- [Instructor] When we think about changes
that happen during puberty,
we usually think about changes that happen to the body.
Things like the development of secondary sex characteristics
or changes in height or an increase in body hair.
But those aren't the only changes that happen.
There are actually a lot of changes
that happen to the brain as well.
Here I have an image of a brain.
This is what you would see if you looked
at the side of the brain.
Here is the front towards the face.
Here's the back.
And then over here,
I have another brain and this brain is sliced in half.
This brain is sliced right down the middle.
These two brains are facing each other.
So here's the front.
And then here's the back of this one.
One of the major changes that we see during adolescence
is the development of the frontal lobe,
particularly the prefrontal cortex.
I'll roughly indicate where on the brain that is.
This is the area of the brain that is responsible
for what scientists call higher order cognition.
Things like thinking about the future,
and planning, and decision making.
And also the ability to inhibit certain behaviors
and focus on longterm goals.
This part of the brain doesn't really stop maturing
until our early twenties.
Because it is still developing during the teenage years,
because it isn't fully developed.
this might help to explain
why teenagers sometimes show poor judgment.
Another area of the brain that continues
to develop during adolescence is the limbic system.
This includes a number of different brain structures.
This image isn't really the best way to view them
because a lot of the structures
are on either side of the midline.
Even so, I want to point out about
where they are in the brain.
One structure included in the limbic system
is the amygdala,
which would be about here.
This is the part of our brain that's responsible
for emotions and emotional responses.
It also includes the hypothalamus,
which is here and let me pick
a slightly different color for that.
This part of the brain regulates
a surprising number of things.
But in particular,
I wanna focus on its role concerning the endocrine system
or the hormone system in our bodies.
To be clear,
the limbic system includes a bunch
of other structures as well,
but I really wanna focus on these two,
because in combination with the prefrontal cortex,
which helps to regulate our emotions,
the fact that these structures are still developing during
the teenage years might help to explain
why teenagers can sometimes be moody,
why they might sometimes have emotional outbursts,
like yelling at their parents
and stomping out of the room and slamming the door.
While I think that this is kind of funny
and while it kind of makes me want to roll my eyes
when teenagers act out,
this does actually have some really
important legal implications,
like whether or not we should be able
to charge teenagers like adults
when they commit certain crimes.
This is a question that I put to you.
Should teenagers get the same treatment as adults
if they commit the same crimes?
Should they be able to be sentenced to death
or to life in prison for acts
that they commit prior to turning 18?
Do you think that this is a good boundary?
Are crimes committed one month
before someone's 18th birthday really different
from crimes that they commit one month after?
Where should this boundary be?
How should we define adulthood?
These are really difficult and serious questions
and it's really not clear what role developmental research
has in solving these problems
or if it should even have a role at all.
Putting that very serious question aside,
another area of the brain that changes during adolescence
is the corpus callosum,
which you can see here.
This is the area of the brain
that connects our left and right hemispheres.
There are a number of things that change
about the structure during adolescence.
But in particular,
I really wanna focus on the changes to connections
that are associated with language and language learning.
These connections grow before and during puberty
but this growth stops soon afterwards.
This might help to explain why learning a second language
is so much easier in childhood as compared to adulthood.
So we see changes to those specific brain areas
but there are also other more global changes
that are happening in the brain during this period
or changes that are happening throughout the brain.
One thing that we see during this period
is an increase in myelination,
especially in the areas that are associated
with higher order functioning.
To quickly review,
this is a neuron and neurons communicate
with each other by sending signals down these long axons.
Myelin is a fatty tissue that covers the axons
of neurons and helps to increase the speed
at which the neurons can communicate.
Faster communication between neurons
means faster communication between brain areas.
This can help explain why adolescents are able
to process information faster than children.
Another thing that we see during this time period
is that there's an increase
in brain volume during early adolescence
and then this shrinks during late adolescence.
This suggests that adolescence
is a period of synaptic pruning
or cutting weak connections in the brain.
So this is your body literally
breaking down connections between neurons.
You might initially think that this is a bad thing,
but this pruning is actually really good
and it's really important
because it allows the body to focus energy
and resources on the connections that are used most.
A kind of scary implication of this is that
what we do during our teenage years
might be literally shaping our brains
for the rest of our lives.
But there's kind of a use it or lose it principle
at work here.
So if we spend our free time reading,
or playing sports,
or focusing on academics,
and having good time management skills,
then that's what's going to be reinforced.
The parts of the brain that are responsible
for those behaviors are physically going to be strengthened.
But if we spend most of our time watching TV
and sitting on our couch and procrastinating,
that's what's going to be strengthened instead.