Sense and Sensibility

Why is tactile perception so fundamental to life?

Surprisingly little is known about this most essential of senses, and researchers investigating touch from all angles have found that it is the most complicated sense to study.

Surprisingly little is known about this most essential of senses, and researchers investigating touch from all angles have found that it is the most complicated sense to study.

Is touch the most powerful of all our senses? As a brand-new grandparent I can personally attest to how closely touch is tied to human emotion and well-being. My granddaughter is almost always immediately calmed by caresses that I find impossible not to bestow. I can’t wait to watch her reaction when she reaches out and feels the fuzzy cover of the classic children’s book, Pat the Bunny.

Artists and philosophers have forever tried to capture and explain the power of touch. Crowds crane their necks to view Michelangelo’s masterful Creation of Adam, the centerpiece of the Sistine Chapel ceiling some 65 feet overhead. Because of its height, it looks at first glance as if the fingertips of God and Adam are touching, though they’re not. Although the interpretation is subjective, the work is very emotionally evocative.

Surprisingly little is known about this most essential of senses, and researchers investigating tactile perception from all angles have found that it is the most complicated sense to study. There are still basics that need elucidation: how exactly are tactile stimuli encoded in the brain, the identity of the physical and molecular players modulating the many different perceptions conveyed by touch—vibration, pressure, temperature, pain—and why touch is so intricately tied to our emotions.

Surprisingly little is known about this most essential of senses, and researchers investigating touch from all angles have found that it is the most complicated sense to study.

In this special issue of The Scientist devoted to the sense of touch, we have chosen to explore the subject by examining some of the more unusual approaches to researching the subject. “A Nose for Touch” describes an amazing tactile organ—the star-nosed mole’s fingertip-size nasal appendage, which is innervated by more than 100,000 sensory neurons and contains “many times more than the total number of touch fibers (17,000) found in the human hand,” according to author Ken Catania, a neuroscientist at Vanderbilt University. By mapping touch areas in the animal’s somatosensory cortex, Catania and his colleagues hope to elucidate some of the “general principles about how brains process and represent sensory information.”

 

While not sporting quite such extraordinary touch-sensing appendages, animals as varied as jumping spiders and elephants sense vibrations and use them to communicate and interpret their surroundings, Cristina Luiggi reports in “Good Vibrations.” In “Pleasant to the Touch,” Sabrina Richards reports on what is known about how we are wired to perceive gentle, pleasurable touches, and why receiving this type of sensation is so important for normal human development and social interaction.

The latest technology for adding a sense of touch to prosthetic arms is the subject of “Missing Touch” by Megan Scudellari. Because arm prostheses on the market today cannot “feel” what they touch, users must always be looking at what they reach for in order not to miss or crush what they grasp. Incorporating feeling into upper-limb prostheses will eventually have the added benefit of giving users something they sorely lack now—a sense that they own their artificial limb, that it is part of their body.

Psychologist Christina Karns writes a Thought Experiment, “The Pliable Brain,” about how she and her colleagues have found that touch perception in deaf people is altered, and suggests that the degree of alteration might be tapped to decide what type of treatment is most suitable for a given person.

Whether you are reading this issue by holding the magazine in your hand, pressing your mouse, or touching the screen of your tablet, I hope you will find this issue “sense-ational.”

 

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