MS. MARIA HINOJOSAHello. And thanks for joining us. I'm Maria Hinojosa. I'm the anchor of NPR's Latino USA and I'm sitting in for Diane Rehm. So I was raised in a family where one of the things that was never denied was a hug. And every time I got a hug, it made me feel really good. But it turns out, there's a science to that. Our sense of touch is rooted in complex and the counterintuitive system of circuits that interact to affect how we experience life and relationships.

MS. MARIA HINOJOSAJohns Hopkins University neuroscientist David Linden explains how touch is very different from our other senses, how it affects pain and emotion, yes, why hairy skin is critical and also why we can't tickle ourselves. The book is titled, "Touch" and "The Science of Hand, Heart and Mind." It's out in paperback and David Linden it's so great to have you in the studio.

MR. DAVID LINDENThanks for having me.

HINOJOSASo the science. You begin the book, actually, by recalling a memory of you being a teenager and playing this game, I think I remember it, would you rather, you know, kind of like what would you rather lose, right?

LINDENAbsolutely.

HINOJOSAAnd the question came up as to -- which I thought was a really interesting question for high schoolers to ask, what sense would you rather lose. And lead you onto this kind of discovery.

LINDENIt did. And the way it was phrased is, if you could only maintain one of your senses, which one would you keep? And what struck me in that time, we were all, you know, amped up, excited, sexually emerging teenagers and we were all obsessed about touch in our day to day life. But no one ever said touch is the sense I would keep. People would say I would keep vision 'cause I have to see the world or I have to experience music or communicate. And I think it left me confused.

LINDENWhy was touch so central to our experience, but it never occurred to us to keep it in this game? And I think part of the reason is that you can close your eyes and imagine losing sight and you can plug your ears and imagine being deaf, if you're not. But you can't turn off your touch. And so you take it for granted.

HINOJOSAI tried to do it last night. I was like what would it be like if I couldn't touch and then actually I felt really, really sad. I want to let you know that if you want to join our conversation, and we're very interested in the stories that you can tell us about how touch has changed your life or revealed something to you, the number to call is 800-433-8850. You can also email us at drshow@wamu.org or Facebook us or Twitter -- or Twitter us, no. But touch us with your messages. We're really interested.

HINOJOSASo, you know, again, when I think back to the most comforting moments in my life, and even now with my own daughter and son, and I'm so happy they do this, they will say, mama, (speaks foreign language) give me a hug. And I never thought of the kind of scientific restorative power of it. What is the power of touch and why is it so important?

LINDENIt turns out that it's not just something nice and a little cherry on top of our human experience. It's absolutely critical. So, for example, a baby can be born without sight and have a rich and fulfilling life and can be born without hearing and have a rich and fulfilling life. But if you're born with functional touch, but you don't receive loving touch as a baby and a toddler -- and this is what happened, for example, in Romania and the Ceausescu regime in the '80s and also afterwards in the early '90s and these grossly understaffed orphanages, then a disaster unfolds.

LINDENThese children have cognitive impairments, emotional impairments, attachment disorders and it's not just psychiatric and learning problems. Actually, their bodies don't develop properly and they have problem with their digestive system and their immune system.

HINOJOSAAnd I got to tell you, when I was reading that, I was like, how can you actually prove that? Like, if they were abandoned and not touched, they probably had all kinds of other issues that they were lacking. And I was like, how can you just pinpoint it to the lack of touch?

LINDENWell, you're right. It's not a laboratory experiment at what's happened in life. But the reason that we believe that the touch is what's crucial and not other things like getting enough food, are that a certain fraction of these kids, there was an intervention. There were volunteers who came in to touch them, even for a half an hour a day, in a loving way. And that alone seemed to be sufficient to rescue both the psychiatric and the somatic deficits that these kids had.

HINOJOSASo I actually -- we're going to go to a caller a little bit early. His name is Chip from San Antonio, Texas. So Chip, you're on the air.

CHIPHi. Thanks for taking the call. The question about sensations that you would -- or what senses you would choose to lose, the game around here when we were growing up if you only had air conditioning for one part of your body, what would it be? And oddly enough, what we found was, through, you know, years of argumentation that everybody wanted their feet to be cold.

LINDENThat’s interesting.

HINOJOSASo thank you for that, Chip. You know, when I think of touching someone's feet who are -- which are cold, or their hands, it's not a nice sensation.

LINDENNo. No, it really isn't. It can be a bit clammy. I think this does segue into something important, though, and that is we think of touch, we experience it as a unified sensation. It's all kinds of different information coming in from our skin. But if you're to actually look in the skin, you would see that there are lots of different specialized sensors. There are ones that are specialized for pressure and texture and caress and sexual touch and heat and cold and pain. All of them are different, but all of that information feeds into the brain where it activates both what we call discriminative centers, that is, just the facts, where in my body am I being touched, how strong is it and what's the quality of that touch, and also emotional centers.

LINDENAnd these are the centers that make pain feel bad and make caress feel good or make sexual sensation feel good.

HINOJOSAIs it about our fingertips? Is it about the fingertips? Because, you know, I'm thinking like, well, I guess when you walk, you know, you've got extraordinary sensation on your feet, you know, thinking about walking on a beach with rocks or the difference with sand. But is it something very particular about our fingertips?

LINDENSo the fingertips are a special place. So there are certain places like the fingertips and the lips that are very sensitive and they're sensitive in a particular way. They have an ending called a merkel ending and this is what allows you to detect fine tactile form. So, for example, if you want to read Braille dots, you can do it fine with your fingertips and you can also do it with your lips. Now, you might...

HINOJOSAWait a second. You're saying that if I -- I could learn to read Braille by putting it up to my lips? Or if I know Braille and I put it up to my lips, I'll be able to read it.

LINDENNo, you could learn Braille on your lips for the first time if you needed to. And people who don't have control of their arms who are also blind will do this. You can learn Braille on your tongue as well and that's because it has a high density of these special merkel endings. Now, there are other places in our body that we think of of being very sensitive, like the cornea of the eye, for example, or the genitals. And they're sensitive in the sense that you detect a very find deflection of the skin there, but you don't know exactly where it is.

LINDENLike, if a piece of grit gets in your eye, it hurts like crazy, but you don't know exactly where in your eye it is. And if you try to read Braille with your genitals, either male or female, it's going to fail. It won't work. Your listeners can go to the ATM when no one's around and do an experiment, if they like, but I'll tell how it's going to happen.

HINOJOSANo. So we're, you know, taking a moment, kind of having a light moment here in the conversation of touch. But one of our callers, actually, Paul from Mint Hill, North Carolina, has a different experience regarding touch. Paul, you're on the line.

PAULGood morning.

HINOJOSAGood morning.

PAULYeah. Unfortunately, for those of us on the autism spectrum, touch is not necessarily something that really gets us excited. You know, if a stranger comes up and embraces us, it really is uncomfortable and it's something that we certainly don't seek out. I used to work in a store where I had a co-worker who, the first time she saw you in the course of the day, she'd give you a hug. And everybody else that worked there just thought this was great and excited. I would do my best to avoid her so that I would not have to do that.

HINOJOSAThank you. Thank you for bringing this up, Paul. What do we say to those people who actually, yes, in some cases, have a not-so-good reaction and some that actually have an aversion to touch?

LINDENWell, we should say there's nothing wrong with you. There's nothing intrinsically wrong or shameful in having an aversive response to touch and we should embrace what we call neuro diversity in that sense. And it's absolutely true and well established that people on the autism spectrum often are aversive to touch, particularly light touch. Now, interestingly, if you look at the nerve endings in the skin of people with these conditions, you can't see anything different if you just looked under a microscope at a biopsy specimen.

LINDENSo it's something in the brain, but we don't actually understand the basis of that. The other thing that is related to this that I think is very important is that there are enormous cultural differences in touching. So there was an anthropologist named Sidney Gerard in the 1960s and he would spy on couples in cafes around the world. Not just romantic couples, but coworkers, friends, what have you. And when he looked in San Juan, Puerto Rico, he would see -- people would touch each other on the average 200 times an hour.

LINDENAnd, in Paris, about 30 times an hour and in New York, three times an hour and in London, zero times an hour. So there is no right or wrong about when and how frequently people should touch. This is something that's culturally constructed.

HINOJOSAAnd we're having a conversation about touch and the neuroscience of touch with neuroscientist David Linden. The name of his book is "Touch: The Science of Hand, Heart and Mind." And coming up, we'll continue our conversation.

HINOJOSAWelcome back to "The Diane Rehm Show." I'm Maria Hinojosa of NPR's Latino USA and I'm sitting in for Diane and it's my honor. We're having a conversation with David Linden, a professor of neuroscience at Johns Hopkins University School of Medicine. His book, now out in paperback, is "Touch: The Science of Hand, Heart and Mind." And you can call us at 800-433-8850. But so I want to ask you something, David.

HINOJOSAWe just got a couple of emails, which I really love. This one from Jared. "Is it still important to hug that teen that recoils with the idea of a loving embrace?" We'll talk about that in a second. I say yes. Email from Anna. "Are you aware of the highly sensitive person and are people born particularly sensitive to touch or is it all learned?" So let's start with Jared. How about that hugging of the teen?

LINDENWell, this is a great question. I think that many parents recoil from hugging their teen not so much because the teen doesn't want it because as they become pubescent, they feel like that perhaps it's not appropriate or they're conflicted or embarrassed and I think the bulk of evidence these days says, keep hugging your teen, that it's a good thing to do. I mean, generally speaking...

HINOJOSAIn private, maybe.

LINDENIn private and, of course, appropriately and, of course, with an eye towards the individual. But social touch is glue. It builds bonds of trust and cooperation and it does it in the family, it does it in the workplace, it does it on sports teams when people do high fives and chest bumps and pats on the rear end. It is just good for social interaction.

HINOJOSAAnd it's interesting because as a journalist, I actually learned from one of the great journalists of our time, Scott Simon, as a young producer when I was watching him. And, you know, when you say context is everything, of course, as a journalist, context is everything, but there were moments when I was with Scott that I would see that he would touch. And it was very powerful in terms of what it did with the person that you're interviewing to let them, as you said, it communicates something.

HINOJOSAAnd I, as a journalist, and I mean, I've been with soldiers suffering from PTSD, which I once experienced, and my natural reaction is I'm going to take your hand. Talk about the issue of touch when you're in a professional setting and how that works when you're a journalist or you're a medical doctor or you're a professor.

LINDENWell, obviously, it's very fraught and you want to be very careful. I don't want to come off as saying, in every setting you should just touch people as much as possible because there are lots of individuals who don't respond. There are power dynamics you want to be aware of. I think the important thing to realize is that our experience of touch is not just based on the physical aspect of the touch alone. And so what I mean is imagine an arm around your shoulder. That arm around your shoulder, with the exact same force and pressure and place on your body, could feel entirely different if it's from an overbearing boss or someone expressing sexual interest that was unwanted or a good friend or your sweetheart or your sweetheart but in the middle of an argument where it's unresolved, every time I would feel different.

LINDENAnd the reason for that is because the part of your brain that's experiencing the physical facts of the touch is having the same activity, but the other part of your brain, called the posterior insula that is taking the social context and blending -- and the expectations and blending that with the facts of the touch can have very, very, very different activity.

HINOJOSAAnd what about the issue of cultural difference, you know? I was thinking how, in Latin America, in some place, you kiss twice. In some places, you kiss once. In some places outside of Latin America, you kiss three times. You know, sometimes there are, after one or two meetings with someone, you would actually give them an (speaks foreign language) a hug when you meet them.

HINOJOSAWhat about the cultural differences and how this played into your research around touch?

LINDENWell, these cultural differences are very important. There are lots of places in the world where it would be a gross violation of social norms to kiss or hug at all, same sex or opposite sex.

HINOJOSAOr touch. Right, or even touch. I remember when I was at the United Nations as a young reporter and I reached out my hand to someone from the Iranian government and it was like, no. And I felt bad, but I shouldn't have, right?

LINDENWell, you shouldn't have 'cause we have to be respectful of everyone's cultural norms. If they refuse to touch you, it's not because they're expressing dislike or revulsion, it's just they're operating within their own context. What's interesting to me is that even though there are all these enormous cultural differences that you've pointed out, there are also some things that are very, very similar.

LINDENSo, for example, when you give someone a caress on the arm, it turns out there's an optimal speed and pressure for that caress to feel good. If you skim your fingers over the arm really fast, that doesn't feel loving. And if you make a crawl, slowly like a bug, that doesn't feel loving. But if you move it about one to two centimeters per second, that does. And you might think, well, is that culturally constructed? No. It's not even constructed in the brain.

LINDENIt's because the nerve endings in the skin that wrap around the hairs in the arm that are special caress sensors are tuned to that speed of touch.

HINOJOSAHave you ever heard of a term called sobradora (sp?) ?

LINDENNo.

HINOJOSAIn Mexico, to sobrar is actually not to caress. It's another thing that is a healing touch and actually there are sobradoras that are not massage therapists. They're just actually touch therapists and they have a name, sobando (sp?) . But I actually want to go to James in Jacksonville, Florida. James, you have a particular issue around touch and feeling. Go ahead.

JAMESYes. Thank you for taking my call. One of the other sides of the spectrum is I have Charcot-Marie-Tooth Syndrome, which is a nerve degeneration. It's in the muscular dystrophy family. I have a neuropathy where I can't feel from my elbows to my fingertips or my knees to my feet so for instance, if I'm holding a cup and I look away, I'll look back and my hand will still be in the same position, but I'll have dropped the cup because I didn't realize I let go of the tactile strength.

HINOJOSASo how does James fit into the work of touch and how important touch is, if there's no sensation?

LINDENWell, so much of what we rely upon, like James mentioned about touching the cup, it happening on a subconscious level. In other words, if I reach right now and grab my coffee cup and bring it to my lips and take a sip, all the details of exactly how I should accelerate and decelerate my arm and how much strength I should use to grab the cup, to not have it fall and how I should bring it to my face, those are all things that I don't have to think about actively. They operate subconsciously, but they're all absolutely dependent upon a continual stream of touch information from sensors in the skin, to some degree in the muscles and also then in the lips.

LINDENAnd when these are gone, either through this kind of disease, when they are lost as they are gradually lost in aging or when certain classes of them are gone in genetic diseases -- for example, there's a genetic disease where you lose all your pain sensors and nothing else -- then there can be substantial impacts on the quality of life.

HINOJOSAShannon from Houston, Texas, has a particular way of having to use touch in the work that she does in hospice. Shannon, joining us from Houston, go ahead.

SHANNONYes, I was just struck by the notion that working with infants and the need for touch in development at that point in life and being a hospice social worker, I work with people who are typically older or facing end of life and we find if those patients are not able to verbally communicate that touch therapy actually is quite a good way to reach them and to be able to enhance their quality of life and so we often use touch therapy in our practice.

HINOJOSAWhat do you think about that? And thank you, Shannon for you call. You know, the notion that if somebody is in hospice in their last days, having someone resting their hand or having some kind of physical touch is important and, at the same time, having recently experienced this, one of the nurses said, you know, it's also a little bit strange because you don't want to be touching someone the entire time. Like, also give that person a break. So a happy medium there?

LINDENWhat I would say is I agree completely with the caller that touch in a hospice situation is enormously beneficial. And we now have lots of studies showing that it improves quality of life, it extends life, it reduces medical complications, but I would say that its benefits in old age is not restricted to hospice at all. People, later in life, a lot of times, they've lost a partner. Sometimes they live apart from their children and so the sort of touch that they would normally have, if they normally had a touch-filled life, the opportunities for that are reduced.

LINDENAnd when that happens, it makes us depressed and it cuts us off from a stream of our humanity. And so it's very, very well established that even casual touch, like getting a haircut or having a massage from a stranger or even you touching a pet, when they bring dogs into retirement communities, for example, there's an enormous psychological and health benefit from that. So yes, as we age, touch is crucial and we have to counter it because everyone, as they age, starting at about age 20, you lose about 1 percent of your touch sensors in your skin every year of your life.

HINOJOSAOh, boy. Well, that -- I wasn't -- no. Oh, I didn't remember reading that. That's kind of sad. But to the other extreme, a mother's touch. I remember saying to a friend of mine just recently who's about to have a baby and I said, you know, that moment when you're nursing is kind of unfettered touch between you and your child and there's nothing that can kind of replace that. What is the science of the power of a mother's touch?

LINDENWell, we know, for example, there's a great story and this happened in Columbia in the 1980s. There was a very poorly equipped hospital there and the premature infants were dying at an enormous rate. They didn't have incubators that were functional. And the doctors there said, you know, what you should do is take these preemies and lay them on the mother's chest without a shirt, without a hat, with as much skin to skin contact as possible.

LINDENAnd their idea was really just to keep the child warm, but it turns out that most of the benefit comes from the touch sensation. And this became called kangaroo care and it is now the standard therapy not just for preemies, but for all newborn. We now know when a baby is born, what you do is you lay the baby on the mother's chest. You lay the baby on the father's chest. And it's not just women, even though men can't breastfeed, they can get in on this tactile bonding.

LINDENAnd we know that this is the most crucial time for developing healthy attachment.

HINOJOSAWas there a time in our history when touch was what you didn't do and you just did not? I'm thinking actually, "Downton Abbey," you've been watching it, you know, the rare touching that happens there.

LINDENIt's true and it wasn’t just in England with the upper class. So in the 1930s in the USA, there was a psychological movement called behaviorism. And the founders of behaviorism believed that you should not coddle your children, that you should just raise them with completely rational precepts and they said, don't touch them, don't hug them, don't kiss them. If they've done a really good job, you maybe -- you can give them a little pat on the head at the end of the day. And this was terrible child raising advice and I'm glad it's mostly gone.

HINOJOSAAnd I want to let you know that my name is Maria Hinojosa. I'm the anchor of NPR's Latino USA, but you are listening to "The Diane Rehm Show." And if you'd like to join us, call 800-433-8850 or send us an email to drshow@wamu.org. Let's take another question. This is from Solon, Ohio and our caller is Denise. Denise, go ahead.

DENISEYes, thank you for taking my call. My question is, it's a little strange. My husband's a marathon runner and so as a runner, he shaves his legs, he shaves his body parts to, you know, glide better in the air kind of a thing. And it's very unnerving to me to feel that smooth skin. It's creepy. And I wonder if there's anything about that.

HINOJOSAThe creepiness. Answer that question for Denise, Doctor.

LINDENWell, I think this is something, I mean, individual. In other words, you were used to him having body hair and now the hair is gone and so it feels odd. I think if your partner had been someone with little body hair, maybe you wouldn't have felt this. I think the more interesting thing is what is his experience like because when you shave your hair off, your hairs are what you rely on for a lot of your tactile sensation. So these special caress sensors that are so important for social touch, they're only found in hairy skin.

LINDENAnd I should mention hairy skin is everywhere on your body, except the palms of your hands, the soles of your feet, your lips and part of the genitals. Everywhere else, even, like, a woman's cheek has tiny hairs on it if you look carefully, or the inside of an arm has tiny hairs on it when you look carefully. And when you remove those hairs, you're depriving yourself of some of your touch input. And we actually know fairly little about what the consequences of that are.

HINOJOSAAll right. So Tim from Celina, Ohio, wants to bring up a question about dads and touch. Go ahead, Tim.

TIMSure. It's more of a comment than a question, but I've just experienced -- I have two boys and the way that we, you know, touch a lot is just through wrestling and physical activity and, you know, I've noticed when I'm gone for a week for work or something and when I come home, my boys are just really eager to wrestle, you know, to basically, you know, it's a way that we touch each other and engage in physical touch. And it's something that they really notice when they miss out on that.

HINOJOSAThank you for your call.

LINDENYes. It's absolutely true. They are looking to reestablish their bond with you in this tactile way and, of course, this isn't just a human thing, right? You see kind of wrestling play in all kinds of -- particularly all kinds of mammals. There was a great study that was done in the national basketball association by a group at UC Berkeley. And what they did is they looked at every game played in the first half of the NBA season by all the teams and they scored all the celebratory touch, the pats on the rear end, the chest bumps, the fist bumps, the high fives and then they looked to see how those teams then played in the second half of the season.

LINDENAnd what they found was that the teams that did the most celebratory touching not only won more games later, but they played in a less individualistic fashion. They didn't -- the star players didn't hog the ball as much. They would pass off more. They would play in a more cooperative team strategy.

HINOJOSASo you write about how we have touch maps. Touch maps? What is a touch map?

LINDENA touch map means that if we were to look in your brain in the part where ultimately the signals from the nerves all over your body come, that there would by a map of your body surface. And that is, there's a place where we could say, oh, here are the neurons that are responding to touch on your face and here on your lips and here on your fingertips. But, of course, some parts of your body have a lot of touch sensors, like your lips and your fingertips, and other ones have very few, like the small of your back.

LINDENSo this map doesn't look like a normal person. It looks like a very distorted person with gigantic representation for those areas that have a lot of touch sensors.

HINOJOSAWe are talking about "Touch: The Science of Hand, Heart and Mind" with David Linden. And coming up, your calls and more questions. Stay tuned.

HINOJOSAAnd welcome back to the Diane Rehm Show. My name is Maria Hinojosa. I'm the anchor of NPR's Latino USA, and I'm sitting in for Diane Rehm. And we're speaking today about touch with David Linden, the author of "Touch." David, we're getting a lot of wonderful response from our listeners, and I just want to read a couple of emails to you, okay?

HINOJOSAFrom Dennis in Texas, I find hugging someone I love is a wonderful feeling while any touching of someone I can't stand is actually painful. Okay. Email from Tracy. "I'm a recently abandoned wife. Though I would never reconcile due to a spouse's immoral actions, it is the touch of a spouse that I miss terribly. Does this make sense?" And from Tim, "I'm a violinist, a pianist and a music teacher. What insight might you provide about the use of touch in refined, disciplined settings, for example in music making or other artistic endeavors?"

HINOJOSAAnd a tweet from Katie. The everyone-needs-seven-significant-touches-per-day meme, is that real?

LINDENWow, there are so many there.

HINOJOSAI know, I put it in front just in case you want to -- yeah, a lot of...

LINDENI don't think there's anything magic about the number seven. I would say 700. So I agree with the spirit of it. Significant touches, socially appropriate touches in the day from your co-workers, from your family, from your friends, from your sweetheart, they're all good, and they make your life better. In terms of the question from Tim, the violinist, this is really, really interesting because we know that people who play musical instruments, so if you play the violin, for example, your fingering hand, that representation in that touch map that we spoke about earlier, it will get larger over years of practice, not your bowing hand but your fingering hand as a result of not just using that touch but having to attend to that touch very, very carefully.

LINDENWe know for example that in mother rats, the representation of their nipples in the touch map expands while they are nursing, and then when they are done nursing their pups, the representation of the nipple compresses again into its pre-pregnancy state. So your brain is changed by your touch experience and in really intensive situations like playing a musical instrument at a professional level, it can be changed in a very profound way.

HINOJOSAAll right, so I'm going to do a little experiment with you because you walked into the studio, I actually walked in when I first met you, and I didn't actually shake your hand, and I came, and I sat back. So I'm going to shake your hand now. We're shaking hands. That was a moment of touch.

LINDENYes.

HINOJOSAWhat did it mean? Did it change anything? Did something happen to my brain just now?

LINDENYou tell me. What does it feel like?

HINOJOSAWell it felt warm. It felt like sometimes you shake somebody's hand, and it's really hard, kind of not, you know, a firm but nice. And I would say mostly warm, which is an important word in the world of touch.

LINDENIt is. Warm is very important because warm -- there's a reason why warm just also means literal warmth, like raised temperature but also meaning essentially someone I can trust, someone who's on my side, who has my best interests at heart. When we -- social psychologists know, pardon me, that when we evaluate people that we're meeting for the first time, we form impressions very rapidly. The first impression that we form is warm versus cold. Is this person an ally or not?

LINDENAnd the second impression we form is are they competent or incompetent. Does it matter if they're an ally or not?

HINOJOSAAll right, we're going to go to a question from, let's see, Scott, in Tacoma Park, Maryland. Scott, you are retired automotive safety engineer. What's your question, Scott?

SCOTTActually, what I basically was going to do was make a comment when you -- the very beginning of the program, you were talking about what sense would you, you know, be willing to keep or lose. And I have a background in human factors, and human factors people always joke whenever somebody talks about the five senses because there's more than that. And probably the most significant other one is what's called the haptic system. And that's how the body senses orientation in space and how it's moving.

SCOTTIf you didn't have the haptic system, you couldn't stand up because it's a combination of the sensation of feel and the sensation of motion you get from your inner ear. In fact it's also the basis of why people get motion-sick.

HINOJOSASo how do you -- thank you...

SCOTTYou see motion with your eyes, but don't feel the motion in the haptic system, it confuses the brain.

HINOJOSASo how does what Scott is bringing up, how does that intersect with the issue of touch?

LINDENWell, Scott is absolutely right in the sense that there are not just five senses. This is a trope that we've all hear that isn't true. And he's also right that we tend to think of the senses that are pointed out to the world to tell us what's going on, like seeing and hearing and touch, but there are also senses that are pointed inward, our senses of self, and these include how is our head oriented, what is the state of the fullness of our gut, what's our blood sugar level like, what's our core temperature and, as he points out correctly, where are our limbs in space.

LINDENSo for example, you can close your eyes and extend your arm, and you know where your arm is in space with a high degree of accuracy even though you can't see it. And the reason for that is because in the muscles in your arm, there are sensors called proprioceptors, and they send messages to your brain that tell you where your arm is. And there are people with a rare genetic disease who don't have that proprioception, and basically they can't walk and have a very hard time moving at all.

HINOJOSANow David, you said that one of the question that you actually love to talk about, and I remember when I first read about it, I was, like, what, which is that you can't tickle yourself, right, and it's kind of like, it's so easy, you can tickle somebody else, but it just doesn't work on yourself. What does that have to do with our brain and the touching?

LINDENWell, the way it works is this. We are hardwired from birth to pay more attention to touches that result from things happening, impinging upon us from the external world, than we are from touches that result from our own movements. Think about walking down the street in your clothes. Your clothes are rubbing against your body. You don't even think about them. They don't -- it doesn't enter your consciousness.

LINDENBut now imagine if you were stopped on the corner, and now the sensations that your clothes normally have rubbing against your body when you walk would happen. Well, you would attend to that very strongly. What's going on in the world? What happens is when you go to tickle yourself, the part of your brain that commands your muscles is sending messages to your muscles, but those muscles are also copied to a part of your brain called the cerebellum.

LINDENAnd the cerebellum is sending inhibitory signals to the place where you are tickling to damp those sensations out because your brain is hardwired to think if I'm the cause of this touch, it -- I should pay less attention to it. And that's why you can't tickle yourself unless if you have damage to your cerebellar circuitry, then you can tickle yourself.

HINOJOSAOh, okay. We have an interesting question from Diana in Houston, Texas. Diana, go ahead.

DIANAYeah, Ms. Hinojosa, thank you so much for taking my call. My daughter, when she was born, she would find some kind of ease whenever she would sleep with her lips against my arm. And she would feel the hairs on my arm. As she grew up, she continued the same pattern, this same behavior. Now she's eight years old, and we've been trying, my husband and I, have been trying to tell her, hey, don't do this, that's enough, Carina, just please don't do it, don't do it, don't do it.

DIANAAnd now she is not -- I'm sorry not performing well in school. She just actually got diagnosed with anxiety, and I wonder if that's -- it has to do anything with us kind of depriving her or telling her not to touch her arm or not to cling to her arm. And this is something that she does just unexpectedly. She does it when she's watching TV, when she wants to go to sleep. And Doctor, I'm wondering what is going on, if that's normal.

HINOJOSAThank you for your question, Diana, to author David Linden.

LINDENWell, so first of all, I should tell you, I'm not a medical doctor, and I shouldn't be giving medical advice on the air. So I can only speak very generally, and I'm sorry to hear this story. What I think I can tell you, though, is that the cause of your daughter's problems in school is not because you have told her to pay less attention to these self-soothing movements.

LINDENFirst of all, she can't help it. It's a strong subconscious drive for her to interact with her arm in that way, and you can't just say, oh, I'm not going to do it any more than you can tell someone who's a cigarette smoker oh, just don't smoke cigarettes anymore. It's a struggle. It's going to be as much of a struggle for her as it would be for someone to give up cigarettes who smoked for years.

LINDENI think what's happening is that very likely, the underlying cause is some issue with anxiety, and the tactile self-soothing with the arm is a symptom of that rather than the cause.

HINOJOSAI love to read about itching. Itching and the context, what is it -- how is itching different? It's that one thing that probably -- I think there's no one who likes to have an itch. Where does that play into this science?

LINDENWell, yeah, itching is just terrible, and for example in Dante's "Inferno," if you go in the ninth circle of hell...

HINOJOSAOh no...

LINDENWithin the ninth circle, there are what are called bolgia, or ditches, which are like subsections of the circles, and in the next-to-the-worst one...

HINOJOSAOh my God, I'm cringing just...

LINDENYou're tormented with the eternal itch.

HINOJOSAI swear I'm just, like, oh, thinking of an eternal itch now.

LINDENSo it's a terrible thing. For years scientists argued is itch its own special sensation, or is it just kind of like a blend of a little bit of pain and a little bit of touch together. We now know that there are special nerve endings in the skin that are specialized to convey itch sensations to the brain, and they are -- they have evolved almost certainly so that when we are infested with bugs or other parasites, we will scratch and remove them for health reasons. But of course evolution is slow, and culture changes quickly. So most of us don't have to worry so much about bug infestation, but these sensors are still there and cause us all kinds of torment in situations where they don't help.

HINOJOSAI wonder, David, because this is the paperback of your book that has done phenomenally well. Is it because there was such a wonderful interest and because we don't really talk about this? And I just want to let you know that I'm Maria Hinojosa, and you're listening to the Diane Rehm Show. So David, is it that we just need to acknowledge and talk about touch that is not sexual?

LINDENAbsolutely. I mean, I think we need to talk about touch that is non-sexual and touch that is sexual, as well, because people talk a lot about sexual touch, but they don't talk about the science of sexual touch.

HINOJOSAUnless you're watching "Masters of Sex" I suppose.

LINDENEven there, even there not all the information is really going to be...

HINOJOSAYeah, right, right, right, right, right.

LINDENIs really going to be the best. Masters, they did great work, but they weren't really biologists fundamentally, and we now know a lot more about the biology of sex. For example, we think of orgasm as being intrinsically pleasurable, but that's a trick our brain plays on us. It's because the pleasure center of the brain lights up during orgasm at the same time as the touch sensors related to certain parts of the body do.

LINDENBut for example if you have damage to your brain's pleasure circuitry, you can have an orgasm that's not pleasurable. It's more convulsive than compelling. It's more like whoops than what one would normally experience.

HINOJOSAAnd we talk about constant pain, right, that people feel on their bodies. But is there in fact an issue of chronic pleasure through touch?

LINDENThat's a great question. There really isn't chronic pleasure in the same way that there is chronic pain, and that's a shame.

HINOJOSAAnd we want to have Ana from Phoenix, Arizona. Ana, you're on the line. Go ahead with your question.

ANAHello, thank you for taking my call. I was wondering about negative touch, touch such as somebody who was, you know, abused or just an unwanted touch and what that does to the brain and the touch system and if there's -- you know, if it's -- it's strange to think of that touch negatively and if there's a way to heal that or, you know, overcome that to think of it as a positive kind of touch again.

HINOJOSAThank you, Ana.

LINDENThat's a great question, and lots of people who have endured physical or sexual abuse have this. It's a very common thing to then be wary of or have negative responses to touches, even in a safe or loving or positive way. And there are changes in the brain that occur when these traumatic touches occur, but they are not permanent. The same way that you can change your touch circuits of your brain by playing violin for years, you can change the emotional touch circuits of your brain though positive touch experience.

LINDENAnd I think for people who are really struggling with this, there is a whole branch of psychotherapists who specialize in this kind of therapy and touch desensitization. Basically it's the same thing you would do if you were scared of snakes or scared of airplanes. It's the kind of therapy that gradually retrains you to realize that touch is not threat.

HINOJOSASo we have a call, really quickly, Kendall, from Indianapolis, Indiana. Real quick with your question.

KENDALLYes, it was more like a comment, actually. I have narcolepsy and cataplexy, which is a sleeping disorder, and so when I have a cataplexic episode, my body just kind of shuts down, and my service dog steps in. And what he does is when I have an episode, and I'm either on my bed, or if I have fallen on the ground, he comes, and he nuzzles next to me. And I can slightly move my fingers, and the sensation of his fur between my fingers really helps me calm down and hopefully quickly get over the episode and recover.

HINOJOSAThank you, Kendall.

LINDENThat's great. I'm so glad to hear that it works out that way positively for you. We know that touching your pet and your pet touching you is very beneficial in all stages of life but particularly with people suffering from depressive and anxiety disorders. As I mentioned earlier, in housing for the elderly, there's an enormous benefit from bringing pets in. Now there's a problem, though, because sometimes people are allergic.

LINDENSo there is an animatronic fur seal called PARO that was developed by a laboratory in Japan that has also been beneficial in this way.

HINOJOSAIt's a purr seal?

LINDENFur, I'm sorry.

HINOJOSAFur seal.

LINDENA fur seal. I didn't enunciate well.

HINOJOSASo that you can touch the fur, but you won't feel, like, allergic?

LINDENThat's right. It's just basically a plush toy with motors in it.

HINOJOSAAll right. So the word that I brought up, sobrar, is a word that you were actually very interested in, David, sobrar, sobradoras, they're using this now in New Mexico, in Albuquerque, to help heroin addicts move beyond their addiction. And just this notion of touch has been helpful for some of these young men, some of them gang members who hadn't been touched in any way. And when they finally go to see the sobradora, they break down.

LINDENI think it's enormous beneficial in so many situations of trauma, both the one you describe, we see it in PTSD, there is now some work that the Veterans Administration is doing also with massage and other forms of non-sexual touch to help -- to help heal. And the amazing thing is that it's best to get loving touch from someone you know, but even a massage or this kind of touch you would get from a sobradora is also -- has tremendous benefits.

HINOJOSADavid Linden, thank you so much for speaking with us. It's called "Touch: The Science of Hand, Heart and Mind." The book is now out in paperback. Thank you so much. I'm Maria Hinojosa, sitting in for Diane Rehm. And I want to thank you for listening.