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Pain signals travel just as fast as touch signals

A team of researchers from Sweden’s Linköping University, the U.K.’s Liverpool John Moores University, and the U.S.’s National Institutes of Health (NIH) have discovered that pain signaling is much more rapid than previously thought, thus challenging our understanding of pain.

“The ability to feel pain is vital to our survival, so why should our pain-signaling system be so much slower than the system used for touch, and so much slower than it could be?” asks Saad Nagi, principal research engineer of the Department of Clinical and Experimental Medicine and the Center for Social and Affective Neuroscience (CSAN) at Linköping University.

Touch signals are conducted by nerves insulated in a fatty sheath of myelin, which helps these nerves transmit signals faster. Pain signals were thought to be carried by nerves encased in thin layers of myelin, if any at all.

The research team examined nerve cells similar to those that detect touch, but had similar characteristics to pain receptors, in 100 healthy participants via a technique that allowed them to detect the signals in the nerve fibers from a single nerve cell. These cells are called nociceptors. 

The team saw that 12% of thickly myelinated nerve cells had the same properties as pain receptors, as well as a high conduction speed was as is in touch-sensitive nerve cells.

“When we activated an individual nerve cell, it caused a perception of pain, so we conclude that these nerve cells are connected to pain centers in the brain,” said Nagi.

Nagi and the team also investigated patients with various rare neurological conditions. One group of people had acquired nerve damage that led to their thickly myelinated nerve fibers being destroyed, while the small fibers were spared, thus damaging their ability to feel light touch. The scientists thought that the loss of myelinated nerve fibers should also affect the newly-identified rapidly conducting pain system. These people had an impaired ability to experience mechanical pain. 

These results could be significant for further pain research, and for the diagnosis and care of patients with pain. These findings are published in Science Advances.

“It’s becoming evident that thickly myelinated nerve fibers contribute to the experience of pain when it has a mechanical cause,” Nagi said. “Our results challenge the textbook description of a rapid system for signaling touch and a slower system for signaling pain. We suggest that pain can be signaled just as rapidly as touch.”

By Olivia Harvey, Staff Writer

Image Credit: Charlotte Perhammar/LiU

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