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The buttery cotton bedsheets against your legs. The annoying tag scratching at the nape of your neck. The gentle breeze tickling the hair on your forearm. Every day, you’re bombarded by an endless stream of tactile information which helps you perceive and make sense of the world around you.
But while you may lose your sense of smell and taste when you have a stuffy nose, plug your ears to block out grating noises outside your windows, or cover your eyes during a scary movie, you can’t turn off your sense of touch.
“You can’t stop yourself from feeling the external world. You need your sense of touch for everything you do throughout the day, from walking down the street to buttoning your shirt,” says Lauren Orefice, Ph.D., postdoctoral fellow at Harvard University.
Yet, scientists are just beginning to understand how we interpret sensory information and discriminate between different textures, temperatures, and even emotions.
Back in high school, your science teacher probably taught you that when someone or something touches your skin, a signal is sent from a sensory neuron through the spinal cord up to the brain where information can be processed. But scientists have discovered that the signaling process isn’t so simple.
“There’s a lot more transformation, integration, and modulation of the signal that happens from the primary sensory neuron to the spinal cord (and then within the spinal cord) than we originally thought,” says Orefice. “It’s not just a faithful recapitulation of the signal from the skin to the neuron to the spinal cord up to the brain.”
Orefice describes different types of sensory neurons which respond to different types of stimuli—vibration, pressure, hair deflection, and stretching. When someone lightly touches your forearm, it activates the sensory neuron endings in your skin. The stimulus then travels from the skin to the spinal cord where other neurons help process incoming information.
Scientists now believe there’s a specific part of the spinal cord that’s critical to the perception of touch—the dorsal horn of the spinal cord. Not only do the neurons here play an excitatory, inhibitory, and processing role, they also modulate a huge amount of information transmitted from our skin and help to determine what stimuli we pay attention to.
“From there, touch information goes to the brain stem and to the primary somatosensory cortex and other areas of the brain involved in how we perceive touch including emotional centers, fear centers, and the frontal cortex,” says Orefice.
Touch is one of the first senses to develop and after birth—parents are encouraged to have skin-to-skin contact and show affection with children early on. That’s because touch plays an important role in cognitive and behavioral development.
“Touch is necessary for the development of larger behavior that we don’t necessarily think of as related to just touching your environment,” says Orefice. “There are critical windows for normal brain development, especially in the cortex and sensory cortices. If you don’t get the appropriate input during that time, things don’t wire up appropriately. You can affect how they feel touch, perceive touch, and other social behaviors.”
For example, years ago, children in Romanian orphanages were raised without normal nurturing touch from adults. As a result, these children had a number of emotional, social, and physical problems. According to Dr. Tiffany Field, director of the Touch Research Institute at the University of Miami School of Medicine, studies of children raised in Paris and Miami found that Parisian preschoolers, who received more affectionate touch from their parents on the playground, were less verbally and physically aggressive compared to the Miami preschoolers, who received far less nurturing touch.
In Orefice’s research, she found that altering the primary sensory neurons in mice while they’re still in the embryo can cause not only tactile hypersensitivity but also anxiety-like behaviors. If you’re adverse to touch, you’ll likely spend less time around others or feel anxious in social situations. However, they’ve also found that if you disturb touch signals in adult mice, it doesn’t affect other social behaviors.
Tactile stimulation can also encourage healing. During an injury, you may initially apply pressure to the area. A massage can help to break up scar tissue and knotted muscles after a hard workout or race. You may rub your elbow after smacking a funny bone. There’s no doubt that touch can be extremely healing.
Researchers at the Touch Research Institute found that the power of touch can provide more than just temporary pain relief. Field and her colleagues have conducted over 100 studies on the effects of massage therapy on many medical conditions. They’ve found that touch can enhance growth in preterm infants, reduce pain in patients with fibromyalgia and enhance immune function in those with HIV and cancer.
“What we’ve found is that if you stimulate pressure receptors deep under the skin, there’s a long chain reaction,” says Field. This cascade stimulates the vagus nerve, a key member of the parasympathetic nervous system, which tells your body to relax. Not only does your breathing slow, but your heart rate, blood pressure, and stress hormone levels drop. Field says they’ve also found increased levels of serotonin as well as the immune system’s natural killer cells.
Touch is more than just processing information from the world around us. And as humans, we need it. A hug, a caress, a pat on the shoulder—these gestures add a rich context to how we interact with others. “Touch can have profound effects on the whole body,” says Orefice. “To a certain extent, it is a large part of who we are as mammals.”
Artwork by CHRIS MARKLAND