so seeing where animals are going so you can avoid them if they're coming after you or if you can catch them if you're going after them right one of the arguably uniquely human abilities is precision throwing right no other animal can do that that's a very human thing although visual motion is shared with lots of ability to see motion is shared with lots of animals what else did you notice what else seemed funny or or you know harder to discern with stop motion yeah we care about small details like the movement to understand what your person is saying yeah yeah so um i was making notes to self i haven't done that demo before but in future it would be really good to have the audio quality terrible because if the audio quality is terrible you would lean more on lip reading and we might have noticed more that it's really hard to do that probably even at relatively fast flicker rates because that motion information is important absolutely what else how about beyond just lip reading what else did you notice about the faces mine or gems could you yeah they were static so it was kind of hard to tell like emotion because like a lot of our um the ways we express emotion is very nuanced exactly exactly facial expressions are incredibly subtle like little micro expressions flicker across the face in a tenth of a second and go away and you guys detect them like we're we're very very sensitive to those things you know if somebody you know sometimes if you see somebody in a hallway and for a moment there's an expression that flickers across their face and then they give you like a normal smile but you can tell from that expression that actually they didn't want to see you for whatever reason right we catch those things we're really really good at catching those little fleeting expressions and those probably have to do with not just sampling with fine temporal frequency but probably seeing the direction of motion of each little part of the face okay okay so this is just common sense reasoning about what we might have motion for okay and so you guys got all the things that i had in mind okay so now next question just kind of thought a thought question speculation question given the these many different things that make motion important to us uh biologically ecologically in our daily lives maybe that's important enough that we might allocate special brain machinery to processing motion what do you think important enough could you get by if you lived in a strobe world all the time could you survive just fine hard to say right might be hard i mean we probably don't need to go hunting down predators but um you know you walk across vassar street and there's some pretty dangerous predators coming down vassar street in the way of cars right you need to know where they're going and whether you can cross in front of them so it's actually pretty hard to live life without being able to see motion and i'll tell you about a woman who has that experience later in the lecture okay next question just think about this i'm not going to test you on it or anything it's not the topic of this course but it's a perspective you should take imagine that this were a cs course and i gave you a segment of video and your task was to take some to write some code that takes that video input and says whether objects are moving in that movie or says which objects are moving or how much they're moving or what direction they're moving what kind of code would you have to write to take that video input to try to figure that out okay so just think about that we're not going to be writing code in this class but a lot of what we're going to be doing is thinking about how do you take this kind of perceptual input and come out with that kind of perceptual inference and what kinds of computations would have to go on in between whether those computations are going on in code that you guys write or in a piece of brain that's doing that computation and thinking about how you might might write the code gives you really important insights about what the brain might be doing okay all right so that's the point of all of that the the mar reading talks about all of this and the key point we're trying to get here is that you can't understand perception without thinking about what each perceptual inference is necessary for ecologically in daily lives and about the computational challenges involved in making that inference okay so we'll get back to all that but next week and beyond but meanwhile here's the agenda for today so here's the agenda we just did the demo we're now going to skip and do some neuroanatomy absolutely bear basics because on wednesday we have this amazing opportunity to have one of the most kind of famous neuroscientists in the world do a dissection of a real human brain right here right in front of you it's going to be awesome and i don't want to waste that opportunity or embarrass ourselves by having people not know the bare basics so we're going to do the bare basics it's all stuff you should know from 900 and 901 and i'm going to whip through it fast so we can get to more interesting stuff and get back to visual motion okay that's the agenda all right so some absolute bare basics of the brain the human brain contains about 100 billion 10 to the 11th neurons and that's a very big number that's such a big number it's approximately jeff bezos is worth well it was until mackenzie got into the picture so we'll see no you don't need to remember this number just know it's a really big number basics of a neuron here's a neuron a neuron is a cell like any other cell in the body it's got a cell body and a nucleus just like any other cell in your body but the thing that's distinctive about a neuron is has a big long process called an axon it's got a bunch of dendrites the little processes little thingies near the cell body and out at the tip of the axon that's your classic neuron many neurons have a myelin sheath a layer of rolled up fat around the axon made up of other cells that makes axon conduct neural signals faster okay you should know all that i'm not trying to insult your intelligence i'm just trying to make sure everybody's with the program here okay so you have thousands of synapses on each neuron and that means you have to put a technically a shitload of synapses in your brain okay another important point um the brain runs on a mere 20 watts and if you're not impressed with that reflect on the fact that ibm's watson runs on 20 000 watts so one of the cool things about the human brain is not just all the awesome stuff that we can do that still no computer can do that i talked about last time but also how incredibly energetically efficiently we do it with our human brains so most of this course is going to talk about the cortex that's all the stuff on the outside of the brain it's a sheet wrapping around the outside of the brain that folded outer surface it's approx approximately the size and area of a large pizza but there are lots of other important bits too and i'm going to just do whirlwind tour of those other bits now okay so you can think of the brain as composed of four major kinds of components deep down in the bottom of the brain you have the brain stem where the spinal cord comes in here and the rest of the brain is up there and the brain stem is right down here and the cerebellum this little cauliflower-like thing that sits out right back there and in the middle of the brain you have the limbic system with a whole bunch of subcortical regions and we'll talk about a few of those in a moment and you have white matter all the cables and connections that go from one part of the brain to another part this is an actual dissected human brain and all those kind of weird fibrous things are bundles of axons connecting remote parts of the brain to each other you can see them in gross dissection okay and of course you have the cortex okay so these are just four major things to think about and before we spend the rest of the course on that we're going to do just a teeny little bit on the other major bits okay and i'm going fast so just stop me if any of this isn't clear all right so the reason we're doing this in part is that with a dissection of a brain some of the main things you see are those subcortical structures right and so even though the course is going to focus on the cortex each little different bit of the cortex to the naked eye looks like any other bit of the cortex it's the subcortical stuff that looks different right so that's why we're doing this okay bear basics on the brain stem you can think of it as a bunch of relays in here different uh centers that connect information coming up from the spinal cord and send it through into the cerebellum so it's in many ways the most primitive part of the brain that means it's shared with animals very that branched off from us very far back in in mammalian evolution but it's also essential to life okay so you can get by with most of your cortex gone like you may not have a lot of fun you may not really know what's going on but you will stay alive but you can't get by without your brain stem right it's a it controls all kinds of basic crucial bodily functions like breathing consciousness temporary temperature regulation etc so it's not interesting cognitively but it's crucial for life cerebellum this beautiful thing here it's basically involved in motor coordination but from there on out there's a huge debate about its possible role in cognition and so there's lots of brain imaging studies where people find that the cerebellum is engaged in all kinds of things from aspects of perception up through aspects of language understanding you can find activations um in brain imaging studies nonetheless the best guess is that you actually don't need a cerebellum uh for any of this so there's if anybody's interested i'm going to actually try to remember to put it up as an optional reading on the site there's a recent article in the atlantic or the new yorker about a kid who had no cerebellum and he learned to walk late and slow nobody knew what his problem was but he learned to do pretty much everything like he's pretty much fine his motor coordination isn't great but he's fine yeah how are you defining consciousness in this context oh that's a good question and it's a big question and it's a question that nobody knows how to answer not just me so christoph koh who does more of work on the neural basis of consciousness than just about anybody has been going around saying for about 15 years we must not get stuck on a premature definition of consciousness because we don't know what that thing is that we're trying to understand so i'll hide behind kristoff's uh perry of that question and say we'll talk about it later in the course but it's there are many different kind of ways of defining it from the difference of difference between being awake versus asleep which is some of the functions that go on here the difference between being kind of knocked out and completely unconscious under general anesthesia which is different from being asleep those kind of states of consciousness are regulated in part in here yeah okay so you can get by without a cerebellum but it's not recommended um moving right along all those subcortical bits we're just going to talk about three of the most important ones the thalamus this big guy right smack in the middle of the brain very large structure the hippocampus and the amygdala okay let's talk about the thalamus think about the thalamus as a grand central station of the brain okay with all of these connections going to all those parts of cortex coming in and out of the thalamus like that okay so one of the key things about the thalamus is that most of the incoming sensory information goes by way of the thalamus on route to the cortex okay so if you start with your ear there's sensory endings in your ear that we'll talk about later in the term and they send neurons into this thalamus here this yellow thing through a bunch of different stages they make a stop in the thalamus and then they come up here to this green patch which is auditory cortex okay similarly somatosensory endings touch sensors in your skin that enable you to feel when you're being touched come in through the skin and they make a stop in the thalamus and then they go up to somatosensory cortex up there okay similarly signals that come in from your eyes make a stop in the thalamus and then go up to visual cortex okay what's the name of the structure in the thalamus that those axons make a synapse in coming up from the eyes you make a synapse here and you go up oops you go up to visual cortex lgn perfect what does it stand for perfect okay you should know that it's this is review from 900 901 okay um yes sorry okay which sensory modality does not go through the thalamus on route to cortex between the sensory nerve endings and the cortex sorry yes yes you guys are on the ball yes olfactory system is the one sensory modality that doesn't make a stop in the cortex you can sort of see that here from the nose it goes straight up into olfactory cortex right there all right so that's the um standard view of the thalamus as this kind of like relay station where all the external sensory information comes in there makes a stop and then goes up to cortex okay that's my thalamus act boom like that right okay but uh increasingly there's evidence that the thalamus is much more than a relay station and why would you bother with a relay anyway kind of doesn't mean anything kind of means like we don't know what's going on here because you wouldn't just make a synapse for no reason right um okay and so the first thing to note is there are lots of connections that go back down the other way there are ten times as many connections that go from primary visual cortex right here in me right here in the sky in red there are ten times as many that go backwards down to the thalamus as go forwards that's mind-blowing right information comes from the eyes up into the brain what the hell are those things doing going backwards okay well they're doing all kinds of interesting things so that's the first indication that the thalamus isn't just relaying stuff in a stupid passive way and the second whole line of work which many people are working on but i think some of the most awesome work on this topic is done by our own mike halasa in this department and he does these incredible studies that you can do in mice with these spectacular methods that we can't use in humans where he can really take apart the circuit in magnificent detail and he's showing that the thalamus is involved in all kinds of high-level cognitive computations in mice it's really stunning work when the mice have to switch from doing one task to another the thalamus plays a key role in gating the flow of information from one cortical region to another okay all right moving along they hit the campus i know you guys all learn about this the number one gripe in this department is we learn about hm in every course so that's going to happen here but it's going to last about 20 seconds so here it goes that's a normal slice of the brain like this here's the hippocampus on either side it's like a whole curled up deal right there and right there and here is hm's brain the famous hm who had surgery to remove his hippocampus on both sides and completely lost his episodic memory for anything that happened after his surgery okay you all remember that right if anybody hasn't heard of hm send me an email i'll give you some background reading okay so very loosely the hippocampus involved both in this kind of long-term episodic memory that hm lost and it also plays a key role in navigation which we'll talk about in great detail in a few weeks and i just want to say that some cases are even more extreme than hm so there's a case of lonnie sue johnson and i am trying to get you guys a video and i didn't get it in time but i'll show it to you later in the term if you're interested lonnie sue johnson had a viral infection that went up into her brain she was an extremely accomplished person she did illustrations on the cover of the new yorker she was a pilot she had her own farm when she raised you know lots of lots of stuff a very smart interesting multi-talented woman who had this terrible tragedy of getting viral encephalitis at i don't know what age but middle age and she now does not remember a single event in her life she's smart she's funny her personality is totally intact she can answer questions she can paint she can do all kinds of things but she does not remember a single event in her life that's pretty astonishing reflect on what it means to have a sense of self if you don't remember anything in your life yeah she remember her again that's a good question i'm not sure she might know her yes she does know her name actually it is evident in this video but the video well so you know she doesn't remember at one point in this video she's asked were you ever married and she's lovely and sweet and gentle and kind of low-key and she's like you know just don't remember i might have been i might have been she was married for 10 years so uh that's the hippocampus important you don't want to lose that one yeah about each other if the campus is using long-term memory why is it that it being removed causing to not form new memories well so long-term memory means you know it's a vague term it means the formation rich and retrieval of memories that are going to last a long time so in hm's case he can access a lot of the memories from before his injury in lonnie sue's case she can't do even that okay all right amygdala okay amygdala is a greek word that means almond because the amygdala is the size and shape of an almond and so just for fun we're passing on her own my favorite kind have some almonds and pass them around all right um okay so the amygdala is involved in experiencing and recognizing emotions especially fear the simple statement that you should remember about what the amygdala does is just remember the four f's you guys all know about the four f's fighting fleeing feeding and mating okay patient sm lost her amygdala on both sides okay she cannot experience fear she doesn't recognize fear on facial expressions of other people and she doesn't experience fear herself okay and so that's a the striking um piece of evidence on what the amygdala does her face recognition is normal recognizing identities her iq is normal she's overly trusting of other people okay um okay so that's all you need to know about the amygdala for now um okay let's talk about white matter just brief review here's a here's a kind of tunnel through a piece of cortex okay so my brain cortex is wrapping around like that if we took a piece like this just took a segment out like that this is the outside of the brain up there cortex runs like this and gray matter is the stuff on the outer surface that's full of cell bodies okay white matter are the axons the processes that come out of those cell bodies and travel elsewhere in the brain okay everybody clear on that okay so we've got gray matter up here and white matter down there mostly myelinated axons that have that layer of fat to make them conduct fast and so you'll see bundles of white matter in the dissection and so here's an actual picture photograph of the slice through a brain so all that white stuff up there is white matter okay and so you might say well it's just a big bunch of wires who cares about that it's a good question but actually the wires are pretty damn interesting and pretty fundamental and so i'll just give you a few reasons and you don't need to memorize every one of these i'm just trying to give you a gist of why we might care about this and there will be a whole other lecture on networks and connectivity later in the course well first of all white matter is 45 of the human brain okay so takes up a lot of space all those wires connecting one bit to another bit and i would say we cannot possibly understand the cortex and how it works or any little piece of it without knowing the connectivity of each piece to each other bit of the cortex right imagine trying to understand a computer or a circuit without being able to see the connections between the bits like it would drive you crazy that's a situation we're in now in human cognitive neuroscience it frankly drives me insane but that's where we are um next thing the long-range connectivity of each little bit of cortex some little bit right there in my brain is connected to some bunch of other remote regions in my brain and that particular set of connections is distinctive for that patch of cortex so you can think of it as a connectivity fingerprint of a patch of cortex okay so one of the ways that the different bits differ from each other is by way of their connectivity fingerprints and i'm going to skip the rest of these because we're going to get back to them later and i'm going to run out of time i'm going to assign the tas to sound the gong at 12 15. okay good all right now we're up to the cortex this is really laughably shallow but whatever that's what we're doing here so here's this cortex and as i mentioned it's a whole big sheet and the different bits look really similar if you just look at them or slice them up so how are we going to figure out how this thing is organized well okay now we're up here talking about cortex all right let's start with the easy parts which you've already seen you've already seen this up here these colored bits visual cortex auditory cortex um somatosensory cortex gustatory taste cortex those bits are like the easy parts of cortex those are called primary sensory regions there's also motor cortex right in front of sensory cortex so those are the primary regions their primary in the sense of this is the first place that sensory information lands up at the cortex coming up from the senses right okay um and all of that input is wired through what structure yes thank you um so how are these regions organized um well they have maps every one of these regions has a map and each of them has a map of a different thing so let's start with visual cortex and we're going to talk about the map that lives in visual cortex but the prior condition for understanding that map is to understand the concept of receptive field which you should know so i'm going to whip through it quickly okay so here is how you map the receptive field as a property of an individual cell in a brain okay so the classic way in animal neuroscience is you place an electrode in the brain next to a neuron in monkey visual cortex okay so here's this monkey's gun electrode right in his brain right next to a neuron and visual cortex and every time that neuron fires you get a spike you hear a spike okay now you train the monkey to stare at a fixation spot without moving its eyes okay i can do this with humans without training you i can just tell you look at the tip of my nose okay so keep your eyes on the tip of my nose i can see if you're looking elsewhere so look at the tip of my nose okay okay so you train a monkey to do that that takes a few months and then they can do that and then while recording from neurons in his brain you put stimuli over here put a flash over there or a flash over here or a flash over here or flash over here okay you can stop looking at my nose it's not all that fabulous knows i realize okay so a receptive field is the place in the visual world that makes a given neuron fire okay so if there's a neuron in your brain that responds to a flash here but not a flash here or here or here or here the receptive field of that neuron is right there everybody got that idea okay so in visual cortex neurons have restricted receptive fields they don't respond to anything anywhere in the visual field they respond to a particular place in space okay if that's confusing at all ask a question because it will come up again and again all right so that's what the rest of this slide says what i just said blah blah blah doesn't matter that's a receptive field different visual neurons have different receptive fields for different parts of space now here comes the important idea in visual cortex two neurons that are next to each other in visual cortex have nearby receptive fields okay so that's the concept of retina topi or the map in visual cortex so you basically have a map of the visual world in your visual cortex because there's this systematic layout just like you have in your retina in your retina visual information comes in and because of optics different parts of your retina respond to different parts of the image but that information is propagated back through the lgn up to primary visual cortex where you still have a map of the visual space up in primary visual cortex okay so that map is called retinotopic in visual cortex because it's oriented like the retina and so here's a particularly kind of gruesome but very literal depiction of this property of retina topi in a monkey brain this is an experiment done very long ago by roger tutel and what he did was um he used a method called deoxyglucose and so what deoxyglucose is a molecule that's a whole lot like glucose but it's got one little change in the molecule which means it gets stuck on the metabolic chain and so it gets taken up by cells that want to take up glucose and then it gets stuck in there and can't be broken down so it builds up in cells that are metabolically active okay so you can put a little radioactive tracer on deoxyglucose inject it into a person or an animal and what happens is it builds up with this radioactive tag on all the cells that were active makes sense okay so tutel did an experiment where he had the monkey fixate on a spot and he presented this stimulus here so the monkey's fixating right there and the stimulus is flashing on and off he injects the radioactive deoxyglucose into the monkey while the monkey's looking at this and then i'm sorry to say he killed the monkey rolled out visual cortex into a sheet and there it is and you can see the bullseye pattern that the monkey was looking at across the surface of visual cortex does everybody get that okay so that shows you very literally what a retinotopic map is in the brain it's just like the map of the visual world in the retina but there it is up in the back of the brain and humans have this too okay and so this can be shown in humans with functional mri we'll talk later more about the methods of functional mri but here's a very high resolution functional mri experiment done by some people over at mgh charlestown by the way when i have names on slides it's just because in science we don't get paid that much and so our credit for our cool data is kind of all we have and so i can't stand to talk about other people's cool experiments without giving them credit i do not expect you to learn the names it's just my little personal tic that i need to have their name there to give them credit even though you don't know who they are okay okay so what this guy john palomani did was show human subjects this stimulus here they were fixating right there and the stimulus is flickering with the dots kind of dancing around and then he looked on the back in visual cortex on the surface of the brain and he sees an n there it's the same stimulus it's just flipped upside down which is not deeper interesting the cortex has to be oriented one way or another the brain doesn't care whether you turn it around right and your map of visual space is upside down in the back of the head and you see that m does everybody get how that also shows retinotopic properties in the brain in human visual cortex okay all right so the key idea of retina toppy is that adjacent parts of the visual seal field are mapped to adjacent parts of the cortex all right okay a little bit of terminology just because people are fast and loose with these things i've already referred to v1 and primary visual cortex it's also sometimes called striat cortex it's all the same thing it's the part of the visual cortex where the information first comes up from the lgn right back here so in me it's right there most of it is in the space between the two hemispheres but a little bit sticks out on the side so in this person that yellowy orange stuff that's primary visual cortex which is the same as v1 and striat cortex okay that's just terminology all right just as we have maps for visual space we have maps for touch space and so you've probably seen this diagram here of the map of touch space going across somatosensory cortex like this so this is a picture of a slice like that showing you which parts of the body are mapped out to which parts of space and you can see that particularly important parts of the body get bigger bits of cortex yeah okay just as we have visual maps and touch maps we have auditory maps in auditory cortex which is right on the top of the temporal lobe right in here and which is what's mapped out in auditory cortex is auditory frequency high versus low versus high frequencies of sound and so you see that here's a piece of auditory cortex in one subject showing you regions that respond to high frequencies low frequencies high frequencies here it is another subject high low high another subject high low high okay so the point of all of this is that primary sensory cortex has maps everybody clear on this the different sensory modalities map different dimensions okay so what about the rest of cortex like you can see most of the cortex is not primary sensory cortex is the rest of cortex just mush or are there separate bits like primary sensory areas and if so do those other bits have maps and if so what are those maps of okay we just took you from 100 years ago to the cutting edge of the field is asking this question in lots of different ways right now okay okay let's back up and ask what counts as a cortical area anyway i just posited that these primary sensory regions count as distinct things they're like the things right they're separate things in the brain okay and if for no other reason then they get direct input from the thalamus right okay um but let's back up and ask what exactly is a cortical area and we're going to consider this question um by considering the three key criteria for what counts as a cortical area okay the first one is that that region of cortex is distinct from its neighbors in function neurons their fire in response to something different from the neurons in the neighboring region okay that's very vague right now but we'll illustrate that the next one as i mentioned this before each distinct region of cortex has a different set of connections to other parts of the brain it has a distinct connectivity fingerprint okay and the third thing is for at least some regions of the cortex they're physically different if you slice them up and stain them and look at them really carefully they might look a little different than other bits of the cortex okay so those are three of the key criteria that have been used to say this bit of cortex it's a thing right it's distinct right okay so let's look at the classic example beyond those primary regions those are the most classic regions the primary regions we've already talked about those are the ones nobody would fight you on that this one is next in line nobody will fight you of say if you say visual area mt that's an area well they might but most people wouldn't okay and then from there on out it's all fighting all the time okay so let's talk about visual area mt it's a little patch of the cortex and a monkey brain this is a side view of a monkey brain and in this human brain it's that little patch right there okay so this region meets all the criteria to be a distinct visual area so how do we know this well we know this from lots and lots of different methods so i'm going to whip through a few of those to give you a gist of how we can find evidence that that region is distinct in function connectivity and the physical stuff sometimes called cyto architecture okay all right function how would we know that region respon has a different function well one way the classic way is to record from individual neurons in monkey brains so if you stick a neuron into monkey visual cortex while the monkey is looking at the stimulus that i'll show you in a second you'll hear the responses of an individual neuron each clique will be the response of an individual neuron to the stimulus so let's play this thing except it's not making any sound chris can you help me oh right duh that part okay see when the bar of light moves this way it makes a lot of firing and not when it moves the other way let's watch it for a second watch the bar move again [Applause] so he responds less when it's moving in a different direction ready got that what is this area right there called yeah this area right here in the middle exactly that's a receptive field that's a part of visual space that makes this neuron fire okay this neuron also has a property called direction it's sensitive to motion as you see but it's also specific to specific directions of motion everybody see that okay so that's a direction selective neuron in monkey area mt and here's a way of showing with data what you guys just saw this is a map of different directions in polar coordinates and this shows you how much this is a this is a single cell being described here this is the direction selectivity of that cell showing you that when motion moves when the stimulus moves in this direction you get a lot of firing when it moves in this direction you get less firing and can everybody see how this plot shows you the direction selectivity of that cell makes sense right okay so that shows you what you just saw in the movie so this is one way to establish the function of visual area mt is stick electrodes in there and record directly from them when a monkey looks at different kinds of stimuli and you see direction selectivity when you do that okay further if you actually do this systematically moving across next door bits of monkey area mt what you find is that as we said before nearby bits of cortex respond to similar things in this case to similar directions of motion so here's a little diagram as you move across the cortex you see a systematic change in the direction selectivity of neurons as you move across the cortex so in mt we have a map of direction preference just as we had a map of spatial location in primary visual cortex make sense okay now because those neurons are clustered like that i forget what my next point was no never mind we'll get that in a second okay what about humans okay so here's a monkey brain here's a neuron and a monkey brain what about humans can we record from single neurons in humans what do you think do we ever get to do that yeah yeah yeah neurosurgeons very occasionally enable us to record from individual neurons in human brains it's the most awesome data ever of course we only do it when the neurosurgeons have decided for clinical reasons to put electrodes in human brains they need to do this to map out epilepsy before surgery and sometimes those patients are super nice and say yes i'll look at your stimuli or listen to your stimuli while you record from my neurons and then we get the most awesome data ever but it's very very rare i don't know of any data where people have reported individual neurons in area mt in humans yeah so how powerful should an fmri be to be able to ignore such information oh we're getting there okay so given that we very rarely uh get uh get to record from individual neurons in humans and we want to know more generally if there is an mt in humans what do we do we pop subjects in an mri scanner and we show them moving dots or stationary dots and we scan them with functional mri we'll go through the details of how this works more in future lectures but what you see basically is this is a slice through the brain like this and you see this region right here responds more to the moving dots this is the response to the time here this is when the moving dots are on high response and then what switches to stationary dots the response drops okay so with functional mri you can also find visual area mt by the higher response to moving than stationary dots does that make sense more or less i mean i'm not giving you any of the details but for now they don't really matter okay so that's cool but does that tell us that neurons in human mt are specific for the direction of motion yes moving in a specific motion removing in all the directions you see here no it doesn't it tells us it's sensitive to the presence of motion but not the direction of motion okay so if if we want to really know is human mt like monkey empty or is this really human empty we want to know are the neurons in there not just responsive to motion but are neurons specific for particular directions of motion okay so how would we do that okay uh well there's lots of ways of doing that but actually one of the charming things is you can do that without an mri scanner that is it won't tell you whether it's empty you're looking at but we can ask the question of whether your brains have neurons that are tuned for particular directions so for this demo i want you to fixate right in the center and do not move your eyes from that dot and i'm going to keep talking for a while while you keep fixating right on that dot and so what we're going to what i'm going to show you is something called an after effect this is also known as the psychophysicist's electrode psychophysicists are people who just measure behavior and from behavior they can infer how individual neurons work and that is about as awesome as it gets that's much more impressive than just recording from the damn neuron inferring from very indirect data how the neuron works from behavior now that is pretty oops okay sorry look directly at my face you see anything i didn't see it stop oh crap we're gonna oh here we go uh oh right okay just fixate on the center again sorry i forgot this guy was going to stop so keep looking at the center and then when it stops in a little bit then keep your eyes right on that dot and you can see what happens oh that's right good point yes right now it's alternating nothing's gonna happen but that's okay we're gonna have the whole experience keep fixating on the dot it's good the tas are on the ball okay fix it on the dot anybody see anything not really that's okay you're not supposed to that's the control condition it was alternating directions okay so i think it's going to start moving again i'm not sure let's go back let's just start it again okay sorry i blew it the first time but let's just get this right okay fixate on the center and just keep your eyes right on that center so this one it's not alternating and it's going to do this for around 30 seconds and so the whole point of this is this is a way with behavior to ask the question of whether you have neurons in your brain tuned to specific directions of motion and something as low-tech and simple as an after effect can tell you that keep looking did you guys see anything what'd you see what happened it wasn't even exactly something they kind of like did it well it actually should well now it's doing something else but it should shrink at the end did you guys see it shrink okay so that's an after effect and the simple version of the story is that you are tiring out your neurons that are sensitive to outward motion while you stare at all that outward motion and after you kind of burn them out and exhaust them then when you look at something stationary it looks like it's going inward okay and the general idea is you have pools of neurons that the the easiest way to account for that is you have pools of neurons tuned for different directions and that's why if you tire out one batch you have a net signal in the other direction does that make sense this is all very relevant to your assignment which is due tomorrow night at 6. this phenomenon was used in the scanner for that experiment and you can think about um how you would use this phenomenon um to ask whether there's direction selectivity not just responses to motion in human mt yeah wait uh i'm just a little bit confused so even when an image is like completely still like even if you're not detecting motion those neurons are still firing ah um that's a good question but but most likely it's the simple cases if this may have not worked beautifully in part because i screwed it up and didn't notice when it stopped but if it works well you should get a pretty powerful sense that after you see it expanding then when it's still it should seem to be contracting so when that happens the reading assigned for today tomorrow tomorrow night tells you what happens in your brain during that time when you are looking at stationary stimuli but experiencing motion so there's no motion in the stimulus but there's motion in your percept okay so that's the question right so read the paper and find out yeah all right all right so all of that tells us just that there are neurons some place in your brain that are sensitive to the direction of motion it doesn't tell us that they're in mt in particular but the assigned reading will talk about that okay right a further bit of evidence is remember i said how in monkeys next door bits in mt have have have similar direction selectivity that means you can also inject an electrical signal in a little patch of mt and give the monkey a net percept of a direction of motion okay if all the neurons were scrambled around spatially so that there was no clustering of neurons sensitive to say this direction of motion then stimulation wouldn't do anything but if you train a monkey to tell you what direction of motion he's seeing and you show them just random dots that aren't moving in any direction and you stimulate one little patch it'll tell you the direction of motion of the neurons in that little patch and that is much more powerful evidence that that region is not only responsive to motion but causally involved in your perception of motion okay i'm a little obsessed with this distinction between you know recording responses and establishing causality so we'll go over this in more detail later but i want you to start getting used to that idea another way to test the causal role of area mt in motion is with patients with brain damage and area mt so there's one famous patient who had brain damage right there which is right where mt usually is and she could not see motion and she reports all kinds of things like difficulty crossing the street difficulty catching balls difficulty pouring water into a cup okay just as you guys saw earlier that's called akinatopsia right can it like kinetics motion a not motion right opsia eyes okay um all right so i started with these criteria for what makes something a visual a distinct area and one piece of evidence is function and i just gave you a whole bunch of different kinds of evidence for distinct function and visual area mt that it's specifically involved in motion processing and the two other criteria which are getting short shrift but i'll just toss them off and we'll return to them one is the distinct connectivity of that region okay so you may have seen this horrific wiring diagram of visual cortex in monkeys i think it comes up in like half the talks and classes in in my field this is the one down here and so there's lots and lots of different visual areas and there's a whole fancy wiring diagram and smack in the middle of this diagram that's visual area mt and if you blow this up and stare at it you'll see that mt has a particular set of connections to other visual regions and cortex and its particular set of connections are different from the connections of any of those other regions it's part of its connectivity fingerprint or signature and that's another piece of evidence that it's a thing okay it's not just another like amorphous bit of cortex it's a particular thing in the brain and finally you might wonder is that bit of cortex physically different are the cells in there different are the layers of cortex different um in any way and from and you may remember from probably 900 about brodman areas like this dude corbinian brodeman sliced up lots of dead brains looked at them under a microscope and argued that were there were 52 different parts just from what it looked like if you slice them up under a microscope okay so we called those brodman areas and area 17 this primary visual cortex comes from brodman's terminology um and so he argued that there he thought these were distinct organs in the brain and he even inferred the specific histological differentiation of the cortical areas proves irrefutably their specific functional differentiation well it doesn't but never mind kind of sounded good anyway that was his idea and these kinds of distinct kind of cellular physical anatomical differences are very salient for primary cortical areas for vision and audition and touch and motor cortex but they're much muckier for lots of other areas one important exception which is why we chose this is area mt and so i'll end in one minute but just to tell you where this is going this is a flattened piece of monkey cortex rolled out like with a baking roller no i don't know some something like that so here's monkey cortex and there's v1 and v2 and it's a big mess but that big dark blob this bit of cortex is stained with something called cytochrome oxidase and that indicates metabolic activity mt neurons are very highly metabolically active and so here's a map of visual cortex and that exactly is area mt so area mt actually is histologically or psychoarchitectonically different from its neighbors and hence fits all of the criteria for a cortical area okay i went one minute over i realize i threw out a lot of terminology i don't want you to memorize too much so i made a list of the kinds of things that you should understand from this lecture the things that i think are important you