and which ones are going

to be cut away this is a picture of the

fetal brain growth from the age of 25

days all the way up to birth

and you can see that the brain starts

very very primitive and very quickly

develops into having the general brain

shape but the main thing that changes is

the folds in the brain the folds in the

brain which give rise to this

characteristic brain pattern are there

because they increase the surface area

by having folds we can get more neurons

into that tissue and the more neurons we

have the more we are able to use that

information to do complex tasks that

humans do so humans have the most folded

brains that there are there are three

major changes that take place during

brain development the first one is that

what we call the proliferation of

dendritic branches just as a tree grows

with a long central stalk which we would

call in the brain and axon it also

develops all of these branches and brain

cells sprout these branches which

connect to other brain cells so that's

one thing that occurs another one is

this process called myelination which

I'll show some pictures of in just a bit

but this is a covering of the axons

these are the major branches that I was

talking about and these this myelin is

made of a very fatty substance that

actually comes from certain kind of

neuron and it's like an insulation

material that allows information to

process and to be sent very quickly from

one brain cell to the next

and finally there's that process of

pruning dying off of brain cells and

brain connections that looks that look

is that they're no longer needed here's

a picture of what it looks like across

development in the newborn brain we have

a fair number of neurons here but as you

can see they're very simple they've got

a single long axon that's not really

connected to anything and only a few

little branches and the cells themselves

are quite small during development these

branches really start growing quite a

bit although the actual number of

neurons is not changing by nine months

you can start to see many of these

connections forming and becoming more

complex but look at the age of two years

look how incredibly dense all those

connections are they're the same number

of neurons here but that's connected

everything is practically connected to

everything else

however if you contrast that with a

young adult brain you can see that a lot

of those connections have started to

prune away and the cells themselves are

larger and the connections between cells

are thicker they've become stronger with

age but they're fewer of them this is

the general process what we talk about a

transition between brain plasticity that

is the potential for the brain to do a

lot of different things and brain

efficiency that is just keeping those

connections that we need so that we can

use our brain energy as efficiently as

possible this is an MRI scan of a seven

year old and a thirty year old to

demonstrate one of these processes and

that is the thinning of the gray matter

the pruning or the breaking away and

dying off of neurons in the young brain

the seven year old brain you can see

that there's a lot of this thick grey

matter around here and you compare that

to the same area in the adult brain

where it looks much thinner so the

between the ages of seven and thirty we

are still losing a lot of neurons this

graph actually shows the statistical

change over time from the age of five

through the age of 20 the brighter

colors mean thicker cortex the darker

colors mean thinner cortex and so the

brain thins although different areas of

the brain thin at different rates over

this period of time and in fact the

frontal lobes are the last areas of the

brain to thin

they don't even complete their

maturation until at least the mid to

late 20s now I'm going to talk a little

bit about myelination these are brain

scans from the age of one week through

the age of ten years and of course you

can see that the brain has gotten a lot

bigger but one of the other changes that

you can see pretty clearly here is that

this brain looks very dark as does this

one whereas these brains look much

lighter well the reason why that's

happening is because we have no myelin

none of that fatty substance in the

infant brain it slowly starts to develop

and then accelerates incredibly rapidly

so it's the myelin that makes this white

matter these connection tissues look

very very white and I'll explain a

little bit more about myelin and how

that works this is a picture of a brain

cell called a neuron and this is the

axon that long central branch that will

lead this brain cell to another brain

cell in order to make connections at

birth there is no insulation around any

of these connections but what happens is

a certain kind of brain cell comes in

and forms a little sheath and wraps

itself around that axon and a number of

these different neurons wrap themselves

around the axon it's like the kind of

insulation that you would see on an

electrical wire we don't actually see

the wires we just see the plastic

surroundings that insulates the wire it

allows that electricity to move safely

within that wire but here in this case

of myelin it also allows something

special to happen since the brain

communicates with electrical signals

this fatty substance allows those

signals to skip over from these

different nodes all the way down it

allows sort of a speed Dimond pathway of

connection and so the more myelin there

is the faster these connections can form

and therefore the better the

communication can be between two

different brain regions in this MRI scan

that we see here we are seeing the

infant brain from the first hundred days

of life up into 300 days of life so this

is early in the first year of life this

is the MRI scan and this area down below

just shows that white matter the part of

the white matter where the myelin is

that fatty substance that helps form

those connections at birth almost

nothing is myelinated in fact there

really only two areas of the brain that

have this myelin that allow for this

rapid connection one is the visual

cortex so eyes through the central part

of the brain into the visual system and

the other is the mouth motor cortex and

you can guess why an infant doesn't have

to do

very much except find what it wants to

suck and have the motor system to suck

it that's all an infant wants to do but

as the infant starts to develop more and

more systems come online this myelin

starts to get formed and it allows that

child to develop faster and better

cognitive skills so the more that brain

is in use the more that this white

matter starts to develop and we see that

within one year of life we go from

almost no myelin in to a well myelinated

brain this is another picture of this

comparing again that same seven year old

with a 30 year old and I've just

outlined here the white matter of the

brain and you can see this is the white

matter this is where the neurons are and

these are where the connections are and

you can see how much that white matter

has grown over that period of time so

where the gray matter has shrunk the

white matter the connections have grown

so it's all about forming connections

here's another picture of connections

that you might have heard about this

connection is called the corpus callosum

it's a connection of those fibers as

connecting fibers between neurons that

connects the left side of the brain to

the right side of the brain and this is

a picture of the brain cut right down

the middle so this would be the nose

this is the back of the brain the top of

the brain and this is right down the

center here you can see in the

seven-year-old here is the corpus

callosum here in white and you can see

how thin it is right here and and in the

back whereas at the 30 year-old level

it's very nice and thick so over time

our two hemispheres have learned how to

talk to one another and to do it very

very quickly and efficiently so why do

we have all of this connection well

different parts of the brain have

different roles each part of the brain

does something different but it doesn't

do it all by itself to work every part

of the brain has to talk to other parts

of the brain it sends electrical signals

throughout the brain through those white

matter tracts to form these connections

so that different areas can talk to each

other and work together to perform

complex tasks

like talking as I am doing with you

today and this is all about connectivity

or what we would call functional

connectivity that is not just the

structure of those pathways but what

those pathways are doing and the

cognitive skills that can emerge because

the brain is using those pathways to

talk to other areas of the brain here's

a picture just of the white matter all

by itself this is from a technique

called diffusion tensor imaging and the

different colors represent what

direction the pathways are going in now

I don't want to focus on the colors

themselves because today we don't care

so much about the direction but rather

about the difference between the infant

brain and the adult brain and here in

the infant brain even at birth we can

see that there are important connections

in the brain

major fiber pathways this one for

example going from the motor system down

through the spinal cord and the corpus

close and connecting the two hemispheres

of the brain but notice on the outside

there is just very little happening

there those fine connections have not

been formed compare that to the adult

brain and see how elaborate and deep all

these connections are so development is

really all about forming connections and

forming them the right way together

these connections form distinct

functional networks there are many

different kinds of networks in the brain

functional networks in the brain I'm

just listing a few of them here for

illustration for example the visual

network collection of brain regions

which together allow us to see the world

and to make sense of what we see figure

out where things are when we see them

the auditory network does the same thing

but with what we hear sensory network

where our bodies are and how we feel our

bodies so these are brain regions that

are connected together left hemisphere

with right hemisphere and several areas

across the brain that work together to

perform the complex tasks of vision

hearing sensation moving but we also

have some more complicated networks with

more elaborate functions

the language network for example so as I

talked to you today I have many regions

of the brain that are involved in

language they're spread all throughout

my brain although mostly for me in the

left hemisphere of my brain and they all

have to work together in a network there

are atention networks there's several

different intention networks and there's

a southern network called the salience

network this is a network of brain

regions that find out what's important

in the environment and distinguish what

is important from things that are less

important so that it can focus on that

which is most meaningful and significant

the default mode network is a completely

different thing we often call this the

task negative Network this is what you

do when you're not thinking this is what

we do when we're at rest essentially we

turn off our brain we let it just wander

and it's very important for us to do

this it gives our brain arrest it allows

our memories to be consolidated without

being bothered by the things that we are

seeing and hearing and it's probably

very active while we're sleeping and we

need all of these networks as well as

many more we can measure these

functional brain networks with

techniques including functional MRI so

functional MRI is a MRI technique it

requires no radiation

it requires no injections it's perfectly

safe and it measures blood flow in the

brain we can measure it during task

performance so if I were in a brain

scanner right now and I were doing a

language task more blood would flow to

my language areas of my brain and we'd

be able to see that in MRI we can also

look at correlated activity across the

brain while we're just at rest sitting

in a scanner because different areas of

our brain which normally communicate

which are normally well connected will

change their blood flow spontaneously at

about the same time so these are great

techniques for learning about brain

function during development because

they're completely safe for children so

fMRI shows the basic outlines of brain

networks at birth and to show you an

example of this I'm going to show you

the brain of an eight week old infant

that we did an MRI scan on and by

looking at this infant just a truss

actually sleeping while in the scanner

we are able to look at the correlated

activity across the brain to identify

key networks this is the sensory motor

Network so this is the motor area of the

brain where we control our movement this

is the auditory Network this is where we

hear the visual network where we see and

even at birth we have the more complex

salience Network the network that tells

babies what is important to them and

it's really quite remarkable that we are

born with the basics of these networks

already connected up in our brains

networks develop however from these very

primitive networks over time usually

with experience so there's a basic

structure that we're born with but these

structures are shaped by our experiences

they are shaped into distinct modules so

for example this is a picture of the

language module the group of language

areas which have to connect together and

work together to perform language and

these modules are highly distinct and

within the modules they're highly

integrated so they talk within a module

to each other but they're separate from

other modules I'll explain what that

means

functional activity through development

changes so that the brain becomes more

modular and it becomes more efficient so

in these functional MRI scans of

language in the young children we see

that there is a great deal of diffuse

activity across the brain it's in both

the left hemisphere and in the right

hemisphere

and it's pretty big when we compare the

same language tasks to young adults we

see the same brain regions but look it's

now mostly centered in the left side of

the brain in the MRI world left is right

and right is left so this is the left

side of the brain we see it's more

specialized and we also see that less

tissue is dedicated to it because what

has happened is these modules have

become specialized and used solely for

language without any of this extra stuff

this extra stuff would have been stuff

that will have been pruned away by the

time we get to adulthood and that is

really the process of brain matter

that helps to support these functional

networks now we can look at functional

networks in a variety of different ways

but one is by looking at graphs so this

is a graph of a brain network where

we've laid out all the different brain

regions in a network and in the adult we

see that this network all talks to each

other but in the children they don't

really talk so closely so the

connections have all not been as well

developed here as in here we can look at

this in another way when we look at the

relationship between two different

networks in this case we're talking

about the tasks positive or attention

network and the tasks negative or our

resting or default mode Network and what

you can see in this typically developing

child is that the networks themselves

form discrete very distinct modules that

all talk to each other but are separate

from the other modules so these are

completely separate except for one point

which allows switching between the two

well contrast with the network

organization of a child with an autism

spectrum disorder where the same modules

exist but they're not as well integrated

within and there's too much crosstalk

between so this makes it so that each

module has interference from another

module and it makes it more difficult to

process information very clearly there

are other things that we could learn

about developmental disabilities

developmental disorders using this kind

of brain connectivity technique here for

example is a study of children who are

typically developing and children with

autism when they're exposed to rewards

and in this case the reward would be

simply seeing a smiling face

most of us respond very nicely to a

smiling face and we have a reward center

in the brain that does that with this

kind of brain scanning we can see that

the reward network while fully intact in

a typically developing kid is not

working as well and the children with

autism and this is the difference

between groups suggesting to us that

there is a problem in the reward network

of the brain of children with autism

environmental exposures can also have

the very major of

on brain development this is prenatal

exposure to alcohol at the top here we

have a typically developing child in the

nine month range and you can see the

corpus callosum here and here and you

can see the white matter and the gray

matter this Chuck this is a MRI scan of

a child who is

sapote was severely exposed to alcohol

prenatally and I think the first thing

that you can see right off the bat is

that there is no corpus callosum at all

so the big major connecting fibers that

connect the right and left sides of the

brain is simply missing and when we look

inside the brain we see a similar

pattern a lack of connectivity some

abnormalities in several different parts

of the brain so environmental exposures

can have a profound effect upon brain

development and I mentioned before that

adolescence is a time of great rapid

brain change with this influx of

hormones the brain becomes very

sensitive to new experiences

it becomes very reward sensitive and it

becomes driven towards novelty and also

in particular to social experiences this

makes a lot of sense because when kids

grow up and become adolescents they need

to find a way to launch and they can't

do that unless they become interested in

new things and in new people of course

their emotion networks also become very

active and yet there's a problem because

the area of the brain that helps to

regulate and control these emotional

experiences and these impulses does not

come online until at least the 20s and

sometimes quite late in the 20s so we

have this situation where there's a lot

of impulsive impulsivity and a lot of

emotional arousal without the ability to

regulate that arousal that's why teens

are the way they are and that's why it's

so difficult for teens because they get

exposed to novel experiences which can

have negative consequences and they

don't have quite the regulation that is

built into the brain to calm that down

and to control it there is so much more

that we do not know about brain

development in fact

we're really just starting to scratch

the surface how did these connection

xions how does the human connectome

develop over time and in particular how

do individual differences in connections

relate to behavior to cognitive

strengths to cognitive weaknesses how do

our individual experiences affect the

development of this connectome and what

are the effects of things that we are

exposed to and particularly our kids

today are exposed to like video games

and social media and things like that

how does that affect brain development

what are the effects of environmental

exposures toxins also things that people

will will take drugs things like that

what are the effects of these on our

brain connections there's so much that

we still don't know and these are

questions that we at UCLA are trying to

answer with research there are a few

research projects we're doing right now

and one is the human connectome

development project where we are

bringing children in from the ages of 5

through 21 and scanning their brains to

look at the functional connections and

the structural connections and also

doing a series of tests on cognition how

they solve problems and what kinds of

things they've been exposed to and also

their emotional experiences to try to

understand this brain development the

adolescent brain and cognitive

development study or ABCD is a study of

10,000 children across the country 1,000

in Los Angeles County alone

they are recruited from select schools

in Los Angeles County at the ages of

nine and ten and followed for ten years

to see what is happening exactly in

adolescence during that very critical

adolescent period we're also studying

the human connectome in older folks

between 35 and a hundred to find out

what makes a brain age well and

gracefully what makes people healthy

throughout their life and what are some

of the changes that can affect that

brain development over time so you if

you're interested you can reach us at HC

P at UCLA edu or this this is our

website or ABC study to see if your

child is in one of our ABCD schools or

hcp at UCLA edu

if you are older and are interested in

thinking about getting a picture of your

own brain and everyone gets a picture of

their brain so I would like to thank you

so much for paying attention and you can

ask questions now on twitter using the

hashtag UCLA UCLA md chat or just go

ahead and contact us with Facebook and I

believe that we already have a few

questions so I will answer a few for

starters okay one question how do you

get children to go into an MRI scanner

well we have special tools in our MRI

scanner to make it easier for children

first we have a practice scanner but

inside the scanner we have special

magnet compatible video projectors video

goggles and audio systems so that the

child essentially experiences something

that looks like a virtual reality

experience and we were able to show the

movies play games while they're in the

scanner so they don't get much of the

feeling of being cooped up in a hole and

we also train them in advance so we've

been very fortunate and able to get most

of our children safely and comfortably

into the scanner without anxiety another

question can we see learning

disabilities when we see a brain scan so

that's a very good question because the

brains of individuals with different

learning problems such as dyslexia or

auditory processing difficulties do have

some subtle differences but

unfortunately they are very very subtle

so we cannot look at a scan and say that

is a child that has or will have a

learning disability the brains look very

much the same there is no brain damage

that causes learning disabilities on the

other hand if we look at many many

children together who have learning

disabilities and compared their brains

with typically developing children then

sometimes we do see some subtle

differences differences in the reading

areas of the brain differences in the

way that different areas of the language

system are connected together so we

can't see them but not at the individual

level

okay what makes the brain of a child

with autism different that's a very good

question there are a number of

differences that we see in the brains of

children with autism and we're doing

many studies right now on on children

with autism young adults with autism and

even infants who are at high risk for

developing autism we believe that autism

is a problem of the development of these

connections that are set on a wrong

trajectory very very early in life we

are getting better at identifying what

some of these problems are and trying to

intervene early so that these children

will have the best outcomes but in

general just as in the learning

disabilities when we look at a brain of

a child with autism we don't see

anything wrong there is not damage to

the brain it's merely developing in a

different trajectory forming different

kinds of connections that the brains of

children with autism will sometimes form

a lot of local connections but the long

range connections may not be as intact

so this is something that we're

beginning to learn more and more about

and hope to be able to have more answers

for you as the years go by and if we

have no more questions

then I would like to thank you so much

for your attention and have a great day

thank you

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you