1 00:00:05,519 --> 00:00:09,840 Speaker 1: Why does a cold pool feel warmer this second time 2 00:00:09,920 --> 00:00:12,799 Speaker 1: you put your toes in. Why does a person who's 3 00:00:12,800 --> 00:00:17,320 Speaker 1: trying to break into a safe run his fingers over sandpaper? 4 00:00:17,960 --> 00:00:20,599 Speaker 1: Would it be great or not so great if you 5 00:00:20,680 --> 00:00:25,920 Speaker 1: couldn't feel any physical pain? Why does stubbing your toe 6 00:00:26,400 --> 00:00:32,000 Speaker 1: have different sensations through time? Why do Mediterranean cultures touch 7 00:00:32,040 --> 00:00:36,199 Speaker 1: each other more while they're talking than Scandinavian cultures? And 8 00:00:36,240 --> 00:00:39,080 Speaker 1: what does this have to do with cuddle puddles, or 9 00:00:39,120 --> 00:00:44,559 Speaker 1: why NBA players bump chests or why puppies sleep in dogpiles. 10 00:00:47,560 --> 00:00:51,080 Speaker 1: Welcome to Inner Cosmos with me David Eagleman. I'm a 11 00:00:51,159 --> 00:00:55,080 Speaker 1: neuroscientist and author at Stanford and in these episodes we 12 00:00:55,160 --> 00:00:59,640 Speaker 1: sail deeply into our three pound universe to understand why 13 00:00:59,760 --> 00:01:11,600 Speaker 1: and how our lives look the way they do. Today's 14 00:01:11,600 --> 00:01:16,319 Speaker 1: episode is a love story about our sense of touch, 15 00:01:17,000 --> 00:01:20,399 Speaker 1: what it is, how it works, and why it plays 16 00:01:20,760 --> 00:01:23,760 Speaker 1: such a critical role in our lives. So let me 17 00:01:23,840 --> 00:01:27,120 Speaker 1: start with an acquaintance of mine, who many years ago 18 00:01:27,880 --> 00:01:31,920 Speaker 1: worked as a midnight phone operator at AT and T. 19 00:01:32,440 --> 00:01:35,319 Speaker 1: He would get calls from people in the middle of 20 00:01:35,360 --> 00:01:37,640 Speaker 1: the night and he'd say, Hello, this is AT and 21 00:01:37,680 --> 00:01:40,680 Speaker 1: t how can I help you? And they would say hi, 22 00:01:40,920 --> 00:01:42,959 Speaker 1: and he'd say what can I help you with? And 23 00:01:43,000 --> 00:01:46,640 Speaker 1: they'd say, I just need someone to talk with. So 24 00:01:46,680 --> 00:01:49,640 Speaker 1: there's a lot of loneliness in the world now. I 25 00:01:49,680 --> 00:01:53,320 Speaker 1: tend to be suspicious when people talk about problems as 26 00:01:53,440 --> 00:01:56,480 Speaker 1: modern phenomenon, given that most things have a deep history, 27 00:01:56,880 --> 00:02:01,480 Speaker 1: but an increase in loneliness might actually be something new. 28 00:02:01,560 --> 00:02:02,360 Speaker 2: If you look back. 29 00:02:02,720 --> 00:02:07,280 Speaker 1: Even just a century ago, people lived in boarding houses 30 00:02:07,320 --> 00:02:09,600 Speaker 1: with lots of other people, and there was lots of 31 00:02:09,960 --> 00:02:14,000 Speaker 1: intergenerational living where you had at least three generations in 32 00:02:14,040 --> 00:02:17,600 Speaker 1: the same household. Now that was probably crazy making, but 33 00:02:17,760 --> 00:02:21,480 Speaker 1: whatever the case, this situation has changed a lot. 34 00:02:21,760 --> 00:02:23,320 Speaker 2: As the middle class grew. 35 00:02:23,800 --> 00:02:28,079 Speaker 1: The aspiration was for nuclear families to each get their 36 00:02:28,160 --> 00:02:31,280 Speaker 1: own house with their own dishwasher and their own washing 37 00:02:31,280 --> 00:02:34,560 Speaker 1: machine and their own television set. And in most neighborhoods, 38 00:02:35,000 --> 00:02:38,480 Speaker 1: yards became more and more private, and at some point 39 00:02:38,520 --> 00:02:41,639 Speaker 1: people stopped hanging out in their front yards and playing 40 00:02:41,639 --> 00:02:44,920 Speaker 1: on the streets, but instead hung out in their backyards 41 00:02:44,960 --> 00:02:48,600 Speaker 1: behind their fences. And by the year two thousand we 42 00:02:48,680 --> 00:02:52,640 Speaker 1: got books like Bowling Alone, which was written by the 43 00:02:52,680 --> 00:02:56,360 Speaker 1: political scientist Robert Putnam, and this book was about the 44 00:02:56,440 --> 00:03:01,320 Speaker 1: decline of civic engagement since the nineteen sixty people used 45 00:03:01,320 --> 00:03:04,680 Speaker 1: to be in bowling clubs and belong to their church 46 00:03:04,720 --> 00:03:08,080 Speaker 1: or synagogue or mosque and see a community of people 47 00:03:08,560 --> 00:03:12,040 Speaker 1: every day and every weekend. And they were in rotary 48 00:03:12,080 --> 00:03:16,680 Speaker 1: clubs and Shriner's clubs and Kawana's clubs, and people who 49 00:03:16,760 --> 00:03:20,920 Speaker 1: were recent immigrants often had clubs from the towns they 50 00:03:20,919 --> 00:03:25,280 Speaker 1: originally came from. And these clubs lasted for decades until 51 00:03:25,320 --> 00:03:28,799 Speaker 1: the wave of immigrants finally died out and their children 52 00:03:28,840 --> 00:03:32,000 Speaker 1: born in America didn't really need to keep this up anymore. 53 00:03:32,440 --> 00:03:36,960 Speaker 1: So because of lots of factors like suburbanization and the 54 00:03:37,080 --> 00:03:40,680 Speaker 1: rise of television, and the decline of unions and the 55 00:03:40,760 --> 00:03:45,320 Speaker 1: disappearance of clubs, we ended up with this decline of 56 00:03:45,440 --> 00:03:46,480 Speaker 1: social capital. 57 00:03:46,840 --> 00:03:47,080 Speaker 2: Now. 58 00:03:47,200 --> 00:03:51,200 Speaker 1: Of note here is that Putnam's book was published before 59 00:03:51,320 --> 00:03:55,960 Speaker 1: the invention of the smartphone, and while the Internet existed 60 00:03:55,960 --> 00:03:58,920 Speaker 1: and video games existed, they were nothing like what they 61 00:03:59,000 --> 00:04:03,400 Speaker 1: quickly became in the first decade after that book was published. 62 00:04:03,720 --> 00:04:07,480 Speaker 1: And so society has changed much further in the past 63 00:04:07,560 --> 00:04:11,320 Speaker 1: quarter century. And the question is, are we now not 64 00:04:11,600 --> 00:04:15,640 Speaker 1: just bowling alone but not even bowling at all. Has 65 00:04:15,920 --> 00:04:20,680 Speaker 1: society actually gotten lonelier? Now, I'm going to address this 66 00:04:20,760 --> 00:04:25,240 Speaker 1: from both sides, arguing that there's more opportunity for relationship 67 00:04:25,320 --> 00:04:30,400 Speaker 1: and less. Now on the side of more opportunity, one 68 00:04:30,440 --> 00:04:33,240 Speaker 1: of the consequences that has always amazed me about the 69 00:04:33,279 --> 00:04:37,240 Speaker 1: Internet is that now every person has the chance to 70 00:04:37,360 --> 00:04:41,720 Speaker 1: find their tribe. If you are a stamp collector, or 71 00:04:41,800 --> 00:04:46,320 Speaker 1: a mathematical poet, or a corporate mystic or a punk 72 00:04:46,440 --> 00:04:51,360 Speaker 1: rocker historian or whatever, you can find your people. There 73 00:04:51,400 --> 00:04:54,680 Speaker 1: will be no end to the websites and subreddits and 74 00:04:54,720 --> 00:04:57,400 Speaker 1: substacks and whatever else you need to make you feel 75 00:04:57,800 --> 00:05:00,880 Speaker 1: like you have your group where if you grew up 76 00:05:01,080 --> 00:05:04,520 Speaker 1: pre Internet, you would never know that so many others 77 00:05:04,720 --> 00:05:07,760 Speaker 1: like you were out there. And related to this, a 78 00:05:07,800 --> 00:05:10,800 Speaker 1: lot of parents lament that kids are spending all their 79 00:05:10,880 --> 00:05:13,800 Speaker 1: time on video games. But most video games have built 80 00:05:13,880 --> 00:05:18,000 Speaker 1: in social mechanisms so that you can chat with other people. Now, 81 00:05:18,200 --> 00:05:21,560 Speaker 1: chatting is not the same as spending time in real life, 82 00:05:21,960 --> 00:05:24,600 Speaker 1: but with a million games to choose from, you end 83 00:05:24,680 --> 00:05:28,520 Speaker 1: up finding people who share your interest and there's a 84 00:05:28,600 --> 00:05:32,640 Speaker 1: lower barrier to entry from making acquaintances, and sometimes these 85 00:05:32,680 --> 00:05:36,960 Speaker 1: become friends. So with multiplayer games, we have gone from 86 00:05:37,240 --> 00:05:42,440 Speaker 1: bowling alone to bowling virtually virtually but not alone with 87 00:05:42,720 --> 00:05:45,880 Speaker 1: other people's avatars who can chat with us and become 88 00:05:46,000 --> 00:05:49,000 Speaker 1: friends of a sort. And there's another important way in 89 00:05:49,040 --> 00:05:53,680 Speaker 1: which I think technology will have a shot at reducing loneliness, 90 00:05:53,720 --> 00:05:57,839 Speaker 1: and this is with AI. Already we've seen an explosion 91 00:05:57,880 --> 00:06:02,000 Speaker 1: of companies selling AI relationships, and if you're interested in 92 00:06:02,040 --> 00:06:05,440 Speaker 1: the complexities of this, please check out episode thirty nine, 93 00:06:05,800 --> 00:06:09,360 Speaker 1: which is on the future of AI relationships. But beyond 94 00:06:09,520 --> 00:06:13,160 Speaker 1: AI girlfriends or boyfriends, I suspect one of the places 95 00:06:13,200 --> 00:06:16,680 Speaker 1: will see the most immediate impact with AI is in 96 00:06:16,839 --> 00:06:20,200 Speaker 1: areas like mental health therapy. The fact that you can 97 00:06:20,240 --> 00:06:23,720 Speaker 1: have a therapist twenty four to seven, someone you can 98 00:06:23,839 --> 00:06:25,880 Speaker 1: talk to in the middle of the night, someone who 99 00:06:26,279 --> 00:06:29,880 Speaker 1: remembers everything you've said, someone who is not at all 100 00:06:29,920 --> 00:06:33,240 Speaker 1: interested in talking about themselves but just about listening to 101 00:06:33,279 --> 00:06:36,560 Speaker 1: you and giving you good advice and being there and 102 00:06:36,600 --> 00:06:39,560 Speaker 1: truly has your best interests in mind. And so the 103 00:06:39,680 --> 00:06:43,240 Speaker 1: question is does new technology like the Internet and AI 104 00:06:43,880 --> 00:06:48,800 Speaker 1: scratch the itch of loneliness. Because I'm generally a cyber optimist, 105 00:06:48,839 --> 00:06:53,120 Speaker 1: I feel like there are many ways that can be correct. However, 106 00:06:53,920 --> 00:06:57,200 Speaker 1: while this hits on many cylinders, what it misses is 107 00:06:57,240 --> 00:07:00,960 Speaker 1: a big one. Touch And we really care about touch. 108 00:07:01,200 --> 00:07:03,440 Speaker 1: So that's what I'm going to talk about in today's episode, 109 00:07:03,520 --> 00:07:07,040 Speaker 1: what touch is all about? Because our world has become 110 00:07:07,080 --> 00:07:11,120 Speaker 1: a lot of screens and less about holding hands or 111 00:07:11,200 --> 00:07:14,960 Speaker 1: hugging with strangers or friends. And the more I surveyed 112 00:07:14,960 --> 00:07:17,280 Speaker 1: friends of mine on this point, I was surprised to 113 00:07:17,400 --> 00:07:21,040 Speaker 1: realize how much touch is lacking in a lot of 114 00:07:21,120 --> 00:07:23,960 Speaker 1: people's lives. One of my friends goes to Burning Man 115 00:07:24,000 --> 00:07:26,520 Speaker 1: every year, and the thing he loves the most is 116 00:07:26,520 --> 00:07:29,920 Speaker 1: that people hug people. Total strangers will say, give me 117 00:07:29,960 --> 00:07:33,480 Speaker 1: a hug, and it's innocent. People can do this without sexuality, 118 00:07:33,760 --> 00:07:37,240 Speaker 1: and people clearly appreciate it. And there get togethers all 119 00:07:37,280 --> 00:07:41,239 Speaker 1: over the world called cuddle puddles or cuddle parties where 120 00:07:41,320 --> 00:07:45,280 Speaker 1: dozens of people lie on mats and cuddle one another 121 00:07:45,320 --> 00:07:49,680 Speaker 1: and it's not sexual. Instead, it's fulfilling the very primitive 122 00:07:49,680 --> 00:07:52,880 Speaker 1: desire we all have for touch. And by the way, 123 00:07:52,920 --> 00:07:56,360 Speaker 1: the same desire is seen to cross the animal kingdom, 124 00:07:56,360 --> 00:08:02,240 Speaker 1: where you constantly see non sexual physical contact among social animals. 125 00:08:02,400 --> 00:08:06,040 Speaker 1: The way you'll see puppies collect into a big dog 126 00:08:06,120 --> 00:08:09,160 Speaker 1: pile when they're sleeping, And so from the point of 127 00:08:09,240 --> 00:08:12,360 Speaker 1: view of the brain, I've become really interested in what 128 00:08:12,560 --> 00:08:16,920 Speaker 1: we might be losing here. We're in an era with 129 00:08:17,120 --> 00:08:23,880 Speaker 1: infinite hyperlinks between people, but fewer physical links. So for 130 00:08:23,920 --> 00:08:26,520 Speaker 1: today's episode, I want to take us on a journey 131 00:08:26,960 --> 00:08:30,880 Speaker 1: about touch, what it's all about, and how it colors 132 00:08:31,000 --> 00:08:35,040 Speaker 1: our lives. When we look at touch across the animal kingdom, 133 00:08:35,080 --> 00:08:37,720 Speaker 1: we see that it plays a critical role in everything 134 00:08:37,760 --> 00:08:42,160 Speaker 1: from child rearing to finding food to getting mates. But 135 00:08:42,240 --> 00:08:46,400 Speaker 1: not everyone thinks highly of it. Plato thought that vision 136 00:08:46,559 --> 00:08:50,640 Speaker 1: was hot stuff and considered touch to be the most carnal, 137 00:08:50,720 --> 00:08:56,040 Speaker 1: the least noble, of the senses. But his student Aristotle 138 00:08:56,440 --> 00:09:00,000 Speaker 1: developed a different view. He felt, we learn the world 139 00:09:00,160 --> 00:09:03,000 Speaker 1: by going out and touching it. That's how we figure 140 00:09:03,080 --> 00:09:07,120 Speaker 1: things out. Not everything can be achieved purely by looking 141 00:09:07,160 --> 00:09:11,840 Speaker 1: around and reasoning. So Aristotle said, quote, while in respect 142 00:09:11,960 --> 00:09:16,080 Speaker 1: of all other senses we fall below many species of animals, 143 00:09:16,559 --> 00:09:21,520 Speaker 1: in respect of touch, we far excel all other species 144 00:09:21,760 --> 00:09:26,520 Speaker 1: in exactness of discrimination. That is why man is the 145 00:09:26,559 --> 00:09:32,880 Speaker 1: most intelligent of all animals. So why did Aristotle privilege touch. 146 00:09:33,000 --> 00:09:35,720 Speaker 1: What is special about touch and how does it all work? 147 00:09:36,400 --> 00:09:40,240 Speaker 1: So let's start at the beginning. The largest organ in 148 00:09:40,280 --> 00:09:44,440 Speaker 1: your body is actually on your body. It's your skin, 149 00:09:44,840 --> 00:09:48,600 Speaker 1: and it is a miraculous sort of material. Unlike your 150 00:09:48,600 --> 00:09:52,040 Speaker 1: other senses, which are focused at your eyes and your 151 00:09:52,080 --> 00:09:55,520 Speaker 1: ears and so on, touch is spread throughout the body, 152 00:09:56,080 --> 00:09:58,440 Speaker 1: and touch is the only sense that puts you in 153 00:09:58,920 --> 00:10:02,800 Speaker 1: direct con tact with your subject, instead of assessing it 154 00:10:02,840 --> 00:10:06,240 Speaker 1: from a distance, as you do with photons with seeing, 155 00:10:06,360 --> 00:10:09,920 Speaker 1: or air compression waves with hearing. In contrast, you have 156 00:10:10,000 --> 00:10:13,440 Speaker 1: to be right up against something. You can't touch something 157 00:10:13,520 --> 00:10:17,560 Speaker 1: without being touched yourself. So the really amazing part is 158 00:10:17,640 --> 00:10:21,960 Speaker 1: how it works. You have a whole zoo of touch 159 00:10:22,040 --> 00:10:27,280 Speaker 1: receptors in your skin. These are specialized sensors for pressure, 160 00:10:27,720 --> 00:10:30,240 Speaker 1: for itch, for stretch, for temperature. 161 00:10:30,640 --> 00:10:32,920 Speaker 2: Some receptors are specialized for pain. 162 00:10:33,600 --> 00:10:36,880 Speaker 1: Some are for pain caused by chemicals like an acid, 163 00:10:37,000 --> 00:10:40,120 Speaker 1: some are for mechanical pain like a cut, and some 164 00:10:40,200 --> 00:10:43,800 Speaker 1: are for thermal pain like a burn. And all of 165 00:10:43,840 --> 00:10:49,679 Speaker 1: these things work in collaboration to read different sensory aspects 166 00:10:49,800 --> 00:10:53,240 Speaker 1: of the world. So when you pass your finger over 167 00:10:53,400 --> 00:10:57,080 Speaker 1: something like the petal of a flower or the sleeve 168 00:10:57,160 --> 00:11:00,800 Speaker 1: of your jacket or the back of your dog. Different 169 00:11:00,840 --> 00:11:05,760 Speaker 1: receptor types read the object in different ways. And what's 170 00:11:05,800 --> 00:11:08,839 Speaker 1: interesting is that feeling doesn't happen in the top layer 171 00:11:08,880 --> 00:11:11,040 Speaker 1: of your skin, but in the layer underneath. And this 172 00:11:11,120 --> 00:11:15,800 Speaker 1: is why safe crackers sand their fingertips to expose the 173 00:11:15,920 --> 00:11:18,880 Speaker 1: sensitive skin in the layer underneath, so they can be 174 00:11:18,960 --> 00:11:22,920 Speaker 1: really sensitive to the tiny, tiny shifts in the locking 175 00:11:22,960 --> 00:11:26,920 Speaker 1: mechanism of the safe. So collectively, this whole zoo of 176 00:11:27,000 --> 00:11:29,760 Speaker 1: receptors inside your skin allows you to tell a lot 177 00:11:29,800 --> 00:11:32,439 Speaker 1: about what's happening in the outside world in terms of 178 00:11:32,840 --> 00:11:36,520 Speaker 1: texture and temperature and pressure and roughness and hardness, and 179 00:11:36,559 --> 00:11:39,680 Speaker 1: your sense of what's out there is totally dependent on 180 00:11:39,800 --> 00:11:40,600 Speaker 1: these sensors. 181 00:11:40,920 --> 00:11:44,400 Speaker 2: If you block their operation with a local. 182 00:11:44,240 --> 00:11:47,520 Speaker 1: Anesthetic, then you don't sense anything out there at all. 183 00:11:47,960 --> 00:11:52,880 Speaker 1: So these sensors work together to give you exquisite sensitivity. 184 00:11:53,320 --> 00:11:55,839 Speaker 1: This is why you can reach into your pocket and 185 00:11:55,880 --> 00:11:58,959 Speaker 1: you can tell a quarter from a nickel without looking. 186 00:11:59,440 --> 00:12:05,480 Speaker 1: Your sensitive fingertips detect the tiny ridges around the quarter's edge, 187 00:12:05,960 --> 00:12:08,679 Speaker 1: and those are very small, but that's nothing. Your fingers 188 00:12:08,679 --> 00:12:12,760 Speaker 1: can actually detect textures that are way finer. You can 189 00:12:12,800 --> 00:12:17,800 Speaker 1: feel a texture seventy five nanometers high. That's one one 190 00:12:17,840 --> 00:12:20,880 Speaker 1: thousandth of a human hair. If you run your fingers 191 00:12:20,960 --> 00:12:23,560 Speaker 1: over that, you can tell it's there. And you know 192 00:12:23,600 --> 00:12:26,720 Speaker 1: all those ridges and grooves on your fingertips they serve 193 00:12:26,880 --> 00:12:33,000 Speaker 1: as sensation amplifiers. They expand the skin's surface area when 194 00:12:33,040 --> 00:12:37,880 Speaker 1: they encounter pressure. So evolution has sculpted your fingertips into 195 00:12:37,960 --> 00:12:43,480 Speaker 1: incredibly fine instruments of touch. They traffic in information we 196 00:12:43,640 --> 00:12:58,600 Speaker 1: can't otherwise perceive with our other senses. So I'm gonna 197 00:12:58,600 --> 00:13:00,480 Speaker 1: come back to skin in just a second, but first 198 00:13:00,559 --> 00:13:02,600 Speaker 1: I want to make it clear that your system of 199 00:13:03,040 --> 00:13:07,080 Speaker 1: sensation from the body picks up information both from the 200 00:13:07,080 --> 00:13:10,960 Speaker 1: outside but also from the inside, and collectively this is 201 00:13:11,000 --> 00:13:15,440 Speaker 1: grouped into what we call the somatosensory system, which just 202 00:13:15,559 --> 00:13:19,640 Speaker 1: means sensing from the body. As I said a minute ago. 203 00:13:19,840 --> 00:13:24,760 Speaker 1: Unlike vision or hearing, somata sensation doesn't happen in a 204 00:13:25,400 --> 00:13:29,559 Speaker 1: discrete sensory organ like eyes or ears. Instead, the receptors 205 00:13:29,640 --> 00:13:33,080 Speaker 1: are widely distributed in the skin, and the muscles and 206 00:13:33,120 --> 00:13:37,080 Speaker 1: the bones and the joints, in internal organs, in the 207 00:13:37,120 --> 00:13:40,640 Speaker 1: cardiovascular system. So even though we call it one system, 208 00:13:40,679 --> 00:13:45,680 Speaker 1: it's giant, and it's distributed, and every second of your life, 209 00:13:45,720 --> 00:13:50,440 Speaker 1: these millions of receptors are streaming information to your brain, 210 00:13:51,000 --> 00:13:55,840 Speaker 1: where the information then steers your behavior. Now, in today's episode, 211 00:13:55,840 --> 00:13:58,680 Speaker 1: I'm not going to talk too much about the internal monitoring, 212 00:13:59,160 --> 00:14:01,960 Speaker 1: but just for sketching out the landscape, I'll tell you 213 00:14:02,040 --> 00:14:04,400 Speaker 1: two of the main things you're doing on the inside. 214 00:14:04,440 --> 00:14:10,120 Speaker 1: The first is constantly determining where your limbs exist in space, 215 00:14:10,320 --> 00:14:14,480 Speaker 1: your body position, and your limbs movement. This is known 216 00:14:14,520 --> 00:14:19,920 Speaker 1: as proprioception. Now, knowing how your body is positioned this 217 00:14:20,000 --> 00:14:22,880 Speaker 1: is something we just take for granted. But if you 218 00:14:23,080 --> 00:14:27,200 Speaker 1: lose this information, as sometimes happens, for example, from a 219 00:14:27,320 --> 00:14:31,600 Speaker 1: viral infection, you can no longer do things like walk 220 00:14:32,000 --> 00:14:35,800 Speaker 1: because now you need to visually look at your feet 221 00:14:35,840 --> 00:14:38,120 Speaker 1: and your hands to have a sense of where they 222 00:14:38,160 --> 00:14:42,360 Speaker 1: even are. So normally, your brain knows where your limbs 223 00:14:42,360 --> 00:14:46,840 Speaker 1: are by constantly drinking in this fat stream of information. 224 00:14:47,520 --> 00:14:51,480 Speaker 1: But if that goes offline, your only way to estimate 225 00:14:51,600 --> 00:14:54,600 Speaker 1: where your limbs are is to look at them visually. 226 00:14:54,920 --> 00:14:57,360 Speaker 1: And if the lights in the room turn off, you 227 00:14:57,400 --> 00:15:00,000 Speaker 1: are going to fall to the floor. You can't maintain 228 00:15:00,720 --> 00:15:04,560 Speaker 1: posture much less make any kind of fine movements without 229 00:15:04,720 --> 00:15:08,040 Speaker 1: having visual feedback. So even though you may or may 230 00:15:08,080 --> 00:15:12,120 Speaker 1: not have even been aware of this crazy thing called proprioception, 231 00:15:12,680 --> 00:15:16,800 Speaker 1: you cannot function without it. And the other internal monitoring 232 00:15:16,800 --> 00:15:21,320 Speaker 1: that I'll mention is called interoception, which is this amazing 233 00:15:21,360 --> 00:15:24,720 Speaker 1: system by which you monitor the inside of your body, 234 00:15:24,840 --> 00:15:28,560 Speaker 1: like movements of your gut or muscle stretch or changes 235 00:15:28,600 --> 00:15:32,320 Speaker 1: in heart rate or stretch receptors in your lungs that 236 00:15:32,480 --> 00:15:36,160 Speaker 1: modulate your breathing rate, or stretch receptors in your stomach 237 00:15:36,240 --> 00:15:38,920 Speaker 1: and guts that tell you when you're full. You also 238 00:15:39,080 --> 00:15:43,520 Speaker 1: have chemical receptors and the brain which monitor carbon dioxide 239 00:15:43,600 --> 00:15:46,000 Speaker 1: levels to tell you if you're suffocating, and you have 240 00:15:46,120 --> 00:15:49,520 Speaker 1: these in the circulatory system to monitor blood levels and 241 00:15:49,520 --> 00:15:53,480 Speaker 1: trigger thirst. You have receptors in the throat that are 242 00:15:53,520 --> 00:15:56,280 Speaker 1: close cousins of the touch receptors in your skin, and 243 00:15:56,320 --> 00:15:58,960 Speaker 1: these are what detect whether there's an object in there 244 00:15:59,000 --> 00:16:03,160 Speaker 1: to trigger gag. And again, all the stuff we tend 245 00:16:03,440 --> 00:16:07,360 Speaker 1: to take for granted, but every single one of these 246 00:16:07,480 --> 00:16:11,560 Speaker 1: receptors is critical for you to have the experience in 247 00:16:11,600 --> 00:16:16,120 Speaker 1: the world that you do. These underpin your ability to 248 00:16:16,200 --> 00:16:20,000 Speaker 1: be a body moving around in the world. But for 249 00:16:20,160 --> 00:16:24,440 Speaker 1: today we're gonna talk about the other side of somatic sensation, 250 00:16:24,640 --> 00:16:28,880 Speaker 1: not monitoring the inside but touching the outside world. 251 00:16:29,320 --> 00:16:30,800 Speaker 2: So for this your. 252 00:16:30,840 --> 00:16:34,280 Speaker 1: Entire body is covered by that one giant sensory organ, 253 00:16:34,360 --> 00:16:41,320 Speaker 1: the skin. Now, this large, seamless sensory sheet is completely 254 00:16:41,360 --> 00:16:44,760 Speaker 1: packed with receptors that allow you to feel when something 255 00:16:44,880 --> 00:16:48,920 Speaker 1: or someone makes contact with you, when a nearby object 256 00:16:48,960 --> 00:16:52,000 Speaker 1: is vibrating, or when something is hot or cold. Now, 257 00:16:52,240 --> 00:16:55,680 Speaker 1: touch seems pretty simple. You just push your skin up 258 00:16:55,680 --> 00:16:58,520 Speaker 1: against something. You say, oh, that's there, and it's hot 259 00:16:58,600 --> 00:17:01,720 Speaker 1: or it's cold, or it's or it's smooth. But this 260 00:17:01,920 --> 00:17:07,520 Speaker 1: apparent simplicity masks the incredible variety and complexity of how 261 00:17:07,880 --> 00:17:12,359 Speaker 1: your brain and body do this. So let's surface the details. 262 00:17:13,000 --> 00:17:17,800 Speaker 1: So first, to detect pressure and vibration, you have a 263 00:17:17,960 --> 00:17:24,040 Speaker 1: specific flavor of sensory receptors in your skin called mechano receptors, 264 00:17:24,320 --> 00:17:27,119 Speaker 1: and these are just built of special structures that make 265 00:17:27,200 --> 00:17:32,000 Speaker 1: them sensitive to being physically stretched or bent. Now you 266 00:17:32,080 --> 00:17:35,200 Speaker 1: have different types of mechanic receptors that are different structures 267 00:17:35,200 --> 00:17:38,479 Speaker 1: and locations, and that gives you the ability to sense 268 00:17:38,640 --> 00:17:41,520 Speaker 1: and interpret a huge range of things. 269 00:17:41,560 --> 00:17:42,240 Speaker 2: In the world. 270 00:17:42,480 --> 00:17:44,520 Speaker 1: I won't go into too much detail, but i'll mention 271 00:17:44,600 --> 00:17:48,960 Speaker 1: you have some receptors which respond to fine light touch 272 00:17:49,040 --> 00:17:53,160 Speaker 1: if you're interested. These are called Meisner's corpuscles or mercle discs. 273 00:17:53,520 --> 00:17:56,280 Speaker 1: And you have other types of receptors found in the 274 00:17:56,320 --> 00:18:00,240 Speaker 1: deeper layers of the skin that respond to stronger and 275 00:18:00,400 --> 00:18:04,720 Speaker 1: cruder pressure if you're interested. These are called Piscinian corpuscles 276 00:18:04,840 --> 00:18:09,120 Speaker 1: or Ruffini's endings. Now, some of these receptor types respond 277 00:18:09,240 --> 00:18:11,840 Speaker 1: quickly right when something gets touched, but then they stop 278 00:18:11,880 --> 00:18:15,800 Speaker 1: responding if the touch remains there, and others of these 279 00:18:15,880 --> 00:18:19,760 Speaker 1: are slowly adapting, which means they keep firing if the 280 00:18:19,760 --> 00:18:24,399 Speaker 1: touch stays there. So the rapidly adapting ones are well 281 00:18:24,520 --> 00:18:27,399 Speaker 1: suited to respond to something that's going on and off 282 00:18:27,600 --> 00:18:30,600 Speaker 1: like a vibration, because they stop responding right after the 283 00:18:30,600 --> 00:18:33,720 Speaker 1: initial thing, and therefore they're ready to respond again a 284 00:18:33,760 --> 00:18:37,800 Speaker 1: moment later. But others stay firing, so you can know 285 00:18:37,880 --> 00:18:40,320 Speaker 1: when you touch your coffee cup that you're still touching it. 286 00:18:40,720 --> 00:18:42,800 Speaker 1: So the thing I want to illustrate here is that 287 00:18:42,840 --> 00:18:46,160 Speaker 1: you have this interplay of different receptor types that gives 288 00:18:46,200 --> 00:18:52,240 Speaker 1: you a very rich, multilayered sensation of touch, fine and coarse, 289 00:18:52,480 --> 00:18:56,080 Speaker 1: fast and slow. Now it's not just mechanicy receptors that 290 00:18:56,119 --> 00:18:57,680 Speaker 1: you have in your skin, but you've got these other 291 00:18:57,760 --> 00:19:02,280 Speaker 1: things called thermo receptor which tell you about temperature, and 292 00:19:02,320 --> 00:19:07,600 Speaker 1: you have separate thermo receptors for cool and warm. Now, 293 00:19:07,640 --> 00:19:10,800 Speaker 1: if this wasn't something you already knew, it's kind of amazing. Right, 294 00:19:10,840 --> 00:19:15,000 Speaker 1: You're like this sophisticated meat robot with all these sensors 295 00:19:15,040 --> 00:19:19,760 Speaker 1: packed into your skin to detect different things in the world. Now, 296 00:19:19,800 --> 00:19:23,600 Speaker 1: what these thermoreceptors do is they detect changes in temperature 297 00:19:23,680 --> 00:19:27,760 Speaker 1: on the skin surface relative to body temperature. So a 298 00:19:27,880 --> 00:19:31,320 Speaker 1: cold thermo receptor in your finger, it's going to signal 299 00:19:31,359 --> 00:19:33,600 Speaker 1: only a little tiny bit of change. When you test 300 00:19:33,640 --> 00:19:35,680 Speaker 1: the water coming out of the sink. There's going to 301 00:19:35,720 --> 00:19:38,280 Speaker 1: trigger a really strong signal when you dunk your hand 302 00:19:38,320 --> 00:19:42,440 Speaker 1: into a bucket of ice water. Now, speaking of cold water, 303 00:19:42,520 --> 00:19:46,480 Speaker 1: you've probably noticed that a cold lake feels warmer the. 304 00:19:46,520 --> 00:19:48,119 Speaker 2: Second time you dip your foot in. 305 00:19:48,840 --> 00:19:52,639 Speaker 1: Why, obviously the temperature the water hasn't changed, but the 306 00:19:52,760 --> 00:19:57,280 Speaker 1: relative temperature of the water compared to your now chilled skin, 307 00:19:58,040 --> 00:20:01,080 Speaker 1: that difference is decreased, and that changes. 308 00:20:00,720 --> 00:20:03,080 Speaker 2: Your perception of the water temperature. 309 00:20:03,560 --> 00:20:07,680 Speaker 1: They have a separate set of receptors that carry information about. 310 00:20:07,640 --> 00:20:10,159 Speaker 2: Warmth, but these cool and. 311 00:20:10,040 --> 00:20:13,959 Speaker 1: Warm receptors, they track temperature changes only to a point, 312 00:20:14,080 --> 00:20:17,560 Speaker 1: and after that there's signaling drops off and information about 313 00:20:17,560 --> 00:20:21,680 Speaker 1: things that are very cold or very hot that gets 314 00:20:21,760 --> 00:20:26,200 Speaker 1: taken over by separate receptors pain receptors, and I'll return 315 00:20:26,200 --> 00:20:28,600 Speaker 1: to those in a moment, but before we get to pain, 316 00:20:28,640 --> 00:20:31,400 Speaker 1: I just want to mention that these cool and warm 317 00:20:31,640 --> 00:20:35,280 Speaker 1: thermoreceptors can get activated by other things. 318 00:20:35,000 --> 00:20:36,720 Speaker 2: Like certain shapes of molecules. 319 00:20:36,960 --> 00:20:41,000 Speaker 1: For example, you have molecules that happen to bind to 320 00:20:41,080 --> 00:20:45,679 Speaker 1: these cold receptors, like menthol. Menthol is just a shape 321 00:20:45,720 --> 00:20:50,600 Speaker 1: that happens to activate these cool thermoreceptors, giving the pleasant 322 00:20:50,720 --> 00:20:54,960 Speaker 1: illusion of coolness. And because we generally like that, we 323 00:20:55,119 --> 00:20:58,960 Speaker 1: dump that molecule into our toothpastes and our shaving creams 324 00:20:59,240 --> 00:21:04,919 Speaker 1: to activate these cool thermoreceptors. Similarly, the active ingredient in 325 00:21:05,040 --> 00:21:09,080 Speaker 1: chili peppers is called capsaicin, and this is a molecule 326 00:21:09,119 --> 00:21:13,399 Speaker 1: of a certain shape that happens to bind to warm thermoreceptors, 327 00:21:13,680 --> 00:21:17,679 Speaker 1: and therefore it creates the illusion of heat. So capsaicin 328 00:21:17,800 --> 00:21:20,840 Speaker 1: is used in ointments that you rub on your skin, 329 00:21:21,040 --> 00:21:24,000 Speaker 1: like icy hot. Okay, so now we've talked about how 330 00:21:24,040 --> 00:21:28,159 Speaker 1: receptors in your skin detect touch and detect temperature, and 331 00:21:28,200 --> 00:21:32,200 Speaker 1: now let's come back to pain. The sensation of pain 332 00:21:33,000 --> 00:21:35,960 Speaker 1: is one that most of us would probably rather not have, 333 00:21:36,119 --> 00:21:39,919 Speaker 1: but it's actually a gift from nature that's critical for 334 00:21:40,000 --> 00:21:43,840 Speaker 1: our survival. Feeling pain is how we detect damage to 335 00:21:43,960 --> 00:21:45,480 Speaker 1: our cells and our tissues. 336 00:21:45,800 --> 00:21:47,400 Speaker 2: Now, our perception of. 337 00:21:47,440 --> 00:21:51,919 Speaker 1: Pain is mediated by another type of little receptors called 338 00:21:52,320 --> 00:21:57,440 Speaker 1: no susceptors, and what activates these is damage to the tissue. 339 00:21:57,800 --> 00:22:01,119 Speaker 1: And even though pain just seems like pain, you actually 340 00:22:01,119 --> 00:22:04,760 Speaker 1: have very different types of no susceptors. First, you have 341 00:22:04,840 --> 00:22:09,160 Speaker 1: no susceptors that are activated by physical damage to the tissue, 342 00:22:09,359 --> 00:22:13,880 Speaker 1: like caused by pressure, a needlestick, a broken bone. These 343 00:22:13,920 --> 00:22:19,040 Speaker 1: are called mechanical no susceptors. Then you have thermal no susceptors, 344 00:22:19,040 --> 00:22:22,720 Speaker 1: which respond to things that are extremely hot or extremely cold. 345 00:22:23,040 --> 00:22:26,440 Speaker 1: Then you have chemical no susceptors, which are activated by 346 00:22:26,480 --> 00:22:29,840 Speaker 1: things like spider toxins when you get bit, or by 347 00:22:30,119 --> 00:22:34,520 Speaker 1: certain cooking spices, or by poisonous gases like the kind 348 00:22:34,600 --> 00:22:38,040 Speaker 1: used as chemical weapons in World War One. Now again, 349 00:22:38,400 --> 00:22:41,840 Speaker 1: you might think that feeling no pain would be a blessing, 350 00:22:41,920 --> 00:22:43,720 Speaker 1: but how would we know whether that's true or not. 351 00:22:43,880 --> 00:22:48,720 Speaker 1: The answer is this sometimes happens because of genetic mutations, 352 00:22:49,080 --> 00:22:53,679 Speaker 1: and the inability to feel pain is a dangerous curse. 353 00:22:53,840 --> 00:22:57,159 Speaker 1: So take as an example a man who I'll call Paul. 354 00:22:57,960 --> 00:23:00,720 Speaker 1: When Paul was a child, he would push swing and 355 00:23:00,800 --> 00:23:03,520 Speaker 1: let it smash into his face. He didn't mind the 356 00:23:03,560 --> 00:23:07,520 Speaker 1: broken nose and chipped teeth because he has never felt 357 00:23:07,880 --> 00:23:12,720 Speaker 1: physical pain. He has a rare disorder called congenital analgesia 358 00:23:12,920 --> 00:23:18,280 Speaker 1: and inability to register painful sensations. By the way, congenital 359 00:23:18,480 --> 00:23:22,240 Speaker 1: just means you're born with it, and algesia means pain, 360 00:23:22,480 --> 00:23:28,680 Speaker 1: and analgesia means no pain. So congenital analgesia just means 361 00:23:28,960 --> 00:23:31,399 Speaker 1: you can't feel any pain and you were born that way. 362 00:23:31,640 --> 00:23:35,119 Speaker 1: So Paul can feel a knife cutting his finger, but 363 00:23:35,200 --> 00:23:39,520 Speaker 1: only the touch is registered, not the pain of the injury. 364 00:23:40,080 --> 00:23:43,840 Speaker 1: And because his thermoreceptors are intact, he can easily tell 365 00:23:43,880 --> 00:23:46,879 Speaker 1: the difference between warm and cool water, but he doesn't 366 00:23:46,880 --> 00:23:50,080 Speaker 1: feel the pain of things that are really hot or 367 00:23:50,119 --> 00:23:51,200 Speaker 1: really cold. 368 00:23:51,720 --> 00:23:53,080 Speaker 2: So feeling no. 369 00:23:53,240 --> 00:23:56,560 Speaker 1: Pain is a curse for someone like Paul, because pain 370 00:23:57,040 --> 00:24:00,919 Speaker 1: is critical to avoiding bodily damage. It's what tells you 371 00:24:00,960 --> 00:24:06,080 Speaker 1: about harms and threats. When Paul interacts with extreme temperatures, 372 00:24:06,400 --> 00:24:10,080 Speaker 1: he doesn't get any immediate feedback telling him to pull 373 00:24:10,160 --> 00:24:13,439 Speaker 1: his hand away or to avoid the situation. One of 374 00:24:13,440 --> 00:24:17,280 Speaker 1: his most frequent injuries as a child was burning himself. 375 00:24:17,600 --> 00:24:21,560 Speaker 1: He was interested in listening to the sizzling sound that 376 00:24:21,640 --> 00:24:25,080 Speaker 1: his skin made, so his parents were constantly forced to 377 00:24:25,160 --> 00:24:29,119 Speaker 1: take creative and desperate measures to keep their son safe, 378 00:24:29,160 --> 00:24:32,520 Speaker 1: like putting socks over both his hands and goggles over 379 00:24:32,560 --> 00:24:35,760 Speaker 1: his eyes. Often they put a helmet on him to 380 00:24:35,840 --> 00:24:38,720 Speaker 1: protect him from his regular risk of hen injury. They 381 00:24:39,119 --> 00:24:43,560 Speaker 1: constantly checked him for swelling and bruising and burns. Because 382 00:24:43,600 --> 00:24:47,120 Speaker 1: of his lack of sensation, this kind of outside inspection 383 00:24:47,320 --> 00:24:49,840 Speaker 1: was the only way that they or he could tell 384 00:24:50,200 --> 00:24:54,080 Speaker 1: whether tissue had been damaged. So much of Paul's childhood 385 00:24:54,200 --> 00:24:58,119 Speaker 1: was spent in hospitals, whether from jumping off extreme heights 386 00:24:58,200 --> 00:25:00,760 Speaker 1: or banging his head against the wall and his forehead 387 00:25:00,800 --> 00:25:05,120 Speaker 1: swelled up. So Paul is lucky to be alive because 388 00:25:05,200 --> 00:25:10,080 Speaker 1: not everyone with congenital analgesia makes it through childhood. The 389 00:25:10,240 --> 00:25:14,800 Speaker 1: moral of Paul's story is that pain is two faced. 390 00:25:14,880 --> 00:25:20,120 Speaker 1: It hurts, but it also protects, So back to normal 391 00:25:20,359 --> 00:25:25,479 Speaker 1: pain perception. Fascinatingly, you have different types of fibers that 392 00:25:25,680 --> 00:25:28,760 Speaker 1: carry these signals to the brain, and they carry information 393 00:25:28,880 --> 00:25:30,480 Speaker 1: at different speeds. 394 00:25:31,000 --> 00:25:32,520 Speaker 2: So let's say you stub your toe. 395 00:25:32,560 --> 00:25:35,200 Speaker 1: The next time you do this, try to pay attention 396 00:25:35,400 --> 00:25:39,080 Speaker 1: to the way the pain is registered, because thanks to 397 00:25:39,560 --> 00:25:45,159 Speaker 1: some fast fibers called a delta fibers, you'll register a fast, 398 00:25:45,320 --> 00:25:48,879 Speaker 1: sharp pain, and then you have these other much slower 399 00:25:48,960 --> 00:25:53,080 Speaker 1: fibers called sea fibers, and when their signals finally catch up, 400 00:25:53,119 --> 00:25:57,320 Speaker 1: you'll feel the more prolonged but slightly less intense pain. 401 00:25:57,840 --> 00:25:59,719 Speaker 1: So if you start paying attention to this, you can 402 00:25:59,720 --> 00:26:03,520 Speaker 1: start unmasking the mechanisms of your body. The last thing 403 00:26:03,560 --> 00:26:05,960 Speaker 1: I just want to note about these no suceptors, these 404 00:26:06,000 --> 00:26:10,640 Speaker 1: pain receptors, is that they're distributed throughout your skin and 405 00:26:10,680 --> 00:26:14,040 Speaker 1: your body, and your internal organs and in your joints. 406 00:26:14,160 --> 00:26:19,000 Speaker 1: But the one notable exception is the brain, which has 407 00:26:19,119 --> 00:26:25,080 Speaker 1: no suception, and that's why patients can be kept conscious 408 00:26:25,480 --> 00:26:30,159 Speaker 1: during brain surgery. I've done experiments before while a patient 409 00:26:30,280 --> 00:26:33,800 Speaker 1: is undergoing brain surgery, and I'm talking with them and 410 00:26:33,920 --> 00:26:37,160 Speaker 1: having them watch things on a screen and asking them questions, 411 00:26:37,359 --> 00:26:39,280 Speaker 1: and the patient can just sit there and talk and 412 00:26:39,359 --> 00:26:44,320 Speaker 1: provide feedback about their perceptions without feeling any pain from 413 00:26:44,320 --> 00:26:49,600 Speaker 1: the surgery itself. It's one of nature's funny ironies that 414 00:26:49,720 --> 00:26:54,159 Speaker 1: the organ that perceives pain for your entire body is 415 00:26:54,200 --> 00:27:12,000 Speaker 1: the one organ that registers no pain itself. So we've 416 00:27:12,000 --> 00:27:15,520 Speaker 1: been talking about these receptors all over the body, and 417 00:27:15,600 --> 00:27:19,080 Speaker 1: from the body, these signals come screaming up the spinal 418 00:27:19,160 --> 00:27:22,960 Speaker 1: cord to the brain, and there these signals come slamming 419 00:27:22,960 --> 00:27:25,920 Speaker 1: into a strip of real estate that we call the 420 00:27:25,960 --> 00:27:31,360 Speaker 1: primary somatosensory cortex, which is just underwhere you would wear headphones. 421 00:27:32,000 --> 00:27:34,119 Speaker 2: If you were to measure brain. 422 00:27:33,920 --> 00:27:36,280 Speaker 1: Activity along the strip, what you find is that every 423 00:27:36,320 --> 00:27:40,240 Speaker 1: little bit of it corresponds to some part of your body. 424 00:27:40,600 --> 00:27:43,399 Speaker 1: And what you find is that not all body parts 425 00:27:43,440 --> 00:27:44,920 Speaker 1: are represented equally. 426 00:27:45,040 --> 00:27:48,520 Speaker 2: Some parts have more real estate devoted. 427 00:27:48,119 --> 00:27:50,919 Speaker 1: To them, like the hands and the mouth and the 428 00:27:51,000 --> 00:27:54,840 Speaker 1: lips and the tongue, and this corresponds to their importance. 429 00:27:55,320 --> 00:27:58,639 Speaker 1: Not surprisingly, as you know from experience, you're able to 430 00:27:58,760 --> 00:28:02,760 Speaker 1: discern much more subtly touch stimuli on these parts of 431 00:28:02,800 --> 00:28:06,000 Speaker 1: your body then, say on your thigh or your back, 432 00:28:06,359 --> 00:28:10,919 Speaker 1: which have smaller representations in the cortex. Now, it's not 433 00:28:10,960 --> 00:28:15,400 Speaker 1: surprising that we devote so much brain territory to our hands. 434 00:28:15,800 --> 00:28:19,400 Speaker 1: Humans began to walk upright several million years ago, and 435 00:28:19,440 --> 00:28:24,720 Speaker 1: that freed up our hands to reach out and examine objects, 436 00:28:25,200 --> 00:28:28,600 Speaker 1: and over time that changed the importance of hands, making 437 00:28:28,640 --> 00:28:31,080 Speaker 1: them some of the most important body parts that we 438 00:28:31,240 --> 00:28:36,040 Speaker 1: have for examining the world, and so our brain changed accordingly. 439 00:28:36,480 --> 00:28:39,040 Speaker 1: The situation now is that each of our fingertips has 440 00:28:39,080 --> 00:28:43,160 Speaker 1: two thousand touch receptors in it, and they're streaming continuous, 441 00:28:43,280 --> 00:28:46,080 Speaker 1: detailed information to the brain. 442 00:28:46,640 --> 00:28:47,480 Speaker 2: The philosopher A. 443 00:28:47,560 --> 00:28:51,920 Speaker 1: Manual Kant once said, quote, the hand is the visible 444 00:28:52,040 --> 00:28:54,880 Speaker 1: part of the brain. Now, what's cool is that in 445 00:28:54,920 --> 00:28:59,920 Speaker 1: different animals, the sizes of different body parts represented in 446 00:28:59,920 --> 00:29:04,840 Speaker 1: the sensory cortex. This differs across species because different animals 447 00:29:04,880 --> 00:29:09,120 Speaker 1: rely on different sensations to survive in their niche. 448 00:29:09,240 --> 00:29:11,640 Speaker 2: So when you look at the rat. 449 00:29:11,600 --> 00:29:14,480 Speaker 1: Sensory cortex and the enormous part of the real estate 450 00:29:14,560 --> 00:29:17,600 Speaker 1: is devoted to the whiskers, because that's a huge part 451 00:29:17,640 --> 00:29:21,320 Speaker 1: of what lets the rat navigate dark spaces to find 452 00:29:21,480 --> 00:29:24,920 Speaker 1: food and avoid obstacles. Or in an elephant, there's an 453 00:29:25,040 --> 00:29:28,480 Speaker 1: enormous amount of real estate devoted to its trunk, or 454 00:29:28,480 --> 00:29:31,080 Speaker 1: in the star nosed mole, it has a lot of 455 00:29:31,200 --> 00:29:34,640 Speaker 1: territory devoted to its snout, which has these fingers on 456 00:29:34,680 --> 00:29:38,320 Speaker 1: it that feel around to construct its three D model 457 00:29:38,680 --> 00:29:41,960 Speaker 1: of its tunnels. Okay, so back to humans. We have 458 00:29:42,080 --> 00:29:46,360 Speaker 1: this strip of cortex that receives the information from the body. 459 00:29:46,960 --> 00:29:51,200 Speaker 1: That's the primary somatosensory cortex, and that neighbors these other 460 00:29:51,240 --> 00:29:54,880 Speaker 1: regions that we call the sensory somatosensory cortex and the 461 00:29:54,960 --> 00:29:59,800 Speaker 1: tertiary somatisentury cortex, and these are involved in more comp 462 00:30:00,800 --> 00:30:05,640 Speaker 1: integration of sense, like what you need to recognize objects 463 00:30:05,680 --> 00:30:09,440 Speaker 1: based on touch. This sort of higher order processing lets 464 00:30:09,480 --> 00:30:12,920 Speaker 1: you translate round and smooth into. 465 00:30:12,680 --> 00:30:14,560 Speaker 2: The recognition of an apple. 466 00:30:15,280 --> 00:30:19,080 Speaker 1: And if you get damage to these higher areas, then 467 00:30:19,120 --> 00:30:24,640 Speaker 1: you get disorders like tactile agnosia, which means not knowing 468 00:30:24,800 --> 00:30:28,960 Speaker 1: what you are touching. So if you have tactile agnosia 469 00:30:29,080 --> 00:30:31,520 Speaker 1: and I have you close your eyes and I put 470 00:30:31,560 --> 00:30:33,920 Speaker 1: a book in your hands, you feel it with your 471 00:30:33,920 --> 00:30:35,720 Speaker 1: fingers and you run your hands over it, and I'll 472 00:30:35,720 --> 00:30:39,280 Speaker 1: say what is that object? And you'll say, I don't know. 473 00:30:40,080 --> 00:30:41,760 Speaker 1: Let's say I put a cell phone in your hands 474 00:30:41,840 --> 00:30:45,360 Speaker 1: or a shoe. You have no idea what they are 475 00:30:45,560 --> 00:30:48,680 Speaker 1: when you feel them. But now I ask you to 476 00:30:49,040 --> 00:30:51,239 Speaker 1: open your eyes and look at those things sitting on 477 00:30:51,240 --> 00:30:53,600 Speaker 1: the table, and you have no trouble saying, oh, that's 478 00:30:53,640 --> 00:30:55,640 Speaker 1: a book, that's a cell phone, that's a shoe. So 479 00:30:55,680 --> 00:30:59,000 Speaker 1: it's not that you don't know what objects are, it's 480 00:30:59,040 --> 00:31:01,480 Speaker 1: that you no longer have the ability to tell what 481 00:31:01,600 --> 00:31:05,360 Speaker 1: something is simply by feeling it, simply by touch. 482 00:31:05,720 --> 00:31:06,800 Speaker 2: What I always find so. 483 00:31:07,400 --> 00:31:12,080 Speaker 1: Fascinating about neuroscience is seeing how the self breaks down. 484 00:31:12,520 --> 00:31:13,680 Speaker 2: Just think about that example. 485 00:31:13,720 --> 00:31:16,800 Speaker 1: It seems so easy and obvious that you can close 486 00:31:16,800 --> 00:31:19,360 Speaker 1: your eyes and feel something with your fingers to determine 487 00:31:19,520 --> 00:31:20,000 Speaker 1: what it is. 488 00:31:20,040 --> 00:31:21,120 Speaker 2: Of course you can do that. 489 00:31:21,720 --> 00:31:27,720 Speaker 1: What we learn from life's cruel natural experiments is that easy, 490 00:31:27,920 --> 00:31:32,560 Speaker 1: obvious things are underpinned by very complex brain networks. They 491 00:31:32,560 --> 00:31:36,840 Speaker 1: don't come for free, and when these delicate pink brain 492 00:31:37,000 --> 00:31:41,480 Speaker 1: areas get damaged, we see that the ease of doing 493 00:31:41,520 --> 00:31:45,720 Speaker 1: the task was just an illusion. The task in fact, 494 00:31:45,920 --> 00:31:49,719 Speaker 1: is massively complex, and it does not come for free. 495 00:31:50,520 --> 00:31:52,240 Speaker 2: So many of the things in our. 496 00:31:52,120 --> 00:31:56,040 Speaker 1: Life result from hundreds of millions of years of evolution 497 00:31:56,600 --> 00:31:59,840 Speaker 1: and super complicated mechanisms running in the brain that you 498 00:32:00,200 --> 00:32:05,120 Speaker 1: didn't even realize you had. Remember that the brain sits 499 00:32:05,560 --> 00:32:09,040 Speaker 1: in chambered in a dark, silent skull, and it doesn't 500 00:32:09,080 --> 00:32:11,520 Speaker 1: have direct access to any of the stuff out there. 501 00:32:11,960 --> 00:32:16,760 Speaker 1: So your skin is a highly specialized machine that converts 502 00:32:16,840 --> 00:32:22,040 Speaker 1: different types of energy mechanical and thermal and chemical into 503 00:32:22,360 --> 00:32:26,760 Speaker 1: electrical energy and sends information racing up the spine to 504 00:32:26,880 --> 00:32:28,320 Speaker 1: the cerebral cortex. 505 00:32:28,600 --> 00:32:31,120 Speaker 2: This is how we read detailed. 506 00:32:30,560 --> 00:32:36,160 Speaker 1: Information from the outside world. Okay, so we've surveyed how 507 00:32:36,280 --> 00:32:39,360 Speaker 1: touch works, and all of the incredible detail of it 508 00:32:39,480 --> 00:32:42,120 Speaker 1: might make you suspect that touch means a lot to 509 00:32:42,160 --> 00:32:45,600 Speaker 1: the brain, and you'd be right. It's fundamental. Now how 510 00:32:45,600 --> 00:32:46,280 Speaker 1: do we know that? 511 00:32:46,560 --> 00:32:46,800 Speaker 2: Well. 512 00:32:46,840 --> 00:32:50,200 Speaker 1: For example, in the nineteen fifties, a scientist named Harry 513 00:32:50,280 --> 00:32:55,760 Speaker 1: Harlow asked questions about the importance of touch to baby monkeys. 514 00:32:56,120 --> 00:32:59,560 Speaker 1: He separated an infant from its mother and he raised 515 00:32:59,600 --> 00:33:04,320 Speaker 1: it in a cage with two substitute wire frame monkeys. 516 00:33:04,360 --> 00:33:06,880 Speaker 1: These were adult monkey shapes that were just built out 517 00:33:06,880 --> 00:33:10,640 Speaker 1: of wire. Now one was bear wire but had a 518 00:33:10,680 --> 00:33:14,120 Speaker 1: bottle of milk for the infant, and the other had 519 00:33:14,160 --> 00:33:17,560 Speaker 1: no milk but was covered in terry cloth. So what 520 00:33:17,680 --> 00:33:20,680 Speaker 1: happened was the baby monkeys would drink some milk and 521 00:33:20,720 --> 00:33:23,959 Speaker 1: then they would immediately steal over to the terry cloth 522 00:33:24,080 --> 00:33:26,920 Speaker 1: mother and clutch at it for the rest of the time. 523 00:33:27,440 --> 00:33:30,440 Speaker 1: And if the babies got frightened, they ran only for 524 00:33:30,520 --> 00:33:34,960 Speaker 1: the terry cloth mother. So these studies confirmed earlier suspicions 525 00:33:35,400 --> 00:33:40,320 Speaker 1: that there was more to the mother infant relationship than nourishment. 526 00:33:41,000 --> 00:33:46,120 Speaker 1: Harlow realized that this contact comfort was essential to the 527 00:33:46,160 --> 00:33:49,840 Speaker 1: normal brain development of monkeys, and by extension, other studies 528 00:33:49,840 --> 00:33:53,440 Speaker 1: have shown how critical this is for human children. Touch 529 00:33:53,880 --> 00:33:57,480 Speaker 1: is a massively important part of the mother child interaction. 530 00:33:57,960 --> 00:34:00,520 Speaker 2: So Harlow did another experiment to under stand this. 531 00:34:00,600 --> 00:34:04,320 Speaker 1: He had infant monkeys raised in cages, and they could 532 00:34:04,360 --> 00:34:07,080 Speaker 1: see other monkeys and could smell them and hear them, 533 00:34:07,080 --> 00:34:11,200 Speaker 1: but they couldn't touch them. And these monkeys were devastated. 534 00:34:11,239 --> 00:34:14,840 Speaker 1: They cried and they paced frantically. But then when the 535 00:34:14,880 --> 00:34:17,719 Speaker 1: screen between the monkeys had holes in it, so the 536 00:34:17,800 --> 00:34:21,839 Speaker 1: mothers and babies could touch. That was enough to keep 537 00:34:21,880 --> 00:34:27,840 Speaker 1: the youngsters from developing behavioral problems. So proper brain development 538 00:34:27,880 --> 00:34:33,239 Speaker 1: in monkeys and humans requires touch. It's not optional for 539 00:34:33,440 --> 00:34:37,479 Speaker 1: a baby having loving adults interact with you and play 540 00:34:37,480 --> 00:34:39,799 Speaker 1: with you, and tickle you and comfort you in an 541 00:34:39,840 --> 00:34:43,720 Speaker 1: early age. These are all requisite for shaping the brain. 542 00:34:44,040 --> 00:34:47,560 Speaker 1: Cuddling a child isn't just something that's nice for the parents. 543 00:34:47,560 --> 00:34:52,480 Speaker 1: It's actually necessary for the child's normal brain development. So 544 00:34:53,160 --> 00:34:56,359 Speaker 1: touch shapes the brain and is the basis for a 545 00:34:56,400 --> 00:34:59,280 Speaker 1: healthy emotional life. But of course it's not just about emotion. 546 00:34:59,360 --> 00:35:03,400 Speaker 1: It's also about information. It's how we come to understand 547 00:35:03,440 --> 00:35:07,279 Speaker 1: our world and exert our own influence over it. In fact, 548 00:35:07,360 --> 00:35:10,840 Speaker 1: the way that we understand and interpret the world, our cognition, 549 00:35:11,360 --> 00:35:16,760 Speaker 1: is fundamentally rooted in our physical bodies. How things feel 550 00:35:16,800 --> 00:35:20,799 Speaker 1: to us, rough or warm or heavy. This interacts with 551 00:35:20,840 --> 00:35:24,760 Speaker 1: our thoughts and our behaviors. We build metaphors on top 552 00:35:24,840 --> 00:35:28,360 Speaker 1: of our interactions with the physical world. We say things 553 00:35:28,400 --> 00:35:33,640 Speaker 1: like that exam was rough, we say she has a 554 00:35:33,880 --> 00:35:39,839 Speaker 1: warm personality, or we say, boy, that was a heavy movie. 555 00:35:40,000 --> 00:35:42,359 Speaker 1: At the root of our language is what we can 556 00:35:42,480 --> 00:35:46,560 Speaker 1: touch and feel. This is called embodied cognition. And I'm 557 00:35:46,680 --> 00:35:49,200 Speaker 1: going to talk about this more in a later episode, 558 00:35:49,200 --> 00:35:51,680 Speaker 1: but for now, I just want to say that not 559 00:35:51,760 --> 00:35:54,560 Speaker 1: only our language, but many other sorts of judgments we 560 00:35:54,680 --> 00:35:58,480 Speaker 1: make are rooted in our bodies, even things like making 561 00:35:58,600 --> 00:36:02,560 Speaker 1: judgments about other people. Is that person warm? Is that 562 00:36:02,920 --> 00:36:07,280 Speaker 1: company competent and trustworthy? These use some of the same 563 00:36:07,440 --> 00:36:13,239 Speaker 1: brain machinery as feeling warmth or solidness and texture and 564 00:36:13,360 --> 00:36:16,840 Speaker 1: all the things our touching exploration of the world gives 565 00:36:16,920 --> 00:36:19,960 Speaker 1: us and in our daily lives. Touch serves as a 566 00:36:20,200 --> 00:36:24,080 Speaker 1: high bandwidth channel that continually moves information back and forth 567 00:36:24,400 --> 00:36:25,480 Speaker 1: between people. 568 00:36:25,800 --> 00:36:28,000 Speaker 2: It's a really powerful communication tool. 569 00:36:28,360 --> 00:36:33,000 Speaker 1: We give assurance by laying a hand on someone's shoulder. 570 00:36:33,640 --> 00:36:36,760 Speaker 1: We give kudos with a slap on the back in 571 00:36:36,800 --> 00:36:40,640 Speaker 1: an aggressive situation, we poke with a finger. In an 572 00:36:40,680 --> 00:36:43,960 Speaker 1: affectionate relationship, we move a hair out of the way, 573 00:36:44,040 --> 00:36:47,960 Speaker 1: or we nuzzle somebody's cheek. In a first meeting, we 574 00:36:48,120 --> 00:36:51,160 Speaker 1: shake hands, and sometimes we make judgments about the other 575 00:36:51,239 --> 00:36:54,960 Speaker 1: person by the firmness of their hold. In fact, people 576 00:36:55,000 --> 00:36:58,719 Speaker 1: communicate much more information through touch than we are typically 577 00:36:58,760 --> 00:37:03,800 Speaker 1: aware of. One study asked volunteers to communicate any motion 578 00:37:03,960 --> 00:37:08,200 Speaker 1: to a stranger just using touch. They were both blindfolded, 579 00:37:08,719 --> 00:37:11,680 Speaker 1: so they would try to communicate things like anger or 580 00:37:11,760 --> 00:37:18,480 Speaker 1: fear or disgust, or love or gratitude or sympathy, or 581 00:37:18,520 --> 00:37:21,640 Speaker 1: happiness or sadness. Think about how you would try to 582 00:37:21,640 --> 00:37:25,120 Speaker 1: communicate these with touch. So most people were pretty sure 583 00:37:25,160 --> 00:37:27,840 Speaker 1: they weren't going to be able to do this accurately. 584 00:37:28,160 --> 00:37:30,920 Speaker 1: But the result turned out that the other person was 585 00:37:30,960 --> 00:37:35,080 Speaker 1: able to understand the social emotion about seventy five percent 586 00:37:35,120 --> 00:37:40,319 Speaker 1: of the time. That's surprisingly good, and it underscores how 587 00:37:40,560 --> 00:37:43,640 Speaker 1: nuanced and sophisticated. 588 00:37:43,080 --> 00:37:46,160 Speaker 2: A communication channel we have in touch. 589 00:37:46,920 --> 00:37:51,120 Speaker 1: And just look at how important touches in the world 590 00:37:51,160 --> 00:37:51,880 Speaker 1: of sports. 591 00:37:52,520 --> 00:37:54,520 Speaker 2: Watch professional basketball players. 592 00:37:54,520 --> 00:37:57,520 Speaker 1: They're constantly patting each other on the back or chest, 593 00:37:57,600 --> 00:37:58,960 Speaker 1: bumping or high fiving. 594 00:37:59,040 --> 00:38:00,360 Speaker 2: What is that all about. 595 00:38:00,800 --> 00:38:03,719 Speaker 1: Well, one possibility is it's just a tradition with no 596 00:38:03,800 --> 00:38:08,439 Speaker 1: particular meaning. But some people started to wonder whether all 597 00:38:08,480 --> 00:38:12,680 Speaker 1: that human touch was about a deeper form of bonding 598 00:38:12,760 --> 00:38:15,759 Speaker 1: and therefore good for their game. So scientists at the 599 00:38:15,840 --> 00:38:20,399 Speaker 1: University of Illinois measured the amount of physical contact each 600 00:38:20,560 --> 00:38:24,640 Speaker 1: team had in the NBA. How many times did players 601 00:38:24,719 --> 00:38:27,719 Speaker 1: make friendly contact with one another on the court. They 602 00:38:27,760 --> 00:38:31,160 Speaker 1: then followed the ranking of all the teams through the seasons, 603 00:38:31,560 --> 00:38:34,840 Speaker 1: and they found that NBA teams who had more contact 604 00:38:35,360 --> 00:38:38,240 Speaker 1: did better by the end of the season. In other words, 605 00:38:38,400 --> 00:38:42,800 Speaker 1: touch seemed to predict performance across all the NBA teams. 606 00:38:43,160 --> 00:38:47,440 Speaker 1: Why well, One hypothesis is that the contact has the 607 00:38:47,520 --> 00:38:53,880 Speaker 1: effect of increasing trust and affiliation while also lowering stress hormones, 608 00:38:54,440 --> 00:38:58,000 Speaker 1: And that sheds light on a tradition in long distance 609 00:38:58,080 --> 00:39:01,560 Speaker 1: bike races. If someone is really slowing down, really out 610 00:39:01,560 --> 00:39:05,640 Speaker 1: of energy, a fellow biker will ride along beside them 611 00:39:05,680 --> 00:39:09,160 Speaker 1: and simply touch them with one finger, and their riding 612 00:39:09,360 --> 00:39:12,799 Speaker 1: speeds up. Apparently it's very effective. Just a bit of 613 00:39:12,880 --> 00:39:16,680 Speaker 1: human touch is enough to reinvigorate someone so they can 614 00:39:16,760 --> 00:39:19,880 Speaker 1: find a second wind. And it's for reasons like these 615 00:39:19,920 --> 00:39:23,839 Speaker 1: that we see bonding touch throughout the primate world. When 616 00:39:24,320 --> 00:39:28,640 Speaker 1: monkeys groom one another, they're using touch as a tool 617 00:39:29,080 --> 00:39:32,640 Speaker 1: to communicate trust and to strengthen bonds. 618 00:39:32,960 --> 00:39:34,720 Speaker 2: And across the world. 619 00:39:34,719 --> 00:39:38,160 Speaker 1: People want to keep their communication channel of touch open, 620 00:39:38,600 --> 00:39:43,120 Speaker 1: but different cultures do it differently. You've probably noticed that 621 00:39:43,200 --> 00:39:46,839 Speaker 1: people in southern climates like the Mediterranean touch each other 622 00:39:46,880 --> 00:39:50,920 Speaker 1: a lot more than people farther north. Like the Scandinavians. 623 00:39:51,280 --> 00:39:54,799 Speaker 1: Those closer to the equator, they hug, they kiss on 624 00:39:54,840 --> 00:39:56,960 Speaker 1: the cheek, they slap each other on the back, they 625 00:39:57,000 --> 00:40:00,879 Speaker 1: hold hands. Why Well, one hypoth this goes that people 626 00:40:00,880 --> 00:40:03,799 Speaker 1: who are closer to the equator, where it's warmer, they 627 00:40:03,880 --> 00:40:07,560 Speaker 1: wear fewer clothes, they have more skin exposed, and it 628 00:40:07,600 --> 00:40:10,520 Speaker 1: only pays off to touch someone if they're going to 629 00:40:10,600 --> 00:40:14,160 Speaker 1: feel it. Up north, they wear heavy clothes, and this 630 00:40:14,200 --> 00:40:18,000 Speaker 1: communication channel is essentially cut off, so it doesn't. 631 00:40:17,719 --> 00:40:19,120 Speaker 2: Get used as much. 632 00:40:19,680 --> 00:40:22,960 Speaker 1: So let's wrap up what we've seen is that touch 633 00:40:23,080 --> 00:40:26,400 Speaker 1: is a system that covers your body, and although we 634 00:40:26,440 --> 00:40:29,840 Speaker 1: take it for granted it's a massive communication channel, that 635 00:40:30,040 --> 00:40:33,160 Speaker 1: it's right at the center of our perception and cognition. 636 00:40:33,760 --> 00:40:37,959 Speaker 1: That big, beautiful sensory organ we come wrapped in tells 637 00:40:38,040 --> 00:40:40,160 Speaker 1: us so much about the physical world. 638 00:40:40,600 --> 00:40:43,440 Speaker 2: So let's come back to the effect of technology. 639 00:40:43,680 --> 00:40:48,080 Speaker 1: I'm generally optimistic about the ways that technology can connect 640 00:40:48,080 --> 00:40:52,160 Speaker 1: people across long distances, but what is not clear is 641 00:40:52,200 --> 00:40:55,760 Speaker 1: what this will mean for the basic sense of touch. 642 00:40:56,360 --> 00:41:00,080 Speaker 1: Brains need touch all throughout development. We drop into the 643 00:41:00,120 --> 00:41:04,320 Speaker 1: world half baked, and mother nature expects certain kinds of input, 644 00:41:04,440 --> 00:41:07,840 Speaker 1: and touch is a major one of those, and we need. 645 00:41:07,760 --> 00:41:10,120 Speaker 2: It as we move throughout our lives. 646 00:41:10,520 --> 00:41:13,040 Speaker 1: So in other episodes, I've talked about hearing and vision, 647 00:41:13,600 --> 00:41:17,440 Speaker 1: but what we've seen today is that the extremely dense 648 00:41:18,080 --> 00:41:21,399 Speaker 1: zoo of receptors in your skin, which pick up touch 649 00:41:21,440 --> 00:41:25,600 Speaker 1: and vibration and stretch and temperature and paint. This zoo 650 00:41:25,640 --> 00:41:30,319 Speaker 1: of receptors is one of your brain's main ways of 651 00:41:30,440 --> 00:41:33,520 Speaker 1: knowing its world. And as we move into an era 652 00:41:33,640 --> 00:41:38,000 Speaker 1: of more screens and Internet protocols and zoom meetings and VR, 653 00:41:38,640 --> 00:41:42,680 Speaker 1: we will fill our eyes and ears with the joys 654 00:41:42,719 --> 00:41:45,160 Speaker 1: of people on the other side of the planet. But 655 00:41:45,239 --> 00:41:50,040 Speaker 1: we should be careful about what this means for touch. So, 656 00:41:50,280 --> 00:41:54,040 Speaker 1: returning to the old phone company AT and T, their 657 00:41:54,160 --> 00:41:58,440 Speaker 1: slogan in the nineteen eighties was reach out and touch someone, 658 00:41:59,200 --> 00:42:01,520 Speaker 1: and I love this sentiment, but I always found the 659 00:42:01,600 --> 00:42:07,000 Speaker 1: slogan ironic because the technology of the telephone actually reduces 660 00:42:07,600 --> 00:42:11,040 Speaker 1: touch interaction. So I hope that after you've heard this 661 00:42:11,120 --> 00:42:15,359 Speaker 1: episode today, you'll think about ways to make sure you're 662 00:42:15,400 --> 00:42:19,000 Speaker 1: getting enough touch, whether from a dog or cat, a cuddle, puddle, 663 00:42:19,040 --> 00:42:22,920 Speaker 1: a friend, a lever, because our bodies are built for this, 664 00:42:23,600 --> 00:42:31,920 Speaker 1: so for real, without technology reach out and touch someone. 665 00:42:32,800 --> 00:42:35,800 Speaker 1: Go to eagleman dot com slash podcast for more information 666 00:42:35,920 --> 00:42:38,960 Speaker 1: and to find further reading. Send me an email at 667 00:42:39,040 --> 00:42:42,880 Speaker 1: podcast at eagleman dot com with questions or discussion, and 668 00:42:43,040 --> 00:42:46,239 Speaker 1: check out and subscribe to Inner Cosmos on YouTube for 669 00:42:46,440 --> 00:42:49,239 Speaker 1: videos of each episode and to leave comments. 670 00:42:50,480 --> 00:42:51,279 Speaker 2: Until next time. 671 00:42:51,600 --> 00:43:05,400 Speaker 1: I'm David Eagleman and this is Inner Cosmos