Human Senses - S1.E4 ∙ Touch
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TVTranscript
00:00Of all our senses, there's only one that actually gets us physically involved with the world.
00:13It's our sense of touch.
00:20I'm going to explore the two extremes of touch, pleasure and pain.
00:27To start with, I'm on my way to meet a man who has made a living out of one of these extremes.
00:36Circus performer Jim Rose has spent his life immersed in the world of pain.
00:42If our skin is so phenomenally sensitive, how is it possible to do something that seems as awfully painful as this?
00:54And apparently not feel a thing. I'm going to learn about this sort of pain.
00:59I've actually agreed to lay on these blades.
01:03And Jim Rose, he's going to do something even worse to me.
01:08Hi, Nige.
01:10I'm going in search of the secrets of our sense of touch.
01:25I'm Nigel Marvin.
01:27As a zoologist, I'm interested in what animals can tell us about ourselves.
01:31I'll be revealing how our sense of touch is just like an elephant's.
01:37I'm going to find out why we love the feel of something so much.
01:42And the extraordinary ability we have to control how much pain we feel.
01:46I can't feel anything.
01:47Before putting everything I've discovered to the test.
01:49There's no turning back.
01:51With the bed of blades.
01:56We use touch to explore the world.
01:59Instantly, we can tell how something feels to us.
02:03It's kind of where it's smooth.
02:05Fleeky and slimy.
02:07Sandy.
02:07Frozen and gangy.
02:09But our sense of touch does much more than just tell us what's there.
02:15Oh, it's horrible.
02:16When we feel something straight away, we know whether we like or loathe it.
02:20That is foul.
02:26There are things most of us find repulsive.
02:29That is really gruesome.
02:31Oh, God.
02:33Oh, my God.
02:33They're maggots.
02:38Strange to believe, but I think I like that one.
02:41But touching something smooth and soft feels lovely.
02:44Oh, that's very nice.
02:46I could sleep in a large mattress of this stuff.
02:51Yeah, nice and flippy.
02:53So why do we care so much about how things feel?
03:03It's just after dawn in Jodhpur in northern India.
03:07I've come to see a troop of Hanuman langurs
03:10because these monkeys hold clues to the origins of our own sense of touch.
03:15For most animals, the occasional touch is part of normal life.
03:23But monkeys adore touching and being touched.
03:27We come from a long line of touchy-feely ancestors.
03:30And for them, like us, touch is more than just simply exploring the world.
03:39These langurs spend hours and hours each day gently grooming one another.
03:44They're the touchiest of monkeys.
03:48It's not about keeping clean.
03:50Touch is how they get along.
03:52Look at those two behind me.
03:53Every part of her is being groomed.
03:56And scientists have shown that grooming actually releases endorphins into the bloodstream,
04:01endorphins, they're feel-good chemicals.
04:04So it's a stress reliever for the monkey that's being groomed
04:09and even the monkey that's doing the grooming.
04:13Grooming just about anything makes them feel good.
04:16And from our monkey ancestors, we've inherited the same strong feelings about touch
04:22and an ingenious way of telling good from bad.
04:47Buried beneath the skin, there are millions of touch receptors.
04:51And it's these that relay the sensation of touch right to our brains.
05:02Sensing what's touching us is actually a remarkable piece of detective work.
05:11Because there are no words to describe it.
05:13Because there are no specific sensors telling us whether something's wet or dry or rough or smooth.
05:23So how can we tell if it's a drop of oil or the stroke of a hand?
05:31Touch receptors only monitor basic things like pressure, temperature and minute vibrations on the skin.
05:38They feed this information as nerve signals to the brain.
05:41It's the exact combination of signals coming from the skin
05:45that allows the brain to work out what's touching us.
05:50But our sense of touch does more than just tell us what's there.
05:55Our skin is also designed to protect us from damaging ourselves.
06:01When a firm touch gets too much, it suddenly feels very different.
06:05It hurts.
06:16This is hurting because special pain receptors are firing.
06:21These pain receptors, they do nothing except scream at us when things get just too rough.
06:35Unfortunately for me, there's a lot more to find out about pain.
06:40This is just the beginning.
06:49And I have to pay you for this. No way.
06:55If we've got such a sensitive skin, how am I going to cope with the blades?
06:59If we've got such a sensitive skin, how am I going to cope with the blades?
07:06Well, back in India, there's a wonderful animal that provides a useful tip on how to avoid pain.
07:15This forest is home to a creature whose sense of touch has always fascinated me, the elephant.
07:21Hello.
07:29Much of an elephant's hide isn't very sensitive at all,
07:32just as well if you spend your life being scratched and scraped by thorns.
07:40The forest of Lampana catches on your skin, catches on your clothes.
07:44To move through stuff like this, you need a hide as tough as old boots.
07:51And that's why elephants, they're not offended if you call them thick-skinned.
07:56In fact, zoologists refer to elephants as pachyderms, which literally means thick-skinned.
08:04The Lantana thorn scrub is tearing my legs to shreds, but these elephants hardly seem to notice it.
08:12Their skin is so thick, it takes a lot to scratch an itch.
08:21Oh, just the sound of it makes me wince.
08:29But not all of an elephant's skin is so tough and insensitive.
08:37The finger-like tip of the trunk is extremely sensitive
08:41and has the highest density of touch receptors anywhere on the elephant's body.
08:47Where they're most sensitive to touch, they're also most sensitive to pain,
08:52so elephants approach things very gingerly with their trunks.
09:17We probably seem as strange to an elephant as they do to us. We look so different.
09:30The sensitivity of the elephant's skin to touch and pain varies enormously over its body,
09:35from the delicate soft snout to its thick, leathery hide.
09:39And we humans are remarkably similar.
09:47Even though every part of our body can sense being touched,
09:51there are some bits of it that are surprisingly insensitive.
10:01Using these, there's a pretty simple way to test that.
10:05But to do the experiment, I need some guinea pigs, and I need guinea pigs with a lot of flesh exposed.
10:12So I've come to Miami Beach.
10:17Hello. Hi. Since I woke you up there. Excuse me. Hello.
10:20I'm doing a science test, and we wondered if you would mind helping out.
10:25It looks like a torch device, but I'm going to try with these little pinpricks on parts of your body,
10:31and you've got to tell whether you can feel one or two.
10:34Astonishingly, some bits of your skin aren't sensitive enough to detect there are two points.
10:39You can only feel one.
10:41One.
10:43One.
10:45Unless the points are really far apart.
10:48Two.
10:50Two. You've got that. It's a long way apart, though.
10:53One.
10:55One.
10:57One.
10:59One.
11:01One.
11:03It's a long way apart, though.
11:05But your fingertips are extremely sensitive,
11:08so you can feel there are two points even when they're only a few millimetres apart.
11:13Two.
11:15Two. Two.
11:17Is it OK if I hold your boyfriend's hand? Oh, yes.
11:23Two. Two. You see, they're not very far apart.
11:27It's jam-packed with touch receptors on your finger.
11:31Can I try another part of your body?
11:33One.
11:35Or on your back and your calves.
11:38One.
11:40One.
11:45One.
11:51Two.
11:53That's outstanding. Nearly four inches apart.
11:56I was almost drawing blood there.
11:59So since we tend to feel less pain in these less sensitive areas,
12:03a tiny paper cut on your finger is excruciating.
12:08But you can cut your leg and it doesn't hurt nearly as much.
12:17So we feel things very differently across our bodies.
12:21But that's not just because of the number of touch receptors in the skin.
12:26It's also to do with how our brains monitor what's going on.
12:35As far as the touch centres in our brain are concerned,
12:38some bits of our body are massively more significant than others.
12:43In fact, if we looked anything like the way the brain sees us,
12:47it wouldn't be a pretty sight.
12:50Your extremely sensitive hands would grow to become four times their size.
13:00Your feet would be as big as your chest,
13:02and your arms would be as long as your legs.
13:06Your feet would be as big as your chest,
13:09and half of their length would be your toes.
13:12No wonder they're so ticklish.
13:18Your super-sensitive face would end up bigger than your chest and back.
13:28And as for your lips, there's as much as your nose,
13:32and as for your lips, there's as much brain space given to them
13:36as the whole of the rest of your face.
13:39They'd put Mick Jaggers to shame.
13:45Your tongue would be as big as your already oversized hands.
13:51Put all this together, and you'd have a body
13:54even a mother would find hard to love.
14:02So because we feel things so differently in different areas of our bodies,
14:06things are always going to hurt a lot less on your back and your legs.
14:13And as for your feet,
14:15things are always going to hurt a lot less on your back and your legs.
14:27Which is great news if I'm going to lie on the bed of blades.
14:31But there's something else about our sense of touch that could also help me.
14:37Sometimes we completely ignore the touch signals coming from our bodies.
14:42It happens all the time.
14:44You don't notice your clothes touching your skin.
14:47It's amazing how little we sometimes feel.
14:53Mark Mitton is a magician who claims he can remove someone's watch
14:57while doing a card trick.
14:59You want to see a quick trick?
15:00Without their feeling a thing.
15:04Are you at all interested in seeing some magic?
15:07The most psychic among you.
15:08Who's the first I can read by?
15:09A little card trick, is that cool?
15:12I want you to name a card.
15:13It's going to appear right here.
15:15Any card you want.
15:16Whatever you want.
15:17Eight of spades.
15:18Four of diamonds.
15:19Six of hearts.
15:20Ten of diamonds.
15:21All right.
15:22And grab it by the wrist.
15:23I want you to name a card.
15:24It's going to appear right here.
15:25Hold them really tight so there's no way I can get off the cards.
15:27It's going to appear in my hand on the count of three.
15:29Seven of spades.
15:30Seven of spades.
15:31Look at his right hand.
15:32I'm going to do it right now.
15:33Really bear down.
15:34I can't cheat.
15:35And yes, there goes the watch.
15:37Right there.
15:38Look, look, look.
15:39Amazingly, no one misses the fin of the watch strap on their skin.
15:43And inside my hand, look.
15:45Look.
15:46Five of diamonds.
15:47Five of diamonds.
15:48Look inside my hand like this.
15:49There.
15:50You see it?
15:51Inside my hand.
15:52You can see it right there.
15:53Oh, shoot.
15:54But something very strange happened.
15:55Did you see it?
15:56No.
15:57What did you do?
15:58Look at my hair.
15:59I didn't get your...
16:00Seriously, there's something.
16:01You see that?
16:02Oh, my God, my watch.
16:04Ten of spades.
16:05Seven of spades.
16:06I'm going to do it right now.
16:07Something more important seems to be happening elsewhere.
16:10Your brain chooses to ignore some touches.
16:13I forgot.
16:14We have a gift for you.
16:15Okay?
16:16It's a special gift.
16:18Oh, my watch.
16:21You got my watch.
16:22You're nuts.
16:23You're so crazy.
16:24Oh, my God.
16:25You're so psycho.
16:26It's not fitting my watch.
16:29Isn't that weird?
16:30Yeah.
16:32How about this?
16:33That's my watch.
16:37Yeah.
16:43You're good.
16:45So if we can tune out gentle touches,
16:48what about more intense sensations?
16:50Can our brains alter how much pain we feel?
17:02Professor Tony Dickinson has devised an experiment
17:05using electric shocks.
17:07If we're expecting something to hurt,
17:09will it feel more painful?
17:16Half the volunteers are given a tablet
17:18that they're told will make them feel more pain.
17:21Actually, it's just sugar.
17:27They feel pain even at low levels
17:29because they're expecting the shocks to hurt.
17:36Ow.
17:39The rest of the volunteers are also given a sugar pill,
17:42but they're told it's a pain killer.
17:52They're hardly bothered by the low-level electric shocks.
17:58And even when the dial is cranked right up,
18:00the group who think they've taken a pain killer
18:03can still cope.
18:06The suggestion that the pill will make them feel less pain works.
18:11Pretty good, aren't they?
18:15But the volunteers who think they're on a pain booster
18:18react very differently.
18:20Argh! Argh!
18:21Stop.
18:24They're actually feeling a lot more pain.
18:26That's the shock.
18:30Ooh! Ow!
18:32So we showed that expectation had a marked effect
18:36on the amount of pain that these two groups felt.
18:39So in the group who'd been told they had a pain killer,
18:42they could put up with much greater electrical shocks.
18:46The other group, where we told them that the pill they'd taken
18:50was going to increase the amount of pain that they would feel,
18:53in that group, they called a halt very early on in the series of shocks.
18:58It's all down to the power of expectation.
19:02If you think something's going to hurt,
19:05then the chances are...
19:07Stop! Stop! Stop! Stop! Stop!
19:09..it will.
19:10Ow!
19:12Ow!
19:13I can cope going higher. It's not nice, eh?
19:17Without even knowing we're doing it,
19:19we can control the amount of pain we feel to a tremendous degree.
19:34So if I put my mind to it,
19:36could I actually tell them that I've got a pain killer?
19:41So if I put my mind to it,
19:43could I actually take an experience that I know should really hurt,
19:48something as extreme as this...
19:57..and make it feel as pleasant as this?
20:11Ooh!
20:17Before I'm ready to lie on a bed of knife blades,
20:20I want to learn more about controlling pain with my mind.
20:33So I've come to Stanford University in California
20:36to meet a world expert in hypnosis.
20:40Professor David Spiegel.
20:43He's studying how hypnosis can sometimes help reduce chronic pain
20:48that can't be treated with drugs.
20:52So if anyone can help me control pain, he should be the man.
20:57David, I mean, what is hypnosis?
20:59Hypnosis is a naturally occurring state of highly focused attention
21:03coupled with physical relaxation.
21:06People go into it all the time, every day.
21:08When you're in a movie and you get so caught up in the movie
21:11that you start to think it's the real world.
21:13So, I mean, I'm not sure what you're going to do to me,
21:16but I shouldn't feel any pain at all?
21:18You shouldn't feel any pain at all,
21:20or what you feel shouldn't seem to matter very much to you at all.
21:25Once I'm hypnotised, David is going to stick pins into my hands.
21:30So get as comfortable as you can.
21:32The aim is to block pain in just my left hand
21:35by imagining it's in numbingly cold water.
21:38I want you to imagine that your left hand is dipped into a bucket of ice water.
21:44My right hand should be totally unaffected.
21:47I'm feeling that, yeah.
21:49OK, so now we're going to see how your hand feels
21:53when we test this sense of pleasant, cool, tingling numbness.
21:58How's your hand feeling now?
22:00It's perfect. Have you stuck the needle in?
22:02Oh, yes, it's been in. Yes.
22:04No...
22:06I can't feel anything at all.
22:10Hypnosis actually changes what happens in the brain.
22:14Normally, the pain signals from my hand would activate two areas.
22:18One, which tells me my hand is numb,
22:21and the other, which tells me it's not.
22:24Hypnosis can activate two areas.
22:26One, which tells me my hand's hurting,
22:29and the other, which controls how painful it feels.
22:33Hypnosis is blocking the pain
22:35by reducing the level of activity in both these brain areas.
22:41So what does it feel like in your left hand and arm? Any discomfort?
22:44It still feels lovely.
22:47Now we're going to see how it feels in your right hand.
22:51Ouch.
22:53Take that out, that's really...
22:55Take that out? OK.
22:57God, a shooting pain up the arm when you...
23:00Sorry. How is it now?
23:02Yeah, it's better.
23:04All right, so now we're going to remove the needles out of your left hand.
23:09Out they come. Do you feel anything now?
23:12No, I feel nothing at all.
23:15Deep breath.
23:17Come out of the state of self-hypnosis.
23:19Three, two, one.
23:23Wow. Did you really?
23:25Oh, yeah.
23:27Oh, yeah.
23:28Extraordinary. I feel like there should be blood gushing out of my hand.
23:32You can't believe it? You really didn't feel it in here?
23:35No, not at all.
23:36Can I do this without you being next to me?
23:38Absolutely.
23:39It's a combination of learning how to get into the state
23:43so that you master your own hypnotic ability,
23:45and then learning a strategy to use to help yourself deal with the pain.
23:49And that you can learn to do all by yourself.
23:52So back to my challenge.
23:54Jim dropped a cannonball on his wife while she was lying on a bed of blades.
23:59But for me, he's thoughtfully lined up something else.
24:03Jim, you're going to smash this breeze block on my chest.
24:08I'm going to come down on it. I'm going to hit once.
24:10You'll feel that, trust me.
24:12Okay, I'm going to come down two.
24:15You're going to feel that, trust me.
24:17And then I'm going to come down on it like Hal.
24:22And then it's over, my friend.
24:24We're helping you up, and you're going to get a standing ovation.
24:27You can do it, Nigel. I've got faith in you.
24:30If you really don't want to get hurt, get someone else to do it.
24:34Find a volunteer, Nigel.
24:36Thanks, Jim.
24:39I'm armed with all the knowledge I should need to cope with the pain.
24:43I know that lying on my back will be better because it's less sensitive.
24:47And that expectation has a lot to do with the amount of pain we feel.
24:52And that despite our keen sense of touch,
24:55we can sometimes dramatically reduce the amount of pain we feel.
24:59Eyes relaxed, but keep them closed and let your body float.
25:04And ultimately, if I can relax and focus on something else,
25:08then being hit with a sledgehammer should be a breeze.
25:15Jim, the stage is ready. It's the moment of truth.
25:18Now, any final tips before I have to go through with this?
25:21You're going to feel the click.
25:23You're going to feel the second click.
25:25The third one, man, that's the big one.
25:29Don't be there when it happens.
25:32All right, good luck, Nigel. Get everything ready.
25:35Ladies and gentlemen, what you're about to see...
25:38I've seen Jim's wife do it, so logically it should be safe.
25:41I know there's not many pain receptors in my back.
25:44And I'm pretty good at putting myself in another place.
25:47I've been thinking about those warm waters, swimming in them all day.
25:51Ladies and gentlemen...
25:53There's no turning back.
25:55The amazing Nigel!