| 00:00 | Sure we are reviewing the we're reviewing circuits here. The photo transaction the |
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| 00:08 | . Please review previous lectures the amount class. I didn't record this particular |
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| 00:15 | here. Review 23 slides of police . Last lecture to catch up with |
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| 00:23 | . The parvo cells. So we the cells that are basically receptive fuel |
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| 00:29 | on off ganglion cells sometimes. But we have some division of these cells |
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| 00:33 | magno and parvo and these magno and cells. They will be forming the |
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| 00:40 | side of the L. G. 80 to 90% regular to L. |
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| 00:44 | . N. From the retina. will go to tech con superior curriculums |
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| 00:48 | process psychotic eye movement. 123% will a super charismatic nucleus which controls the |
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| 00:54 | rhythm. We talked about the visual loss. Is here using these |
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| 01:01 | So please please review these are very labeling questions in the exam and then |
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| 01:06 | started talking about lateral nucleus as a layer structure. It has to magna |
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| 01:12 | and four power layers. Magna 12 the cells that are located ventral to |
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| 01:19 | one of these layers are called intermediary Kanye cellular or non NPC subtypes of |
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| 01:26 | and what L. G. N most of the inputs that L. |
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| 01:30 | . M receives 82 or more percent from the cortex. So that's why |
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| 01:36 | . G. N. What we with L. G. M. |
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| 01:40 | influenced by how we feel because other areas visual and non visual cortical areas |
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| 01:45 | into the L. G. Can and modulate the sensor information is growing |
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| 01:51 | the retina as it is being modulated the lateral nucleus. So if you |
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| 01:57 | the temporal retina states the lateral nasal contra lateral the layers for the |
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| 02:04 | G. M. R. Do remember the pneumonic? Uh See I |
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| 02:14 | see I see I see I I I see. So I guess the |
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| 02:20 | way to remember is I see. ci instead of ci is instead of |
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| 02:26 | . C. C. I. the two layers is contra lateral it's |
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| 02:31 | and then the bilateral contra lateral it's contra lateral. These are the four |
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| 02:37 | layers. You have that same The projections from the lateral nucleus go |
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| 02:45 | the area 17. This is the visual cortical areas 17. uh as |
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| 02:52 | to Macaque monkeys and humans. This is much smaller and there's retina topic |
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| 02:58 | as we talked about retina, these . And so this part of the |
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| 03:02 | is looking over there in the periphery the nose the temporal is looking over |
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| 03:07 | and central retina is looking straight So there's a point in space which |
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| 03:13 | to a point in the retina that that space just like we talked about |
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| 03:17 | moon. And when you're looking at moon there's going to be a certain |
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| 03:20 | of the retina that is processing information that particular point in space. And |
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| 03:25 | this retina topic map point by point from the retina to the L. |
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| 03:31 | . M. One through A through nine is traveling through the optic nerves |
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| 03:37 | optic radiations from the lateral in the visual cortex where you have this point |
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| 03:44 | point representation in the primary visual cortex is a point that corresponds to a |
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| 03:49 | in the L. G. That corresponds to a point in the |
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| 03:53 | , it corresponds to a point in sky that is the moon. |
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| 03:57 | so this is referred to as retina map primary visual cortex. And in |
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| 04:03 | neocortex as we already saw has both and columnar structures. This is the |
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| 04:12 | structure. It has six layers most one, the deepest layers six. |
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| 04:19 | it also as we saw has this structure with these micro columns that are |
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| 04:24 | of south that are connected instead of through the layers vertically. Through the |
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| 04:30 | represent these simple functional units that process locally in the cortex. And if |
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| 04:38 | were to inject a fluorescent dye or the older days it was radioactively labeled |
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| 04:47 | lean protein and one eye projections from one eye on one side of the |
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| 04:54 | . G. M would innovate three right 14 and six. And they |
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| 05:01 | project from that one I from the . G. I. Into the |
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| 05:05 | visual cortex. And if you were take these six layers of the primary |
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| 05:11 | cortex. If you were to peel 12 and three from the surface and |
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| 05:17 | what you see in layer four looking the side view it's hard to see |
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| 05:22 | from the top view you really you this zebra like pattern. The zebra |
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| 05:29 | pattern is referred to stride cortex or each strides like strife cortex. Each |
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| 05:38 | of these stripes represents cells that process only from one eye. And these |
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| 05:45 | referred to as ocular dominance columns. in layer four what you're seeing is |
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| 05:52 | the level of the retina information is one eye at the level of |
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| 05:57 | G. N. Layers those layers binocular and at the level of the |
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| 06:02 | visual cortex where most of the projections the L. G. N. |
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| 06:07 | into layer four of the primary visual you have ocular dominance which means all |
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| 06:13 | the south under this white stripe process from one eye under black stripe information |
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| 06:20 | that. I so this is a anatomical structure that you have in the |
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| 06:27 | visual cortex. Now when does this in the primary visual cortex become |
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| 06:35 | In other words we're still tracing the here from min ocular layers 14 and |
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| 06:42 | in two layer four off the G. N. And these blue |
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| 06:48 | next to green squares And layer in four of the neocortex. I'm |
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| 06:52 | And layer four the neocortex you're seeing these blue areas in these green areas |
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| 06:59 | is mon ocular cells. So those receive inputs just from one eye from |
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| 07:04 | layer of the L. G. . And what this experiment shows is |
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| 07:10 | it E. This is an electrode is placed in position A. And |
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| 07:15 | is placed in position A. In layer to layer 23. And when |
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| 07:21 | is placed in position A. In 23 the response. If you stimulate |
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| 07:28 | system here and you're recording from the cortex and your recording from this area |
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| 07:34 | where the electrode is an A. only response that cells would have would |
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| 07:40 | to the contra lateral eyes stimulation. if you stimulate it it's a lateral |
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| 07:45 | the cells are not responsive to But interestingly if you move into position |
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| 07:51 | position B. Is now in between you would call these ocular dominance column |
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| 07:59 | that are shown here in blue and and in position B. You would |
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| 08:04 | now an equal response from both the and contra lateral eyes. So if |
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| 08:11 | do these recordings in layer four all the south are going to be responsive |
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| 08:16 | either one eye or the other one eye or the other. I |
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| 08:20 | you do a recording immediately in the zone of this ocular dominance columns in |
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| 08:26 | 23 it's stillman ocular but there's something the connectivity. They have connections between |
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| 08:34 | four going to less to three. there's something in the connectivity at the |
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| 08:41 | above In layers 2 3 that make cells now. Finally binocular now they're |
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| 08:48 | integrating information from both eyes and becoming and then part of me. Oh |
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| 09:00 | right so and if you move this in to see this electorate into |
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| 09:07 | see you can again see that in position because it's above immediately. The |
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| 09:14 | ocular dominance columns that sell or those located in areas you will only be |
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| 09:22 | to bilateral stimulation, only tips a a lot of stimulation. Okay so |
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| 09:30 | have this gypsy contra contra and you these ocular dominance columns. It's a |
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| 09:37 | interesting anatomy and there is a connectivity that from the lateral Jinich Hewlett nucleus |
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| 09:45 | will mostly enter into layer for from cells magnum and powerful inputs will enter |
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| 09:54 | layer for the intermediary or Kanye cellular inputs into the cortex are gonna bypass |
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| 10:03 | for they're far and few in Remember they're just not that many of |
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| 10:07 | non NPC subtypes of cells that bypass four and innovate layers 23. And |
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| 10:14 | believe that their function is concerned with color processing with color information processing. |
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| 10:23 | these projections that go into there for malleable to activity and there is a |
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| 10:32 | plasticity that can happen in retina Jinich Orjan irregular cortical or thalamic cortical connectivity |
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| 10:41 | cortical salama connectivity. Remember when I the first word retina. Jinich Hewlett |
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| 10:45 | means that originates in retina and is to Jinich Hewlett nucleus, if it's |
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| 10:50 | llama cortical, it originates in Kalamazoo goes to cortex. If it's cortical |
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| 10:54 | it goes from cortex back in If its cortical cortical, that means |
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| 10:59 | 11 area of the cortex to another in cortex. Okay. And if |
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| 11:04 | recall, we talked about descending we also talked about things like spinal |
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| 11:09 | and things like that. Uh and for the descending pathways, the motor |
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| 11:14 | to we use this terminology. So come back and look at this loop |
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| 11:20 | . This is the circuit for processing information and the cortex and the primary |
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| 11:24 | cortex will come back and look at . But I'm gonna go back and |
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| 11:29 | you that we have this really interesting slide here and I'd like to talk |
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| 11:36 | the slide because I'd like to remind that connections in the brain of plastic |
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| 11:42 | that especially during the early development there very high levels of plasticity. That |
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| 11:48 | that you can reshape the anatomy and connectivity of neural circuits which will result |
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| 11:54 | reshaping the activity and some of these can be transient. However, if |
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| 12:00 | a critical period of development during this early period of development. If some |
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| 12:06 | the stimuli are persistent. Therefore the changes in anatomy and function can also |
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| 12:13 | uh instead of transient, become long . So what are we talking about |
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| 12:21 | . So if if an animal receives visual inputs, the retina is being |
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| 12:28 | , the thalamus is being stimulated and projections from the thalamus are going to |
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| 12:34 | into the layer for primary visual In Sydney and this critical period of |
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| 12:44 | in rodents, we call it critical of development because during that period and |
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| 12:51 | rodents is the first month of life that period, the brain is most |
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| 12:57 | to changes. Also during critical period plasticity, the brain has the most |
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| 13:05 | to recover from injury and trauma in in humans. This critical period of |
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| 13:12 | after we're born is the first few of life where we're forming a lot |
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| 13:18 | our cognitive and physical abilities. and then we have another kind of |
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| 13:26 | period of plasticity and a good example use within that context is learning a |
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| 13:32 | language. So a lot of us you have agent on this city, |
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| 13:40 | the city, in this country have backgrounds and some of us have Come |
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| 13:47 | and I've been here for generations. of us have come here at six |
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| 13:52 | old and if you were immersed in culture at six years old, it's |
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| 13:58 | likely you would be bilingual and it's likely that you will speak both. |
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| 14:03 | it's english and spanish or english and or english and mandarin, maybe you |
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| 14:12 | them equally as well and nobody really tell that you have an accent. |
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| 14:18 | , if you come here as a , you still can pass as |
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| 14:24 | as a sort of a, as , as a local so to |
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| 14:29 | I've come to this country when I 17 and I was learning English before |
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| 14:34 | came here and I have been teaching doing research for many, many years |
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| 14:41 | you can still tell that I have accent. Yeah, and this is |
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| 14:46 | primary language now but I have this because they came here at 17 and |
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| 14:53 | I were to come here during the part of the critical period of |
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| 14:59 | let's say it's six or eight, pronunciation would probably be indistinguishable from, |
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| 15:10 | the, from the local speakers. , this is also the reason why |
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| 15:15 | want Children for example, to start languages at early age and not at |
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| 15:23 | or 16, you want them to picking up languages at the kindergarten, |
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| 15:29 | the first grades of 456 years Also the kids that are bilingual quite |
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| 15:37 | can be behind the first three grades both languages, let's say english and |
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| 15:43 | . But by the time they're in 4th and 5th grade, they actually |
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| 15:47 | exceeding the native speakers in english if spanish or if they're if they're english |
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| 15:54 | that start exceeding spanish speakers of language these brain areas and language areas and |
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| 16:00 | centers are being stimulated in different ways a lot of activities dedicated to two |
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| 16:10 | to, to speaking to understanding, languages in different languages to that |
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| 16:14 | So what does this have to do vision and this example that we're looking |
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| 16:20 | well and what does it have to with injury? For example. So |
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| 16:25 | you have a brain injury as a , you have a much greater chance |
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| 16:29 | recovery without significant loss of function, without the loss of function because of |
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| 16:36 | plasticity, because the connections can regrow different parts of the areas of the |
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| 16:43 | , can extend to the damage and surrounding areas and can change the anatomy |
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| 16:48 | change the function of these neural So in this example we're looking at |
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| 16:56 | happens if you deprive an animal of in one eye during the critical period |
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| 17:02 | development. Does that significantly impact the and the function? And in this |
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| 17:09 | , what is done is one island sutured temporarily for three days. It's |
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| 17:17 | closed for three days, so there's ambient amount of light actually coming through |
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| 17:22 | island, but there is no direct rays of light, there's no clear |
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| 17:26 | , there's no visual information that is in. So and then you take |
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| 17:36 | suture off and the animal now has eye open for another month. And |
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| 17:43 | the end of two months you perform experiment where you're stimulating contra lateral eye |
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| 17:50 | it's a lateral eye to the cortex you're recording the activity and what you |
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| 17:56 | is that the I the contra lateral that was closed for three days a |
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| 18:02 | later. So you've given an animal month to recover from this temporary loss |
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| 18:08 | sensory input. And you can see there's already reduced number of cells they've |
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| 18:15 | reacting to the stimulus in the cultural high. So something has already changed |
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| 18:22 | following three days. And in the there are more cells that are responsive |
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| 18:29 | the visual stimulus to the insula lateral . So the system in three days |
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| 18:35 | already gotten biased toward the eye that active and remained open but you still |
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| 18:41 | inputs here and you haven't completely eliminated function of these cells to react to |
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| 18:47 | contra lateral by stimulation. Now here exactly an experiment. Except you put |
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| 18:58 | eyelid suture for six days and you the animals wearing a patch that's why |
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| 19:02 | look like pirates. And these experiments done in rodents that were also done |
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| 19:08 | higher order species and cats with with results at different points in the development |
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| 19:15 | of this critical period of development and switch on the island for six |
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| 19:21 | You open the island at the end one month, wait for a month |
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| 19:25 | the animal recover. You stimulate the lateral I stimulate the bilateral eye and |
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| 19:31 | in the cortex and you're recording from many cells as you can. And |
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| 19:36 | notice that the I contra lateral I cortex is not responsive. There's no |
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| 19:44 | itty to when the flight is being contra lateral eye but it's a lateral |
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| 19:50 | all of the cells and now completely to only projections and the visual stimulus |
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| 19:56 | one eye. So that speaks to fact that even during this critical period |
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| 20:02 | development if you have an injury if have a loss function or partial reduction |
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| 20:12 | deprivations called HMAN ocular deprivation in this to deprive an animal of the visual |
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| 20:19 | . That these deprivations can lead to of the cell anatomy in the circuits |
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| 20:27 | in normal animals that would be equally to solano and contra lateral eye. |
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| 20:34 | . And the longer periods of deprivation lead to permanent changes that even a |
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| 20:41 | later you still don't see a recovery the cortex and the cells is still |
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| 20:47 | reactive to the contra lotto. I is what it looks like on the |
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| 20:53 | term binoculars deprivation. The eye that open. These are the llama cortical |
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| 21:00 | and you can see these very robust inputs coming in with pretty complex processes |
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| 21:09 | into layer form and this is the from the thalamus toma cortical inputs from |
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| 21:17 | deprived I. And what are you here? That you have significantly changed |
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| 21:25 | anatomy alter the anatomy. So you the structure. You alter the connectivity |
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| 21:32 | you don't have as many synapses. your processes are not as sophisticated as |
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| 21:38 | seeing here. Therefore you alter the as well. And that's how you |
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| 21:44 | everything forward domination of one eye and inputs from the other eye are not |
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| 21:51 | dominant now but not as it is to to this visual cortex. So |
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| 21:58 | is an example of plasticity that the home messages from. This is critical |
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| 22:06 | of development that happens during early postnatal rodents during the first month of |
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| 22:14 | That it applies to the fact that have the cellular plasticity. So you |
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| 22:20 | anatomical and functional rearrangement and the fact normal connectivity is dependent on normal |
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| 22:28 | So these are activity dependent changes that seeing normal activity. This is the |
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| 22:36 | inputs deprivation of activity. You have synopses left. So uh these are |
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| 22:45 | of the several things that would be to know for the examine in general |
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| 22:51 | we talk about plasticity and we'll talk more about plasticity later in the |
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| 22:57 | So let's come back now that once have these normal projections coming into layers |
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| 23:03 | from layers four, they go into 23. And that's where you gain |
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| 23:07 | binocular vision letters to three projections go to other extra stride. They go |
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| 23:15 | of the primary visual cortical areas to . V. Two which is |
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| 23:22 | One is area 17. Primary the secondary visual cortex very 18 V. |
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| 23:28 | . Area 19 tertiary visual area Four. V. Five M. |
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| 23:33 | . And remember the pathways that split temporal uh pathway and posterior parietal pathways |
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| 23:41 | information processing. So what does that ? That means that now this information |
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| 23:46 | the primary visual cortical areas being communicated secondary tertiary ordinary and going into the |
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| 23:53 | areas to bind the visual stimuli and of visual information with auditory with the |
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| 24:01 | and other sensory stimuli. From layers . Besides these extra stride cortical projections |
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| 24:12 | have a loop back from layers 23 layers 56. And from layer six |
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| 24:17 | have the output back into the lateral Nicollet nucleus. That is the most |
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| 24:23 | for us that we talked about. this is the llama for tickle you |
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| 24:29 | here an inter cortical loop. Those from six are not only gonna go |
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| 24:34 | sub cortical to thomas, they're also to inform and project into layers |
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| 24:39 | So you have Elena for tickle inputs four. Then you have inter cortical |
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| 24:45 | 4 to 3 to three. Long is 5642356423564 to 3. And then |
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| 24:54 | have cortical salami six cortex, the cortex, the thalamus. And so |
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| 25:01 | can actually envision this. This is of a fun. You have three |
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| 25:05 | to play with and as far as the information. You know you have |
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| 25:10 | input loop. You have sort of like modular torrey loop within then you |
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| 25:15 | the output loop that's coming out from cortex into thalamus In layers 2 |
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| 25:24 | If you were to use another stain is ah side across the stain for |
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| 25:31 | oxidase is and it will reveal these structures and you can see them here |
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| 25:39 | of a darkening darker Patrick's. So this horizontal view looking from the top |
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| 25:48 | 23, seeing these darker patches. is an illustration of these darker |
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| 25:53 | We refer to them as barrels. sorry blobs, barrels. Sorry, |
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| 25:59 | a matter sense of context we're talking barrels. But these are blobs and |
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| 26:05 | you are. There should be. always say there should be like a |
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| 26:08 | made about blobs. Blobs are coming blobs in the visual Cortex are these |
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| 26:17 | in last 23, several public structures those. This is the Solomon, |
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| 26:23 | and G. All cells that received olympics Primary from non empty cells. |
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| 26:31 | Kanye Saleh. So these are projections bypass layer four intermediary cells and go |
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| 26:39 | layers 2 3. And so little known about the function of the blobs |
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| 26:45 | this is another important anatomical feature in primary visual cortex, the involved in |
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| 26:51 | processing. It's interesting that uh this enzyme is involved in energy production. |
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| 27:03 | it somehow indicates that those areas are more active because of cytochrome oxidase. |
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| 27:13 | there's something interesting going on in the visual cortex related to metabolism and these |
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| 27:23 | appearances of the of the blobs that responsible for color processing. What are |
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| 27:33 | south uh and what are the receptive properties of the cells and the primary |
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| 27:40 | cortex? We so far saw that cells in the retina the best respond |
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| 27:48 | these center surround stimulant. This is you get the maximal activation. If |
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| 27:54 | on, if you center is If it's off then when the surround |
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| 28:00 | activated, these are the receptive field in the retina. So what is |
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| 28:07 | cortex, the cells and the primary cortex? If you were to put |
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| 28:11 | micro electrode and the straight cortex and and you say what is the cell |
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| 28:17 | to be most responsive to? How I get the most action potentials from |
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| 28:21 | cell? And the experiment is that subject animals focused on the screen. |
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| 28:30 | is the field of view and there this wide box or this black |
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| 28:37 | It's called the receptive field. this is the border of the receptive |
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| 28:44 | , This wide box of this black . And so this is an experiment |
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| 28:50 | you have an animal, you put electorate in there and how do you |
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| 28:57 | what seller you're recording from? How you know the retinal topic of the |
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| 29:02 | in the cortex? You don't. you have the screen and you pass |
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| 29:08 | life of bars in the screen until you get lucky 45 minutes into |
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| 29:15 | But this part of the screen boom action potentials in that cell and you're |
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| 29:22 | this is what that cell is looking . That's the receptive field. That |
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| 29:27 | in the primary visual cortex that's what looking for. And what is illustrated |
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| 29:32 | is that this is the receptive field . And now instead of the circles |
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| 29:41 | light, the cells are most responsive bars of light. And also when |
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| 29:48 | turn a bar of light in this and this receptive field you get a |
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| 29:53 | bunch of action potentials recorded from this neuron here. But then if you |
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| 30:01 | the bar into the opposite orientation through same receptor field you get no action |
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| 30:12 | . You turn it a little bit you make it vertical. A few |
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| 30:16 | potentials. Turn it a little bit the left, more turn it a |
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| 30:20 | bit counterclockwise the maximum action potentials more less action potentials. So now we're |
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| 30:31 | about the fact that in the okay this is L. G. |
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| 30:38 | . And retina with and the We have bars of light. This |
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| 30:47 | what the cells are most responsive to that they're responsive to bars of light |
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| 30:53 | are most responsive to bars of light a certain orientation. So the primary |
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| 30:59 | cortical cells have orientation selectivity. Their not only for a bar of light |
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| 31:05 | they're selected for a bar of light a specific orientation. This is just |
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| 31:13 | example of uh orientation by degrees as changes as you track the distance through |
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| 31:23 | layer again, just orientation selectivity. other feature is that once you find |
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| 31:29 | receptive field in this experiment, you the receptive field here in this |
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| 31:34 | you found this receptive field here on screen. You pass the visual |
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| 31:40 | the light of bar from left to . And you get a lot of |
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| 31:44 | potentials that cell response to that bar light traveling from left to right very |
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| 31:51 | . But in the same spot that same cell is looking at. You |
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| 31:56 | the bar of light and opposite right to left. And besides just |
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| 32:01 | is what we call the edge effect the action potentials that get generated here |
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| 32:06 | cell is silent. That means that cell not only prefers a certain |
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| 32:14 | In this case it's vertical but a direction of movement of the bar of |
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| 32:20 | . So you're now getting into the for direction which starts signaling motion movement |
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| 32:27 | the left and right perception of that and selectivity for direction. In the |
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| 32:37 | primary visual cortex we have these simple . So we're talking about simple |
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| 32:42 | Remember that in L. G. . We had relay cells and this |
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| 32:47 | an example of how you can construct bar of lights in the L. |
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| 32:58 | . M. You would have the off and in the lair for visual |
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| 33:04 | you can have convergence of these receptive properties onto oneself. Yeah. And |
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| 33:13 | these cells converge together. So these three cells. You can put three |
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| 33:19 | together. These on center. These not cells. You can put three |
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| 33:26 | center receptive field properties that are being Into one cortical cell in the |
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| 33:37 | And now in the cortex you have bar of white. Okay so convergence |
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| 33:46 | these concentric shapes can now produce bars light, convergence of these. On |
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| 33:54 | off. Concentric shapes can now produce complex receptive field properties in the primary |
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| 34:01 | cortex that will have this edge is in the center inhibited half of it |
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| 34:11 | and the other half inhibited a stripe the middle, stimulated the center and |
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| 34:16 | periphery excited. The stripe inhibited the , excited and so on. It's |
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| 34:23 | important that you uh think about these of how these come about. These |
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| 34:31 | receptive fields of simple south of primary cortex and the simple cells and primary |
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| 34:38 | cortex can converge those bars of light the complex cells in the primary visual |
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| 34:47 | . So this is becoming a lot fun because now you can converge three |
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| 34:55 | of light and maybe out of these bars of light you can make the |
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| 35:04 | . Okay so if you were you all of these shapes. If you're |
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| 35:19 | these shapes the concentric centers around. can make these last bars of |
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| 35:27 | you can have them in other you can make them more complex than |
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| 35:36 | would have these half circles, You can have lives. Still have |
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| 36:01 | . I was. Yeah. What how circle Now this is fun, |
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| 36:18 | ? So primary visual cortical cells can a lot of fun. These guys |
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| 36:24 | L. G. N. Are to this center surround. Okay but |
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| 36:32 | the center surrounds converge and start forming shaped bars of light, different shapes |
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| 36:39 | these receptive fields that you can process the primary visual cortex. You can |
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| 36:46 | construct of what is called the primal of the outside world. So this |
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| 36:53 | how the anatomy from the retina, this retinol circuit and the receptive field |
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| 36:58 | in the retina. In the G. M. Their convergence in |
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| 37:02 | cortex allow us to now produce the , this primal sketch of the outside |
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| 37:09 | . The visual sketch. Yeah so is like finally sketch, this is |
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| 37:13 | the final sketch. So like facial um from somewhere else actually. Uh |
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| 37:21 | there's even there's a different area for recognition altogether. And facial recognition is |
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| 37:28 | complex too because there's also another So you would recognize the contours of |
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| 37:35 | face but you may not be able say if it is exactly that person |
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| 37:40 | the primary visual cortex. Uh And example visual cortex will not tell you |
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| 37:49 | that face feels and just how it like. So you're gonna have another |
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| 37:55 | in the brain uh that is uh to Magdala that will process the emotion |
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| 38:04 | that face. Angry face versus happy cortex will just say I'm looking at |
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| 38:10 | and I'm looking but the primary visual cannot say this is a happy |
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| 38:16 | It says this is what I'm seeing when it goes from the primary visual |
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| 38:21 | into the secondary tertiary co ordinary there's and more complexity in this processing that |
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| 38:28 | being added here. We're already seeing eyes were seeing these shapes, we're |
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| 38:36 | orientation selectivity, we're seeing direction selectivity signals motion and we're seeing color. |
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| 38:46 | that's that's that's quite quite a So if you were to connect now |
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| 38:52 | visual cortex to the computer and see do you see? It would show |
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| 38:57 | exactly this primal sketch with color with motion and not exactly with the highest |
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| 39:03 | with the depth perception and everything else happens at the late later stages of |
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| 39:09 | but it will show you this. even if you hooked into later stages |
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| 39:14 | processing where uh the two of the that would still not tell you the |
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| 39:21 | on that phase. So you have communicate now through the association areas to |
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| 39:26 | join all of these sensory modalities So I hope that you can see |
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| 39:33 | this is receptive field properties. You the circuit underneath there. Of course |
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| 39:37 | didn't even talk about the L. . N. Circuit. The retinal |
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| 39:41 | cells are they're interconnected. But the and the shape of these receptive fields |
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| 39:45 | how you get the primal sketch in primary visual cortex. And this is |
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| 39:52 | way of thinking about this these orientation . And what is illustrated here in |
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| 40:02 | is that each color here represents a direction of the light of bar. |
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| 40:09 | yellow is this direction, green is vertical. Red is completely horizontal. |
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| 40:19 | is what the color represents and Huebel weasel to neuroscientists, they studied these |
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| 40:28 | dominance columns in cats and in monkeys they were poking around the lectures and |
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| 40:38 | discovered this orientation selectivity. And they discovered that if they poke an electrode |
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| 40:45 | the column here in this yellow zone the cells will be most responsive to |
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| 40:51 | orientation of the bar and right adjacent the cells are gonna be responsive to |
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| 40:58 | different orientation and writer Jason slightly And so as you walk around this |
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| 41:06 | column which is 30 to 105 50 wide. And as cortex is about |
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| 41:14 | millimeters deep or so you have the column that is basically orientation column where |
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| 41:22 | cells that are adjacent in this column responsive to very similar orientation bars of |
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| 41:30 | . This is where we talk about processing or redundancy. So if there |
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| 41:35 | an injury to the whole yellow part this column, you would only lose |
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| 41:43 | orientations, you wouldn't lose perception of of their orientations and you would still |
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| 41:48 | quite event that would process orientations in different angles here. The south in |
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| 41:55 | middle, it's a mix of all south that our response itself to all |
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| 42:01 | the orientations. You'll find them in middle. So they look like a |
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| 42:05 | like this pinwheel like structures with the will have the cells with overlapping orientation |
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| 42:12 | functions. And the further you go the periphery of this 100 micrometers. |
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| 42:20 | , micro column you get the south are most responsive to very specific orientation |
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| 42:25 | adjacent to them to very slightly different of the bar of light. Uh |
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| 42:32 | are voltage sensitive dyes. So besides able to image calcium fluctuations, we |
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| 42:40 | about imaging ion fluctuations like calcium and synaptic terminals. You can also image |
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| 42:46 | changes in member and potential or in . And those guys are referred to |
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| 42:52 | voltage sensitive dyes. And in the days, imagine how many cells you |
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| 43:00 | to poke in the monkey's brain and many experiments we had and how many |
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| 43:09 | of bars and different stations you had pass in order to discover these orientation |
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| 43:15 | . It was cell by cell screen screen orientation by orientation. Years and |
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| 43:22 | and years to derive this discovery and of it voltage sensitive dyes are really |
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| 43:29 | because voltage sensitive dyes get picked up all of the cells. And now |
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| 43:34 | can activate the eye and instead of from one cell electro physiological, you |
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| 43:40 | image number of cells that are active so you can image all of the |
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| 43:46 | that are active to disorientation of You can image all of the cells |
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| 43:51 | are active to different orientation of light you no longer have to do it |
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| 43:56 | , buy, sell, buy buy sell. So this is another |
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| 44:00 | technique, wealth of sensitive dyes that reveal activity. This is experimental |
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| 44:06 | So this is not something that is in a clinical setting with pet scans |
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| 44:10 | F. M. R. This is an experimental technique where you |
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| 44:14 | a chemical dye that dye soaks into cells and if the cells are responsive |
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| 44:20 | the stimulus, the dye will change reflective properties. Yeah, so each |
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| 44:26 | is a single cell. Each dot a single sound here. Yes. |
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| 44:31 | then once you put all of these together this here, you're zooming into |
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| 44:35 | pinwheel basically. And if you zoom one of these pinwheels, you will |
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| 44:40 | this individual units that are responsive mostly to the particular orientation of of |
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| 44:50 | Besides these orientation columns, we also hyper columns and this is sort of |
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| 44:56 | one millimeter size now. So we're in size and we're talking about this |
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| 45:02 | I think it should be also interesting you that I guess the microprocessing units |
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| 45:08 | about 100 micrometers in size. And the larger processing units, the what |
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| 45:15 | call hyper columns, there are about millimeter In diameter. So now we're |
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| 45:22 | about 10 times the size of the that orientation column gives you something about |
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| 45:29 | scale of processing the information and and scales are such that this is our |
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| 45:37 | from L. G. M. their poor to have the blobs predominantly |
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| 45:42 | 23. Uh This is you have ocular dominance columns. Remember these are |
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| 45:48 | stripes. So you have these stripe and therefore these are the boundaries of |
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| 45:55 | stripes shown here in black. That that within this stripe information belongs to |
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| 46:00 | high within this other stripe information belongs the opposite. I within each ocular |
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| 46:09 | columns you have multiple pinwheels with disorientation . In the middle of the ocular |
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| 46:17 | columns. You seem to have dominance cytochrome oxidase days. So color processing |
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| 46:23 | increased metabolism here and then multiple. I stands for cultural lateral, it's |
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| 46:33 | I contra lateral, the lateral So multiple ocular dominance columns contra contra |
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| 46:42 | comprise a single hyper column and single ocular dominance columns will have multiple orientation |
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| 46:55 | areas and multiple of these cytochrome oxidase . Finally there's one more really interesting |
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| 47:05 | technique that doesn't require any die applications it's referred to as intrinsic optical signal |
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| 47:14 | it's really pretty remarkable that some way stimulated when they stimulated to high degree |
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| 47:25 | changed their reflect its properties. intrinsic optical signal can only image the |
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| 47:31 | just like the vaulter sensitive damaging can image the surface of the cortex. |
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| 47:38 | can look through the layers and focus two different layers of different focal |
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| 47:42 | If you have a powerful microscope, optical signal will only be on the |
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| 47:49 | . Remember that pet scan and FmR will actually get to the deep internal |
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| 47:55 | . Intrinsic optical signal will only show how the changes in the reflective properties |
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| 48:00 | neurons changed on the surface of you them and the neurons that are more |
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| 48:06 | as we talked about, they will oxygen, it will consume glucose. |
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| 48:12 | what else? They're also going to . And as they swell, they're |
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| 48:18 | stretch on their membranes. And as stretch on their membranes and the density |
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| 48:23 | the spatial different distances between the cells , the reflected in that area from |
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| 48:32 | regular light that you're shining regular there's no diner the reflective properties of |
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| 48:37 | tissue will change. And what is here is the ocular dominance columns. |
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| 48:43 | same ocular dominance columns. You can this y here, you can see |
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| 48:48 | y here in much lighter shade. , on the right, I'm referring |
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| 48:55 | this wire right here, this right here. This ocular dominance |
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| 49:00 | So that means that you can stimulate i if you're looking at the surface |
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| 49:05 | the cortex you can visualize the changes are called intrinsic optical signal reflecting changes |
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| 49:14 | activation of cells from one eye or eye. Again this is an experimental |
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| 49:21 | although it can be used in clinical and you can see brain tissue and |
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| 49:31 | having seizures and having especially an event is called cortical spreading depression. They're |
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| 49:38 | deep polarizing event. So you can observe them on the surface of the |
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| 49:42 | . The reflective properties of the of brain surface will change. There's another |
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| 49:47 | technique worth mentioning. Um Okay, . So obviously we have vasculature and |
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| 49:55 | is the supply of the oxygen and nutrients we have the super spinal |
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| 50:00 | We have the ocular dominance columns. have the maps of preferred orientation and |
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| 50:08 | intrinsic optical imaging and voltage sensitive Or two. Of the techniques that |
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| 50:15 | be used for optical imaging of neural . Experimental so not in the clinical |
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| 50:21 | experimentally. Although like I mentioned, optical signal can be used in a |
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| 50:27 | setting to a certain degree. so this is all for visual system |
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| 50:36 | . And I will see you back um monday So please study for the |
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| 50:45 | and come to the review session. see everyone on |
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