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Book by Hopkins neuroscientist explains science of pain, tickling, pleasure

For The Baltimore Sun
Why can't most people tickle themselves? A book by a Hopkins neuroscientist answers that question and much mor

Reach into your pocket and grab a handful of coins. Now close your eyes; without looking, can you tell the denomination of each coin?

You probably can, thanks to specialized touch sensors on your fingertips and the messages that those sensors send to your brain. The interaction between our senses and our brains is an endlessly fascinating subject.

David Linden, a professor of neuroscience at the Johns Hopkins University School of Medicine, agrees. In his book "Touch: The Science of Hand, Heart and Mind," released earlier this year, Linden explores and explains the role of touch in our lives and in our emotions.

Linden, a Poplar Hill resident who has been at Hopkins for 24 years and works on recovery of function after brain injury, said he was motivated to write about touch for two reasons: because it matters and because at Hopkins he is surrounded by experts in a world center of touch research.

"I became a fanboy," he said. "I became so impressed with the progress in this area that it motivated me to tell the story."

His book bounces back and forth between the technical and the anecdotal. Linden tells stories about puppies and basketball players and his own life, and backs up the narrative with detailed (but understandable) explanations of scientific studies.

Linden also tackles sex, offering up plenty of salacious details, including some funny stories, about how and why we feel what we do.

On the scientific front, the sex talk focuses in part on specialized nerve endings — called Genitalnervenkorperchen in German — that cluster in the genitals and other highly sensitive areas. The nerves' locations, which differ from person to person, along with other variations of sensory nerves in the genitals, may influence why people prefer different sexual activities. (Linden emphasizes the word "may" in this discussion, noting that causal links have not been established.)

The questions Linden fields most frequently aren't about sex, but about pain thresholds and tickling.

"Pain thresholds are interesting — some of that can be explained by circumstance," said Linden, referring to parts of the book that discuss increased pain associated with anxiety (like a child anticipating a shot) or not feeling pain in certain scenarios, such as combat situations.

Questions about tickling often focus on why most people can't tickle themselves — and why some people can. The answer to both questions lies in the cerebellum's ability to make connections between the active tickling motion and the sensation of tickling. Basically, if your brain can sense that you're tickling yourself, it dulls the sensation of being tickled.

There's still a lot we don't know about sensations like tickling and pain, though, including whether genetic variation plays a role in how people experience them. There may be "mutations in genes responsible for touch that may change pain thresholds and sensitivity to tickling and may determine if people like or dislike interpersonal touch," Linden said.

Touch overlaps with another sense: taste. "We use a lot of touch sensors for food," Linden said. "A lot of what makes the difference between a really good food and not so good has to do with mouth feel," he said, offering examples like apples ("a lot is about snap") and tempura, which can be perfectly crispy versus sloppy and oily.

"We don't think about touch as being central to food experience, but it is," he said.

People around Baltimore put these theories to use, underscoring he practical applicaitons of the research presented in Linden's book.

Tim Riley, the beverage director for Fleet Street Kitchen and the rest of the restaurants under the Bagby Group umbrella, said he thinks a lot about mouth feel when creating drinks.

"I think about those things in terms of alcohol and sugar," he said. "If I'm looking for richness and roundness, I might use a more concentrated sugar syrup and more alcoholic ingredients."

Adding more concentrated sugar doesn't necessarily mean adding more sweetness, he said. A simple syrup made with a higher concentration of sugar will feel more viscous on the tongue, and the extra sweetness can be counteracted with bitters or lemon juice.

Texture is equally important in the kitchen at Fleet Street. Executive chef Michael Correll said touch plays a role in every dish he makes. "I always try to hit all five senses when I come up with a dish," he said. "Texture wakens your palate."

Recently, Correll created an amuse bouche for Fleet Street Kitchen using roasted baby carrots tossed with mole sauce and served with Greek yogurt. "It had great flavor but needed something," he said. "I toasted some pumpkin seeds, roughly chopped them and put them on top. It made a huge difference adding texture."

Correll says he looks to chefs like Alinea's Grant Achatz in Chicago for inspiration. "He's trying to evoke emotions and uses textures," Correll said. Achatz is known for creating unusual dishes that spur reactions, like a crispy helium-filled sugar balloon that's funny and relaxing.

This suggests a potential link between sensory perceptions and emotions. According to Linden, though touch is inherently emotional, it is not always comprehensive and specific. Touch alone, without other context, can convey some specific emotions, though not all.

Linden hopes that readers of the book will take away a message about the importance of interpersonal touch. "I'm hoping people will realize that interpersonal touch is just good for you," he said. "It's best in the context of people with whom you have emotional relationships but good even in the context of strangers — like massage."

In her role as spa director at the Four Seasons Hotel, Toni Sullivan regularly witnesses the positive effect of touch. When people get massages, they can experience "a physical feeling of being loved and cared about," she said. "Touch is a way of communication. It's such comfort. People need to touch people."

Ryan Moschell, an Annapolis-based Hanna Somatics educator and licensed massage therapist, learned early in his career about studies indicating that premature babies who are touched have better outcomes than those who are touch-deprived; Linden cites similar studies in his book. For Moschell, this knowledge resonates with his experience as a practitioner, seeing how much touch could help.

Hanna Somatics is an approach to pain relief based on re-education of the mind and body. Moschell uses touch to help people learn and remember the movements he teaches them.

"I'm showing people how to move their muscles," he explained. "If I show someone, their nervous system gets it immediately. If I told you how to do it, you'd get a sense of it, but if I touch and show you, you get it on a very deep level."

Even in business settings, this holds true, said Keith Scott and Rebecca Klein of TallSmall Productions, a Baltimore public speaking and communications consultancy. They recommend that when people are speaking at an event, they shake hands before and after their presentations.

"Making the connection at the beginning generates interest, and when leaving, a hug or handshake builds a connection the audience remembers," said Scott. "Touch has a lasting impact on the process."

The effect lingers in other parts of life, too.

"I like to write about things people find compelling in their everyday lives," Linden said. "I was thinking about the things that, in the course of my normal day, matter. Interpersonal touch is one of those. This is a story to tell because it is emotional, humane and central to our lives."

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About the book

David Linden's "Touch: The Science of Hand, Heart and Mind" is available through Amazon, Barnes & Noble, iTunes, Powell's, Indiebound and Books-A-Million.

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