9 surprising facts about the sense of touch

Touch is perhaps the most overlooked sense.

Every one of us receives tactile information about the world around us every second of the day. Right now, if you're sitting, your butt is being squished into your chair. Your fingertips are probably touching a mouse, or swiping the glass of your phone. All this information is so omnipresent, in fact, that the only way to make sense of it is to tune most of it out — you probably weren't paying attention to these sensations until you read those words.

"You can't turn off touch. It never goes away," says David Linden, a neurobiologist at Johns Hopkins and author of the new book Touch: The Science of Hand, Heart, and Mind. "You can close your eyes and imagine what it's like to be blind, and you can stop up your ears and imagine what it's like to be deaf. But touch is so central and ever-present in our lives that we can't imagine losing it."

In the book, Linden explores all sorts of fascinating aspects about this enigmatic sense. He recently spoke with me about some of what he's learned.

1) Your brain pays wildly disproportionate attention to touch on different parts of your body

The cortical homunculus — a human figure scaled to match the proportions of how touch sensors are represented in the brain. (OpenStax College)

"The part of your brain that processes touch information has a map of your body surface. But this map is very highly distorted," Linden says.

"It over-represents areas that have lots of fine touch receptors (like the face, the lips, the tongue, and the fingers) and under-represents areas that don't have many receptors (like the small of your back, your chest, and your thighs)."

These receptors, he says, come in four varieties. "There's one receptor for sensing vibration, one for tiny amounts of slippage, one for stretching of the skin, and one that senses the finest kinds of textures. The last one, called a Merkel ending, is only in the parts of your body you use to feel something really finely — like your fingertips and lips."

2) Your sense of touch gets worse as you age

(Shutterstock.com)

"From work in both humans and lab animals, we've found that areas of the touch-sensing parts of your brain that you use a lot tend to expand and take over neighboring territory," Linden says. "So a violin player who uses her left hand more than her bowing hand will have the area of her brain that processes information from her left hand expand."

"we all lose touch receptors over the course of our lives"

"But another interesting thing has to do with the effects of aging. It seems as though we all lose touch receptors over the course of our lives. It's not like we have them until a certain age, then they suddenly disappear — we lose them very, very slowly. They peak around age 16 or 18, then disappear slowly."

"You also lose pain and temperature receptors — which might actually be a good thing. It may be that when you're older, you might not feel as much surface pain in your skin. But there are other interesting implications of this: it may be that part of the reason it becomes harder to achieve orgasm as you grow older is that touch receptors in the skin of the genitals become less dense."

"This might also be one of the factors that lead the elderly to take falls. We stay upright in part because of sensations on the bottom of our feet, and we get less of that information the older we get."

3) People can be "touch-blind"

"It's amazing, because we don't even have a word for lacking touch," Linden says. "But touch-blindness is very real. I wrote about a woman named 'G.L.' who has a very rare disorder called primary sensory neuropathy. That means she's lost all her sensors for mechanical touch."

"She claims she can't feel anything at all. She can't read braille. If she puts her hands in her pockets, she can't tell a penny from a quarter. But remarkably, if you get her in the lab, you find that she has one form of sensation left: if you caress her forearm, or her leg, or another area of skin, she can tell roughly where it is, and she knows it's pleasant. That's because she has retained a different, emotional touch system."

4) You have a special system for feeling emotional, social touch

(Shutterstock.com)

"There are two touch systems," Linden says. "One that gives the 'facts' — the location, movement, and strength of a touch — and we call that discriminative touch."

"But then there's the emotional touch system. It's mediated by special sensors called C tactile fibers, and it conveys information much more slowly. It's vague — in terms of where the touch is happening — but it sends information to a part of the brain called the posterior insula that is crucial for socially-bonding touch. This includes things like a hug from a friend, to the touch you got as a child from your mother, to sexual touch."

"It's not just a different kind of information that's conveyed by the same sensors in the skin that allow you to feel a quarter in your pocket. It's a completely different set of sensors and nerve fibers that wind up in a different part of your brain."

5) You also have a special system that makes pain hurt

(Shutterstock.com)

"In the pain circuitry, there's also one set of sensors that tells you exactly where the pain is, how strong it is, etc. And then, again, there's another system that just conveys the negative emotional aspect of the pain," Linden says.

"It's the second system that can be modified by drugs, like morphine, or by meditative practice. And there are also some rare cases — people called 'pain asymbolics' — who lack the emotional pain system. So they have the 'facts' of pain, they're aware of it, but it doesn't bother them. If you stick their hand in a bucket of ice water (a standard way of inflicting pain in a lab), they know it hurts, but they don't actually mind it."

6) Touch is mysteriously crucial for a baby's development

(Shutterstock.com)

"The best examples of this come from Romanian orphanages after Ceaușescu's fall, when there just weren't enough people around to take care of babies. They were barely touched during the day," Linden says.

"These kids didn't just have a host of emotional problems — though they were depressed and had high instances of schizophrenia, bipolar disorder, and other issues — but they also had a whole raft of physical ailments. They had weakened immune systems, and skin ailments."

"they had weakened immune systems and skin ailments"

"Other research has confirmed this phenomenon. We're not entirely sure why it happens, but it seems that early touch experience is extraordinarily important for development both cognitive function and a healthy body."

"This is why, nowadays, when premature infants are born and put in isolators, they're taken out for a few hours a day, and pressed against a parent's skin. Initially, when isolators were first invented, people thought you should just leave them in there alone, so they don't get infected. But then they might not get touched for the first two months of life, which turns out to be disastrous."

7) Touch shapes first impressions of people in weird ways

(Shutterstock.com)

"Incidental touch can help form our impressions of people's character," Linden says. "In one of the classic experiments, people were holding either a cold iced drink or a hot drink when meeting someone, and those with a hot drink literally rated the people they met as warmer — as in, having a more pro-social personality. They didn't rate them better overall — say, as smarter, or more competent — they just rated them as warmer."

"There was another famous study in which people evaluated others' resumes on a clipboard, and if they were on a heavy clipboard — rather than a really light one — they were rated as having more gravitas, more authority. Once again, people didn't think they were smarter, or better team players, or things like that. The weight made them seem weighty."

"those with a hot drink literally rated the people they met as warmer"

"When these studies first came out, no one really believed them — but they've since been well reproduced. It's also not a quirk of English, it happens across cultures. It's been done in Papua New Guinea."

"It points to an idea that's come up in social psychology again and again: if you're evaluating someone for the first time, the first decision you make is friend or foe. Is this person warm, or are they a threat? Then the second thing you evaluate is whether they're competent — which means that it matters if they're a threat or not. And it seems that touch information helps us make these distinctions, even when it's irrelevant."

8) We still don't really understand how sexual touch works

"We know embarrassingly little about it," Linden says. "Here's a very basic question that we can't fully answer: what makes the genitals different from the rest of the body? Obviously other parts of the body can lead to sexual stimulation, but there's something special about the genitals. And we just don't know what it is."

"If you look at the skin in the genitals, there are some structures — including one called a mucocutaneous end organ — that are present there at higher densities, especially in places like the head of the penis and the clitoris. So it seems likely that it's involved in sexual sensation. But in truth, we don't have a way of activating those nerve endings on their own, so we just don't know."

"Sexual sensation affects so much in our lives, our social organization, and what makes us human — and we don't know the biology of it."

9) Your emotions can warp how you experience pleasure and pain

(Shutterstock.com)

"The fact that our cognitive state — what we're thinking about and paying attention to — can modulate our perception of touch is both a blessing and a curse," Linden says.

"It's a blessing because it means modulate negative touch through positive experiences, like meditation, exercise, and mindfulness training. But it's a negative in that if we obsess over pain, we can get into a spiral where we make it worse: you attend to it more, and it feels more painful, and you attend to it more. It also means that if you want to maximize pain to torture someone, you can manipulate their emotional state to make it feel worse. If they feel threatened, or are sleep deprived, or don't know when pain will arrive, it's perceived as being worse."

"This isn't just true of pain, but of pleasant sensations too. Imagine you're with your significant other, and he or she caresses your arm — it feels nice. Now imagine you're in the middle of a heated argument, and you get that exact same caress. The very same nerves will be activated, but it will actually feel different to you — annoying, and unwelcome. That's because the parts of the brain that are processing emotional touch are affected by the other parts of your brain as well."

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