[Music] visual cortex okay so again when we make a fist the occipital cortex is going to be where your arm is connecting into your wrist on the very back end here and on the medial surface we're going to have this calcarine sulcus or hook like sulcus separating the superior and infra lobe we have the cunious the cunit lobe and the lingual gyrus this more inferior aspect and in this image we can again inflate and expand so visual cortex is going to be located here we have in color various retinotopically mapped areas of the brain on average from about 20 or 30 subjects and as we inflate and unfold that we can see the occipital lobe multiple visual distinct visual areas each one of these colored areas of cortex has a visual topic map from a central out to periphery map of the visual field of one hemi visual field as we'll see in a moment but point to mark here is there's our calcan sulcus primary visual cortex in the purple here is where this is located we've got areas for motion processing and a multitude of other areas that's two more lectures of material on that one but there's our visual cortex one last piece i'll put on to there is as a review you have to remember after the optic chiasm we had our optic nerves come to the optic chiasm about half the retinal ganglion fibers cross so that we have going into this lateral geniculate nucleus you've got all the input from the left nasal retina side is going to be looking at your left visual space it goes to the right side of your brain and in your right eye that temporal retina which is also conveying the left visual field is going to the right side so everything in the right side of your vision of where you're if you're looking straight ahead and if i put up my fingers here how many fingers do you see that is in your i'm assuming your right visual field that is going to your left occipital cortex for conscious level perception of what you are seeing there and so that is occurring at the cross the optic chiasm so once we get behind the optic chiasm here in the optic tract you have a hemifield representation the contralateral hemifield is represented here going to the lgn lateral geniculate nucleus and to memorize lgn from mgn l is for light light lgn m as for music or sound sound processing is more your medial genician nucleus lgn is like lateral geniculate nucleus okay and then we have our optic radiations that would be coming back here to the calcium sulcus and these other visual areas and these inputs are all retina topically organized or visual topically organized so you can have lesions back in here taking out myers loop or optic radiations and you can tell or predict what kind of visual field deficits the patient's going to have won't go into those details just to remind you that those are kind of high yield concepts that that come up on step exams bigger picture level what's going into the visual cortex then we start thinking about streams and major pathways so as you go dorsally directed from say these magnacellular layers in the lgn to various areas of cortex to more parietal superior regions are going to be involved with your perception of motion and location where are things in space so if you have to reach out and grab your beverage where is it in space then you have information flowing along the infra-temporal cortices and these are going to be more about well what is that is it what color is that cup is it blue is it red what is the shape if you had to um state what the shape is and so the information of form or what is it is going to be going down toward vision for perception towards these infra-temporal regions of the brain so gross level object for action going dorsal and the object for what is it for perception going more eventually then interestingly with carbon monoxide poisoning um it's not terribly uncommon to have what's called a condition called blind site for whatever reasons this region's cortex is more sensitive to carbon monoxide poisoning and if you take out both the left and right occipital cortices along the calcare and solar slide for instance you lose your perception of what you are seeing however uh conscious level perception however you can still quote unquote c and have more reflexive level of vision so for instance here's a patient with blind site who's uh the doctors hearing okay what is the orientation of this bar on the tv screen they're like well consciously i can't see anything well just make a guess all right a horizontal like what so that information is getting through to the brain and other areas but not at a conscious level of perception and so this and other lesions like that gives us some more clues to understanding how vision works in the human brain still don't fully understand it obviously but there's some fascinating knowledge about different pathways and routes of information flow and there are numerous other type of visual lesions prostapagnosia achromatopsias and so forth which again is a topic of another lecture dr lewis is that a permanent is that a permanent change that happens with the blind side or does that um does that heal over time my understanding is that's permanent if it's yeah my guess is permanent but i don't see patients and i don't have a full answer for that i would imagine you can have a condition where it could be transient but with the carbon monoxide poisoning once your neurons die that's it the the central nervous system they're not coming back you're not going to be uh getting that conscious perception coming back [Music] hey everyone ryan rad here from neurosurgerytraining.org if you like that video subscribe and donate to keep our content available for medical students across the world