Short Wave - How Many Senses Do We Really Have?

Episode Date: February 16, 2022

You're likely familiar with touch, taste, smell, sight, and hearing - but there are actually more than five senses. Emily Kwong speaks to neurobiologist André White, assistant professor at Mount Holyoke College, about the beautiful, intricate system that carries information from the outside world in. (ENCORE)See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

So this episode, which is a back-to-school episode, was born out of a simple question from a listener. How many senses do we humans have? Are sight, hearing, touch, smell, and taste all we have going for us? Well, the answer is a simple no. But the why is complex and honestly fascinating. Our guest is Andre White, who teaches neurobiology at Mount Holyo College, where he encourages his students to think deeply about neuroscience, addiction, and ethics. This man knows a lot about the human brain. So sit back and engage your senses for this throwback episode,

which features Shortwave OG Maddie Safaya. Hey, everybody, Maddie Safaya here. And Emily Kwong. And today we have for you another back-to-school episode. We'll revisit something you may have learned in science class and dig in a little deeper. Yes, many of you wrote in with back-to-school ideas, and we got this one from listener Michael Saulwark. who wrote, my five-year-old granddaughter is learning about the five senses. It's frustrating because I know there are a few more. And Michael, you are right. Yes, there are more than five. This is Andre White, assistant professor at Mount Holyo College, where he teaches neurobiology. I can understand Michael's frustration, but part of it has to do with the fact that those five senses or sensory systems have disconsed.

discreet identifiable organs. Totally. I remember in kindergarten, we learned that eyes were for sight, ears were for hearing, nose was for nosen, mouth for taste, and skin for touch. Honestly, we can blame Aristotle for this oversimplification because he described the five senses in day anima in 350 BC. Come on, Aristotle. Okay. All right.

out of your head and replace with what modern science has to say about sensory organs, sensing, and yes, additional senses. Today on the show, your senses and you, the beautiful, intricate system that carries information from the outside world in. And how we all may be living in our very own version of The Matrix. This is Shortwave, the Daily Science Podcast from NPR. All right, Emily Kwong, I can think of few things more fundamental. to our existence than our senses.

Like this morning, I was drinking my coffee, and coffee is such a multi-sensory experience if you pay attention to it. You've got that little sloshing coffee sound, the warm mug on the inside of your little paws, that smell. Honestly, the tagline of our show should be shortwave, brought to you by coffee.

And of all the senses, I asked our neurobiologist Andre White, his favorite. I'm a foodie, so I'm going to say, I asked him, when the pandemic is over and travel restrictions are lifted, what would you eat first? And he said, no question. Aki and saltfish in Jamaica, where he grew up. Aki is a fruit that grows on a tree there that you can boil. And saltfish is cod that has been preserved in salt. And I just, I love it all. I mean, it sounds delicious, Kwan.

Yeah, sensory information is potent. Andre says that from a neurological perspective, you can think of our sense. as an internal representation of our external environment. As well as our place and movement through that environment. More on that in a minute. But first, I want to talk about what makes this all possible, your sensory nervous system. What I didn't realize until talking to Andre is that this system, Maddie, is finally, finally tuned. So the unique thing about our senses is that we have specialized receptors that are tuned to individual.

stimulus. What? Right. So the reason why... That blows my mind. Right. So the reason why you can see light with your eyes is because we have photoreceptors in our eyes. And the reason you can't see light using your ears is because we don't have photoreceptors in our ears.

And so the information for those individual types of stimulus, they get converted into electrical and chemical signals into the nervous system? So chemoreceptors figure heavily into taste and smell. For touch, which he defines as our somatosensory system, we have a variety of receptors. Some pick up pressure and temperature, but also pain, itch. Some help with proprioception, which keeps track of where our limbs are at any moment, like whether your arm is reaching out for that cup of coffee or scratching your head. I know these aren't like senses, but what about like hunger or thirst?

Yeah, Andre would describe those more as motivational states than part of our somatosensory system. I have often been motivated by those states. You know what I mean? Okay. Yeah. Okay. So a sense could be broadly defined not as a specific type of stimuli of information from the outside world, but this highly specialized circuitry in our bodies with all these receptors paying attention to different stimuli and then converting them into

signals our brains can understand. You nailed it. Yep. And it all gets put together in the brain to give us, in large part, without consciousness, a representation of the things we see, feel, hear, taste. You know, I feel like this is getting into some, like, almost philosophical territory, Kwong, you know, like, because if our senses are just a representation of the outside world in our brain, how do we know if the world is real, you know? Do you mean, are we living in the Matrix?

I mean, I'm not mean in that. Andre personally says this question is best left to philosophers because there's debate about how to even define a sense, right? But no matter how you argue it, his point is that knowledge of the senses can help us modify them. It also allows us to take advantage of that circuitry. So if we think of hearing aids, understanding how we hear allows us to convert sound,

waves in the environment into electrical signals artificially and then tap into our auditory system so that people who have, whether it's they were born with an inability to hear or they receive damage to the hearing system, we can now bypass that inability in order to convert sound into signals that our brains can interpret. All right. So we've got hearing, taste, somato, sensation, smell, and sight. Kwong, I got to know. What's the sixth sense? I know you want to know.

I did too. But like I said, there's scientific debate about how to divide up and define the senses. Andre was comfortable naming number six. He said it was the vestibular system. So your sense of balance and where you are in space. Right. Super important. And that sensory organ is like in your ear area, right?

Exactly. ears do a lot more than help us listen. Your inner ear is lined with hair cells and when you move your head to the left or to the right, these hair cells pick up on the direction of the fluid that's in our ears. Think of it

like this. If you think about the hair on your arm. Okay. I'll look at it as you explain this. Okay. If you brush the hair on your arm from your wrist to your elbow, that's in one direction. If you brush it from your

elbow to your wrist, that's a different direction. Your body has to be able to tell which direction that motion is going. Right. So for these cells, when the hair cells are bent or moved in one direction, they can cause a different signal to be sent to the nervous system as opposed to when they're bent in the opposite direction. And this activity in our inner ear provides critical intel about where our bodies are in space, allowing us to know whether we're, accelerating or decelerating. The reason you can even close your eyes and still know where you're moving owes its credit to the vestibular system. For a sense that's so important, Kwong, it's surprising to me that we don't really talk about it more. Yeah, the vestibular system is pretty

subtle, though, right? Many of us take our balance for granted. You start to notice it when there's, let's say, damage to your ear, that can impair your balance. Or motion sickness. That's when your vestibular system, for example, says you're going in one direction. and your eyes, say you're going in another direction. Basically, the vestibular and other systems send conflicting messages. You get all nauseous, but you really don't want to put that book down because it's really good and you're reading the back of your car. You know what I mean. Been there?

Done that. And just to underscore all the value the vestibular system provides, I then invited Andre into a thought experiment. I asked him, what would our lives be like without it? Oh, wow. And his response was pretty illuminating. I would say that we would have very tired eyes. Imagine going up and downstairs. You're not thinking about each rung on the stairs.

But if you weren't able to feel your sense of self in that space and balance, you would have to look at every time your foot was going to make a step on a stair. Sports would move like molasses, because athletes would have to constantly be looking at, where their body was in space and to know which way to go. And I'll say it. Just forget about flashlight tag, the best kind of tag, you know? Oh, forget about it.

Too dark to know where you are without your vestibular system. And say goodbye to TikTok dance videos. It would actually make life a lot more boring. Wow, I'll tell you what. I will never take my vestibular system for granted again, Kwong. Like, I feel like maybe I'm going to go juggle right now, maybe, you know, something like that. You can even juggle with your eyes closed. And then you'd really appreciate your vestibular system.

Could I? Could I? All right, Emily Kwong, my forever learning buddy and definitely previous teachers, Pat, I'll say that. Thank you for taking us back to school today. I try my very best. This episode was produced by Burley McCoy, whoop, edited by Giselle Grayson and fact-checked by Rasha Auretti and Arellia Zabidi. Thanks also to Michael Salwasser for the question. I'm Maddie Safaya.

And I'm Emily Kwong, and this is Shortwave from NPR.