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Emotions: cerebral hemispheres and prefrontal cortex

Video transcript
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.