| 00:05 | This is lecture 17 of neuroscience. in the previous two lectures we talked |
|
| 00:12 | the visual system, we covered the of the eye. We discussed the |
|
| 00:20 | in the retina. The circuit the visual information, the directionality of the |
|
| 00:27 | of information within that circuit activation of receptors and trans deduction of the light |
|
| 00:35 | an electrochemical signal through medical tropic protean Doosan. We also discussed what retina |
|
| 00:44 | seeing and what are the properties the field properties in retina. And we |
|
| 00:51 | that retina has these concentric centers around the field properties where each one of |
|
| 01:01 | receptive fields round center surround or If it's in the center on center |
|
| 01:08 | center if it's on the surround activation this is what retina would be essentially |
|
| 01:16 | . It would be perceiving these round of photo receptors. Get activated underneath |
|
| 01:25 | circuit of bipolar cells or retina ganglion . Retinal ganglion cells will be producing |
|
| 01:31 | potentials. So when you're looking at stick recordings, these action potentials and |
|
| 01:36 | recorded from retinal ganglion cells. And happens is the best way retinal ganglion |
|
| 01:43 | perceive information from retina. The best they get activated is if there is |
|
| 01:49 | spot of light either in the center spot or bright spot of light in |
|
| 01:55 | center or dark, surround or bright in the surround. That's just the |
|
| 02:02 | anatomically the retina is bell. And the L. G. M. |
|
| 02:07 | we saw and walked up through the system. The properties of the lateral |
|
| 02:13 | nuclear cells. They're receptive field properties also these concentric center surround like |
|
| 02:23 | So if for example there was a of retina that was being activated from |
|
| 02:28 | given field of view that you're focusing would perceive that visual information across a |
|
| 02:38 | area of the retina by activating these field structures and communicating that information to |
|
| 02:47 | underlying circuit. The circuit here that discussed is there's several ways that information |
|
| 02:58 | and the neurotransmitters glutamate in all of cells. However we talked about the |
|
| 03:06 | that first of all in the dark are d polarized photo receptors in the |
|
| 03:12 | they're hyper polarized. So this example a cell that is in the center |
|
| 03:19 | there's a light in the center so voter receptor is going to be hyper |
|
| 03:24 | . The rest. What we discussed that the pluses in this diagram sent |
|
| 03:31 | signed. Conserving synopsis and the minuses sign inverting synopses it's signed conserving because |
|
| 03:40 | this cell is D polarized and it glutamate, glutamate will bind to Emma |
|
| 03:46 | with receptors and will d polarized the cell. However if this cell is |
|
| 03:52 | polarized like it would be the case exposure to light. This sign conserving |
|
| 03:59 | in the absence of glutamate would also hyper polarization of this bipolar cell communication |
|
| 04:06 | bipolar cells and ganglion cells are all the M. 14 and M. |
|
| 04:12 | . A. I. Am a dramaturgical signaling. So now if this |
|
| 04:16 | hyper polarized and there is no Subsequently the ganglion cells hyper polarized and |
|
| 04:22 | called off center sells because it's not to the stimulus in the center the |
|
| 04:28 | is in the center and it's likely to react to photo receptor that is |
|
| 04:33 | in the surrounding. So it's off . Now this on central gaming itself |
|
| 04:38 | the presence of light, glutamate is , this is sign and burning, |
|
| 04:45 | that if glutamate is here and activates tropic with centers it will cause hyper |
|
| 04:50 | . If there is no glutamate this will now cause deep polarization Simon |
|
| 04:59 | and subsequently deep polarization of a ganglion which would be an on center ganglion |
|
| 05:06 | . Uh huh. Then we discussed level of control and the circuit the |
|
| 05:13 | cells in particular and the features that important here is that first of all |
|
| 05:19 | whole pathway from photoreceptors bipolar on center cells or glutamate mediated and the inhibition |
|
| 05:29 | from horizontal cells releases gaba and coordinates . And also horizontal cells will be |
|
| 05:38 | by glue to mix but they will cause inhibition through this negative inhibitory feedback |
|
| 05:49 | . So if you understand these last slides as I described to you just |
|
| 05:57 | you should be able to answer the in the exam and you should be |
|
| 06:05 | to recognize the neurotransmitters in these different circuits um and the cells that express |
|
| 06:12 | neurotransmitters and what would be the consequence the light or in the dark to |
|
| 06:17 | number of potential. And if you sign conserving sign inverting you're gonna be |
|
| 06:22 | to uh handle the exam questions really . We have to get rid of |
|
| 06:30 | there we go. So we talk receptive fuel properties. We talked about |
|
| 06:37 | off retinal ganglion cells but retinal ganglion also coming magno and parvo subtypes and |
|
| 06:46 | NPC subtypes that we discussed. And at the level of the retina and |
|
| 06:52 | even L. G. N. pattern of the outside visual world would |
|
| 06:57 | . These contrast changes, luminescence changes the center surround like perception regions if |
|
| 07:06 | may. The central processing is capable putting very complex patterns together motion within |
|
| 07:12 | patterns. And we will learn about that comes about. I'll come back |
|
| 07:16 | this slide talked about how 80-90% of projections go from the retina two |
|
| 07:27 | G. M. So most of comes out from Retina, goes to |
|
| 07:36 | Jinich Hewlett nucleus. Then about 10% to text. Um which is superior |
|
| 07:45 | responsible for psychotic eye movements. And few percentage of these fibers from optic |
|
| 07:51 | innovate super charismatic nucleus which is controlling circadian rhythms. So we call that |
|
| 08:02 | have the right and the left hemi that you have a binocular zone and |
|
| 08:08 | you have sort of a peripheral The binocular zone is the zone that |
|
| 08:13 | be seen by both eyes and the vision on each side can only be |
|
| 08:19 | by one. I always remember that retina is like this kind of a |
|
| 08:27 | . Okay? It's round and it's in the back of the eye. |
|
| 08:32 | if you wanted to expose this side the cup to the light you wouldn't |
|
| 08:38 | the light from there, you would the light from there which would be |
|
| 08:42 | . Therefore the nasal retinas looking onto periphery and temporal retinas looking on to |
|
| 08:51 | edge of what would be forward the . Okay so we then talked about |
|
| 08:57 | damage to these pathways but before that that there's going to be nasal fibers |
|
| 09:04 | crossover become contra lateral temporal fibers are following the optic eye. ASM this |
|
| 09:13 | optic track that carries fibers from the and the right eyes. It innovates |
|
| 09:20 | . G. M. And from it innovates the primary visual cortex through |
|
| 09:26 | we call the optic radiations on both of the brain. So damage to |
|
| 09:32 | left nerve with essentially or left. would cause an equivalent damage If you |
|
| 09:40 | to close your left hand. Those I what you lose is the |
|
| 09:46 | Um one side. Okay because you a binocular zone. So this binocular |
|
| 09:53 | here the red fibers are going to seeing this red binocular zone and and |
|
| 09:59 | fibers are seeing this binocular zone and fibers is seeing the periphery on the |
|
| 10:05 | . The nasal fibers are seeing periphery the right. So the only loss |
|
| 10:09 | would have is on the same side the peripheral vision. If there is |
|
| 10:15 | transaction a cut damage or otherwise to optic tract on one side. Now |
|
| 10:21 | having fibers and a nasal that crossover that crossover nasal is looking over there |
|
| 10:30 | so you lose the periphery already. what else you have? The temporal |
|
| 10:38 | that are staying? Iptc lateral temporal are staying in bilateral. Okay and |
|
| 10:46 | is from the other side temporal looking the middle zone here again. So |
|
| 10:53 | lose half of the field of view the opposite side. You have damage |
|
| 10:57 | super charismatic nucleus. You have peripheral loss otherwise called the tunnel vision. |
|
| 11:05 | fibers from the retina. Again, . Six layers in the L. |
|
| 11:10 | . M. To magna. For layers eventual to each one of these |
|
| 11:16 | there parsley populated south that are non subtypes of cells they are also referred |
|
| 11:22 | as intermediary of Kanye cellular and they're in information processing that's related to |
|
| 11:33 | You have parallel processing through these layers both eyes from both eyes these |
|
| 11:40 | Armen ocular so all of the cells . If you were to record from |
|
| 11:44 | they would be responsive from one I if you record from here they'll be |
|
| 11:49 | to the uh another i on and receptive field properties. So similar type |
|
| 11:56 | information. L. G. Would essentially see a similar type of |
|
| 12:02 | of the visual information and you don't this primitive and primal sketch of the |
|
| 12:09 | world the contours and motion until you to the primary visual cortex and we'll |
|
| 12:17 | that together today. So 80% or of projections into L. G. |
|
| 12:25 | . Come from cortex. So most what innovates L. G. |
|
| 12:34 | Is cortex. Okay Visa cortical Cortical remember cortical thalamic originates in cortex |
|
| 12:42 | to the thalamus thalamus. Cortical original goes to cortex. Cortical cortical originates |
|
| 12:49 | cortex just another part of cortex. we talked about these also when we |
|
| 12:53 | about descending and ascending fibers we talked the detective spinal spinal thalamic. So |
|
| 13:01 | call some of this terminology. So you have is blue layers are obviously |
|
| 13:10 | a lateral right eye. So 235 gypsy. The red are contra lateral |
|
| 13:18 | . Or contract. You have this that gets communicated again. Multilateral I |
|
| 13:26 | one it's a lateral to they each a mag nall layer and then there's |
|
| 13:32 | powerful layers sub divided and then you the non np cells that eventual to |
|
| 13:38 | principal layer. The principal layers that the six layers that you see with |
|
| 13:43 | populated relay cells. Now there's relay in the L. G. |
|
| 13:48 | Uh Communicate the information to area 17 the primary visual Cortex in this image |
|
| 13:57 | can see that the primary visual cortex the information gets passed on to the |
|
| 14:03 | visual cortex which is V. Two which is the three ordinary which is |
|
| 14:09 | . Four. And further up through information processing stream. As you can |
|
| 14:15 | the primary visual cortex area is very relative to the overall size of the |
|
| 14:21 | . In macaque monkeys, this area still relatively large. The primary visual |
|
| 14:27 | tells you what you're seeing. It's really telling you how you feel about |
|
| 14:32 | you're seeing. It just says what see. So that information that is |
|
| 14:37 | complex and can be co joined with senses and emotions is occurring later upstream |
|
| 14:44 | these pathways. And in the association as we talked in the past, |
|
| 14:50 | has a retina topic map. We from the very beginning that there's a |
|
| 14:55 | in the sky that moon far away that moon is not going to activate |
|
| 15:01 | entire retina that half a degree angle away. In the space we talked |
|
| 15:07 | activating only 140 micro meters of space the retina. What if there were |
|
| 15:14 | moons or three bright stars? But about if they were in different |
|
| 15:20 | That means that they would occupy different in the retina. So moon over |
|
| 15:26 | moon over here and moon over there the retina. So now you have |
|
| 15:34 | point by point representation in the At this point of space is looking |
|
| 15:38 | that room at this point in retina looking at that point in space. |
|
| 15:43 | point in space is looking to this . Its point by point representation. |
|
| 15:48 | called retina topic map. And this by point representation is carried through the |
|
| 15:55 | neuronal fibers from the retina into the manipulate nucleus and into the primary visual |
|
| 16:03 | . We still have a point by through nine points here representation of algae |
|
| 16:10 | and gets reconstructed in the primary visual . This is called retina topic |
|
| 16:16 | Okay now once the information leaves G. N. And by the |
|
| 16:24 | remember that L. G. Is not passive in the sense of |
|
| 16:30 | in the sense of just relaying that . That's why the south and |
|
| 16:35 | G. Ana called relay cells if haven't mentioned because at first it was |
|
| 16:38 | it was like a passive relay Kind of will deliver the goods to |
|
| 16:42 | . G. M bibles are too to go to the primary visual |
|
| 16:47 | L. G. M will will the baton to the primary visual cortex |
|
| 16:51 | the relay. That's not the There's quite a bit of modulation of |
|
| 16:56 | activity by L. G. M the primary inputs that come in get |
|
| 17:03 | by all GM. But then you see that cortex can also affect very |
|
| 17:08 | what LG N. Is seeing as say how GM feels about what retinal |
|
| 17:15 | information should be maybe gained on like volume, Turn the volume up and |
|
| 17:23 | some instances turn the volume down or it like a decibels right? Like |
|
| 17:29 | mid range high low but for Right? So this is what cortex |
|
| 17:35 | capable of doing through this. Communications to the L. G. |
|
| 17:38 | Is influencing this primary sensory input coming the L. G. M. |
|
| 17:45 | cortex just like we discussed earlier, is comprised of six layers and the |
|
| 17:50 | superficial is one of the deepest hilarious . Most of the inputs that are |
|
| 17:55 | come in from the thalamus of thalamic inputs are going to innovate layer |
|
| 18:01 | There are no very clear lines. no clear line that says, look |
|
| 18:05 | this line, don't you see this between layer two and three. There's |
|
| 18:08 | clear lines. So it's not like it's definitive. For example a lot |
|
| 18:13 | times in experimental descriptions you will find we performed recordings in the parameter cells |
|
| 18:21 | layer 23 of the new york or it two? Or is it |
|
| 18:26 | Why is it to three? Because in particular doesn't have very clear boundary |
|
| 18:32 | . When you come to four you dense bands and there's very clear changes |
|
| 18:37 | densities five is not as populated as than GNC. More dense somatic |
|
| 18:45 | Oh uh this will stain cells You see these parameter cells these parameter |
|
| 18:52 | will have projections. You'll have local neurons. We know that the subtype |
|
| 18:59 | subtype diversity just like in the And neocortex would come from the inhibitory |
|
| 19:05 | . Parameter cells are a fairly typical their behavior in hippocampus, occipital |
|
| 19:13 | frontal lobe, parietal lobe where you the recordings or study their activity. |
|
| 19:19 | the projections that come from the algae they go through the primary visual |
|
| 19:26 | And I mentioned they internet mostly layer . So in this experiment which is |
|
| 19:32 | older experiment and radioactive pro line is in one eye. And as is |
|
| 19:40 | in one eye it will follow the and innovate in this case 14 and |
|
| 19:49 | layers of the lateral nucleus nucleus. then if you were to take the |
|
| 19:55 | and literally like kind of appeal. one peel layers 23, you would |
|
| 20:02 | this beautiful zebra like pattern that you're here. So you can't really see |
|
| 20:09 | if you did a cross section or section through the brain because you would |
|
| 20:14 | these just little uh little spots here layer four. But if you feel |
|
| 20:21 | your perspective is you're looking down on letter four, you remove layer 123 |
|
| 20:29 | . Now you're looking at layer four you're like wow look at these strides |
|
| 20:34 | And so the primary visual cortex is a stride cortex, stride or the |
|
| 20:43 | that are formed belongs to the south process information from only one eye to |
|
| 20:51 | name of the stride cortex or description stride cortex refers to ocular dominance |
|
| 20:59 | Because we know that the anatomy and is not only laminar layers but that |
|
| 21:04 | is a column or communication. We're to talk some more about that. |
|
| 21:09 | not just horizontal projections but there are projections from columns into the cortex and |
|
| 21:16 | the cortex. And we'll talk about micro processing units, the micro columns |
|
| 21:21 | larger processing units we call hyper columns a few slides. But if you |
|
| 21:28 | this 23 layer you see this beautiful . So all of the cells and |
|
| 21:36 | that are within the white zones will responsible and only reactive to activity from |
|
| 21:44 | the cells located underneath the black contra south white area, Iptc ultra |
|
| 21:56 | you have this ocular dominance columns that present in layer four. This is |
|
| 22:03 | you would see the ocular dominance So you have the projections one for |
|
| 22:10 | . And this is gonna be forming color layers. So the cells and |
|
| 22:17 | Forman ocular and within these men ocular you have uh patches or columns that |
|
| 22:27 | responsive to information from only one I or they're only responsive to information from |
|
| 22:36 | other eye in green 235. Again these are the optic radiations that |
|
| 22:43 | that information with the primary visual Now the layers come together and as |
|
| 22:49 | as 146 information from these layers. once they're in layer four information is |
|
| 22:57 | ocular that means that all of the and layer for in blue area are |
|
| 23:02 | to be responsive to only stimulation from eye in green area only to the |
|
| 23:09 | from the other eye. So when that signal become binocular? When do |
|
| 23:15 | bind the left information from the left the right eye together? And that |
|
| 23:21 | upstream? The information that comes in the lateral Nicollet nucleus. Innovates layers |
|
| 23:31 | innovate layers four. And these layers ocular but least layer four cells will |
|
| 23:39 | up into layers to three. So communication between layer four and layer is |
|
| 23:47 | starts blending the information from two Will come back and talk about this |
|
| 23:53 | a little bit more. But let's back to this slide. So in |
|
| 23:57 | experiment, What you have is an . Can you place electrodes in position |
|
| 24:04 | . And you're placing an electrode in 2 3. Okay. And then |
|
| 24:11 | A. And notice that position Is located above the center of the |
|
| 24:20 | dominance called. And the electorate in A. You have stimulation of both |
|
| 24:28 | , electorate in position A. Is responsive just to the contra lateral |
|
| 24:34 | That means that the 1000 layer 23 still min ocular if they are located |
|
| 24:42 | center above the ocular dominance columns. you move your electorate into position |
|
| 24:50 | Now remember you know where the strides . So you can determine that |
|
| 24:56 | You can determine it uh with stains you can also determine it with fluorescent |
|
| 25:03 | . You don't have to have radioactive . And you can also visualize it |
|
| 25:08 | another technique that we'll talk about a bit later, intrinsic optical signal or |
|
| 25:13 | sensitive damaging. But we'll come back that in a second. But in |
|
| 25:16 | B. What's interesting in position Which is in between The two Ocular |
|
| 25:23 | Columns that belong to two separate In position B. The cells are |
|
| 25:31 | responsive to both eyes equally. It's lateral and contra lateral. You move |
|
| 25:37 | electorate into position see which is right the middle of the column. In |
|
| 25:43 | 23. Again these are the projections from 4 to 23 but right above |
|
| 25:49 | center. It's only bilateral in between D. Iptc contra E only contra |
|
| 25:58 | in between zone so that tells us it layers to three. The cells |
|
| 26:04 | finally joining the information and that information becoming binocular. So the processing on |
|
| 26:11 | visual cortex at last 23 is binocular processing co joints information from both |
|
| 26:20 | So these projections that are shown here that we're discussing. There's a slide |
|
| 26:27 | I left some notes space for you . Uh And I'm not gonna talk |
|
| 26:33 | retinol waves and movie but it's it's interesting and anatomy of contra zone. |
|
| 26:38 | I'm gonna leave that to uh graduate course next semester, but I want |
|
| 26:45 | talk to you about some interesting concepts that we already touched upon. The |
|
| 26:51 | are plastic. What does that That means you can strengthen existing |
|
| 26:57 | weaken existing synopsis. You can also synoptic connectivity or you can grow new |
|
| 27:05 | and form new connections. The brain mostly plastic during what we call the |
|
| 27:12 | period of plasticity and critical period of . This critical period of development is |
|
| 27:21 | the environment in the brain, chemical such as neurotrophic factors is making neuronal |
|
| 27:30 | . Most malleable. They're most And a good example of plasticity And |
|
| 27:40 | period of development is I always use languages. I came to this country |
|
| 27:46 | I was 17 and you can still my accent if I came here when |
|
| 27:51 | was six and I was equally emerged fully emerged into the english environment. |
|
| 27:59 | would not be able to tell that have an accent. Why is |
|
| 28:03 | I studied even more than a six old did when I was here at |
|
| 28:08 | and 18. In fact I studied language even before I came here and |
|
| 28:11 | was about 50% fluent in English. still have an accent. Uh think |
|
| 28:18 | this, How many of your parents are older that maybe are immigrants or |
|
| 28:26 | to learn a foreign language because they to learn a foreign language and how |
|
| 28:32 | it was and how difficult it is do this and to become fluent, |
|
| 28:39 | not in comprehension but in pronunciation. a very difficult task for special and |
|
| 28:47 | person. There's a reason why we our Children to learn foreign languages at |
|
| 28:52 | ages. Don't want them to start 18. You know, you want |
|
| 28:58 | to start at 56 kindergarten first grade early as possible. Kids that go |
|
| 29:04 | bilingual schools and in Houston we have schools that are english and mandarin and |
|
| 29:11 | and um spanish kids that go whether first language is english. Second language |
|
| 29:19 | spanish, let's say our first language and second language is english. They |
|
| 29:23 | to these schools. They actually underperformed first three grades compared to their |
|
| 29:30 | So even if their primary language is , they're gonna be underperforming in english |
|
| 29:35 | there are also learning spanish the same until about the 4th, 5th |
|
| 29:40 | And then it all flips now they in their native language over their native |
|
| 29:48 | speakers and over the second language who have native language speakers but do not |
|
| 29:55 | the second language. So there's a of stimulation in the language areas, |
|
| 30:01 | a lot of plasticity, communication and that are built in language areas and |
|
| 30:07 | developed plasticity also is protective. So you have damage to the brain, |
|
| 30:13 | traumatic brain injury if there is uh of brain tissue such as after explosion |
|
| 30:22 | cancer growth or something like that, is much easier for Children's brains. |
|
| 30:29 | brains to recover, younger brains would less loss of function, suffering consequences |
|
| 30:38 | such harsh traumas compared to adults. people can't remember things and don't want |
|
| 30:47 | learn new things either. Right. is also a process that with |
|
| 30:52 | it starts going away. There's a spot. You don't go to college |
|
| 30:58 | 52. Typose could. There's also reason for it. First of |
|
| 31:03 | you want to do something before you're using your knowledge and degrees. Another |
|
| 31:08 | is you're actually learning really well at age too. So it doesn't stop |
|
| 31:14 | learning doesn't stop. And I think more you learn, the better your |
|
| 31:17 | is adapted to learning and continue learning things. As an example of some |
|
| 31:22 | our parents are okay with emails and can touch them and that's just a |
|
| 31:29 | . They may be the same age the technology came about the same |
|
| 31:32 | but some chose to pursue this or , you know, ability to do |
|
| 31:38 | or whatnot and other parents didn't and the same house household actually with the |
|
| 31:42 | income and that really makes a difference their world and their communication with |
|
| 31:49 | So this process of plasticity is early languages again, the best is to |
|
| 31:58 | learning them and as early as possible you look at the language plasticity graph |
|
| 32:02 | drops down after the age of 18 20 pretty drastically down, which means |
|
| 32:07 | have to put a lot more effort to sound like a native. Now |
|
| 32:14 | is all related to this slide And what you're seeing on the |
|
| 32:19 | our projections from the thalamus. The is therefore of neocortex and these projections |
|
| 32:28 | retinol projections. Now they're thalamic projections balance into cortex. Cortical projections. |
|
| 32:36 | see they form these sophisticated synaptic Dendrites axons here you're seeing that the |
|
| 32:45 | that are projecting into lair. For these are following a cortical axons that |
|
| 32:50 | coming into layer forms in rodents. critical period of development is the first |
|
| 32:58 | of life. That means that they the most plasticity, the best ability |
|
| 33:05 | recover if there's an injury or uh uh deprivation. A sensor deprivation. |
|
| 33:15 | so look what happens in this experiment . This experiment Three days for three |
|
| 33:23 | at the very end of its first of life animal gets an eyelid suture |
|
| 33:30 | and against a pirate patch put on for three days this animal basically does |
|
| 33:36 | have a stimulation visual stimulation. For guy following three days, patches taken |
|
| 33:43 | , the future is taken off and eyelid is open. The animal can |
|
| 33:49 | with both eyes and one month later experiment was performed, electrodes are being |
|
| 33:58 | into the occipital lobe okay into the for the primary visual cortex the light |
|
| 34:06 | stimulating the contra lateral I that was and the hips ular lateral I that |
|
| 34:14 | open. And what you're seeing is three days of Manaka color one I |
|
| 34:22 | . The creation of vision in one . You already have a bias to |
|
| 34:28 | information to the it's a lateral eye you cannot have, you do not |
|
| 34:35 | as many cells that are responsive to to the cultural lateral party. So |
|
| 34:43 | in three days if it was normal would see equal amount of stimulation in |
|
| 34:51 | and if the eyes and here you're that the system and the cortex is |
|
| 34:57 | attuned to. It's a lateral eye remained open, it wasn't closed. |
|
| 35:05 | something that means that something has changed connectivity and the functionality of the brain |
|
| 35:12 | changed. After three days of the deprivation. Now you repeat the same |
|
| 35:19 | except you double the time of So in this case the island is |
|
| 35:26 | for six days, The 3rd of month, then sutures taken off animal |
|
| 35:33 | for a month. Animals contra and a lateral eyes are stimulated with |
|
| 35:39 | recordings are done in layer four occipital and there's absolutely no response whenever the |
|
| 35:48 | lateral is stimulated, there's no response new york cortex. Whenever there's collateralize |
|
| 35:55 | , there is huge response and now whole cortical system has shifted to perceiving |
|
| 36:01 | from just one time. So even these significant times toward the end of |
|
| 36:09 | period, even at these significant times deprivation of something for six days or |
|
| 36:18 | week sensory deprivation. You can think other types of deprivations and auditory, |
|
| 36:26 | can think of other types of even emotional or touch for like a |
|
| 36:32 | and stuff like that. You know alters the brain circuits, it alters |
|
| 36:37 | brain circuits. And if it is short lived deprivation yeah you can see |
|
| 36:43 | recovery here, right? These styles still responsive to cultural out alive but |
|
| 36:48 | a lesser degree. But if this is prolonged then you lose responsive itty |
|
| 36:54 | that I altogether go ahead. You your question person, I think what |
|
| 37:03 | to the other? I like it far as can the other. I |
|
| 37:07 | see that's a great question. Uh can still see but these circuits in |
|
| 37:21 | retina are formed much earlier. In that's why I have a previous slide |
|
| 37:28 | waves. It's like this uh anatomical we call anatomical segregation and retinal circus |
|
| 37:37 | before it happens in L. M. Before it happens in |
|
| 37:43 | So the timeline would be such that even the funny thing in these |
|
| 37:50 | their eyes open at P- 14, , day 14. But even before |
|
| 37:56 | eyes are open, their photo receptors already functional producing this waves of |
|
| 38:02 | So the retina does not necessarily get to the same extent the circuits already |
|
| 38:09 | like you would see in the cortex this particular time period of development. |
|
| 38:16 | if you did that earlier, if deprive the animal earlier when the retinal |
|
| 38:22 | were basically entrenching themselves into this visual then you probably mess up the retinal |
|
| 38:30 | too. And that has been So there are these spontaneous waves of |
|
| 38:35 | that goes through the retina without any . It's like a code that builds |
|
| 38:41 | circuits and if you block these waves don't develop the retinal service. So |
|
| 38:48 | there are studies that are that are to that extent but you have to |
|
| 38:52 | earlier in time in order to to see that. And in this particular |
|
| 38:57 | we're looking really an establishment of this cortical projections that this time period 1-2 |
|
| 39:06 | of age. Yeah. I think may have kind of answered my |
|
| 39:11 | What I was gonna say is on sixth day one where they're showing no |
|
| 39:16 | . Does that mean the animals blind that eye? Even though I know |
|
| 39:20 | it doesn't the cortex is blind to i it doesn't kill photo receptors. |
|
| 39:28 | doesn't kill the retinal circuit. But . Yeah now so so here is |
|
| 39:43 | an image of open eye level cortical versus short term without the deprivation 3-6 |
|
| 39:54 | and you can see massive patrician and of inputs coming into the cortex from |
|
| 40:02 | and that's why there's no south that really responsive to to these inputs any |
|
| 40:08 | if their eyes just a few and a certain period of time. |
|
| 40:15 | Okay so this is what this slide about. Um better flow to explain |
|
| 40:21 | after explain the ocular dominance columns. now we're gonna come back to the |
|
| 40:26 | . So salama cortical inputs coming to four except for intermediary for the Kanye |
|
| 40:33 | one, thereby bypassing therefore by by bypass layer four and go directly to |
|
| 40:41 | 23. Okay they're concerned with color processing. Is that interesting? So |
|
| 40:53 | means that the empty cells are going form staying molecular for a minute before |
|
| 41:01 | information is sent to list 23 from four. But color doesn't care to |
|
| 41:08 | in these binoculars owns and goes directly the binoculars owns, interesting color is |
|
| 41:19 | in as far as like color. perception of color is not necessarily uh |
|
| 41:27 | can survive without seeing color. So you think about it evolutionarily uh did |
|
| 41:38 | have more chromatic vision that we have types of cones or did we have |
|
| 41:44 | than than they formed into three subtypes did we have like a nighttime grayscale |
|
| 41:54 | first. That's an interesting question for neuroscientists and probably should look into it |
|
| 42:00 | I'm asking it but this is the . So we have a lot of |
|
| 42:04 | projections from into layer four from layer they go 2 to 3 layers 23 |
|
| 42:10 | send these projections through the long range projection. Through gravity, two other |
|
| 42:17 | stride or outside of the final visual areas for example. V. Two |
|
| 42:24 | B. Three B. Four Five empty medial temporal. Remember the |
|
| 42:28 | from visual cortex and we're gonna split posterior parietal and uh then the temporal |
|
| 42:36 | from 23. The information goes down and from six information goes back to |
|
| 42:44 | columns back to L. G. . So here you have the protocol |
|
| 42:51 | you have cortical Sulaiman and with them have an inter cortical loop. These |
|
| 42:59 | that go from deep layers into balance also sent influence into their form. |
|
| 43:06 | if your engineer like minded or map minded or computation like minded. Each |
|
| 43:16 | does a different kind of computation in way. And you have three |
|
| 43:21 | You have the the llama cortical input and cortical thalamic. So this is |
|
| 43:27 | llama cortical cortical Islamic. And then have this inter cortical loop. So |
|
| 43:33 | four has been activated it's 23 long to other areas 56423564 to 3. |
|
| 43:42 | that information will actually circle through here it comes into four and gets sent |
|
| 43:48 | to two and communicated. Will come here. Come back here and we |
|
| 43:54 | refer to as reverberating type of activity the brain. But this is the |
|
| 44:00 | circuit, the llama cortical intra cortical circuit and then you have the cortical |
|
| 44:08 | output. What's the difference between four . And three going? There are |
|
| 44:13 | differences in where the projections are going . It's shown for example that would |
|
| 44:19 | uh targeting some of these lower Just distribution of cells but uh probably |
|
| 44:29 | differences and processing. And we know these are larger receptive fields that are |
|
| 44:34 | processed slightly different cells would be processing information. Magna versus parvo. I'm |
|
| 44:41 | about like when it goes to the critical areas, oh where it goes |
|
| 44:47 | what's the difference between two and three ? Oh what's the difference? So |
|
| 44:52 | one is the primary visual particle the two is secondary. The one |
|
| 44:57 | area 17. V. Two is 18. The threes. Area |
|
| 45:03 | At each step the information becomes more hierarchically in what visual cortex perceives and |
|
| 45:12 | it interprets information. And it also outside of the visual cortical areas |
|
| 45:20 | I was just asking under what All conditions. Yeah. At the |
|
| 45:27 | of the primary visual cortex you're gonna primal sketch that we're about to discuss |
|
| 45:34 | in order for you to have a visual perception with all of the complex |
|
| 45:43 | such as depth perception. This happens higher areas like V two V 3 |
|
| 45:51 | then you sometimes want to look at things and sometimes you don't that's because |
|
| 46:00 | other senses are influenced and that goes association areas and we talked about remember |
|
| 46:08 | streams that go here that process more and form streams that go here that |
|
| 46:15 | more kind of a contour form Okay and color forward hearing areas. |
|
| 46:24 | another interesting feature of the anatomy in visual cortex is that in layers 23 |
|
| 46:31 | have blobs and visa cytochrome oxidase. stained kind of a darker spots that |
|
| 46:40 | seeing. Cytochrome oxidase is involved in production. So the signals higher metabolic |
|
| 46:48 | areas in particular in layer 23 we these blob like formations we believe they're |
|
| 46:56 | with Alana and G. L. . G. N. South receiving |
|
| 47:01 | primarily from this non and peace attack cellular intermediary south. And they are |
|
| 47:09 | in color processing. So somehow maybe requires additional metabolic activity in layers 23 |
|
| 47:19 | these blobs owns. So we discussed the level of the retina and |
|
| 47:28 | G. N. But the cells information using these on center surround off |
|
| 47:38 | field properties. And now we're interested know and how do we know |
|
| 47:46 | Because if you shine instead of a image if you shine a square image |
|
| 47:54 | not going to the list of the action potentials in reverend game themselves. |
|
| 48:00 | that's how we know that it reacts it has these receptive properties properties in |
|
| 48:05 | retina. Now we come to cortex this is an experiment. the |
|
| 48:13 | the cat monkey sitting typically not allowed humans? Micro electrode recordings uh for |
|
| 48:24 | or experimental purposes? So you're the is seeing the screen here. That's |
|
| 48:32 | field of view of the subject. that screen experimental places an electrode and |
|
| 48:39 | four of the primary visual cortex. it takes about four hours to get |
|
| 48:46 | this point experimentally because you have to the animal, you have to do |
|
| 48:57 | little surgery on the occipital lobe. have to restrain animal. You have |
|
| 49:03 | have all of your optics set up screen and then 234 hours into |
|
| 49:11 | You have a cell final in gotta stimulated produces action potentials also. Now |
|
| 49:20 | is this cell looking at? What you have to do? So you're |
|
| 49:27 | now stimulate the screen and there were sorts of stimulations that were done on |
|
| 49:32 | screen. Around square triangles and so . Until boom you stimulate in this |
|
| 49:43 | area which is the border of the field. And you got lucky another |
|
| 49:48 | hours later you actually get a recording the south. And every time you |
|
| 49:55 | in this white square you get a from that south. So now you |
|
| 50:01 | that you're recording from the south that looking at this area here which is |
|
| 50:07 | field from that south. Then you a question. Well what is the |
|
| 50:13 | excitation from that for that primary visual cell? What is the maximal |
|
| 50:20 | How can I induce the most number action potentials? What happens if you |
|
| 50:27 | this bar of light that sell a of light? And if you show |
|
| 50:32 | of light in this orientation that cortical I see it, I see |
|
| 50:38 | I see it. And then you that bar of light in the same |
|
| 50:45 | field. But you rotate that bar light slightly by an angle and now |
|
| 50:51 | response from yourself. It's not as to look at it. We rotated |
|
| 51:01 | this position. You're recording from the south but there's no response at |
|
| 51:10 | So it is still within the same field. But now it's in a |
|
| 51:16 | different orientation from where you got the action potentials. And so that tells |
|
| 51:24 | that the cells in the primary visual as opposed to processing concentric centers around |
|
| 51:33 | of having these receptive fuel properties their responsive. The bars of white and |
|
| 51:41 | most responsive to bars of light in orientations which is referred to as orientation |
|
| 51:51 | . So this particular cell in which electrode is placed is most responsive to |
|
| 51:58 | . It's most selective to this orientation most responsive to this orientation. A |
|
| 52:05 | next to it. You were to the elector to move it over and |
|
| 52:10 | another cell and find this receptive field passes bar of light and adjacent cell |
|
| 52:19 | most responsive to this orientation of But this time the recording to who's |
|
| 52:26 | responsive to this orientation and the bar light. So now we have a |
|
| 52:31 | of light that we can work The other thing is the same |
|
| 52:40 | You have an electrode. You found border receptive field you're stimulating in the |
|
| 52:45 | field. But now you decided I'm gonna move the stimulus across the receptive |
|
| 52:53 | borders while I'm recording from the cortical here and then move it from this |
|
| 53:01 | , your left to write. And this bar enters into their self the |
|
| 53:08 | the cell here goes blue boop I see I see I see I |
|
| 53:12 | I see you moving, see you you see you see and then as |
|
| 53:16 | moves out of the receptive field the is more or less silent. And |
|
| 53:23 | you repeat the same experiment. But you passed the bar of light from |
|
| 53:29 | to left in the opposite direction. was off the field at the same |
|
| 53:35 | you just saw a massive response. now besides these couple of action potentials |
|
| 53:42 | called the edge of fact as the wine Anderson to yourself. The |
|
| 53:47 | The cell in the cortex remained So that's told the scientists that were |
|
| 53:54 | these experiments that the primary visual cortical are not only orientation selective. There |
|
| 54:03 | also direction selective. There is selectivity direction direction now implies movement and perception |
|
| 54:15 | movement. You're more sensitive to movement right to left and one cell and |
|
| 54:20 | install from left to right up and diagonally and so on in different |
|
| 54:29 | These neurons that you seen in the , the on off the project into |
|
| 54:38 | L. G. N neurons. you still have centers around on off |
|
| 54:44 | field properties in the L. N neurons. And a lot of |
|
| 54:48 | . G. N neurons will then onto the primary visual cortical south. |
|
| 54:54 | therefore um simple cells will converge on cells. Complex cells will also have |
|
| 55:09 | direction, selectivity, orientation, And now the receptive fields become quite |
|
| 55:20 | because you can take three on these And converge information from these three receptive |
|
| 55:38 | . And what you got is you a bar of life now. |
|
| 55:47 | So in the cortex in the cortex have bars of light. You have |
|
| 55:54 | shape right? You have a shape goes like this. Then you have |
|
| 56:02 | shape cooking like this. You have are septic field properties. You can |
|
| 56:08 | another bar of light on top Okay you have these diagonal bars of |
|
| 56:16 | . Okay you can put I've below iron bar of light like that. |
|
| 56:27 | . Put 1 1 here. Maybe a bar of light here. Something |
|
| 56:31 | this. Right then you can put like this. Like a bar of |
|
| 56:35 | here. Oh maybe a bar of in here. Let's add a little |
|
| 56:43 | or half circle here and you have primal sketch. Uh a face, |
|
| 56:54 | a primal sketch of the chair, have a primal sketch of an outside |
|
| 56:59 | and now you can construct because you these cells from L. G. |
|
| 57:04 | . That all of these bars, bars converge from simple cells of the |
|
| 57:09 | cells. And even within simple cells already start seeing different perception of different |
|
| 57:18 | essentially orientations that you couldn't perceive in retina. L. G. |
|
| 57:25 | On top of that you have Right? Because we're processing color, |
|
| 57:32 | visual cortex, you have, we about orientation, you have direction so |
|
| 57:39 | wind is blowing the hair into this or something. Oh uh and it's |
|
| 57:47 | lot more fun. You can do lot of things with us now. |
|
| 57:53 | that gonna tell you how this face ? The primary visual cortex? No |
|
| 58:03 | are emotional centers there's a limbic system processes emotional information. There are special |
|
| 58:14 | that are responsible for facial recognition. outside of the primary visual cortical areas |
|
| 58:26 | are areas that are responsible like amygdala interpreting the emotion on the face. |
|
| 58:36 | visual cortex, it's only going to you this and then the emotional centers |
|
| 58:46 | the brain and the amygdala is gonna smiling. Primary visual cortex is going |
|
| 58:55 | say, this is what I This is what I see and that's |
|
| 58:58 | from the earlier slides when I talked the association areas that we dedicate a |
|
| 59:04 | of our brain space to association This is where we think about what |
|
| 59:10 | see. We're influenced how we feel what we see we're seeing and we're |
|
| 59:17 | to music at the same time and something. And also without even external |
|
| 59:24 | , we're thinking stuff and it's sometimes always say it's difficult to get stuff |
|
| 59:31 | of your head, like it's really special talent, A lot of |
|
| 59:36 | A lot of us may have things our head that we hear that we |
|
| 59:40 | , but it takes a special talent the skill to take it from there |
|
| 59:46 | your circuits into the spinal cord and as a painting or a symphony that's |
|
| 59:55 | your head. A lot of us things in our heads, but it's |
|
| 60:00 | getting it out. I'm still working that really. So these two |
|
| 60:07 | Google and Weasel contributed a lot to understanding what we're talking about today. |
|
| 60:12 | orientation specificity, direction, selectivity Huebel Weasel also discovered what we call orientation |
|
| 60:21 | . And they did that with micro recordings. So these orientation columns or |
|
| 60:27 | columns, we typically consider them anywhere 3200 and 50 micro meters In size |
|
| 60:36 | diameter, about two in in So they're not necessarily all uniform |
|
| 60:42 | more or less they are and they in size across different species, but |
|
| 60:48 | you have and what Huebel and weasel is these experiments will be stuck in |
|
| 60:53 | and they passed the stimulus and they , hi, the cell is responsive |
|
| 60:57 | this bar in line and then they to the post doc, you're gonna |
|
| 61:01 | here for the next two days, food, no sleep, a lot |
|
| 61:06 | coffee. And you're gonna do these with stab as many cells as you |
|
| 61:14 | . And they did that and they that for months and years until we |
|
| 61:19 | that there are these micro columns that orientation columns, orientation selective columns. |
|
| 61:27 | the cells in these columns, the bar of life represents that the cells |
|
| 61:31 | this area are most responsive to this of life. The cells in that |
|
| 61:36 | are responsive to this orientation of life you can see that similar orientations. |
|
| 61:42 | almost like 360 that you go We realize that as you circle this |
|
| 61:51 | , you turn this 360° around into same position. So this one orientation |
|
| 62:05 | will then process this information from the of the possible orientations for that bar |
|
| 62:15 | light. The center will contain cells are responsive to different orientations and that's |
|
| 62:24 | these orientation columns appear like pinwheels. the center will have cells responsive to |
|
| 62:34 | orientation. Blue orientation. These colors imply orientation of the bar of life |
|
| 62:42 | the sensitivity to those cells. So specific orientation of the bar of life |
|
| 62:49 | you have what is called voltage sensitive and voltage sensitive dye imaging. So |
|
| 62:55 | talked about how we can image activity human brains. We discuss tet scans |
|
| 63:03 | FMR eyes functional imaging of activity in brains. We talked about how you |
|
| 63:10 | image activity in neurons. We looked imaging of calcium when we talked about |
|
| 63:16 | release, we said that calcium gathers these pre synaptic active zones and when |
|
| 63:23 | is deep polarization you'll see the calcium and your imaging calcium like calcium. |
|
| 63:30 | can also image voltage, meaning that this case you will see the south |
|
| 63:37 | are active in the cells that are active. They're not going to show |
|
| 63:42 | now both of sensitive guys work in way that you apply them to the |
|
| 63:46 | tissue and that all of the cells suck up the dye. And so |
|
| 63:53 | makes these kinds of experiments much easier instead of stabbing individual cells here, |
|
| 64:03 | cell takes an hour or two to do experiment, you stay all of |
|
| 64:09 | cells and in this case you can that each one of these dots is |
|
| 64:13 | individual cells and you present a certain of light and you're looking at this |
|
| 64:19 | column, present certain orientation of life you see all of the cells that |
|
| 64:25 | be activated by disorientation which is yellow of life. Then you see all |
|
| 64:31 | the cells that are activated by red of light, purple orientation of |
|
| 64:38 | And so voltage sensitive dyes is a nice technique to visualize the orientation columns |
|
| 64:45 | larger areas in primary visual cortex because could only have so many positive post |
|
| 64:53 | for so many years uh stabbing millions neurons to illustrate that definitively throughout the |
|
| 65:02 | structure with multiple sensitive dyes is helping with that. So those are the |
|
| 65:08 | that are sensitive to a change in number of potential and there is deep |
|
| 65:12 | . They basically glow. There is deep polarization. They don't glow when |
|
| 65:17 | glow, you can see it under microscope and you can see it in |
|
| 65:21 | single cell resolution or small collections of also. So you have these 10 |
|
| 65:28 | like structures in this uh elementary micro orientation column is processing orientation but we |
|
| 65:40 | to process orientation from both eyes and want to start co joining that |
|
| 65:47 | So here what you're seeing here are ocular dominance columns that are now extended |
|
| 65:54 | layers 1 to 6. Ocular dominance that really present in layer four where |
|
| 65:59 | have binoculars south. These are the of the ocular dominance columns. So |
|
| 66:04 | see the same why here for the lateral you're seeing this is the same |
|
| 66:09 | of this ocular dominance zone. So put it all within a perspective. |
|
| 66:16 | hyper column is organization of orientation Ocular dominance columns In the primary visual |
|
| 66:27 | . So within these ocular dominance columns . This area belongs to information from |
|
| 66:34 | eye. You'll have multiple orientation columns the middle of the ocular dominance columns |
|
| 66:43 | contain blogs. And the processing of information. And remember blobs will primarily |
|
| 66:50 | located in Larry's 2 3. And , there's the last technique for |
|
| 67:00 | Now, all the sensitive dyes that talked about. That's an experimental neuroscience |
|
| 67:05 | . This is not a clinical imaging . You cannot apply dyes to human |
|
| 67:11 | and then put them under a microscope stimulate an image activity. So this |
|
| 67:16 | experimentally that is done in animal And there's another technique which is intrinsic |
|
| 67:25 | signal. So recall that active neurons what they consume more oxygen, They |
|
| 67:33 | more food or glucose. Is there ? And what else they do if |
|
| 67:42 | active and they're persistently active, they swelling as they start swallowing neurons start |
|
| 67:50 | closer to each other, Their membranes stretching a little bit. Remember. |
|
| 67:56 | it's a it's a fluid membrane The cell is getting bigger can accommodate |
|
| 68:01 | course it's too big, it's gonna . But active cells swell as the |
|
| 68:09 | cells swell, The reflective properties of membranes will change. And so it |
|
| 68:16 | that if you shine a light on surface of the brain or the surface |
|
| 68:21 | the tissue surface of layer four. you activate these neurons, there is |
|
| 68:28 | optical signal that you can pick It's called intrinsic optical signal. Its |
|
| 68:34 | because you're not staining anything. There's calcium diet. There's no voltage sensitive |
|
| 68:38 | , there's no radioactively labeled material. just looking at the changes in the |
|
| 68:44 | ints or absorptive properties of life by tissue. You can see this why |
|
| 68:52 | , this is the y that you're here. So with intrinsic optical |
|
| 68:56 | you can actually visualize if you stimulate I repeatedly and you have a window |
|
| 69:02 | you can see where four. Without dye. You're gonna be able to |
|
| 69:08 | the signal in the form of intrinsic signal. And can this technique be |
|
| 69:15 | clinically. Typically it is not used . However pre operatively a lot of |
|
| 69:23 | a neurosurgeon let's say needs to resect part of the brain that's generating seizures |
|
| 69:32 | they will open the skull and open window into the brain. Together with |
|
| 69:37 | neurophysiologist. Then they're going to poke a little bit to make sure that |
|
| 69:45 | identify the zone for resection to be small as possible to cause the least |
|
| 69:50 | as possible. And as they're looking the surface of the brain, the |
|
| 69:56 | has a seizure and they would be to see it because the reflective properties |
|
| 70:04 | the seizure was in the surface of cortex. It would come almost like |
|
| 70:08 | wave of darker wave of activity that pass. So typically it is not |
|
| 70:15 | but it can be observed in in clinical setting, especially when you have |
|
| 70:21 | window. Only if you have a into the brain and can image the |
|
| 70:27 | of the brain. So recall that brain is innovated with this micro |
|
| 70:34 | So the micro vasculature is going to the oxygen and the settling some, |
|
| 70:42 | of the things that is needed to brain from the blood. Have these |
|
| 70:49 | dominance columns. You can visualize them intrinsic optical signal. They actually have |
|
| 70:55 | section in your book, both optical of neural activity and you can use |
|
| 71:01 | sensitive dyes to reconstruct many of these columns and specific orientations of the south |
|
| 71:08 | than doing single electorate recordings using Right. Thank you very much. |
|
| 71:14 | may have gone two minutes over I appreciate everyone's time. Hope that |
|
| 71:19 | followed me through the circuit into the sketch and I'll see everyone at the |
|
| 71:25 | on Tuesday, have a good weekend hopefully everyone gets to review the material |
|
| 71:31 | the exam. Thank you |
|
