Fingerprints Enhance Our Sense of Touch | Nutrition Fit

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Summary: Sensory neurons in the fingertips are able to detect tactile stimuli at the scale of a single fingerprint ridge.

Source: SfN

Fingerprints may be more useful to us than helping us nab criminal suspects: they also improve our sense of touch.

Sensory neurons in the finger can detect touch on the scale of a single fingerprint ridge, according to new research published in Journal of Neuroscience.

The hand contains tens of thousands of sensory neurons. Each neuron tunes in to a small surface area on the skin — a receptive field — and detects touch, vibration, pressure, and other tactile stimuli. The human hand possesses a refined sense of touch, but the exact sensitivity of a single sensory neuron has not been studied before.

To address this, Jarocka et al. measured the electrical activity of the sensory neurons in human fingertips when they stimulated with raised dots swept over the skin.

The research team calculated the detection areas of the sensory neurons and mapped them onto the fingerprints.

This shows a finger with a heatmap over the fingerprint area showing where the sensory neurons are
Receptive fields of sensory neurons in the hand, mapped onto a fingertip. Credit: Jarocka et al., JNeurosci 2021

The width of the detection areas matched the width of a single fingerprint ridge. These areas stayed on the same fingerprint ridges during different scanning speeds and directions, indicating that they are anchored to the fingerprint ridges.

The overlap of receptive fields with small detection areas explains how humans have such a sensitive and accurate sense of touch.

About this sensory perception research news

Source: SfN
Contact: Calli McMurray – SfN
Image: The image is credited to Jarocka et al., JNeurosci 2021

Original Research: Closed access.
Human Touch Receptors Are Sensitive To Spatial Details on the Scale of Single Fingerprint Ridges” by Ewa Jarocka, J Andrew Pruszynski and Roland S Johansson. Journal of Neuroscience


Abstract

Human Touch Receptors Are Sensitive To Spatial Details on the Scale of Single Fingerprint Ridges

Fast-adapting type 1 (FA-1) and slowly-adapting type 1 (SA-1) first-order tactile neurons provide detailed spatiotemporal tactile information when we touch objects with fingertips.

The distal axon of these neuron types branches in the skin and innervates many receptor organs associated with fingerprint ridges (Meissner corpuscles and Merkel cell neurite complexes, respectively), resulting in heterogeneous receptive fields whose sensitivity topography includes many highly sensitive zones or ‘subfields’. In experiments on humans of both sexes, using raised dots that tangentially scanned the receptive field we examined the spatial acuity of the subfields of FA-1 and SA-1 neurons and its constancy across scanning speed and direction.

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We report that the sensitivity of the subfield arrangement for both neuron types on average corresponds to a spatial period of ∼0.4 mm and provide evidence that a subfield’s spatial selectivity arises because its associated receptor organ measures mechanical events limited to a single papillary ridge.

Accordingly, the sensitivity topography of a neuron’s receptive fields is quite stable over repeated mappings and over scanning speeds representative of real-world hand use.

The sensitivity topography is substantially conserved also for different scanning directions, but the subfields can be relatively displaced by direction-dependent shear deformations of the skin surface.

SIGNIFICANCE STATEMENT

The branching of the distal axon of human first-order tactile neurons with receptor organs associated with fingerprint ridges (Meissner and Merkel end-organs) results in cutaneous receptive fields composed of several distinct subfields spread across multiple ridges.

We show that the subfields’ spatial selectivity typically corresponds to the dimension of the ridges (∼0.4 mm) and a neuron’s subfield layout is well preserved across tangential movement speeds and directions representative of natural use of the fingertips.

We submit that the receptor organs underlying subfields essentially measure mechanical events at individual ridges. That neurons receive convergent input from multiple subfields does not preclude the possibility that spatial details can be resolved on the scale of single fingerprint ridges by a population code.

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