Today, we will talk about the chemoreception. Actually this lecture and the next one, both of these will talk about the chemoreception. So for chemoreception, of course, that is to detect the chemical information in the environment. So, for these two pictures what kind of chemoreception do we use? The first one, this one, of course this is smell right? The sense of olfaction. And the other one probably involve the two, smell and also the taste, or the sense of taste or gustation, okay. What's the difference between these two? The obvious difference is they detect different kind of chemicals, all right? For this one, for the olfaction, they detect those chemicals can be we into the air and then diffuse, and then go into your cavity of the nose. So those chemicals have different properties, okay. And for the sense of taste, and then those chemicals they should be is direct, can contact your sensor in the tongue, right? So those actually consider not the chemical, okay? So for example, sugar can cause the sweet taste, right? And the bitter, you cannot smell a bitter substance. Most likely you need directly contact with your tongue with those chemicals, then you can get the perception, right? So these actually are two broadly distinct chemoreceptions, okay? So of course there are other chemoreceptions in our body, can you cite examples? These are actually for the touching, the external world chemical. But in our body, we always need to monitor the chemical information from the blood, from the other source, right? In the blood, what kind of chemical you detect? >> [INAUDIBLE] >> Oxygen, CO2, right, and also pH, right, so this also used to detect those chemicals. So the chemical reception, so in this lectures we only talk about the sense of smell, okay? This is just with our nose, and the next time we will talk about mainly the taste perception or detection. So, the chemoreception, especially the olfaction it's quite unique. The uniqueness is sometimes actually across a long term memory. Do you have any experience with the olfactory memory? Search your memories, maybe you can find something to share with us. [INAUDIBLE] >> [INAUDIBLE] >> Okay. >> [INAUDIBLE] >> Okay, yeah, that's good, yeah. This indeed, the olfactory system is really profound, actually, effect our lives and sometimes, especially the emotion or memory. [FOREIGN] Maybe I consider a pretty short, like last year memory. Here we have one example actually, again, it's from a book. There was a book, a quite famous book, Memory of Things Past. There also actually is, I guess it's a French and then this book actually translates into quite a bit of different language including Chinese. [FOREIGN] Apparently from here they also, the QA, this liking, you can appreciate it, what we're talking about, okay? [FOREIGN] [FOREIGN] >> [INAUDIBLE] >> [FOREIGN] [FOREIGN] Sometimes you have those kinds of emotions appear from nowhere. [FOREIGN] The smell. [FOREIGN] Memory. [FOREIGN] [FOREIGN] The olfactory system, that is really profound for a human being for example, long term memory and also the emotion. And for most animals actually that is more critical. The olfactory system helps them to survive in the environment and also reproduce for the next generation. There's actually, for example, when they needed to look for food or some avoid enemies. And then basically olfactory queue is very important. For example like in the dark if kind of predator approaching of course you can hear the sound but sometimes also to carry some special smell and then they can recognize immediately. There is another quite Famous case is the salmon homing. The homing [FOREIGN] The cue, a lot of cues, kay? For this guy, actually, they mainly rely on the olfactory cue. For example, this salmon, they were born in the fresh water, okay? And then they will stay in those fresh water for maybe one to two years to grow up, okay? And then when they, Are large enough, then they will swim to the ocean. [FOREIGN] Okay. When, in those waters, there is a lot of food, those kind of food, very rich food and in the end they just actually eat a lot, and they grow up, grow much larger. And then they are ready for the mating, for example sexual mature. And then they will swim back to the fresh water, okay? And then they eggs there and then [FOREIGN] there's a cycle okay? So people did a field experiment okay? [FOREIGN] It's like this, they treated the salmon are when they Ii the fresh water, they treated the salmon with morphing and also another chemical, is PA, two different chemicals, okay, different groups of fish. And then they release the fish here in the ocean. And later as we talk about, when they're really ready for mating, reproduce the next generation. They will swim back to the fresh water, the river, to dip in the river, okay. You just need to collect those salmon from the river when they come back. And then you count, see what happens. And then here, this stream of the water, this stream of the river and then has individual chemical treatment. For example, here, this river is PA, this is morphing. And then this award, this reward costs nothing special. And then you count the fish you caught from different locations. You found actually that morphing M-treated the most likely actually happened here, in this region, 90%. Of course how a sound. Occasionally a sound as a kind of fish or salmon would go to this region, and of course for this one, again is special because of the this chemical attracts those fish. And of course in this control region, most of those fish are not treated and then you count from this region. So, what it tells, it tells you when the fish, when they live in this fresh water and it's a local environment. For example, maybe it's the soil, could be these chemicals and then they imprint it in their brain. [FOREIGN] Later when they came back in order to lay eggs in the fresh water, they will use those memories actually, to find the same river they were born. And, of course, actually it's quite a challenge then, because the environment, actually, maybe some other river actually when you swim in this direction. If you followed this direction, then you were contaminated by different chemicals. And in any case, they're quite precise it's kind of a 90% fish cracked. These apparently, this fish, this fish, salmon, rely on chemical cue. And also the homing is usually, sometimes actually the swim may be 1,000 miles, okay? That is quite long and then these kind of cues help then to find the home, okay?