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Subsurface of fingernails found to have precise tactile localization

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A psychologist at the University of London has found that humans have a surprisingly precise degree of tactile localization beneath their fingernails. In his study, published in the Proceedings of the Royal Society B, Matthew Longo tested how well volunteers could pinpoint the part of their fingernail being stimulated and outlines possible reasons.

Humans, like other primates, have nails on the ends of their fingers rather than claws—an that has not been explained. In this new effort, Longo investigated the sensitivity of the skin below the to learn more about how they were used by our ancestors.

The human fingernail does not have any nerves; thus, it cannot sense , pressure, heat, cold or other environmental characteristics. But there is skin beneath the fingernail that is capable of sensations, as evidenced by people who accidentally hit their thumb with a hammer or lose a nail.

To learn more about the sensitivity of the subsurface of the fingernail, Longo recruited 38 adult volunteers. Each agreed to have their fingernails poked while they indicated on a photograph of a fingernail where they thought their fingernail was being touched. In the experiments, half of the volunteers had their nails touched by a stick, the other half by a filament. Only the thumb and were tested.

Longo found that humans have highly precise localization in their nails—they can tell clearly which part of their nail is being touched. He suggests that this is due to mechanoreceptors called Pacinian corpuscles, buried in the skin beneath the nails. He notes that it is the same mechanism that allows to localize touch using a cane. Pacinian corpuscles are able to detect small amounts of vibration, which happens when a slight impact occurs between a foreign object and a fingernail.

Unfortunately, the experiment did not reveal why humans developed fingernails instead of claws or why the beneath them is so sensitive. Longo theorizes that they likely served a sensorimotor function, giving humans more information about whatever their hands encounter.

More information: Matthew R. Longo, Precise tactile localization on the human fingernail, Proceedings of the Royal Society B: Biological Sciences (2024). DOI: 10.1098/rspb.2024.1200

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Citation: Subsurface of fingernails found to have precise tactile localization (2024, July 10) retrieved 25 July 2024 from
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