We typically think of touch as a pleasant, but not particularly important part of life. But touch, which is the interface between our bodies and the outside world, does a lot more than bring us sensual pleasure.
Often ignored when we talk about our fundamental senses, the sensation of touch is a fundamental part of our daily experience, influencing what we buy, who we love and even how we heal. We use this sense to gather information about our surroundings and as a means of establishing trust and social bonds with other people.
In his book, Touch: The Science of Hand, Heart and Mind, Dr. David Linden convincingly argues that the "genes, cells and neural circuits involved in the sense of touch have been crucial to creating our unique human experience."
Linden describes the body's touch circuits as a "weird, complex and often counterintuitive system." Largely due to this complexity, our scientific understanding of touch -- particularly how it is processed in the brain -- is limited compared to our knowledge of other senses.
"It's only in the last couple years in studies of mice that we actually can identify what particular types of cells convey which types of touch sensation," Linden told The Huffington Post. "There is enormous progress to be made in very clinically-relevant areas."
Recently, Linden and other scientists have begun to demystify the influence of touch on our lives. Here are six things you should know about the latest neuroscience of touch.
There are two pathways in the brain for processing touch.
The human brain has evolved to have two distinct but parallel pathways for processing touch information. The first is a sensory pathway, which gives us the facts about touch -- like vibration, pressure, location and fine texture.
Linden explained that part of the sensory pathway is a brain region called the primary somatosensory cortex, which is the first region to be hit by the experience of touch. "It basically analyzes information through a series of processing stages that extract more and more complicated information," said Linden. "It's all about figuring out the facts, and it uses sequential stages of processing to gradually build up tactile images and perform the recognition of objects."
The second pathway processes social and emotional information, determining the emotional content of mostly interpersonal touch using different sensors in the skin. This pathway activates brain regions associated with social bonding, pleasure and pain centers.
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.
"There's the fact, then there's the emotional component of it -- it happens for social touch, it happens for pain, and it also happens for a very specialized kind of social touch, which is orgasm," said Linden. "So if you have damage to the part of the brain that damages the emotional part of touch, you'll have orgasms that seem more like 'whoops.' It's not the kind of intrinsically positive emotional experience that we usually have."
This means that you could put an electrode in the brain to produce non-pleasurable orgasms -- not that you'd probably want to. Or, you could produce the pleasurable aspect of orgasm without any tactile aspect associated with it.
Touch is important for child development.
Drastic examples of young children who have been deprived of touch and have suffered as a result have shown the devastating consequences of touch deprivation. However, there's still not much research on the consequences of touch deprivation in later childhood and adulthood.
"If you don't get touch right after you're born, all kinds of terrible things happen, and not just cognitive and emotional," said Linden. "Your immune system doesn't develop properly, your digestive system tends to have problem -- there's a whole rack of health problems that can develop if you don't receive touch in early life."
In the 1950s, parenting manuals advised parents not to touch their children too much -- recommending, instead of hugs and kisses, giving kids a "pat on the head." But Linden warns that touch deprivation denies children a chance to become socially integrated with the people around them.
"A parent's touch is very crucial for a child's development," said Linden. "It's not optional."
Touch is a critical part of our relationships.
When it comes to social situations, the primary purpose of touch is to forge trust and cooperation. Friendly touch communicates to someone, You can trust me. Research has found that players on sports teams that have lots of celebratory touch tend to perform better, while studies have also shown that in a romantic relationship, touch (both sexual and non-sexual) is enormously important.
"In both kids and adults, touch is the glue that makes social bonds," said Linden.
So what's happening in the brain and body when we experience a warm touch of a loved one? The touch stimulates C-fibers (a type of nerve fiber which Linden refers to as "caress sensors") that convey information to the brain about interpersonal touch -- specifically, the light caress. These fibers send signals to the posterior insula (a brain area involved in perception and motor control), which produces a soft, pleasant sensation.
Our sense of touch deteriorates as we get older.
Unfortunately, like eyesight and hearing, our sense of touch is vulnerable to the effects of age. The touch sense steadily deteriorates as we get older, starting around the age of 18. Every year, we lose around one percent of our tactile sense.
"By the time you're old, you've lost a whole lot of the touch sense," said Linden. "The main way is because the density of nerve endings in your hands has just decreased. Those nerves die off and they don't come back. Another reason is that the insulating material, called myelin, that coats the fast-conducting nerve fibers and makes them project quickly to the brain breaks down, so the information gets to your brain more slowly."
Part of the reason that elderly people are so prone to falls is that they are getting less tactile information from the soles of their feet. One of the ways for the elderly to combat falling is actually to go barefoot so that they have a better sense of the ground, Linden explains.
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. Some research has also suggested that massage may be an effect way to treat anxiety, insomnia, headaches and digestive problems.