| 00:02 | Mhm. So this is uh dead of the Central Pathways Individual System which |
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| 00:18 | will call lecture 17. And I post this separately as a video from |
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| 00:24 | review we discussed last time the projections the retina. Majority of it goes |
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| 00:30 | the L. G. N. the thalamus sent to the spirit calculus |
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| 00:34 | psychotic eye movements. And finally to super cosmetic nucleus uh which is responsible |
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| 00:43 | the diurnal cycle. We discussed how visual field at which you're looking has |
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| 00:50 | own means both eyes are looking at part of the visual field if you're |
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| 00:55 | right ahead of you and that the nasal retina is processing the left temporal |
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| 01:05 | , left periphery in the visual Uh huh. Right uh uh |
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| 01:17 | The nasal retina on the right is to be processing the peripheral zone here |
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| 01:25 | the right. Okay so remember that fibers coming from the i the optic |
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| 01:31 | are bundles that contain fibers that will over the nasal fibers that will become |
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| 01:39 | lateral to the side of the origin . The luxury crossover to the to |
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| 01:44 | opposite side and the temporal bundles. can take a retina. It's inverted |
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| 01:51 | divided into half one half as close to the nose, the other |
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| 01:55 | is temporal, close to the The temporal component stays absolute literal on |
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| 02:01 | same side. So if you have damage to the optic nerve on one |
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| 02:06 | you lose the peripheral vision on that of the damage. If you have |
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| 02:12 | to the optic track from one side will lose half follow the visual |
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| 02:17 | And if you have damage to the as um which is nasal fibers crossing |
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| 02:23 | nasal fibers looking in the periphery. lose periphery on both sides. Or |
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| 02:28 | will have a formation of what is the tunnel vision without having peripheral |
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| 02:34 | But having the overlapping binoculars, jones are sub served by the fibers that |
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| 02:39 | it's lateral LG. N. Is into six layers as you saw two |
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| 02:45 | magno. For normal parvo Kanye cellular that are located ventral to H. |
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| 02:51 | . G. N. Layer are and P. Type cells that are |
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| 02:56 | for color processing each one of these in the L. G. |
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| 03:01 | Is man ocular layers themselves received inputs left and right eye. But within |
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| 03:07 | layer itself it's only the input from eye on our perceptive field properties. |
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| 03:13 | when we discuss the receptive field properties the retina that looked something like this |
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| 03:23 | centers around. Yeah so this is the retina you'll see it in the |
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| 03:32 | and you will see the same receptive properties in the algerian. So what |
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| 03:38 | receptive field is a field from which information is coming which is point by |
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| 03:43 | representation of the Southside world that receptive in the retina is this concentric on |
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| 03:51 | off, surround off center on surround that same organization that we set the |
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| 03:58 | and processing continues through the lateral gesticulate , lateral nuclear nuclear receives most of |
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| 04:05 | projections from the cortex. Most of output from the retina 90% goes to |
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| 04:10 | L G. M. L. . M actually receives most of this |
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| 04:15 | from the cortex to the direct sensory is a minority of what LG in |
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| 04:22 | . And then there's a strong cortical and cortical Islamic communication. So |
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| 04:28 | have this right uh temporal retina, lateral layers 235 contra lateral from the |
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| 04:37 | retina are going to project the 2 layers 14 and six. Again |
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| 04:42 | and two being magna 3456 Being Parvo layers. Magna and Kanye cellular which |
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| 04:52 | central to each uh these six layers are shown here in L. |
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| 04:58 | On the special cells, the primary cortical area in humans is very small |
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| 05:06 | relatively to the overall size of the . And even in very advanced non |
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| 05:11 | primates such as macaques. The primary areas still occupy very large portions of |
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| 05:17 | brain, demand a lot of space demand a lot of energy and we |
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| 05:21 | that the further away you go from primary processing areas the more complex that |
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| 05:27 | information, picture or hearing. The complex that sense of information becomes and |
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| 05:36 | becomes perceived in a more complex way with other sensory modalities. So a |
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| 05:42 | by point representation is what we call , topic maps if you took the |
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| 05:46 | and all of these photo receptors And said there's a point here in this |
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| 05:50 | that's looking over there in space. is a point that it's actually looking |
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| 05:55 | there is next to it. There's point that's looking in the space right |
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| 05:58 | to that other first point the third is next to that of the second |
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| 06:03 | one back one representation and that has google Adalja nicolas nicolas and through the |
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| 06:09 | cortex in the primary visual cortex. we call it stride cortex again because |
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| 06:16 | has both the laminar and the colonists and the neocortex. So it has |
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| 06:22 | layers that we've discussed the most superficial there. One the deepest closest to |
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| 06:28 | to the Dyin cephalon is layer six you can see the menace cell stain |
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| 06:36 | therefore were majority of the thalamic inputs into the cortex from algae on into |
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| 06:41 | primary visual cortex as far as have into for A. B. |
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| 06:45 | And C's have divided into alpha Now the reason why the primary visual |
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| 06:52 | is called stride cortex is if you to inject radioactively labeled pro lean if |
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| 06:58 | within Giaka fluorescent lee labeled markers some into one I the projections from that |
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| 07:05 | I would go into its own respective Ocular L. G. M layers |
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| 07:12 | . And then from these layers that gone to cortex. And if you |
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| 07:16 | to take the cortex and need to layers one and two and therefore you |
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| 07:21 | see these stripe like arrangements Australia. why it's referred to stride cortex. |
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| 07:28 | primary visual cortex where each one of stripes represents either the left for the |
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| 07:34 | guy. So these are also referred as ocular dominance columns. Because as |
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| 07:40 | recall the structure of the cortex is only laminar but it's also columnar. |
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| 07:46 | it's a part of the column and part of the column is dominated by |
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| 07:49 | eye. Left eye let's say. this other life part of the column |
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| 07:53 | dominated by the right eye. So have the stacking of left, |
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| 07:58 | left, right and what we call ocular dominance columns. They're dominated by |
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| 08:02 | left eye or the right eye at level of the primary visual cortex and |
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| 08:07 | for So if you were to uh a recording and you were to penetrate |
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| 08:15 | electrode into the into the primary visual to the strike cortex. And this |
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| 08:22 | again repeating the connectivity showing how this one, layer four and layer six |
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| 08:28 | are part of the binoculars. Gm will actually project into layer four of |
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| 08:34 | neocortex and at the level a flair in the primary visual cortex that information |
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| 08:41 | still mon ocular. So the primary cortex and learn for the information is |
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| 08:49 | Oculus still segregated between columns of cells process left eye and columns of cells |
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| 08:55 | process right. Hi. Can I a quick clarification question. Sure. |
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| 09:02 | The strike cortex and the visual cortex interchangeable. Those are the same thing |
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| 09:06 | correct. Yes. The visual cortex is larger than just the stride |
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| 09:13 | Try it. You can layer four the primary visual cortex area if you |
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| 09:19 | is also a portion of the overall cortex Which will contain a secondary visual |
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| 09:25 | , the two tertiary v. three . 4. And then it will |
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| 09:30 | split onto the temporal side of the side those pathways. So you're |
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| 09:37 | It's only a portion. It's only in V. One and it's only |
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| 09:41 | in this fourth layer where the Islamic are coming in. And uh this |
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| 09:47 | a very good question and I'll continue that same note that in this example |
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| 09:52 | it shows that then we're going to about the connectivity. So everything that |
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| 09:56 | been telling you about the visual you have to understand the anatomy or |
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| 10:00 | anatomy. You have function. You certain connectivity and you also have the |
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| 10:07 | and pharmacology. That means you have transmitters and then you have pharmacology. |
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| 10:12 | in the retina the photo receptors connected Iran a tropic bipolar cell. It's |
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| 10:20 | conserving if it's connected to meddle. tropic bipolar cell it's signed inverting. |
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| 10:26 | this all is built on top of structure or that structure. That segregation |
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| 10:30 | weapon right input continues through the lateral nucleus layers and that man ocular input |
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| 10:36 | still present in one form. If want to stick an electrode here, |
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| 10:40 | is an experiment where you're sticking an And you are recording the signal now |
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| 10:47 | layer two in A. And when record the signal and A. And |
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| 10:52 | stimulate either the left eye or the high, you only get response from |
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| 10:57 | contra lateral from one high. But you position that electrode in position B |
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| 11:05 | is essentially above the two ocular dominance . And it's telling you that in |
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| 11:10 | 23 that information becomes blended and now neurons and layers to three. If |
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| 11:17 | flash the light on the laughter gypsy the contra lateral right eye you'll get |
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| 11:22 | equal response from both eyes. So you find neurons in these regions here |
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| 11:29 | layer four and layer 23 that are responsive to binocular input. They're now |
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| 11:36 | to the signal from both eyes. how is that accomplished? And to |
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| 11:41 | that. And to understand this And this is one more diagram that |
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| 11:46 | you of really nice projections that you seeing. They go from the thalamus |
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| 11:51 | project all the way into the primary cortex informing these thalamic projections forming the |
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| 11:57 | layer for. Okay, and how you have these ocular dominance columns first |
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| 12:04 | all at layer four and how come do become binocular At Layers 2 |
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| 12:11 | Well here's why because of the connectivity the cortex and so this is really |
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| 12:18 | that you understand that these are certain . Those are thalamic inputs. There |
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| 12:23 | magnolia harbor and a lot of times cellular is also referred to as intermediary |
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| 12:29 | are intermediary inputs And it's showing you MP cells are going into layer |
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| 12:37 | This is now a circuit of the . This is the connectivity that you |
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| 12:42 | in the neocortex and is excited to landing layer four C. Alfa four |
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| 12:49 | . Beta predominantly telling you that the . And P cell axons terminate and |
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| 12:56 | of the cortex. And this is you still have the woman ocular |
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| 13:00 | So the cells and therefore still responsive just signals from one hot. What's |
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| 13:05 | and is different is the intermediary or selling ourselves. They bypass is an |
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| 13:11 | . So where most of the thalamic on that and learned for the intermediary |
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| 13:16 | the ones that are not as densely the cells in the thalamus. They |
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| 13:21 | the rack in the last 2 That's an exception. They bypassed layers |
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| 13:27 | and they project directly into list 2 . Now what does that tell you |
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| 13:32 | intermediary projections in the in the primary cortex or binocular. So it does |
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| 13:38 | necessarily have to do much with left right and the function of these intermediary |
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| 13:43 | this color processing. So then it's as important that whether it's left or |
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| 13:50 | it's important what color it is and do you process the color? So |
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| 13:55 | this the llama cortical input you also this intra cortical loop. So the |
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| 14:01 | from layer four communicate that information to 23 and that's why above in last |
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| 14:07 | now the inputs coming in from an cells and foreign last 23 and now |
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| 14:13 | becoming binocular. Now they're mixing them left and the right time. Then |
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| 14:18 | from letters to three gets spread to extra stride areas and other cortical areas |
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| 14:25 | goes to B two B three. 45 to mt uh temporal pathway. |
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| 14:33 | what does that mean? That means in layer 23 you have a lot |
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| 14:36 | parameter cells that have these lateral long projections and they will communicate that information |
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| 14:43 | the primary view on interview to and that information further out. And that |
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| 14:49 | again when you communicate to the to complexity of processing increases in B. |
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| 14:54 | B three before and so on. that information gets spread through these superficial |
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| 15:00 | . Okay? There are 23. goes very nicely but that information and |
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| 15:05 | activation of where to three South also deep layers 56 in the south and |
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| 15:12 | 56. Now send the output from cortex back into the thalamus to the |
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| 15:18 | . G. M. Okay and it is sending this output into |
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| 15:24 | G. N. It's also completing intra cortical loop by communicating to the |
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| 15:30 | and layer four where the input is up. So if I were to |
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| 15:37 | it in very simplistic cartoon like terms input coming in and four it's allman |
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| 15:44 | . Let's send it up to layer . Make it binocular. Let's spread |
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| 15:49 | log laterally through the last 23 communicate other cortical layers. Alright let's inform |
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| 15:56 | deep layers and the L. M. That we got the signal |
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| 16:00 | in the cortex. We're working on we're spreading this laterally and at the |
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| 16:05 | time as we're informing following this again inform these inputs this layer for this |
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| 16:12 | inputs that we're working on stuff And we're informing columns. So that's |
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| 16:17 | of the whole thing that happens at salama cortical input. You have this |
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| 16:22 | cortical loop and sharing of the information cortical regions and finally have this critical |
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| 16:30 | outlet and it's all intertwined and it's controlled by economic cortical and sub cortical |
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| 16:35 | cortical Islamic outlet back into the sensor . Not back into the periphery let |
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| 16:42 | the processing of sensory systems. What do we have in last 23 we |
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| 16:48 | blobs somebody should make a science fiction blobs or make a gummy brand called |
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| 17:00 | Globs are these interesting structures. If take the cortex and you stain it |
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| 17:07 | cytochrome oxidase days you will see these . Patrick's in these darkened Patrick's existing |
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| 17:12 | 2 3 especially the cytochrome oxidase. enzyme involved in energy production. It's |
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| 17:20 | energy production. That means that there higher levels of energy and higher levels |
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| 17:25 | metabolism that are taking for some reason the last 23 maybe it has to |
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| 17:28 | with the color processing. It is a special structure and not in |
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| 17:33 | And you find in the primary visual . So the inter laminar LG themselves |
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| 17:39 | received their retinal inputs primarily from ganglion other than non mp. And they |
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| 17:45 | into these barrels and it's not barrel into the blob region and it is |
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| 17:52 | that is involved in color processing. are the cells responsible for in the |
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| 18:01 | visual cortex. So the South. is an experiment where you want to |
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| 18:06 | what are the receptive field properties in primary visual cortex. You describe them |
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| 18:11 | the rattan and algae in a concentric and off on surround. Now what |
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| 18:17 | they in the primary visual cortex? what you can do is this is |
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| 18:22 | an experiment that is described here is can place an electorate into south and |
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| 18:27 | primary visual cortex metaphor and you have subject. Well obviously it's an animal |
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| 18:35 | this is the field of view and find this square. This this this |
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| 18:42 | blue square here. This blue square the area in which that one neuron |
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| 18:48 | looking. So you just happen. very complicated experiment. You have an |
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| 18:54 | , you hook that the animal to . You're showing them the stimulus. |
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| 18:59 | a lecture in there and you may get a response. Things may not |
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| 19:03 | know it's billions of cells and you not get to that input may not |
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| 19:08 | strong enough and so on. But found it. Huh? That's the |
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| 19:13 | . This is the square into which cell is looking at. So now |
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| 19:18 | see what is it responding to? flash round beams of light. Let's |
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| 19:26 | triangle side it flash different colors. in all of this experimental experimental implementation |
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| 19:33 | discovered that receptive field properties in the visual cortical cells. The cells here |
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| 19:41 | most responsive to and you show them bar of light so that's different. |
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| 19:47 | now these cells in the cortex are for a bar of light seeing a |
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| 19:54 | of light and on top of that prefer seeing a bar of light in |
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| 19:59 | specific orientation. So if you put bar of light into dispatch of view |
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| 20:06 | this one cell is looking over there dispatch of you and you pass a |
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| 20:10 | of light and you pass a bar light in the in the horizontal position |
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| 20:15 | at the bottom and you barely produce or two or three actions actions and |
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| 20:21 | you rotate that bar you change the of that bar you rotate it into |
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| 20:27 | other degree angle other position. And cell here. Individual cortex goes gets |
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| 20:34 | excited. You rotate it a little more straight and if you start to |
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| 20:38 | rotate it even more to and then rotated more and then it stops firing |
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| 20:45 | . Yeah. So orientation selectivity that you that the primary visual cortical cells |
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| 20:54 | a bar of light and they prefer bar of light in a specific |
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| 21:01 | They will produce the most action potentials that bar of light in their field |
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| 21:05 | view and they're receptive field is passing a specific orientation. So there's orientation |
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| 21:13 | . What else can the cells And this is just another example of |
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| 21:18 | same experiment orientation selectivity. What else these cells recognize? Those are the |
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| 21:26 | that retina couldn't see and we couldn't any difference when we did these |
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| 21:31 | Scientists in these experiments. But let's you have a receptive field, We |
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| 21:36 | that cell is the same experiment. have an electorate. We discovered receptive |
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| 21:40 | . We discovered that it responds to vertical bar of light. And now |
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| 21:46 | say, okay, what happens is if I pass this bar of life |
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| 21:49 | left to right. And as it passing here, it's moving from left |
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| 21:54 | right, as it hits here, receptive field, the cell goes lots |
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| 22:00 | action potentials. It exits out of receptive field and the cell is quiet |
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| 22:07 | it's out of its receptive field and cell next it will then pick up |
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| 22:12 | information because it's going to be another in space is going to be processing |
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| 22:17 | . Okay so now let's repeat the experiment. Let's pass this bar of |
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| 22:21 | from right to left. And when pass this bar of rock bar of |
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| 22:24 | from right to left, okay through receptive field you only get to a |
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| 22:32 | actions put on shelves at the edge there are no action potentials as it's |
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| 22:38 | through this whole receptive field into which cells look. So it's the direction |
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| 22:43 | to right. Lots of action So what are the self sensitive for |
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| 22:49 | ? It's not only the orientation of bar of light but if you move |
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| 22:52 | bar of light left or right or and down, that cell is now |
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| 22:57 | to produce more or less action So now we have orientation selectivity. |
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| 23:03 | have direction selectivity that we have simple in the primary visual cortex and these |
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| 23:14 | selves can be described in the following . So remember we had retinal ganglion |
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| 23:23 | of retina with these on and off clumps of photo receptors that communicate that |
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| 23:28 | retinal ganglion cells, these concentric on off receptive fields and look what happens |
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| 23:36 | the information that point by point information three lateral articulate nuclear cells from three |
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| 23:42 | . G. M cells overlaps with single layer for neuron. What happens |
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| 23:49 | these three on zones? If you three on zones And you overlap these |
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| 24:02 | on zones. The cells in putting information. Guess what you get |
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| 24:10 | You get a bar of light. so this is again you look at |
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| 24:16 | connectivity this circuitry. The circuitry says if you take three of these overlapping |
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| 24:22 | . N cells and put them into that converges onto single cortical cell simple |
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| 24:30 | instead of these luminescence around spots and . Now you have bars of light |
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| 24:36 | have bars of light in different Have bars of light moving in different |
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| 24:40 | and that's what the cells are doing the primary visual cortex. Okay and |
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| 24:46 | there's complex cells. So on top the simple cells if you have convergence |
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| 24:51 | these three L. G. Cells into one simple cell the simple |
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| 24:55 | can converge onto complex cells and now get more fun. Things get more |
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| 25:03 | . How so because these are the fields of simple cells of primary visual |
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| 25:09 | . This is how you create concentric concentric south you'll create a bar of |
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| 25:15 | here and this gets a lot more mm. You know what? This |
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| 25:21 | a lot more fun because now Yes what's underneath? We're gonna |
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| 25:39 | Uh working as it should. Yeah it's a lot more fun because you |
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| 25:49 | the bars in different orientation. Okay have these what are these like half |
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| 25:58 | ? Half ovals. That's pretty You have that uh It was something |
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| 26:06 | those. Yeah, what else do have there while you have something that |
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| 26:11 | like this sort of like where a is empty and the size of field |
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| 26:19 | . That's the stuff that field properties the primary visual cortex. Can you |
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| 26:27 | a lot with this? Can you a lot of with this? Like |
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| 26:31 | you do art and you have to these things close together to each |
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| 26:37 | Can you do a lot with Like how how much art can you |
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| 26:41 | from these overlapping circles? You miss most interesting part. Can you produce |
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| 26:50 | lot of art? You have these here and it's the only shape you |
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| 26:54 | in the retina and LG on. just circles right now. Not much |
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| 27:01 | . What about this, wow, a lot. You know why? |
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| 27:08 | this year? Okay, that's It's here. Yeah. Yeah. |
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| 27:29 | is that? That's a face. . There you have it. |
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| 27:36 | you've walked through the entire circuit that you the primal sketch of the outside |
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| 27:41 | . And in this sketch in the visual cortex this sketch comes from receptive |
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| 27:47 | coming together forming the bars forming more receptive field processing properties, you're putting |
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| 27:54 | together and the primary visual cortex v is now seeing color is now seeing |
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| 28:01 | primal sketch is seeing direction of movement it pays attention to the moving lights |
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| 28:07 | bars and prefers a certain direction. you have this primal schedule it develops |
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| 28:14 | that's really neat. So now if think about what's happening in the two |
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| 28:20 | things are getting more complex now there's to be depth now there's gonna be |
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| 28:25 | for changes in death so that you're thinking that the person decreased in size |
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| 28:30 | things like that that are happening more . But if you follow the last |
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| 28:35 | lectures through the circuit, you actually understand how the level of the visual |
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| 28:43 | . You have these orientation columns, have all of this direction selectivity and |
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| 28:47 | have the cells with the properties that put the primary schedule, the outside |
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| 28:51 | together. So when you put all this anatomy together you have something like |
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| 29:02 | . Uh you have orientation columns. called Ala google Louisa. All those |
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| 29:09 | two very famous scientists that studied the system and micro electorate recordings and trying |
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| 29:15 | understand because you'd have to stab a of the cells in the cortex and |
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| 29:20 | a lot of this stimulus in different and movement to actually derive the structure |
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| 29:26 | you're seeing. Some of these later were done with multi sensitive guys which |
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| 29:31 | know, will allow you to track of networks and clumps of cells and |
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| 29:36 | networks and this is in the usual of the monkey but you'll also see |
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| 29:41 | in humans too. So you have columns and these are the orientation |
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| 29:47 | And you can see here in orange this column and orange all of the |
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| 29:52 | are going to be responsive to this of light. That means it will |
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| 29:56 | if you stab a cell in this Colin here, all of the south |
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| 29:59 | produce most of the action potentials when see this orientation of the bar of |
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| 30:05 | . But if you are in this in the back here and the purple |
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| 30:08 | blue, those cells will process a orientation of lights. And you have |
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| 30:12 | pinwheel, pinwheel like structures. The in the middle actually responsive to all |
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| 30:17 | the orientations. And as you go the edges of this column, the |
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| 30:21 | will be responsive, do more uh strongly to a given orientation. You |
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| 30:29 | simple and complex cells voltage sensitive dyes allow you to visualize this activity on |
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| 30:34 | dynamics and actually I'll show you an of voltage sensitive dye. I'm going |
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| 30:39 | remind myself by writing here today that follow the cortical connectivity to. So |
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| 30:46 | are the orientation columns but they're also columns. So if the orientation columns |
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| 30:51 | about 3200 and 50 micro meters, hyper columns are on the order off |
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| 30:59 | millimeter and hyper columns really is the of everything that we talked about. |
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| 31:05 | hyper columns. You're seeing the blogs hyper columns. You see several ocular |
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| 31:12 | columns left, right left left over . You're seeing the blogs of cytochrome |
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| 31:20 | stains. Each one of these ocular columns here, left to right will |
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| 31:25 | multiple orientation columns of multiple cells. is all about parallel processing, redundancy |
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| 31:33 | segregation of these implicit at least in level four before it goes into levels |
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| 31:39 | three when it becomes binocular. So of these is putting together. And |
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| 31:45 | been talking about imaging and so we'll back and talk about imaging for a |
|
| 31:50 | . But let me tell you what in the early development if you have |
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| 31:56 | an impaired sensory input. So let's back to the slide. Okay, |
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| 32:04 | this slide shows is, the following slide shows is that it's an experiment |
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| 32:11 | which you're now trying to see what if during early development you deprive an |
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| 32:18 | of a sensor input. In this it's a visual input. We talked |
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| 32:22 | plasticity and how plasticity and the fibers the synapses can reorganize critical structure, |
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| 32:30 | reorganize to synaptic connectivity on anatomy. also reorganized its plastic and it's especially |
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| 32:37 | and early ages and early developmental postnatal . And humans are the post natal |
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| 32:42 | a lot of prenatal plasticity is happening the brain as well. But there's |
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| 32:48 | lot of this post natal and and . one of the examples of lay |
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| 32:53 | system is the visual system uh in sense that their eyes are actually the |
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| 32:59 | are closed the first week of life the second week of life. And |
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| 33:05 | and then the eyes open. And this very intense period of plasticity during |
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| 33:11 | you have the segregation of the fibers the right man to this precise anatomy |
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| 33:16 | the L. G. On. different from the six layers in the |
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| 33:20 | and it's gypsy and contra lateral But there's still segregation from the two |
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| 33:25 | and you still have the ocular dominance that are forming in the primary visual |
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| 33:32 | . This is an example where at month of age approximately you future one |
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| 33:38 | and you basically deprive this rodent uh axles rays of light. There's some |
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| 33:46 | light that's coming through eyelid. And days later you take the future off |
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| 33:53 | this is measuring activity by flashing the on the left and the right eye |
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| 33:58 | recording from the cells whether they're responsive the left of the right eye and |
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| 34:02 | cortex. And three days later the that remained open is a little bit |
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| 34:08 | responsive than the eye that was I that was closed. The cells |
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| 34:12 | the cortex is still responsible to the of the stimulus. But they're more |
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| 34:17 | to the flash of the I have open. And you repeat that experiment |
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| 34:24 | you close the high instead of for days for six days and say what's |
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| 34:28 | big deal just three more days and close and you do the same experiment |
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| 34:33 | flash the light on the left and eye and you poke electrodes to see |
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| 34:37 | cells are responsive to and look what . The cells are no longer responsive |
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| 34:43 | the stimulus from the eye that was permanently permanently. So just six days |
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| 34:51 | sensor deprivation has reorganized and has shifted ocular dominance completely. Which means that |
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| 34:58 | of the cortical area energy is now to seeing information from the other |
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| 35:04 | Independently of this I already being opened is a critical period in plasticity. |
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| 35:11 | is a critical period of development and why Children can recover from trauma and |
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| 35:18 | surgery is much easier because there's high of plasticity now if you pass that |
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| 35:24 | period and you're testing this a month . This flashing experiment and a month |
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| 35:31 | you still don't get a response from . I that means you passed that |
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| 35:35 | of critical period of development where things change back into normal a month |
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| 35:41 | Or just be shifted a little This important concepts here. Ocular dominance |
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| 35:47 | plasticity and critical period of development In simple terms critical period development for foreign |
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| 35:55 | up to 18 years of age. you start learning foreign language at 34 |
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| 36:00 | of age 18 you will be indistinguishable from native speakers. If you start |
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| 36:05 | at 18 you will forever have an . Doesn't matter if you spend more |
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| 36:09 | studying that language. Just that critical of development for plasticity absorbing that information |
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| 36:15 | absorbing information absorbing. Now if your is very very important and these changes |
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| 36:21 | then be long lasting and permanent plastic . What does that look like? |
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| 36:27 | is a functional change where now the are not responsive to the flash or |
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| 36:31 | to that. I what does that like anatomically? This is an open |
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| 36:37 | . These are the salama cortical inputs into layer for from the open eye |
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| 36:43 | these are the inputs now from the I. So what happened in just |
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| 36:48 | days? These salama cortical inputs have pruned they've been basically clicked off a |
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| 36:56 | existent and if you miss that critical of development where you can clip things |
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| 37:01 | let them regrow again. You missed now it's being clipped and now you |
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| 37:06 | a reorganization. It's true anatomical and reorganization off the cortical circuit, the |
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| 37:15 | circuit is just responsive to information from high. Have a question. Maybe |
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| 37:30 | no there is no way to let pathways we grow if you damage |
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| 37:34 | If you catch that critical period of . Yes but unfortunately now and you |
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| 37:42 | about it again when we talk about hearing. Once you lose your hair |
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| 37:47 | they don't regrow. So and it's even the plasticity is just that certain |
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| 37:56 | if you do not rebuild it during critical period, that's why if you |
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| 38:01 | a child developmental problems learning mental you catch it early on and you |
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| 38:07 | the course sensory stimulation, human stimulation , all of that. There's a |
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| 38:14 | to to change the course and the of that disease. But if it |
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| 38:17 | into an older age where those things us, the chemistry changes neurotrophic factors |
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| 38:25 | are being released and expressed by the are no longer there and they very |
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| 38:29 | influence the plasticity. The neurochemistry of brain changes too. Mhm. |
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| 38:35 | let me pose this for for a here. Yeah, I was |
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| 38:44 | So you get some special effects in . That's not on the recording. |
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| 38:52 | And finally, you know, there levels of activity that can be detected |
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| 38:58 | the naked eye. Whoa ! You us to stay in again and the |
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| 39:04 | is mainly in the stain and now telling us naked. Odd. |
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| 39:08 | I told you that you cannot see but you actually can see activity. |
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| 39:13 | does that mean? Well, we about MRI Fmri. We said, |
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| 39:19 | is the brain needed brain brain. active centers of the brain active areas |
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| 39:24 | the brain. They need blood. need oxygen, They need glucose, |
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| 39:27 | need to eat, consume things. you have this whole vasculature covers the |
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| 39:33 | and this is what is called intrinsic signal imaging. So neurons that get |
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| 39:39 | active that are activated, they start oxygen, they start eating glucose and |
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| 39:46 | also swell and when they swell and just shine a light on them. |
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| 39:52 | light on them. Guess what happens the cells when they swell, they |
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| 39:57 | their reflective properties. So intrinsic optical imaging allows you to visualize the surface |
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| 40:03 | the brain if there are very high of activity taking place. And such |
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| 40:08 | an example here with the strident cortex is visualized with the naked eye. |
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| 40:14 | if the signal is really strong enough an epileptic wave, you can actually |
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| 40:19 | in the lab looking at the slice see it move through the slides. |
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| 40:25 | . Did you see that? You like this is really visual because this |
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| 40:29 | really cool because this equates the electrical . It this equates to neurons that |
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| 40:35 | active in one eye. On their being stimulated and they're just playing ocular |
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| 40:40 | call. Yeah. So now on right, you have the voltage sensitive |
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| 40:48 | imaging which again does not give you single cell level that will tell you |
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| 40:52 | these cells are responsive in this orientation and so on. So is this |
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| 40:59 | imaging? Absolutely. Can you do non invasively? Now you have to |
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| 41:04 | at the surface of the tissue. have to look at the surface of |
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| 41:07 | brain. So you have to open skull again to do it voltage sensitive |
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| 41:13 | . Is it the same way it's have to open look in the |
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| 41:17 | look in the brain. Plus your the voltage sensitive dyes. Remember the |
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| 41:21 | that are sensitive to changes in the potential? Yeah. So this folks |
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| 41:29 | the digital system, the circuitry, central projections, the cortical inputs and |
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| 41:36 | the primary school sketch that you and the way in which we can |
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| 41:41 | this anatomy by using some really cool , such as voltage sensitive dye imaging |
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| 41:48 | article intrinsic signal image. So I'm stop the recording |
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