Whether it’s the rough texture of a pair of jeans, the lumpy bark of a tree, or the smooth skin of a lover, our intuition is an important aspect of how we deal with the world around us.
Now scientists say they are shedding new light on why human fingertips are so sensitive, revealing that the culprit is hiding in our fingerprints.
It has already been known that small receptors that are sensitive to mechanical stimuli occur in the fingers of the fingertips, and this interacts with two types of neurons in the fingers. The result is a ‘receptive field’: a skin area where touch activates a particular neuron.
However, it was previously unclear how small a structure could be detected by each neuron. ‘You would expect a single papillary ridge to play a role, but it has not been shown [before], ”Says Dr Ewa Jarocka, co-author of the study from Umeå University in Sweden.
To investigate the issue, Jarocka and colleagues asked 12 participants to each sit in a dentist’s chair, with their right arm slanted and their fingernails glued to a plastic container.
In the Journal of Neuroscience, the researchers write that they used a robotic drum device to run a surface of raised dots across the fingers of each participant, with each point 0.4 mm in diameter and the points 7 mm apart. . The team monitored the response of single neurons in the fingertips using electrode placed in a nerve in the participant’s arm.
Using these answers, along with the position of the dots, the researchers were able to map the receptive field for each neuron. The results confirmed that each receptive field covers an area that extends over several fingertip edges, and that there were particularly sensitive zones within each field. But it also revealed that these zones are sensitive to a single point – an object the same size as the width of a fingertip comb. In fact, they found stronger neural responses within these zones mapped to the fingertips.
“It’s enough to bend one ridge to elicit a neural response,” Jarocka said, keeping track of the results no matter how fast the drum rotated or in the direction in which it was moving.
Chris Miall, professor emeritus of motor neuroscience at the University of Birmingham, who was not involved in the research, said the study has a better understanding of how the information the brain receives from countless neurons represents the object that is affected. word.
‘What the authors show is that the fine detail of the’ receptive fields’ of individual nerve fibers that come into contact with the mechanoreceptors in the fingertips corresponds to the bowls and ridges of the fingertips. “Our very high sensitivity in the fingertips is therefore because there are many, many nerve fibers with very small receptive fields,” he said.
Prof Nathan Lepora, an expert in tangible robotics at the University of Bristol, agrees. “This work is welcome because it shows for the first time that areas of the skin that are felt by tangible neurons seem to match the fingerprint edges, which shows that these edges are directly involved in our sensation,” he said.
Miall added that while fingerprints also allow for better grip, the study highlights their role in helping us locate small details on a surface. “Wearing gloves – even thin surgical gloves – has a big impact. “So save a thought for everyone who is forced by the Covid pandemic to wear clinical gloves all day,” he said.