That Neuroscience Guy - Neuroscience Bites-Smell

Episode Date: May 11, 2022

Last week, we talked about the neuroscience of taste. But, the taste is also affected by our sense of smell, which itself has an intriguing connection to our brains. In today's Neuroscience Bite, we discuss the neuroscience behind our sense of smell. 

Hi, my name is Olaf Krigolsen and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to another neuroscience bite. Last week on our bite, we talked about our sense of taste and how we have five primary tastes and how the brain processes that. Well, as a logical extension of that, I thought this week on The Bite would talk quickly about the neuroscience of smell. Now, when I dove into this, again, it's something that we talk about in grad school. You get a couple classes on it, but unless it's your area of research, you don't spend a lot of time with it.

So I was fascinated relearning stuff that I used to know back in the day. You know that human beings can actually detect approximately a trillion different smells? I was astounded by that number, especially when you can think of the fact that we have sort of five primary tastes. And an example I found for instance is that chocolate is basically comprised of up to 600 chemical components, each which contribute to a unique smell for chocolate, which is why different types of chocolate have different smells. So what's actually going on in the brain? Well, basically, when you have an odor,

it's comprised of molecules, and those molecules interact with olfactory receptors in your nose. There's about 400 of them at the top of the nasal cavity. So basically when you inhale a smell, you get that those molecules interact with these receptors and it causes them to fire. Because remember at the end of the day, what we always say is that these receptors are just waiting for something to activate them. Now, then the receptor transmits an odor message to a structure at the bottom of the brain, basically called the olfactory bulb. If you google image it you'll see it sticks out and the olfactory bulb is basically processing information about the odor so it's taking the signal that comes in which is just pure detection of the

odor itself and it's transforming it into a code that the brain can recognize and from there from the olfactory bulb, the message is sent along via neurons to the olfactory cortex, which is in the temporal lobe of the brain. And that's where your brain begins to sort of decode what you're actually smelling. Now, one of the reasons it can do this is the olfactory cortex is connected directly to the amygdala, our old friend, the emotional center of the brain, and also to your hippocampus, so a region that plays a role in memory. So that's why smells are very quick to sort of trigger emotional responses or memories because it has these direct connections from the

olfactory cortex to the emotional and memory parts of the brain. And this is also how we help process smells, is we have an emotional response to them. Ooh, that smells horrible. Oh, that smells amazing. And we also have memories. The last time I smelled that, you know, that food that I was eating tasted so good. So just quickly to review, the smell is basically a sense of molecules. They drift into the nose. You've got your olfactory receptors. They bind or attach to these things. That triggers neurons firing. The message is sent to the olfactory bulb. It sort of transforms this into a neural code your brain can understand. And then it goes to the olfactory cortex, which interprets that code and translates it into meaning, working directly

with the emotional part of the brain, the amygdala, and the hippocampus. Now, I did mention that smell plays a key role in taste. If you remember from taste in the tongue, we talked about the primary things you can sense through taste. Well, researchers are estimating that taste is actually, what we think of as taste, is actually 75 to 95% based on smell. So the smell of your food is really helping your brain interpret what you're tasting so you're consciously think you're tasting all these things but it's primarily being driven by smell now one last thing a lot of people use aromatherapy it's a really popular

trendy area now and there's cool evidence about this basically certain odors evoke positive mood states. They cause the amygdala to fire or they trigger positive memories. So it is true that a well-scented candle or a certain aroma can make you feel better. Well I hope you learned a little bit on that neuroscience bite. We'll be back on Sunday for a full episode on headaches and migraines with Dr. Marla Mikoboro from the University of Saskatchewan. Remember, of course, the website, thatneuroscienceguy.com. Follow me on Twitter, at thatneuroscienceguy, where you can DM me with episode ideas. And of course,

thanks for listening to the podcast and subscribing. We'll see you on Sunday for a full episode. My name is Olof Kregolsen, and I'm that neuroscience guy. Thanks for listening.