This is the last of a three-part series examining the fascinating anatomy of human touch. In the first part, we touched on the story of Igor Spetic, who lost his arm to industrial machinery, yet continued to feel sensation in the space it once occupied. In the second part, we talked about the neuron teams that make up our “blanket with a brain” known commonly as our skin. In this final post, we will sink our teeth into the body parts at the frontlines of human touch: fingers!
We have learned that the human brain (specifically, the somatosensory cortex) houses a league of neuron teams. Each body part—arm, hand, tongue, hip, foot—comprises a team, and each team takes up space in the cortex. But not all teams are created equal: more space is devoted in the cortex for body parts engaged in feeling, like fingers. This phenomenon, also called the somatosensory map, is an example of the brain organizing itself based on the body’s ability to feel.
Within the teams there are receptors that specialize in different sensations, like itch, pain, temperature, and pressure. The receptors responsible for pressure, which abound in hands and fingers, are called Meissner’s corpuscle. Georg Meissner, a German anatomist, discovered them in the middle of the 19th century and was kind enough to lend them his name.
Researchers took samples of skin tissue from different parts of the finger (L). They found that the receptors that detect pressure, known as Meissner’s corpuscles, vary between people (R) and are mostly located in the fingertips.
Meissner's corpuscles are encapsulated, fluid-filled neurons embedded in the dermis, that skin layer where hair follicles and sweat glands can also be found. Yet they extend into the epidermis, that last (or first) layer of defense between inside and outside, between you and the world. As soon as the skin’s surface is deformed (by, say, typing a key), the corpuscle springs into action.
Researchers Brian Beatty and Joseph Ciano wanted to know more about these neurons that translate touch. Were they dispersed evenly throughout the hands and fingers? Did every individual have the same amount?
No and no, it turns out. Ciano zoomed in on skin tissue from the right hands of sixteen cadavers. He compared the number of corpuscles across the interphalangeal joints and finger pads from palm to fingertip. Not only did he find a small number of corpuscles closer to the palm—he found a high concentration in the fingertips. The fingertip corpuscles did not vary much between fingers of an individual (a thumb does not have more than a pinky), though the amount in each person varies.
The results mean that 1) everybody’s different and 2) not everyone has the same “tactile sensitivity.” If you are a deft piano player, a sculptor, or massage therapist, you may have your Meissner’s corpuscles to thank. And if you are not, well, you may a scapegoat on your hands.
Touch tells us a lot about how to navigate the world—whether something is hot or cold, dangerous or safe, spiky or smooth. The relay of information made possible by Meissner’s corpuscles happens seemingly at light-speed. We know instantly, just by touching,” says a researcher working with Igor Spetic, “whether to gently squeeze the toothpaste or crush the can.”
Human touch may not be the most appreciated of the five senses. But as Berkeley psychologist Dacher Keltner explains in his work, “our experience of our bodies—the things they feel, the moves they make, and the textures and the people they touch—is the primary experience of our minds.” And remember, as a baby—before you saw, before you smelled, before you tasted, before you heard—you touched