[MUSIC] Okay, so let's look at an overview of visual pathways. Remember that we're looking at the base of the brain. This is the front, this is the back. And remember that there are these indents right here in, in the base of the frontal cortex. This is called orbital frontal because the orbit indents it, that's what's indenting it. This is where the eyes sit. One eye sits here, one eye sits there. And here's the retina. And we know that instead of mapping this eye to this cortex, what we actually map is this visual field to this cortex, and this visual field to this cortex. So everything on the left side of the world, the left visual world is going to end up in the right occipital cortex, everything on the right side of the world is gonna end up in the left occipital cortex. So we've gotta get information from the world across. And that means that, okay, so, let's remember one more thing, which is that this retina is looking at both the opposite side of the world and the same side of the world. So the information coming in from the same side of the world, that has to cross and it's gonna cross In the optic chiasm, and that's right here. So the retina's here, there's an optic nerve which is not shown, it's cut off, and that is going to lead to the optic chiasm and it's going to end up on the opposite side of the brain. But the information coming in from the opposite side of the world is gonna stay, it's not gonna cross, it's just gonna stay on the same side of the brain. It's gonna continue back past the chiasm. Okay, so where do we go from the optic chiasm? These are the optic nerves, here's the chiasm, here, remember, is the stalk that attaches the pituitary. That's why pituitary tumors cause visual problems. So from this nerve we go to something called the optic tract. Now note that the optic nerve and the optic tract contain the same axons. They're just called different things. These have been named for hundreds of years. And you can see, I hope, that this optic tract is coming back. Do you see that? Here's the optic nerve. Here's the chaism. Here's the optic tract coming back. And it's coming back and back, and look at that, look at that. Okay, so as it comes back, it actually is going to stop in thalamus. So it's gonna stop in the lateral geniculate nucleus, which is the visual part of thalamus. So information's gonna go from the eye to thalamus. And from thalamus it's gonna end up in visual cortex. Now we have not really looked at visual cortex very much, but we're gonna look at it right now. Visual cortex sits on the medial surface of the hemisphere, it's not on the outside, it's on the inside of the hemisphere. And it surrounds this valley, or sulcus, and this is called the calcarine sulcus, and the banks of the calcarine sulcus are primary visual cortex. So from the lateral geniculate, from thalamus, the information is going to radiate. It's the optic radiation and it will end up being over here. So this is the right or left? Think about it. And the answer is right. This is the right hemisphere. This is the right hemisphere. So this visual cortex is mapping the left visual world. There is another cute inversion here which is that the bottom bank, the lower bank maps the upper half of the visual world. The upper bank maps the lower half of the visual world. From the primary visual cortex information is then sent out by a dorsal stream, which is a where stream, where is it? How is it moving? In a what stream? What is it? What am I looking at? What's the, who's face is that? What is that object with red polygons on it? Is that a rose? Etcetera. So the dorsal stream and the ventral stream come from the visual cortex. Perception is not produced in the visual cortex, although the visual cortex is critical to perception. Perception takes place farther down in these visual streams. So one other thing to remember is as we move from the eyes past the chiasm, and on route to the visual cortex. That any lesion past the chiasm is going to produce blindness to the opposite side of the world. If there's a lesion right here in the optic tract, the person will be blind to the opposite side of the world, okay. Both eyes will be blind to the opposite side of the world. It's not a blindness of an eye. You can get blindness of the eye, but that has to be a lesion of this optic nerve. In front of the optic chiasm to the retina. That will produce blindness, okay? Blindness of an eye. [MUSIC]
