Emotions: cerebral hemispheres and prefrontal cortex | MCAT | Khan Academy

So what we have here is a brain. And this is like we’re
above the person, looking down into their brain. To orient you, let me
draw two eyes here. And this is the
front of the brain and this is the
back of the brain. And we’re looking at it,
like I said, from the top. Now, why are we
looking at a brain? Well, I want to talk about a
certain area of the brain known as the cerebral cortex and how
it plays a role in emotions. And there’s a number
of different ways that you can divide
up the cerebral cortex and organize it. So we’re going to look at
a few in terms of emotion. So one way that you
can view the brain is in terms of hemispheres. And in your brain, you
have two hemispheres. You have a left hemisphere
and a right hemisphere. And the way you
think of hemispheres, it’s as if you draw the
line down the brain. And you can split it into
two different hemispheres. You have the left hemisphere
and the right hemisphere. And there’s actually
some differences between the left and
right hemisphere. Researchers actually found
that positive emotions evoke more electrical activity
on the left side of the brain than on the right. Whereas negative emotions
tend to elicit more activity in the right hemisphere. Now, you might be wondering
how did they figure that out? Well, what they did is they had
participants in the research study watch a TV screen. So let’s draw a TV here. And this was several years ago. So I bet TVs had
bunny ears back then. So we’ll draw some
bunny ears here. So what this research
study did was they had their
participants watch films, either evoked
pleasure or disgust. And pleasure films were
things like the kind of videos that people share with
each other on YouTube. I mean obviously YouTube
back then didn’t exist. So they just got films of things
that evoked positive emotions, like puppies playing in
flowers and actually a gorilla taking a bath at the zoo. I guess that does bring
quite a bit of pleasure. But that wouldn’t be the first
thing that came to my mind. And they had them
watch other videos that evoked feelings of disgust. And these were like
shock films, like videos of third-degree burns and very
like gory leg amputations, things that would evoke
negative emotions. And while these participants
were watching these films, the researchers videotaped
their facial expressions and also recorded
their brain activity through something
called an EEG recording. And EEG recordings basically
measure the electrical activity of your brain. And what they found was
that pleasure films increase activity in the left hemisphere
because the pleasure films are associated with
positive emotions. Now, it’s not to say
that there wasn’t any activity in the
right hemisphere. There’s just more activity
in the left hemisphere because positive emotions
increase activity in the left hemisphere. And the same could be said for
the disgusting shock films. On EEG recording, they
found that participants had more activity in
the right hemisphere and these disgusting
films are more associated with
negative emotions, like fear and disgust. So I think it’s pretty neat
that while the brain is such a complicated structure, is that
you can actually just split it down the middle and think of
it in terms of left and right. So you can associate
the left hemisphere with positive emotions
and the right hemisphere with negative emotions. But that’s not all in
terms of hemispheres. This concept of left and
right hemispheres becoming more active in
certain situations can also be applied
to social interaction and how outgoing and
sociable you are. And in a different
study, researchers observed a group of
four-year-olds playing in a group. So I’m going to draw
some little kids here. So you have someone here. The researchers watched the
kids interacting in groups and saw how they
interacted with each other. So here are two guys. And you can see them
sharing in a cool toy here. And check out their expression. They’re smiling and
they look like they’re having a great time. And some kids,
that’s how they act. Other kids tend to
be more isolative. Some kids like to isolate a
little bit more and be alone. And here’s an example. Here’s one kid here. He’s just kind of sitting. He’s all alone. He’s frowning. He’s kind of
isolating over here. So after observing and noting
how these children behaved, they did a similar experiment
to what we mentioned above. And they took EEG recordings. And notice something
kind of interesting. That the kids who were more
sociable, playing in a group, they tended to have an
increased level of activity in their left hemisphere. So I’ll put “sociable.” On the other hand, they
noticed that the children who isolated more,
like this guy here, they tended to
have more activity in the right hemisphere. And to represent that,
I’ll write “isolative.” And of course there’s been
other studies as well. And other research shows that
people with more active left hemispheres, they tend to
be more interested, joyful, and enthusiastic about things. Whereas those with more
active right hemispheres, tend to be more timid, fearful,
avoidant, and even depressed. So that’s the basic
overview of emotions in terms of brain hemispheres. Now another way you can
look at the cerebral cortex is by dividing it into
functional divisions. So I’m going to erase
these structures up here. And some of these
functional divisions you can already see in
different colors here. But the one that I want to focus
on is the prefrontal cortex. And the prefrontal cortex is
basically this area right here, this area all the way in
the front of your brain. And it’s actually right
behind your forehead. And this area of the brain is
responsible for many high order functions, like language,
information processing, all the things that
you think of that make humans, humans– the
ability to solve math problems, think through
philosophical issues. Sometimes these are
referred to as very like cerebral activities. And where do you think
that term comes from? Well, the cerebral cortex
and the prefrontal cortex, a part of the cerebral cortex. And like I said, the
prefrontal cortex is really what
distinguishes humans. And because of that,
it’s extremely well developed in humans. And it undergoes the greatest
amount of development after birth. I mean think of how you become
more mature as you get older, or so they say. In terms of the
prefrontal cortex, you use this part
of the brain when you’re trying to solve problems,
make decisions, and manage how you behave in social situations. For instance, you probably
behave differently during a job interview than
you do during a wild sporting event. And even if you don’t, you know
that there are certain norms and expectations
in job interviews than there are in
sporting events. And the ability
to know that comes from your prefrontal cortex. And I mention this
because in another video, we talked about the amygdala. And the amygdala causes fear,
anxiety, anger, and aggression. And I’m sure you’ve had
the experience in your life where you felt very
angry at someone. And when you have those
sorts of feelings, maybe your primal reaction
is to attack the person or physically hit them. But of course, many
people don’t do that. And why is that? Well, because they have a
well-developed prefrontal cortex and the
ability to understand, well, violence isn’t the answer. You shouldn’t attack someone,
no matter how you feel. And that thinking that you have
your mind where you say no, no, I should restrict my
behavior, I should walk away, all those thoughts that you have
come from the prefrontal cortex because that helps
to manage how you behave in social situations. One question that’s
interesting to consider is what would happen if you
damaged your prefrontal cortex? How would you act? Well, there’s a famous example
of this where someone actually did have that happen to them. And his name was Phineas Gage. Now, Phineas Gage was 25 years
old, back when it was 1848. And he was a railroad worker. So I’ll draw some
train tracks here. And as part of
building this railroad, they had to do controlled
explosions to make way for it. And Phineas Gage was
responsible for overseeing that. So here he is. And he was just overseeing
these explosions. Now during one of
these explosions, an iron rod was sent
flying through the air. And it actually penetrated
through his skull. It went in one side
and out the other. And during its course
through his skull, it destroyed much of
his prefrontal cortex. The man that Phineas Gage
was after the accident was not the same
man he was before. You see before, his
friends and coworkers known as a hard working
and well-liked guy. After he experienced
this trauma to his head, he became rude and gruff. He swore a lot and just behaved
inappropriately overall. And that’s because he no longer
had a functioning prefrontal cortex. So that’s the cerebral cortex. So if you ever wonder
what makes a human, human, well, a lot
of it’s actually right behind your
forehead, in the area known as the prefrontal cortex.


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