The Cortical Forebrain : Study with Video Lessons, Practice Problems & Examples

The Cerebrum

This video we're going to begin talking about the forebrain by going over the cerebrum. So the cerebrum is basically the entire upper portion of the brain, so it is the largest part of the brain making up about 80% of total brain mass. And the cerebrum consists of 2 hemispheres, the left hemisphere and the right hemisphere, and these hemispheres are connected by a bridge of fibers called the corpus callosum. So the corpus callosum basically relays information between the two hemispheres, so it allows those two hemispheres to communicate. So if you look at our image here, for this first one we're basically looking straight down at a brain.

So this is the front and this is the back and you can see this little kind of divide between the two sides of the brain. So over here on the left, we have, of course, the left hemisphere and then on the right we have the right hemisphere and you can see that nicely in our other image as well. This is called a coronal slice of the brain. Basically, if you kind of slice the brain right down like that and you can see that nice divide between the hemispheres there. So if you basically kind of peeled back the top layer of the brain, you would see these fibers running right through and on our coronal slice you can see it right here and that is our corpus callosum.

One really interesting phenomenon that we see in our cerebrum is something called hemispheric specialization, which is the phenomenon of each hemisphere being specialized for certain functions. So in general, for most people, not all but for most, the left hemisphere tends to be specialized for things like language and logical thinking, and the right hemisphere tends to be a bit more specialized for things like emotional thinking, creativity, art, and music. Although it is important to keep in mind that even while we do see hemispheric specialization, the 2 hemispheres of the brain are always communicating and kind of working in tandem, so just keep that in mind. And one other really cool phenomenon that we see in our cerebrum is something called contralateral control, and contra means opposite and lateral means side, so this literally means opposite side control. What we see is that each hemisphere actually controls the opposite side of the body.

So the left hemisphere is responsible for the sensation and movement of the right side of the body and vice versa, and we don't actually know why we have contralateral control, but we see it in most vertebrates, so mammals, birds, and even some fish species. So scientists think that it probably gave us some kind of evolutionary advantage but we're not exactly sure what that might have been, but it's very interesting regardless. Alright? So that is our introduction into the cerebrum and I will see you guys in our next video. Bye bye.

The Cortical Forebrain Example 1

Okay, so based on what we know about hemispheric specialization as well as contralateral control, determine if the left or right hemisphere would be more active for each of the actions listed below. First up, we have learning a new language, and for most people, the left hemisphere tends to be more dominant when it comes to language. So we're going to just circle left there. The next one is kicking a soccer ball with your left leg, and because of that contralateral or opposite side control, if we're kicking with our left leg, it is actually the right side of the brain controlling that movement. So we'll circle right.

The next is painting a landscape, and in general, the right side of our brain seems to get used a little bit more for creative pursuits like art. So we're going to circle right there. Finally, we have squinting through a keyhole with your right eye, and again, because of that contralateral control, that movement would be getting handled by the left side of the brain. Alright? So there is our example, and I'll see you guys in the next one. Bye-bye.

One treatment for severe epilepsy is to surgically sever the connection between the hemispheres of the cerebrum. What structure is severed in this procedure?

• A. Corpus callosum.
• B. Pons.
• C. Cerebral cortex.
• D. Midbrain.

The Cerebral Cortex

In this video, we are going to be going over the cerebral cortex, which is basically the outer layer of the cerebrum. If you have ever just looked at the surface of the brain, that is the cerebral cortex, and, as I am sure you have noticed, it tends to have pretty prominent grooves and ridges that give it a very wrinkled appearance. There are actually 2 specific features that give it its very distinct look. The first of those are gyri, the singular of this being gyrus. Gyri are basically the elevated ridges of tissue on the surface of the brain. We have gyri, and we also have features called sulci, the singular of this being sulcus. These are basically little shallow grooves of tissue that separate the gyri.

So, if we were to take a little chunk of our cerebral cortex and kind of zoom in on it, it would look a bit like this, and we can see along the top we have these little bumps or ridges. Each of those bumps would be a gyrus. And then we can see these little shallow grooves that separate our gyri, and each of those grooves would be a sulcus. Gyri and sulci are really important because our brains are really big, and folding and convoluting the brain allows us to maintain a pretty large surface area while having our brain still fit inside our relatively smaller human skulls. So, it is pretty cool how that works.

Now, the cerebral cortex is basically divided into 4 lobes, and we have divided these lobes based on their function. We are actually going to go over some specific regions in these lobes in more detail in our next video, and that will make some of these functions make a little bit more sense. So, for this video, just focus on getting a sense of where each of these lobes is, what the lobes are called, and a general idea of their function. Do not worry too much about memorizing all of this stuff yet. We are going to begin with the frontal lobe, which we have depicted here in pink, and it is right in the front of the brain.

The frontal lobe is important for things like conscious thought, your awareness of what is going on around you. It is also really important for complex cognitions as well as things like voluntary movement and speech. Again, we are going to go over specific regions that cover a lot of these functions in our next video. That is our frontal lobe, right in the front. Next up, we have our temporal lobe, and the temporal lobe is found literally right near the temple, so it is kind of right near your ears.

It makes sense that it's near your ears because the temporal lobe is important for things like auditory processing, language comprehension, as well as memory. Moving up toward the top, kind of like the top back of the brain, we have this region in blue, and that is the parietal lobe. The parietal lobe is important for sensations, specifically like touch sensations such as temperature, pressure, pain, proprioception, knowing where your body is in space, and just general spatial awareness. That is happening on the top there in the parietal lobe. And then finally, way in the back, we have the occipital lobe, and the occipital lobe is devoted mainly to vision.

I always remember that because I think it is interesting and almost ironic how the part of our brain that is responsible for seeing is as far away from our eyes as humanly possible. It is just kind of interesting how that worked out. And those of you who are interested in anatomy may have noticed that the lobes of the brain are actually named after the cranial bone that they are underneath. So, that is a nice easy way to memorize the lobes if you know anything about anatomy. Alright, and as I mentioned, we are going to go over some specific regions in those lobes in our next video, so I will see you guys there.

Bye-bye.

The Cortical Forebrain Example 2

Okay, so in a few words, why are gyri and sulci important? Gyri and sulci are important because human brains are big, right? We are a very intelligent species, we have a lot of neurons, we have a lot of neuronal connections, and so folding our brains basically allows us to have more surface area in less space. So I want you to imagine, you know, imagine you had, like, a blanket or a towel. Let's say it was, like, 2 square feet.

If you took that and you just kind of crumpled it up and folded it you could probably make it the size of like a softball, right? So you're basically taking that huge amount of surface area and just having it take up less space and that way our brains fit inside of our heads a little bit better. Alright, there you have it and I'll see you guys in the next one. Bye bye.

A gyrus is a(n) ___________ while a sulcus is a(n) ___________.

• A. Groove: elevated ridge.
• B. Elevated ridge: groove.
• C. Lobe: elevated ridge.
• D. Elevated ridge: lobe.

Important Regions In The Lobes

Okay, so now that we've covered those lobes more generally, let's go over some important regions within the lobes that you may need to know. Now, as you can see, we have the lobes of the brain kind of delineated here with these darker lines; we have our frontal lobe right in the front, the parietal lobe kind of in the top back, the occipital lobe right in the back of the brain, and then the temporal lobe kind of running along the temple or like the ear area. Alright, so we're going to begin in the parietal lobe. You guys may remember that the parietal lobe does a lot of sensory processing and so it contains our primary somatosensory cortex. Now we're actually going to go over this region in an upcoming video so you don't have to know what it does in detail yet, but sensory is right in the name, right?

So, you can probably guess it's going to be doing some sensory processing. So for now, just know that the primary somatosensory cortex is located in the parietal lobe. Alright, moving around to the back of the brain to the occipital lobe, you guys remember that the occipital lobe pretty much exclusively handles vision and so it should come as no surprise that it contains our primary visual cortex. This is basically the region of the brain where visual stimuli will go to get processed. So the occipital lobe, again, is just handling vision, though it has our primary visual cortex in it.

Alright, swinging around to our temporal lobe, you guys may remember that the temporal lobe handles auditory processing as well as language comprehension, and we have 2 regions that specialize in those two things. So first up here in purple we have our primary auditory cortex, and this is just the region of the brain where auditory stimuli go to get processed. So, you know, right now you are hearing sound waves. Those sound waves are my voice, and they're going right to that primary auditory cortex in order to process what that sound is, you know, distinguish it as a human voice, things like that. And then right next to that primary auditory cortex, we have this region here in yellow and that is Wernicke's area, and Wernicke's area is the region that is essential for language comprehension.

So I always like to think about how these kind of fit together very nicely. So you have that auditory stimuli coming in, getting processed, and then right next to that, assuming that that stimuli is human speech, it's going to be getting actually understood and comprehended right next door in Wernicke's area. So some people like to remember the phrase Wernicke tells you what you are hearing. They're kind of thinking about the W in what and the W in Wernicke's going together. So Wernicke's tells you what you are hearing.

Alright, so now moving back around to the front of the brain to our frontal lobe, we have a couple of important regions here. First up, we have our primary motor cortex located here in the frontal lobe depicted in red, and we're actually going to talk about this in an upcoming video as well. We ended up grouping together the motor and somatosensory cortices because they get talked about in a very similar way - you'll see what I mean in a few minutes - but motor means movement, right? So this is going to be doing some movement basically. So right next to that, we have this region here in orange, and this is Broca's area.

Broca's area is essential for speech production. And when I say speech production, I mean the actual, like, movement of your mouth, so the movement of your jaw, your tongue, your lips, in order to articulate speech. So I always like to think about how this region of the brain that helps to control the motor coordination of our mouth is right next to the motor cortex of our brain or the primary motor cortex of our brain. So that kind of goes together, and some people like to think about the phrase Broca's builds speech.

So, putting those ideas together, Broca's builds. If you are a Spanish speaker, this one's kind of easy to remember because Broca sounds a lot like boca or mouth, so you can think about how Broca's controls la boca. And then finally, we have this region here in green, and this is the prefrontal cortex. And prefrontal literally means as frontal as you can get. It's like the front tip of the brain, and the prefrontal cortex is super important.

This is what controls a lot of complex cognitive processing, so things like executive functions, working memory, self-control, logic, planning. We also see some integration of memory, knowledge, and emotion happening here. But the prefrontal cortex is very important for what sets us apart as human beings more generally, but also really it's what makes you you. A lot of your personality and who you are comes from the processing that occurs in your prefrontal cortex. Alright.

So like we talked about, some of these are pretty intuitive, like the visual cortex and auditory cortex. Some like Broca's area and Wernicke's area are a bit less intuitive, so we are going to have all of these memory tools laid out for you in that big summary sheet that is coming up at the end of this section, so stick around for that, and I will see you in our next video to talk about the motor and somatosensory cortices. Bye bye!

The Cortical Forebrain Example 3

All right, so a stroke is a medical emergency where blood flow to the brain is blocked. Imagine you are a neurologist treating stroke patients. You have 4 patients and each has had a stroke in a different lobe of the brain. For each patient, we're going to write down one function that may have been impacted because a stroke in that region. So patient A had a stroke in their occipital lobe and because the occipital lobe is pretty much entirely devoted to vision, a stroke in this area would probably impair vision.

All right, patient B had a stroke in the frontal lobe, and this could really have a variety of impacts. If that stroke was more like the prefrontal region, we may see impairments with cognitions, especially more complex cognitions, things like logical thinking. If it was more in Broca's area, we may see difficulty with speech production. If it was in the primary motor cortex, we may see difficulty with voluntary movement. So, I'm going to write voluntary movement here but really, any of those could have been impacted.

Alright, patient C had a stroke in their temporal lobe. So, if we are thinking temporal lobe, we have the primary auditory cortex, so hearing might be impacted. We also have Wernicke's area, so language comprehension might be impacted, and the temporal lobe is also important for memory. So, I'm just going to write down language comprehension, but again, really, we could see impacts in any of those functions. We have language comprehension there, and then finally, patient D had a stroke in their parietal lobe.

The parietal lobe is really important for sensation, so we have our primary somatosensory cortex in there, and it's also important for spatial processing. I'm just going to write down sensation, but, again, we could be seeing a variety of impacts. Alright. There you guys have it, and I will see you in the next one. Bye bye.

Broca’s area is responsible for _________, while Wernicke’s area is responsible for ________.

• A. Language comprehension: speech production.
• B. Executive functions: auditory processing.
• C. Speech production: language comprehension.
• D. Auditory processing: executive functions.

The primary auditory cortex is located in the ____________ lobe.

• A. Frontal
• B. Parietal
• C. Temporal
• D. Occipital

The Sensory and Motor Cortices

Alright, so now that we understand the function and layout of the cortex a bit better, let's dive into those sensory and motor cortices. And like I mentioned, we group these together here because they're often visually depicted in a very similar way, which I will explain in a moment. So first up we have our primary motor cortex which you guys remember is located in the frontal lobes and this is going to be responsible for initiating voluntary movement. The primary motor cortex is basically under the control of the somatic nervous system which controls, of course, voluntary movement and skeletal muscle. Next up we have the primary somatosensory cortex which you guys remember is located in the parietal lobe right next to that motor cortex, so they are kind of like on the bridge where the frontal lobe ends and the parietal lobe begins.

And the primary somatosensory cortex processes sensory information, as you probably guessed, specifically sensory information related to touch. So things like temperature, pressure, as well as proprioception which is basically your sense and understanding of where your body is in space and how your body is moving through space. Now both the primary motor cortex and primary somatosensory cortex are often visually depicted using a homunculus which is basically like an image of the human body that has been distorted so that the size of the body parts is proportionate to the number of neural connections that it has. And I'll explain that more in a second. So here we're looking at these two images and this is a motor homunculus and this one over here with the blue is a sensory homunculus.

So just to kind of orient you to what you are looking at here we have our primary motor cortex here in red, that is again in our frontal lobe, and our primary somatosensory cortex in blue, again that is in the parietal lobe, and so again over here we have our motor homunculus and so what's happening here is that a larger area or a larger body part on the motor homunculus means that we have more motor control over that area. And so you can see we have things like our face. Our face we're obviously able to make a lot of, like, really tiny different micro expressions of our face to depict different emotions. We have really great motor control over things like our lips and our tongue which allow us to articulate words really well. Again our hands are really large because we have really great fine motor control over our hands but then you can see how things like, you know, the wrist is not particularly large here.

We, of course, do have control over our wrist but not like superfine-tuned control, and then things like, you know, the thigh and the ankle are, like, even smaller. Again, we obviously have voluntary motor control over those regions but not like fine motor control, so the areas that are largest tend to be regions that we have more fine motor control over. So that is our motor homunculus, and then over here we have our sensory homunculus. So what's going on here is that a larger area on the sensory homunculus essentially means that we have more sensation in that region. And this one looks fairly similar.

You can see, you know, the face is quite large, the lips, the tongue, the hands again, and then again regions like the ankle, you know, the calf, and the thigh tend to be a little bit smaller. And when I say like more sensation I mean like you know imagine like a fruit fly landed on you. You know, if a fruit fly landed on your lips like you'd probably feel it immediately and be able to pinpoint where it was but if it landed like on your back if you even felt it you probably couldn't, like, locate it with pinpoint precision, right? So that's what I mean by, like, more sensation. One kind of interesting thing to note here is that you may have seen on our sensory homunculus we have some organs there and we don't have any organs on our motor homunculus because we don't have any voluntary control over them.

Right? But we can have sensation in our organs, particularly like pain sensations, maybe some like temperature perception a little bit as well. So we do see some organs appear on the sensory homunculus and not on the motor homunculus. Alright, so those are the sensory and motor cortices and I will see you guys in the next video. Bye bye!

The Cortical Forebrain Example 4

Alright, so for the following situations, we're going to be writing an m if that situation would be processed by our primary motor cortex and an s if it would get processed by our primary somatosensory cortex. So our first one is: a feather is brushed across your face, that, of course, would be a touch sensation which would get processed by our primary somatosensory cortex.

B is you slip a ring off of your finger; that would be a voluntary movement, right? So that's going to get processed by our motor cortex. C, if you notice that you have a stomachache, and like we talked about, we can have sensation in many of our organs, particularly pain sensation, and that would get processed by our primary somatosensory cortex.

D is you stir a pot of soup, another voluntary motor function, so that would be our motor cortex. And then finally, we feel the heat of a fire, that is going to be a touch sensation related to temperature, of course, which would get processed by our primary somatosensory cortex. Alright, there you have it, and I'll see you in the next one. Bye bye.

Within the homunculus, what does a larger area on the primary motor cortex correspond to?

• A. More motor control for that body part.
• B. Less motor control for that body part.
• C. More sensation for that body part.
• D. Less sensation for that body part.