Hi everybody, Dr. Mike here. In this video we're going to take a look at the parietal lobe. Now as a quick run-through, remember the four main lobes include the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. There's also the insula, which sits just sort of underneath the temporal lobe. It's like the ground floor of the cerebral cortex.
Now we're going to focus on, in this video, the parietal lobe, which is sitting here. Now when we have a look at the parietal lobe, the way you should think about it is it is the sensory cortex. Now think about when we spoke about the frontal lobe, it's the motor cortex, the action area.
The parietal lobe is the sensory cortex. This is where we get an understanding of the things that we are experiencing in our body and also in the environment around us. So it's important when it comes to understanding tactile information. Touch, for example. It could be touch, proprioception, temperature and pain.
This is where we understand it again in the parietal lobe. But first we need to talk about... the anatomical margins that you should be aware of.
Remember that we have right here an area called the central sulcus. Now central sulcus, central because it's right in the middle, sulcus because it's a dip down. And it's spoken about the fact that when there's a dip down either side you're going to have a bump up.
So dip down being a sulcus, a bump up is called a gyrus. Now with the frontal lobe here we've got the pre-central gyrus. and therefore here for the parietal lobe it's called the post central gyrus. When we spoke about the frontal lobe we said that the pre-central gyrus was the primary motor cortex.
This has a map of the body on it, of all the muscles that we can consciously move. Now the post central gyrus here of the parietal lobe has also a map of the body of areas that can feel sensation, areas that can feel fine touch, two-point discrimination, proprioception, pressure. pain, temperature, all those things, we have a map of the body right here.
And it's called our sensory homunculus. And I've drawn it up here and it looks very similar to that of the primary motor cortex, in which we have genitalia, feet, legs, bum, back, neck, head, arm, hand, face, lips, tongue, pharynx and larynx. Now importantly, you can see that even though it's a map of the body, it's not really in the order and fashion that we...
see the body in and also some areas are enlarged. Areas for example like the hand and the lips. Why is this the case? It's because we have the very sensitive areas right. So when we look at the hand for example there's a large amount of sensory neurons in the hand.
Therefore there needs to be a larger area of the brain or the somatosensory cortex dedicated to it. Same for the lips. If you think about two-point discrimination. Two-point discrimination is if you get two-point discrimination. two points.
Now they could be sharp pencils, they could be pinpricks, they could be whatever it may be. And if you put these two points, get somebody, get them to close their eyes and put it in an area of the body. And you ask them, can you feel two separate points?
And they'll say, yes, I can, or no, I can't. And you move them closer together. So then you get them like this and say, can you discern that there's two points? Now you'll find that on the hand, the two point discrimination is millimeters, even smaller than that.
before they go, no it feels like only one object. But on the back it's centimeters. You could probably place two points this far apart on somebody's back and say, does this feel like one object or two?
And they'll probably go, yeah it feels like one object. Now have a look, the back has a very small area of the somatosensory cortex dedicated to it. So there's not many neurons there for sensation.
But for the hand it's huge and same for the lips, it's huge. Large areas dedicated to it. So anytime these areas have some sensation, right, it's going to be sent up to this area called the somatosensory cortex, which is in the post central gyrus.
And just to reiterate, what we are getting here is touch, pressure, pain, temperature, and proprioception. Do you remember what proprioception is? Proprioception is knowing your posture and position. So knowing if I close my eyes that my arm is out here, I know where it is. If I can touch my nose with my eyes closed, the reason why I can do it is because I know where I am in my own space.
I know that my arm is out here, bent at a particular angle, at a particular position. Because we've got various types of receptors in our joints, muscles and areas like that, that tell us where we are in our space. That's proprioception. Okay. Another really important point here is that you can see that unlike the body, the hand for the somatosensory cortex is mapped right next to the face.
Now the reason why this is important is because there's some individuals who lose a limb. Now if this limb is lost, let's think about it. They lose their limb at the elbow.
That hand no longer exists. So the sensory neurons in the hand no longer exist. But the neurons dedicated to having a map of the hand on the brain right here, they still exist. But they're not receiving any information because the hand doesn't exist. There's nothing to stimulate the receptors here to send the signal down the arm, into the spine, up to the thalamus and then project it from the thalamus to the hand and say hey you're feeling something.
So these neurons get starved of information. Now the brain loves sensory information and it doesn't want to be starved of input. So this is where a term called neuroplasticity comes into play.
The neurons of the hand start to have a conversation with their neighbours and what's their neighbouring neurons? Those of the face, right? And so what that can mean is for some individuals who have lost a limb, You can tell them to close their eyes and you can touch their face and say, what do you feel?
Now think about it, you're touching the face, sends a signal in, and it goes to this area and it's stimulating these neurons. And he goes, oh, I'm feeling you touch my face. But because they're now having conversations with neurons of the starved hand area, they can also say, but now I feel you touching my index finger, ring finger, and pinky finger, because there's a conversation being had and that is neuroplasticity.
Amazing. Now it doesn't happen with all people who have lost a limb, but it does happen with a subset of individuals. So when we look at the somatosensory cortex, it allows for us to understand that we are feeling something.
Touch, pressure, pain, temperature, proprioception, whatever it may be. Now in addition to that, it allows for us to make a judgment of what we're feeling as well. So it tells us whether, it tells us basically the size of an object, the weight of an object, the texture of an object. So it does tell us this information but it still doesn't actually tell us what the object is.
This is where we need to bring the next area called the association cortex. Now first let's just highlight here this is our somatosensory cortex moving down like that. We now need to talk about the association cortex and the association cortex is sitting around about here.
And what the association cortex does, similar to that of the association cortex of the motor cortex, is it brings in information from other areas of the brain and brings in previous experience to tell you exactly what's happening. So in this scenario, let's just think I put my hand in my pocket and there's a coin in there. So I'm feeling that coin.
I'm feeling it through touch, the temperature of the coin for example, its size, its weight, its texture. All of this information is going to my primary motor cortex, but I don't know it's a coin. Now, what the association cortex does is it takes information from the thalamus, a deep area of the brain, which projects up, takes area from the visual cortex, brings it back up, takes area from the auditory cortex and brings it up, and takes information from all these other areas of the brain to tell me what this object is. So if I take a look at it.
visual information coming up, I see it. Past experience and understanding, I can say I've felt something like this before, I've seen it before, this is a coin and that's what the association cortex does, allows you to identify that object. Alright, so if you have damage to that area, it's hard to identify what things are whether that is a shoe or a lamp for example or a coin, but you can still understand the various aspects of that object through the primary motor cortex.
So that's what the association cortex does. It allows for you to identify objects. Now importantly, there's some other areas of the association cortex that you need to be aware of.
And these areas, there's another sulcus that sits here for example, and there's going to be another gyrus here, and another gyrus here. Now these areas are important, they're part of the association cortex. This one here is called the supramarginal gyrus and this one here is called the angular gyrus. Now again, these two are part of the association cortex.
Now what they importantly do, supramarginal gyrus is important for telling you about your body. Posture and your position. So posture and position. So let's write that down. Supra marginal.
I'll just write supra marginal is important for posture and position. Now what's posture and position? Posture and position is proprioception, right?
So the supra marginal drives tells you about proprioception. But here's the really cool thing. It's not just your posture and position.
It's other people's posture and position. So you can actually see that by the way somebody holds themselves and presents themselves. Whether that individual is a threat or maybe they're there to help you or whether it's a kind act or whether it's potentially malicious act. Now what this is telling us is it's part of the mirror neuron system. Mirror neurons allow for us to understand the motivations and intent of another person.
Therefore the super marginal gyrus is not just important for your proprioception posture and position but other people's posture and position and whether it's a threat and this is important for demonstrating empathy. If somebody is showing you a kind posture, you may want to reciprocate that kind posture. And if they're showing you maybe a not so kind posture, you may want to reciprocate that as well.
Therefore, we know this because if there's damage to the supermarginal gyrus, people have problems demonstrating empathy. All right. So now we look at the angular gyrus here. And the angular gyrus is important for word. choice.
It's important for word choice because it actually brings information down to an area right here called Wernicke's area or Wernicke's area. So right here there is an area called Wernicke's area obviously named after somebody called Wernicke or Wernicke. You can see that Wernicke's area is actually not just part of the parietal lobe but also part of the temporal lobe as well. Some people discuss it when they talk about the temporal lobe, but let's just talk about it here for the parietal.
It is important when it comes to recognizing and interpreting speech and written text. So recognizing, recognizing, and interpreting written text and speech. So it's basically seen as our speech production area. So if there's damage to Wernicke's area, the individual may have a problem with producing speech.
Now they don't have a problem, uh sorry not producing speech, with interpreting speech. Let me just revise that. Wernicke's area is important when it comes to understanding speech, understanding written text. So they may not be able to read what's in front of them, but they still understand those words.
Broca's area, which I've spoken about before, is a problem with speech production. So they can understand what they read, but they can't produce speech. This is the opposite.
They can produce speech, but they can't understand it. All right. So again, it has a close relationship with the angular gyrus, which helps with word choice. Okay.
So what we've gone through for the parietal lobe is that it's the sensory cortex or the sensory lobe. We've got the primary somatosensory or the somatosensory cortex here, which has a map of the body called the sensory homunculus on it. It's important because if we want to understand the touch, pressure, pain, whatever it may be about that tactile experience, we get that information going straight here, right?
Via the thalamus, goes straight to the somatosensory cortex. If we want to understand more deeper, detailed information about what we are experiencing, we need to bring in the association cortex. And that includes that of the supramarginal gyrus and angular gyrus. Supramarginal gyrus is about posture and position, not just of yourself, but of others, and therefore plays a role in empathy.
And angular gyrus, when it comes to language and word choice, has a close relationship with that of Wernicke's area, which is important with trying to understand and interpret written speech or auditory speech. That is a run-through of the parietal lobe.