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Whether it’s feeling the coarse texture of jeans, the gnarled bark of a tree, or the smooth skin of a lover, our sense of touch is a crucial aspect of how we interact with the world. that surrounds us.
Now scientists say they’ve shed new light on why human fingers are so sensitive, revealing the culprit is in our fingerprints.
It was already known that tiny receptors sensitive to mechanical stimuli are found in the ridges of the fingertips, and these interact with two types of neurons in the fingers. The result is a “receptive field”: an area of skin where touch activates a particular neuron.
However, it was previously difficult to know how well a structure could be detected by each neuron. “One would expect only one papillary ridge to play a role, but this has not been shown [before]Said Dr Ewa Jarocka, co-author of the study from Umeå University in Sweden.
To investigate the problem, Jarocka and her colleagues asked 12 participants to each sit in a dentist’s chair, with their right arm tilted and their fingernails glued to a plastic holder.
Writing in the Journal of Neuroscience, the researchers report that they used a robotic drum to pass a surface of raised dots over the fingertips of each participant, with each dot 0.4mm in diameter and the dots separated. of 7 mm. The team monitored the response of single neurons in the fingertips using electrodes inserted into a nerve in the participant’s arm.
Using these responses, along with the position of the points, the researchers were able to map the receptive field of each neuron. The results confirmed that each receptive field covered an area spanning several fingertip ridges, and that within each field there were particularly sensitive areas. But he also revealed that those areas were sensitive to a single point – an object the same size as the width of a fingertip ridge. In fact, they found stronger neural responses in these areas mapped to the fingertip ridges.
“You only need to deflect an edge to evoke a neural response,” Jarocka said, adding the results kept regardless of the speed of the drum’s rotation or 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 provided insight into how information received by the brains of myriad neurons represented the object touch.
“What the authors show is that the fine details of the ‘receptor fields’ of individual nerve fibers that contact mechanoreceptors with the fingertips closely match the hollows and ridges of the fingertips. So our very high sensitivity at the fingertips is due to the fact that there are so many nerve fibers with very small receptive fields, ”he said.
Professor Nathan Lepora, an expert in tactile robotics at the University of Bristol, agrees. “This work is welcome because it shows for the first time that the regions of the skin felt by the tactile neurons seem to line up with the ridges of the fingerprints, showing that these ridges are directly involved in our sense of touch,” he said. he declared.
Miall added that while fingerprints also provide better grip, the study highlights their role in helping us detect small details on a surface. “Wearing gloves – even thin surgical gloves – has a huge impact. So think of all those who are forced by the Covid pandemic to spend all day wearing clinical gloves, ”he said.
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