15-08 Story 2: The Sense of Touch

 

Synopsis: The sense of touch is often taken lightly, yet it conveys more emotion than any other sense because it literally has a separate emotional wiring system. A neuroscientist explains the sense of touch, how it works, the power it has over everyday decisions, and what can happen when it’s not working as it should.

Host: Nancy Benson. Guest: Dr. David Linden, Professor of Neuroscience, Johns Hopkins University School of Medicine and author, Touch: The Science of Hand, Heart, and Mind

Links for more information:


The Sense of Touch

Nancy Benson: Almost everyone has had a discussion at one time or another about which of the body’s five senses they could most easily live without. Virtually no one picks sight, and only a few people ever say they’d give up their hearing. We seem far too dependent on those senses. That leaves taste, smell, and touch… And often, touch is the loser.

David Linden: I think the reason that we undervalue touch is because we can’t imagine being without it. You can close your eyes for a moment and try to imagine what it’s like to be blind you can pinch your nose shut and imagine what it would be like to have no sense of smell, or to plug your ears and imagine what it would be like to be deaf, but there’s no simple way to imagine losing your tactile sense. And as a consequence, I think it is so deeply embedded in our humanity that we can’t even imagine what it would be like to lose it.

Nancy Benson: But Dr. David linden disagrees. Linden is Professor Of Neuroscience at the Johns Hopkins University School of Medicine and author of the new book Touch: The Science Of Hand, Heart And Mind. He says touch may be the most important of our senses because it conveys what the others don’t–emotion. And it’s reflected in our language.

David Linden: We have touch metaphors that deal with emotions all the time. I mean it may seem like a silly thing, but even the expression “my feelings” to mean my tender emotions, it’s something you might say, well that’s just something of modern English, that’s just a linguistic quirk. No, it isn’t actually, it turns out to be not in every language but in many, many languages– it’s in Basque, it’s there in Chinese. When we talk about someone who is emotionally clumsy we call them tactless– literally they lack touch. When we go to describe social emotional interactions with people, we might say that person rubs me the wrong way. I had a rough day with a hairy situation, everything went smoothly. These tactile metaphors are so deeply embedded on our language we don’t even think of them as relating touch and emotion anymore. We just take them for granted.

Nancy Benson: Linden says touch and emotion are so firmly linked because the body literally has an emotional touch sensory system, one of two networks, wired independently and ending up in two different places in the brain. But it’s the other system that usually comes to mind when we think about touch. That’s the discriminative touch system, the one that gives you all the facts.

David Linden: So, if I were to take my pencil eraser and press it against the skin on the back of your arm you would be able to tell where it was located and how hard I was pressing and something about the texture of the object was contacting your skin and that would all be because there are nerve endings in the skin that are specialized for detecting that information.

Nancy Benson: The other touch system is much different it’s the emotional touch system.

David Linden: So, if I were to caress the hairy skin on your upper arm there are other detectors. There are little nerve endings that wrap around the bases of hairs and detect hair deflection. And instead of being designed to extract the facts and send them quickly to the brain they instead are tuned for social information and they send that information to a different part of the brain called the posterior insula that responds specifically to emotional touch.

Nancy Benson: Every touch we feel–every caress or kiss and every jab of pain–is really a combination of the two senses. But occasionally, the two touch systems get disconnected, or one of them doesn’t work at all. For example, if the emotional system stops working, the sensation of pain is completely different.

David Linden: If you have them in a pain lab and you stick their hand in a bucket of icy water, which is a standard pain lab test, they’ll say yep that hurts that hurts a lot, but they’ll have no emotion in their voice. Whereas if you do that with someone who’s brain is in tactile they’ll say “Ow! That hurt that’s terrible oh my gosh that’s such an awful thing.” You can have the opposite leision, people who have damage to the discriminative pain system. If you stick their hand in the bucket of ice water, they’ll say “Oh that’s terrible” and if you say well where on your body is the pain and what are its qualities, they’ll say I have no idea it’s just bad. We experience all these touches as a gestalt as a unified percept where the emotion and the discriminative aspects are blended together but this is a trick brain plays on us.

Nancy Benson: It’s very rare to have no sense of touch at all. But along with no sense of touch, Linden says these people also feel no pain.

David Linden: If they hit their thumb with a hammer they’ll feel some pressure and the thumb will swell up, but they won’t feel any pain whatsoever, and you might think oh this is great no pain, what a terrific life but it turns out that people with congenital total insensitivity to pain tend to have very short lifespans. And often times that comes from very simple things, like their clothes are too tight, or their shoes are too tight and rub them and they get bacterial infections. They burn themselves, they swallow foods and drinks that are too hot and scar the esophagus because they don’t have protective reaction. Certainly that one aspect of touch is absolutely crucial for our functioning in the world, and if you don’t have it it’s very hard to keep yourself alive.

Nancy Benson: It’s also rough start to life when the sense of touch is denied. Lynden recounts what happened to newborns who were left alone and not cuddled in understaffed Romanian orphanages 30 years ago.

David Linden: These kids grew up to have terrible neuropsychiatric problems they struggled with schizophrenia and depression and impulsive behavior at much higher rates than normal. And it wasn’t just neuropsychiatric problems, they also had long lasting changes in the functions of their immune systems and their digestive systems. So when we think about it, you can be born blind and you can have a fine life– all you lack is your sight, and you could have a very very rich life and you can be born deaf, and likewise have a fine life, and everything other than your lack of hearing goes very well. But if you don’t get social touch in the first year and a half of your life, you will be drastically compromised in your development and it is essentially irreversible after a few years.

Nancy Benson: Fortunately, Linden says it takes only about an hour of touch every day for newborns to avoid disaster later in life. We simply can’t go without it. But that doesn’t stop our sense of touch from eroding later in life after about age 18. We lose about 1% of our touch sensitive nerve endings each year.

David Linden: And this is all kinds of touch: mechanical touch, like what you would need to find a quarter in your pocket and pull it out, sexual touch, pain, heat, cold, all of those sensations ramp down very, very, very slowly over life. This is part of the reason– not the entire reason– but part of the reason why it takes elderly people longer to achieve orgasm during sexual behavior. It’s also part of the reason why elderly people are more prone to falls, in addition to having slower conducting nerves and weaker muscles and problems with their sense of balance. They also can’t feel the ground as well through the soles of their feet.

Nancy Benson: research shows that our sense of touch affects our evaluation of every person we meet. For example, if you’re holding a warm cup of coffee when you first meet someone, you’ll judge them as warmer and more trustworthy than you would otherwise. If you look at a resume on a light clipboard, you’ll literally rate that person as a lightweight compared to the same resume on a heavy clipboard. Female servers in restaurants get better tips if they lightly touch patrons on the arm. And doctors get much higher ratings from patients who they touch appropriately. Touches are also culturally mediated. For example, Latin Americans touch each other far more than the reserved English. But linden says the touches we share with those we love make the sense of touch much more important than we know.

David Linden: Social touching is the glue that binds teams into cohesive units. It binds couples into lasting partnerships, it binds families together, it makes co-workers into effective organizations. So, one can certainly imagine that on a broader societal basis, when social touch is inhibited, that there is a price to pay in terms of the cohesiveness of a society.

Nancy Benson: You can find out much more about the book Touch on David Linden’s website, davidlinden.org. Or through a link on our website, radiohealthjournal.net. Our production directors are Sean Waldron and Nick Hofstra. I’m Nancy Benson.

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