 Hi, and welcome to this video course on biological psychology. In this video, video 3.7, we're going to take a look at perception of taste and smell. So let's start with taste. So what is taste? Taste is a chemical sensation. So it is the sensation of molecules, essentially, in our mouth. Another word for taste is gustation. That's the Latinized word for taste. And taste perception occurs, sensation of taste occurs through chemical receptors that are located on the tongue. And we know of a few primary tastes. So all of our tastes, the different things that we can taste, are a mixture of a limited number of primary tastes. And you probably know those, except maybe for one. So salty is a primary taste, and salty, the taste of salty things is mediated through NA plus receptors on the tongue. Sour is a primary taste, is mediated by H plus receptors on the tongue. Sweet, of course, is a primary taste. That is, there is not one clear sweet receptor, but rather there are many different photoreceptors that are sensitive to various things that we consider to be sweet. So sweet is not really one very clearly defined taste. But to us, it is a primary taste. Bitter is a taste. And again, there are many different things that to us taste bitter that are quite different, chemically quite different in nature and also sensed by different receptors. And the idea there is, I suppose that what all those things that to us taste bitter have in common is that they are probably bad for us. Bitter is a warning sign. Just like sweetness is an attraction, it's a good sign. Sweet food is generally good, it's rich in sugar, etc. And then the final primary taste that to me, I find difficult to accept as a primary taste, but people, authorities assure me that it is, is umami or savory. And that is a Japanese word in Japanese culture. This is generally considered to be a real taste, but to my Western mind, my Western cultural mind, I'm not really sure what they mean by that. But it's a glutamate receptor and it corresponds to the kind of brothy, meaty taste that a lot of people find very agreeable and that I actually, I'm mostly vegetarian, but I also enjoy meat every once in a while. And I suppose it's the kind of taste that you get when you eat, for example, a hamburger and you have that meaty taste to it. That would be umami. And real tastes are a mixture of those primary tastes. Taste is processed in the insula or the primary taste cortex. So I found this image of the primary taste cortex and that's part of the temporal cortex. And different areas of the primary taste cortex of the insula are sensitive to different tastes. So there's again the concept of topography. So things that taste similar activate very similar regions in your primary taste cortex. So the topography of taste is preserved. Just like the topography of your retinas preserved in vision, topography of sound is preserved in your auditory cortex. Let's move on to smell. Smell and taste are of course related and they interact also in our daily life when we eat and smell things, smell and taste are very related. But there are nevertheless different senses. So smell is also a sensation of chemicals. It's a chemical sensation, also called olfaction. And it occurs through chemical receptors located in the nose, sort of deep down here at the top of the nose as you can see in this figure. There are in contrast to taste where we have a few very clearly defined primary tastes. There's no such thing as a primary smell. We have hundreds of different receptors in our nose that respond to different kind of smells and smells are always a mixture of all those. That very complicated pattern of activity essentially that arises. But I think this also explains the fact that we don't have a very clear primary smells, explains maybe also why it is so difficult to describe smells. It's very difficult to say that one thing smells like another thing. You can recognize a smell, you can have a very strong emotional response to a smell for sure, but it's difficult to really talk in quantitative terms about how things smell, I find. And that may be due to the fact that we have so many different receptors for smells. So in these hundreds of olfactory receptors combine into endless varieties of smells. And animals, for example, like dogs, that are even better at smelling things, have even more receptors sensitive to smell. Now a smell is processed in the olfactory cortex, which is located sort of on the edge of the temporal and frontal lobes as indicated in this figure. And what is kind of special about smell compared to the other senses, I didn't really touch upon that, but sensory information for every sense except smell travels through a brain area that is called the thalamus. And the thalamus is often thought as kind of a relay station of the brain where basically all input output flows through. For some reason, smell does not travel through the thalamus. I don't know what the meaning of that is or whether it even has any special significance or whether that's just one of these quirks of evolution that we evolved that way. But it's at any rate something that sets smells apart from the other senses that we have. So that's different from all the other senses. With that, let's move on to the next video, video 3.8, in which we're going to take a look at another sense, namely balance.