Ep56 "Why do we care so much about touch?"

each other more while they're talking than Scandinavian cultures? And what does this have to do with cuddle puddles, or why NBA players bump chests or why puppies sleep in dogpiles. Welcome to Inner Cosmos with me David Eagleman. I'm a neuroscientist and author at Stanford and in these episodes we sail deeply into our three pound universe to understand why and how our lives look the way they do. Today's episode is a love story about our sense of touch, what it is, how it works, and why it plays

such a critical role in our lives. So let me start with an acquaintance of mine, who many years ago worked as a midnight phone operator at AT and T. He would get calls from people in the middle of the night and he'd say, Hello, this is AT and t how can I help you? And they would say hi, and he'd say what can I help you with? And they'd say, I just need someone to talk with. So

there's a lot of loneliness in the world now. I tend to be suspicious when people talk about problems as modern phenomenon, given that most things have a deep history, but an increase in loneliness might actually be something new.

behind their fences. And by the year two thousand we got books like Bowling Alone, which was written by the political scientist Robert Putnam, and this book was about the decline of civic engagement since the nineteen sixty people used to be in bowling clubs and belong to their church or synagogue or mosque and see a community of people

every day and every weekend. And they were in rotary clubs and Shriner's clubs and Kawana's clubs, and people who were recent immigrants often had clubs from the towns they originally came from. And these clubs lasted for decades until the wave of immigrants finally died out and their children born in America didn't really need to keep this up anymore.

So because of lots of factors like suburbanization and the rise of television, and the decline of unions and the disappearance of clubs, we ended up with this decline of social capital.

society actually gotten lonelier? Now, I'm going to address this from both sides, arguing that there's more opportunity for relationship and less. Now on the side of more opportunity, one of the consequences that has always amazed me about the Internet is that now every person has the chance to find their tribe. If you are a stamp collector, or a mathematical poet, or a corporate mystic or a punk

rocker historian or whatever, you can find your people. There will be no end to the websites and subreddits and substacks and whatever else you need to make you feel like you have your group where if you grew up pre Internet, you would never know that so many others like you were out there. And related to this, a lot of parents lament that kids are spending all their time on video games. But most video games have built

in social mechanisms so that you can chat with other people. Now, chatting is not the same as spending time in real life, but with a million games to choose from, you end up finding people who share your interest and there's a lower barrier to entry from making acquaintances, and sometimes these become friends. So with multiplayer games, we have gone from bowling alone to bowling virtually virtually but not alone with other people's avatars who can chat with us and become

friends of a sort. And there's another important way in which I think technology will have a shot at reducing loneliness, and this is with AI. Already we've seen an explosion of companies selling AI relationships, and if you're interested in the complexities of this, please check out episode thirty nine, which is on the future of AI relationships. But beyond AI girlfriends or boyfriends, I suspect one of the places will see the most immediate impact with AI is in

areas like mental health therapy. The fact that you can have a therapist twenty four to seven, someone you can talk to in the middle of the night, someone who remembers everything you've said, someone who is not at all interested in talking about themselves but just about listening to you and giving you good advice and being there and truly has your best interests in mind. And so the question is does new technology like the Internet and AI

scratch the itch of loneliness. Because I'm generally a cyber optimist, I feel like there are many ways that can be correct. However, while this hits on many cylinders, what it misses is a big one. Touch And we really care about touch. So that's what I'm going to talk about in today's episode, what touch is all about? Because our world has become a lot of screens and less about holding hands or

hugging with strangers or friends. And the more I surveyed friends of mine on this point, I was surprised to realize how much touch is lacking in a lot of people's lives. One of my friends goes to Burning Man every year, and the thing he loves the most is that people hug people. Total strangers will say, give me a hug, and it's innocent. People can do this without sexuality,

and people clearly appreciate it. And there get togethers all over the world called cuddle puddles or cuddle parties where dozens of people lie on mats and cuddle one another and it's not sexual. Instead, it's fulfilling the very primitive desire we all have for touch. And by the way, the same desire is seen to cross the animal kingdom, where you constantly see non sexual physical contact among social animals.

The way you'll see puppies collect into a big dog pile when they're sleeping, And so from the point of view of the brain, I've become really interested in what we might be losing here. We're in an era with infinite hyperlinks between people, but fewer physical links. So for today's episode, I want to take us on a journey about touch, what it's all about, and how it colors our lives. When we look at touch across the animal kingdom, we see that it plays a critical role in everything

from child rearing to finding food to getting mates. But not everyone thinks highly of it. Plato thought that vision was hot stuff and considered touch to be the most carnal, the least noble, of the senses. But his student Aristotle developed a different view. He felt, we learn the world by going out and touching it. That's how we figure things out. Not everything can be achieved purely by looking

around and reasoning. So Aristotle said, quote, while in respect of all other senses we fall below many species of animals, in respect of touch, we far excel all other species in exactness of discrimination. That is why man is the most intelligent of all animals. So why did Aristotle privilege touch. What is special about touch and how does it all work? So let's start at the beginning. The largest organ in your body is actually on your body. It's your skin,

and it is a miraculous sort of material. Unlike your other senses, which are focused at your eyes and your ears and so on, touch is spread throughout the body, and touch is the only sense that puts you in direct con tact with your subject, instead of assessing it from a distance, as you do with photons with seeing, or air compression waves with hearing. In contrast, you have to be right up against something. You can't touch something without being touched yourself. So the really amazing part is

how it works. You have a whole zoo of touch receptors in your skin. These are specialized sensors for pressure, for itch, for stretch, for temperature.

of your skin, but in the layer underneath. And this is why safe crackers sand their fingertips to expose the sensitive skin in the layer underneath, so they can be really sensitive to the tiny, tiny shifts in the locking

mechanism of the safe. So collectively, this whole zoo of receptors inside your skin allows you to tell a lot about what's happening in the outside world in terms of texture and temperature and pressure and roughness and hardness, and your sense of what's out there is totally dependent on these sensors.

thousandth of a human hair. If you run your fingers over that, you can tell it's there. And you know all those ridges and grooves on your fingertips they serve as sensation amplifiers. They expand the skin's surface area when they encounter pressure. So evolution has sculpted your fingertips into incredibly fine instruments of touch. They traffic in information we

can't otherwise perceive with our other senses. So I'm gonna come back to skin in just a second, but first I want to make it clear that your system of sensation from the body picks up information both from the outside but also from the inside, and collectively this is grouped into what we call the somatosensory system, which just means sensing from the body. As I said a minute ago. Unlike vision or hearing, somata sensation doesn't happen in a

discrete sensory organ like eyes or ears. Instead, the receptors are widely distributed in the skin, and the muscles and the bones and the joints, in internal organs, in the cardiovascular system. So even though we call it one system, it's giant, and it's distributed, and every second of your life, these millions of receptors are streaming information to your brain,

where the information then steers your behavior. Now, in today's episode, I'm not going to talk too much about the internal monitoring, but just for sketching out the landscape, I'll tell you two of the main things you're doing on the inside. The first is constantly determining where your limbs exist in space, your body position, and your limbs movement. This is known as proprioception. Now, knowing how your body is positioned this

is something we just take for granted. But if you lose this information, as sometimes happens, for example, from a viral infection, you can no longer do things like walk because now you need to visually look at your feet and your hands to have a sense of where they even are. So normally, your brain knows where your limbs are by constantly drinking in this fat stream of information. But if that goes offline, your only way to estimate where your limbs are is to look at them visually.

And if the lights in the room turn off, you are going to fall to the floor. You can't maintain posture much less make any kind of fine movements without having visual feedback. So even though you may or may not have even been aware of this crazy thing called proprioception,

you cannot function without it. And the other internal monitoring that I'll mention is called interoception, which is this amazing system by which you monitor the inside of your body, like movements of your gut or muscle stretch or changes in heart rate or stretch receptors in your lungs that modulate your breathing rate, or stretch receptors in your stomach

and guts that tell you when you're full. You also have chemical receptors and the brain which monitor carbon dioxide levels to tell you if you're suffocating, and you have these in the circulatory system to monitor blood levels and trigger thirst. You have receptors in the throat that are close cousins of the touch receptors in your skin, and these are what detect whether there's an object in there

to trigger gag. And again, all the stuff we tend to take for granted, but every single one of these receptors is critical for you to have the experience in the world that you do. These underpin your ability to be a body moving around in the world. But for today we're gonna talk about the other side of somatic sensation, not monitoring the inside but touching the outside world.

or it's cold, or it's or it's smooth. But this apparent simplicity masks the incredible variety and complexity of how your brain and body do this. So let's surface the details. So first, to detect pressure and vibration, you have a specific flavor of sensory receptors in your skin called mechano receptors, and these are just built of special structures that make

them sensitive to being physically stretched or bent. Now you have different types of mechanic receptors that are different structures and locations, and that gives you the ability to sense and interpret a huge range of things.

or Ruffini's endings. Now, some of these receptor types respond quickly right when something gets touched, but then they stop responding if the touch remains there, and others of these are slowly adapting, which means they keep firing if the touch stays there. So the rapidly adapting ones are well suited to respond to something that's going on and off like a vibration, because they stop responding right after the initial thing, and therefore they're ready to respond again a

moment later. But others stay firing, so you can know when you touch your coffee cup that you're still touching it. So the thing I want to illustrate here is that you have this interplay of different receptor types that gives you a very rich, multilayered sensation of touch, fine and coarse, fast and slow. Now it's not just mechanicy receptors that you have in your skin, but you've got these other things called thermo receptor which tell you about temperature, and

you have separate thermo receptors for cool and warm. Now, if this wasn't something you already knew, it's kind of amazing. Right, You're like this sophisticated meat robot with all these sensors packed into your skin to detect different things in the world. Now, what these thermoreceptors do is they detect changes in temperature on the skin surface relative to body temperature. So a cold thermo receptor in your finger, it's going to signal only a little tiny bit of change. When you test

the water coming out of the sink. There's going to trigger a really strong signal when you dunk your hand into a bucket of ice water. Now, speaking of cold water, you've probably noticed that a cold lake feels warmer the.

to activate these cool thermoreceptors. Similarly, the active ingredient in chili peppers is called capsaicin, and this is a molecule of a certain shape that happens to bind to warm thermoreceptors, and therefore it creates the illusion of heat. So capsaicin is used in ointments that you rub on your skin, like icy hot. Okay, so now we've talked about how receptors in your skin detect touch and detect temperature, and

now let's come back to pain. The sensation of pain is one that most of us would probably rather not have, but it's actually a gift from nature that's critical for our survival. Feeling pain is how we detect damage to our cells and our tissues.

are called mechanical no susceptors. Then you have thermal no susceptors, which respond to things that are extremely hot or extremely cold. Then you have chemical no susceptors, which are activated by things like spider toxins when you get bit, or by certain cooking spices, or by poisonous gases like the kind used as chemical weapons in World War One. Now again, you might think that feeling no pain would be a blessing, but how would we know whether that's true or not.

The answer is this sometimes happens because of genetic mutations, and the inability to feel pain is a dangerous curse. So take as an example a man who I'll call Paul. When Paul was a child, he would push swing and let it smash into his face. He didn't mind the broken nose and chipped teeth because he has never felt physical pain. He has a rare disorder called congenital analgesia

and inability to register painful sensations. By the way, congenital just means you're born with it, and algesia means pain, and analgesia means no pain. So congenital analgesia just means you can't feel any pain and you were born that way. So Paul can feel a knife cutting his finger, but only the touch is registered, not the pain of the injury.

And because his thermoreceptors are intact, he can easily tell the difference between warm and cool water, but he doesn't feel the pain of things that are really hot or really cold.

He was interested in listening to the sizzling sound that his skin made, so his parents were constantly forced to take creative and desperate measures to keep their son safe, like putting socks over both his hands and goggles over his eyes. Often they put a helmet on him to protect him from his regular risk of hen injury. They constantly checked him for swelling and bruising and burns. Because of his lack of sensation, this kind of outside inspection was the only way that they or he could tell

whether tissue had been damaged. So much of Paul's childhood was spent in hospitals, whether from jumping off extreme heights or banging his head against the wall and his forehead swelled up. So Paul is lucky to be alive because not everyone with congenital analgesia makes it through childhood. The moral of Paul's story is that pain is two faced. It hurts, but it also protects, So back to normal

pain perception. Fascinatingly, you have different types of fibers that carry these signals to the brain, and they carry information at different speeds.

start unmasking the mechanisms of your body. The last thing I just want to note about these no suceptors, these pain receptors, is that they're distributed throughout your skin and your body, and your internal organs and in your joints. But the one notable exception is the brain, which has no suception, and that's why patients can be kept conscious

during brain surgery. I've done experiments before while a patient is undergoing brain surgery, and I'm talking with them and having them watch things on a screen and asking them questions, and the patient can just sit there and talk and provide feedback about their perceptions without feeling any pain from the surgery itself. It's one of nature's funny ironies that the organ that perceives pain for your entire body is

the one organ that registers no pain itself. So we've been talking about these receptors all over the body, and from the body, these signals come screaming up the spinal cord to the brain, and there these signals come slamming into a strip of real estate that we call the primary somatosensory cortex, which is just underwhere you would wear headphones.

Humans began to walk upright several million years ago, and that freed up our hands to reach out and examine objects, and over time that changed the importance of hands, making them some of the most important body parts that we have for examining the world, and so our brain changed accordingly. The situation now is that each of our fingertips has two thousand touch receptors in it, and they're streaming continuous, detailed information to the brain.

of its tunnels. Okay, so back to humans. We have this strip of cortex that receives the information from the body. That's the primary somatosensory cortex, and that neighbors these other regions that we call the sensory somatosensory cortex and the tertiary somatisentury cortex, and these are involved in more comp integration of sense, like what you need to recognize objects based on touch. This sort of higher order processing lets you translate round and smooth into.

when you feel them. But now I ask you to open your eyes and look at those things sitting on the table, and you have no trouble saying, oh, that's a book, that's a cell phone, that's a shoe. So it's not that you don't know what objects are, it's that you no longer have the ability to tell what something is simply by feeling it, simply by touch.

no milk but was covered in terry cloth. So what happened was the baby monkeys would drink some milk and then they would immediately steal over to the terry cloth mother and clutch at it for the rest of the time. And if the babies got frightened, they ran only for the terry cloth mother. So these studies confirmed earlier suspicions that there was more to the mother infant relationship than nourishment.

Harlow realized that this contact comfort was essential to the normal brain development of monkeys, and by extension, other studies have shown how critical this is for human children. Touch is a massively important part of the mother child interaction.

in monkeys and humans requires touch. It's not optional for a baby having loving adults interact with you and play with you, and tickle you and comfort you in an early age. These are all requisite for shaping the brain. Cuddling a child isn't just something that's nice for the parents. It's actually necessary for the child's normal brain development. So touch shapes the brain and is the basis for a healthy emotional life. But of course it's not just about emotion.

It's also about information. It's how we come to understand our world and exert our own influence over it. In fact, the way that we understand and interpret the world, our cognition, is fundamentally rooted in our physical bodies. How things feel to us, rough or warm or heavy. This interacts with our thoughts and our behaviors. We build metaphors on top

of our interactions with the physical world. We say things like that exam was rough, we say she has a warm personality, or we say, boy, that was a heavy movie. At the root of our language is what we can touch and feel. This is called embodied cognition. And I'm going to talk about this more in a later episode, but for now, I just want to say that not only our language, but many other sorts of judgments we make are rooted in our bodies, even things like making

judgments about other people. Is that person warm? Is that company competent and trustworthy? These use some of the same brain machinery as feeling warmth or solidness and texture and all the things our touching exploration of the world gives us and in our daily lives. Touch serves as a high bandwidth channel that continually moves information back and forth between people.

aware of. One study asked volunteers to communicate any motion to a stranger just using touch. They were both blindfolded, so they would try to communicate things like anger or fear or disgust, or love or gratitude or sympathy, or happiness or sadness. Think about how you would try to communicate these with touch. So most people were pretty sure they weren't going to be able to do this accurately.

But the result turned out that the other person was able to understand the social emotion about seventy five percent of the time. That's surprisingly good, and it underscores how nuanced and sophisticated.

make friendly contact with one another on the court. They then followed the ranking of all the teams through the seasons, and they found that NBA teams who had more contact did better by the end of the season. In other words, touch seemed to predict performance across all the NBA teams. Why well, One hypothesis is that the contact has the effect of increasing trust and affiliation while also lowering stress hormones, And that sheds light on a tradition in long distance

bike races. If someone is really slowing down, really out of energy, a fellow biker will ride along beside them and simply touch them with one finger, and their riding speeds up. Apparently it's very effective. Just a bit of human touch is enough to reinvigorate someone so they can find a second wind. And it's for reasons like these that we see bonding touch throughout the primate world. When monkeys groom one another, they're using touch as a tool to communicate trust and to strengthen bonds.

hold hands. Why Well, one hypoth this goes that people who are closer to the equator, where it's warmer, they wear fewer clothes, they have more skin exposed, and it only pays off to touch someone if they're going to feel it. Up north, they wear heavy clothes, and this communication channel is essentially cut off, so it doesn't.

we should be careful about what this means for touch. So, returning to the old phone company AT and T, their slogan in the nineteen eighties was reach out and touch someone, and I love this sentiment, but I always found the slogan ironic because the technology of the telephone actually reduces

touch interaction. So I hope that after you've heard this episode today, you'll think about ways to make sure you're getting enough touch, whether from a dog or cat, a cuddle, puddle, a friend, a lever, because our bodies are built for this, so for real, without technology reach out and touch someone. Go to eagleman dot com slash podcast for more information

and to find further reading. Send me an email at podcast at eagleman dot com with questions or discussion, and check out and subscribe to Inner Cosmos on YouTube for videos of each episode and to leave comments.