Surprising facts about 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 bottom 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.
Your brain pays wildly disproportionate attention to touch on different parts of your body
The cortical homunculus — is a human figure scaled to match the proportions of how touch sensors are represented in the brain.
"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."
You have a special system for feeling emotional, social touch
"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."
Touch is mysteriously crucial for a baby's development
"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."
"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."
The emotional context changes our physical experience of touch
As we all know well, touch can actually feel physically different based on the social context of the encounter. Consider the example of an arm around the shoulder, said Linden: Whether it's coming from a good friend, your lover, your boss or a person you don't like very much will change the way you experience that touch, even if your skin is being stimulated in the exact same way.
"It's not just that the context is different -- it will actually feel different," Linden explained. "The reason is because these emotional touch brain areas are getting information about the social context from other parts of the brain."
Because of this separation of the two pathways used for processing touch, is that in some people with certain brain disorders, the physical sensation of pain can be separated from its emotional impact. So too, can the pleasurable aspect of touch be removed from the actual sensation.
Touch shapes first impressions of people in weird ways
"Incidental touch can help form our impressions of people's character," Linden says. "In one experiment
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 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."
"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."
We still don't really completely 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. 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 yet we know embarrassingly little about the biology of it.
Touch can be therapeutic
A large body of research -- much of which has been conducted by Tiffany Field of the Touch Research Institute at the University of Miami -- suggests that therapeutic massage can be useful for a number of physical and mental ailments.
These therapeutic applications include pain relief, addiction recovery, and maintaining emotional equilibrium, cognitive function and mobility among an aging population, Linden suggested. Research has also shown that massage may be an effect way to treat anxiety, insomnia, headaches and digestive problems.
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