So, today, let's continue. The last time we still left the center-surround receptive field, the neural mechanism. So the first actually [INAUDIBLE] is actually the ganglion cell. We will have the center-surround receptive field because pupillary from the ganglion cell. If you give a light spot maybe the cell will fire action potential. But then you increase the light spot size, got very strange results. The cell actually would be more silent. Give it less response there, right, and then if you give it kind of a ring of light in the center there should be no stimulation. Then you will get the inhibition response, right. So this ganglion cell receptive field actually it's coming from, inherent from the bipolar cell. That means, actually in the retina, the center-surround receptive field is first generated in the bipolar cell. Okay people, recording from bipolar cell also found the same thing. Okay, we talk about actually, some point here, talk about the bipolar cell, the generation for the Center-Surround Receptive Field. So, remember, when we talk about there is a another important cell called horizontal cell, right? Horizontal cell is actually a between the photoreceptor and the ganglion cell, this region. And then the cell will make a, like a lateral connection to many, many photoreceptors. But they would not send it to exxon, to the other cell. Only connect which is the photoreceptor. This is so special, and this is so important. We talk about the functions used to generate the center-surround receptive field. Let's look at how it works. So, this is a cartoon, these are photoreceptors and then this is the artificial bipolar cell. This cell has an expressed empire receptor. So of course then you know this bipolar cell will be an off bipolar cell right? Or h bipolar cell hyperpolarization bipolar cell, okay? So because HDT bipolar cell you can see the dendrites here, actually can connect, meaning photoreceptors, but here, to demo, make a distinct for the demonstration, we omit the other photoreceptors. We just show one, okay. It doesn't matter if it's 10 or 20. So the one work, okay, so this is called a center-surround receptive field, it's the photoreceptor directly connect the area of the photoreceptor. This is the center. Let's see how it works. So if you view a spot like only illuminate or stimulate the center region. These photoreceptors will not activated right? Only the center would be activated. Then the cell will be hyper polarized. And the cell really is less glutamate. And this bipolar cell also hyper polarized. This is the central response, okay. So, let's look at the surround response. So the surrounding, okay we can give you a light stimulation. A ring offers the light stimulation, so the center is black, no stimulation. That means this cell is still kind of, will be polarized in the dark. But these cells, right now, you stimulate them with the light, okay. So these cells actually does not directly connect with the bipolar cell. All right, because you have a horizontal cell here, make the connection. Let's see what happens to the horizontal cell. The horizontal cell, one important feature is actually we are get the synaptic input from the photoreceptor. At the same time, it will feed back the photoreceptor. That means it's a kind of mutual bidirectional synaptic connection from input from the photoreceptor and then output also to the photoreceptor. And then this output to the photoreceptor, actually, is inhibition. So this inhibition mechanism is not clear yet, okay. But people talk about this, there is a lot of like a GABA effect. That means the photoreceptor can release GABA. The GABA is the gamma angiotensin 1 like lecture. You probably talk about it, actually it's the inhibition right? [FOREIGN] is a [FOREIGN] channel and then the cell will hyper polarize. So look at this one will release the GABA for example maybe we will have some other mechanism for the feedback, but at this point we can use GABA as a discussion with this mechanism, okay? When the cell be polarized, this cell will release GABA to the photo receptor and the photo receptor will be inhibit and then release less glutamate. Okay this is in the dark where it happened because this all this cells, they polarize, and also this cell express the n-paraceptor, and then we are also depolarized in the dark. But they way you have a light phenotype. This cell, what would happen? These cells have been polarized, these cells also have polarised right? And then feed it back, less feedback. And then just these inhibition. [FOREIGN]. This inhibition will cost this this photoreceptor more and then released more will be polarized. You see? This is how the Center-Surround Receptive Field works. [FOREIGN] Horizontal photoreceptor. It's this inhibition, this is a key point. [FOREIGN] Of course, these cells, you're looking at these cells. These are photoreceptor. They also receive their feedback from this horizontal cell, right? But because this cell already kind of hyperpolarize so strongly by the light signaling. And then these cells actually to feed back depolarization will be very minor because you have very strong light effect. But for this cell you don't have the light stimulating, right? So you have a depolarizing effect. Then the cell will be more depolarized, okay? All right so if we talk about a center-surround for example if we talk about actually this cell is its own bipolar cell expressing the mGluR6. [FOREIGN]. You will get a cell with a center of its own. Center if you add stimulation it will depolarize. If you have a surround stimulation then you will get inhibition, right. For this right now in the middle is a minus. It's inhibition, is off response. The surround is it's own response, okay. But if we switch this bipolar cell to a non bipolar cell then quite simple, just flip the polarity. In the same then you get excitation. In the surround, then you'll get inhibition. I can see three to four, right. Okay, so this is the bipolar cell you can generate the centers around response. And you just imagine, okay, the down stream of the bipolar cell is ganglial cell. Ganglial cell direct connect with this cell. If one ganglial cell direct connects with this bipolar cell what happened to the ganglion cell? Because this bipolar cell also releases glutamate. And the ganglion cell, in most cases, they express receptor. So then it means the ganglion cell will directly follow the response prompt is off of the bipolar cell. Right? So this receptor field actually there is very elegant, actually it's a mechanism actually where people work out, those connections. And also this one can explain some kind of psycho-physical study.
