The skin – the largest organ in the human body – envelops us from head to toe, allowing us to touch, feel and interact with the outside world. But there is a part of that organ that is even more attuned to the touch than any other.
A new study has revealed how receptive sensory neurons are in our fingers: after all, we can detect the touch on the tiny scale of a single fingerprint crest.
“You would expect a single papillary crest to play a role, but it was not shown [before], “Ewa Jarocka, co-author of the study at Umeå University in Sweden, said The Guardian.
Sensory neurons linked to receptors are spread just below the skin’s surface, allowing us to detect touch, vibration, pressure, pain and more. Our hands alone contain tens of thousands of these neurons, each with receptors in a small area of the skin’s surface, called the receptive field.
To map these fields, the researchers tied the arms of 12 healthy people and stuck their nails on plastic supports to make sure they couldn’t move. A machine then spun tiny 0.4mm wide cones about 7mm apart on its skin (you can see how it looks below) and the team recorded the response of each neuron using an electrode on the participants’ arms.
The configuration. (Jarocka et al., J. Neurosci, 2021)
Specifically, they were mapping the most sensitive zones – known as subfields – within these receptive fields.
By calculating the detection areas of sensory neurons and mapping them on the fingerprint, the team found that the width of the detection area was equivalent to the width of a fingerprint crest.
These subfields also did not move when the machine spun the dots faster or slower, or changed direction, suggesting that these sensitive areas are anchored in the fingerprint ridges themselves.
“We report that the sensitivity of the subfield arrangement for both types of neurons on average corresponds to a spatial period of ~ 0.4 mm and provide evidence that the spatial selectivity of a subfield arises because its associated receptor organ measures limited mechanical events to a single papillary crest, “the researchers write in their new article.
Receptive fields projected on a fingerprint. (Jarocka et al., J. Neurosci, 2021)
Excitingly, this is the first study to show that the crests of our fingerprints are helping us to feel the world around us more accurately.
“We have all of these multiple access points, and each one responds to the details of 0.4 millimeters, which is the approximate width of the [fingerprint] summit, “said Jarocka New Scientist.
“So our brain gets all this information. It really does offer an explanation of how it is possible for us to be so skilled and have such a high sensitivity at our fingertips.”
The research was published in The Journal of Neuroscience.