All right, on with the tour. we started at the back of the brain. We did the occipital lobes at the very back, moved sort of towards the ears, and did the temporal lobes. Now, we're going to kind of go up but still staying near the back of the head an area that we're going to call the parietal lobes. And well, I, I think this is true of, of all parts of the brain. A really fascinating and cool part of the brain that does some really neat stuff. on with the tour. All right, so Week 2 Lecture 6, The Parietal Lobes. Actually, when you see this little colored thing here you know, the parietal lobes would be this green area just so we have our geography straight. You're going to see that, you know, sometimes the way these, the, the size of these things is, is represented changes. and you'll actually see that going right from here, where I say the green is the parietal lobe. I think this is a pretty accurate representation. This would be what we're going to call the frontal lobes, and you see how much of it there is. And the parietal lobe's just sort of along the back. compared to this diagram, where the parietal lobe seems to be a lot more forward. but artistic license, I guess. But by now, of course, this should start to feel very familiar to you. You're getting to know the brain quite well. Brain stem, cerebellum, occipital lobe at the back, temporal lobe under the ears. And so, yeah, now we're up here in the parietal lobe. and there's some really cool things about the brain that are really represented strongly in the parietal lobe. So we're going to learn about the brain in general while we're also learning about the parietal specifically. So, remember I said occipital lobe has primary visual cortex, temporal lobe has primary auditory cortex, so for vision that's where the raw visual stimulus came in. For for the temporal lobe that was where the raw auditory stimulus came in. Well, for the parietal lobes, that primary cortex is devoted to sensation. Okay, literally feelings on our body. Okay? when something touches our body it, it basically activates parts of this part of the temporal lobe, something we're going to call the somatosensory cortex. Some people just call it the sensory strip, or the somatosensory strip. because you see,it is kind of organized on a strip, and with the rest of the parietal lobe kind of behind it here. You also see that it's right adjacent to another strip of cortex we're going to call the motor strip. Let me, let me get back to the motor strip for a second. because even though the motor strip is actually part of the frontal lobes, these things share so much in common that, that it makes sense to talk a little bit about them together. But let's start with the green area, somatosensory cortex, right here. And again, as I said, what it's doing is receiving input from the body. and in fact, you can find out exactly what part of the body relates to what part of this cortex by measuring electrical activities. So, you can literally, and of course, they typically did this in animal brains initially, you can put probes in the brain, and then you can stimulate parts of the body. And when you stimulate a part of the body related to that specific part of the brain, you will see an electrical signal. and so by moving the probe around, and touching different parts of the body, you can essentially map this somatosensory cortex, and find there exactly what parts react to what parts of the body. When you do that, this is what you find. And, and there's a couple of interesting things. So, first of all we have this weird cross-wiring going on. The left side of the brain responds to sensations on the right side of the body. And vice versa, the right side to sensations on the left side of body. So there's a little bit of what we sometimes call contra-lateral wiring, cross-wiring. Why? I've never heard a good explanation. I don't know, but that's how it is. But what we also see is that the amount of brain tissue devoted to a given part of our body does not depend on the size of that part of the body, but rather on its importance, in terms of sensory input. Okay? So you'll notice for example that, our facial areas are, are very strongly represented, as are our hands. Our hands are what we use primarily to touch and feel things, right? There's a lot of sensory cortex, a lot of brain devoted to your hand, which gives you a very high-detailed, if you want, high resolution sensory experience with things you touch with your hand. if, if you want to get a sense of the opposite of this, well do, do the following things. First of all, let's do it with your lip, because notice, there's a lot of lips here. Pinch your lip really hard. most of us won't even pinch our lips really hard, because if you pinch it too hard, it starts to hurt, right? And, and you don't want to pinch it too hard so that it starts to hurt. Now do the same thing with your elbow. Pinch your elbow. You can pinch your elbow as hard as you want. You don't feel a thing when you pinch your elbow. It turns out, there's really no sensory cortex devoted to your elbow. And you know, that makes sense when you think of it, because what do we do with our elbows? We, we sit on them. We put a lot of weight on them. and so we don't really want pain. We don't really want sensitivity in the elbows, but we want sensitivity in the lips, we want it in the hands, et cetera. And so you see that the amount of cortical tissue reflects that, how important that body part is for sensory input. and even things like the tongue and the mouth get a lot of tissue because we're using that to, to produce words. And yes, that's motor, it's output, but we also need to feel what's going on in there in order to shape our mouths appropriately. And so there's a lot of tissue devoted to that, too. So kind of cool. and yeah there's, there's some tissue devoted to your genitals as well. It turns out we like sensory input from those regions. In fact, sometimes by the way, this is represented in this kind of form, by something called the sensory homunculus. So this is just basically an art, artist's rendition of what we would look like if our outer bodies were proportioned according to how much brain tissue is devoted to them. And so, you see the big lips and mouth, and the big hands. In some depictions, you see much bigger genitals as well, by the way. And this is just another example of that, of that motor strip. Now, I'm very quickly, we're going to come back to it. .But I'm very quickly just going to highlight that this strip actually belongs to the frontal lobe. So we'll talk about it in detail next lecture. But it's really going to tell the same kind of story. Again, the left side corresponds to the right side of the body. But in this case, it's not about sensory input, but about motor output. So this strip when, when I move my hand, that signal originates somewhere. So it's literally, a part of this cortex gets active, and that makes my hand move. So this is what outputs behavior, this is what inputs sensory input. but otherwise again, you see the motor strip also has that representational thing. It does have an elbow. It's good to move your elbow a little bit. but really the same kind of story, input versus output. so I'll just mention that quick. All right, now there's also another interesting aspect of the parietal lobe that's related to laterality. Remember, the temporal lobe, language versus other sounds. in the parietal lobe, it seems as though the left and the right are, are focused on body and world respectively. So literally, in order, if you think for a while, in order to move around the world effectively, you really have to know two things. You have to know, where is my body, and you have to know, where are things in the world? Because in a sense, you can think of your body as the vehicle. You have to move this vehicle through the world. You have to negotiate it. And in order to do that effectively, you need to know where the vehicle is, you need to know where things are in the world. And it kind of seems as though the brain is lateralized in accord with that. Let me give you a couple of examples. This, once again, is Oliver Sacks, the neural psychologist. and once again, in his book, The Man Who Mistook His Wife for a Hat, he's got a different story about a woman who's lost her ability to, to sense something we call proprioception. What's proprioception? It's this weird sixth sense, as it were, that we have about where parts of our body are at any given moment. So it, you know, think for a second. Just sit where you are, relax, and now let me ask you the following question. what does your left big toe feel like right now? And notice that you can kind of mentally move to your left big toe. You can kind of feel the position it's in, what it's doing. move to your right buttock. What does it feel like right now? What sensation is on it? We can kind of move mentally through our whole body, and have a feeling where our body parts are. and again we do really take that for granted, but it can get really odd when you lose that. So in the story Oliver Sacks tells, he tells of a patient who woke up in the middle of the night, and to her horror, there was a human leg in bed with her. And this is like Godfather, with a horse head in the bed. There's a human leg in the bed with her, and it horrifies her. So, she does what maybe many of us would do. She grabs the leg, and throws it out of the bed. now the problem is, it was her leg. And she went tumbling out of the bed after it, because it turns out, legs weigh quite a bit. but it didn't seem like her leg, because she couldn't feel it from the inside, for lack of a better term. That sounds really weird to us, but really you've probably experienced it. If, if you're like most people, you've fallen asleep sometime with your hand over your head like this [SOUND]. So you're asleep. All the blood drains out of your arm. When that happens you might wake up, and you might see this hand, and it might freak you out at first. Because it doesn't seem like it's your hand, because when the blood all drains, you become like that patient. You can't feel this from the inside. and so it freaks you out. Like, what the heck, where'd that come from? Same idea. It's not my hand. But most of us realize oh, that is our hand. And you've probably also had the feeling of grabbing that hand and lifting it up, and moving it somewhere. And it feels like this heavy ton of, of stuff that you hadn't intended to drop. That's what life would feel like without proprioception. and, and that's what the left part of the parietal lobe seems to deal with, handling where our body is all the time, sensing. More sensing than, than moving, of course, because that'll be frontal. But sensing where the parts of our body are all the time. That seems to be the left. The right seems to more focused on the world, the outer world. What's out there? and in fact there's, there's some interesting odd cases of what happens when the right parietal lobe is damaged. So when the left is damaged, you lose proprioception. When the right is damaged, it seems as though people lose the ability to sense the world properly. specifically, they show something called unilateral visual neglect. if you gave patients these figures and you said, hey, can you please draw these? They would draw them, but you would note this common bias in the sense that, the right side of the figures, they copy with pretty good detail. But the left side, they tend to leave a bunch of stuff out. In fact, it's kind of like, with a lot of these studies, it's like they just don't see things on the left. The funny story I remember that, that always stuck in my head, is if you give one of these patients a plate of food, they will quite often eat all the food on the right side of the plate and put their utensils down. Now why do they do that? Are they full? Well, it turns out, if you just spin the plate, they will go, oh, and then they will eat the rest of their food. So they weren't really full. It's just kind of like, and they're not blind to the left side, but they, we talk about it as an intentional phenomenon. It's just like they never attend to it, and they don't kind of notice it's there. a fascinating thing. But again, it points to the fact that this part of the brain is somehow taking the parts of our world, and giving us this perception of what's out there. but when that part of the brain is damaged, that perception is damaged too. Now, it always tends to be the left side of the world that gets lost. Haven't heard a good explanation for that, too, which, which by the way this is a good point for me to mention. Remember me talking about how young psychology was as a science? Well, it is very young, especially with you know, really good scientific techniques being applied to it. And, so, there's still a lot of points in this course, where I will do things like this, and say, you know, it's only the left side. We don't know why yet. and for me, that makes it kind of cool. It's, it's like, you know, I'm not telling you all these laws and facts. I'm telling you about data and ideas, what we think is going on, but we got a long way to go. and, and again, I think that makes it a lot of fun. All right, so, if you'd like to learn more about the parietal lobes, well, first of all generally, here's Oliver Sacks giving a TED talk. So he will talk about a number of different brain regions, and a, and a number of the patients who have suffered damages to the regions, and the things they show. Always fascinating. This is much more specifically a video featuring a visual neglect patient, so you can get a really good sense of what visual neglect is like. generally speaking, here's a reading on parietal lobes and stroke and some of the various issues that arise when people have strokes. A stroke, usually a blood vessel will explode or swell, and brain tissue will be damaged. so you can learn little bit about damage that way. This one, I think you'll find really fascinating. It's, it's one of these things that, when I heard about it for the first time, I just kind of went, wow. it turns out that the brain doesn't just you know, accept sensory input in a very static way. It desires sensory input. It's hungry for sensory input. So they devised these chambers in the 1960s where you could go in and they would block off all forms of sensory input. You'd have these things around you. You'd be floating in this highly salinated water, and after you're there for a while, you don't feel any sensory input. And it turns out, that's fine for a while. You know, people could maybe sleep for a while, or whatever. But before too long, if they didn't get sensory input, their brain started to create illusory sensory input. That is, the people began to hallucinate sights, sounds, feelings. And people generally cannot stay in these chambers very long because they start to go a little crazy. our brain is hungry for input. And if we don't feed it, it makes its own which is really kind of cool, weird. There was a movie called Altered States. It's a fanciful movie. I, I'm not suggesting it's scientifically correct at all. It's not, but if the sensory deprivation thing is, is fascinating for you, check out that Altered States movie. but in the meantime, read that, and, and that'll get you going. Okay? Good. That's the parietal lobe. from here we go to what's perhaps the most important lobe in the brain, at least the one that makes us most human, I would say, the frontal lobe. I will see you there. Follow me. [BLANK_AUDIO].
