Our fingertips can provide us with detailed sensory information about anything we touch. Now, a new study, published this week in the Journal of Neuroscience, reveals that the whorled ridges of our fingerprints may help explain the extraordinary sensitivity of human touch, reports Nicola Davis for the Guardian.
In the past, some researchers have suggested that fingerprints evolved to help humans grip objects. But, because current models of human touch don’t quite account for the sensitivity of our fingertips, Ewa Jarocka, a researcher studying human physiology at Umeå University in Sweden, and her colleagues set about investigating whether fingerprints might offer an explanation, reports Christa Leste-Lasserre for New Scientist.
Humans’ sense of touch comes from the network of sensory neurons with thousands of receptors spread across our skin. Each of these touch receptors is tied to a small area of skin called its receptive field where it is responsible for detecting sensations such as pressure, vibration or texture. To test out just how finely tuned these receptive fields are, Jarocka and her team conducted experiments using six men and women between the ages of 20 and 30.
In the experiments each subject was placed in a dentist’s chair with their fingers immobilized; the researchers then used a robot to brush cards covered in tiny cones against the subject’s fingertips at different speeds and in different directions. The bumps on the cards were less than 0.02 inches (0.5 millimeters) high, 0.016 inches in diameter (0.4 millimeters) and spread about a quarter inch (7 millimeters) apart, per the Guardian.
To measure whether the bumpy cards elicited the telltale electrical activity of nerve impulses, the researchers inserted electrodes in the main upper arm nerve of each participant.
Per New Scientist, the results of these experiments allowed the team to create a map of the many tiny receptive fields covering the subjects’ fingertips. Specifically, they found that the receptive fields were just 0.016 inches (0.4 millimeters) wide.
“We have all those multiple hotspots, and each one responds to the details of 0.4 millimeters, which is the approximate width of the [fingerprint] ridge,” Jarocka tells New Scientist. “Then our brain receives all that information. This really offers an explanation to how it’s possible that we’re so dexterous and have such a high sensitivity in our fingertips.”
These finely tuned receptive fields also followed the patterns of the person’s fingerprint ridges and stayed anchored to the same spots on the fingertip regardless of the textured card’s direction of movement or speed.
“It is enough to deflect one ridge to evoke a neural response,” Jarocka tells the Guardian.
Also speaking with the Guardian, Nathan Lepora, an expert in tactile robotics at the University of Bristol, says the work “shows for the first time that regions of the skin felt by tactile neurons appear to align with the fingerprint ridges, showing these ridges are directly involved in our sense of touch.”
Jarocka tells New Scientist this doesn’t mean that fingerprints don’t also improve our grip or provide us with other advantages, but that the study’s results finally reveal how our fingertips achieve their precise, detailed sense of touch.