All mammals possess the neuroanatomy to perceive pain, the differences lie in the manner in which the signals travel…or so we thought.
In order to better interpret pain in children and species that are unable to articulate suffering as artfully as for example, an adult human might, researchers have developed something called a “grimace scale.” This allows experts to estimate the severity of pain in non-humans according to objective and blinded scoring. It was previously thought that the travel time for the nerve signals that relay pain in human skin was uniquely slower than the ones that communicate touch, as compared to other mammals. However new findings published in the journal Science Advances posits the contrary.
Follow Ladders on Flipboard!
“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?” explained Saad Nagi to Medical News Today.
Humans are equipped with high-threshold and very fast conducting primary afferents.
Nagi is the principal researcher behind the latest report and an engineer at the Department of Clinical and Experimental Medicine, and the Center for Social and Affective Neuroscience at Linkoping University in Sweden. Previous research determined that other non-human mammals had ultrafast nociceptors that enabled them to detect pain stimuli almost instantaneously. Using a technique called, microneurography Nagi and his team of researchers were able to track pain and touch signals in the nerve fibers of a single neuron. The team applied brush strokes to these neurons, but they did not react. However, these nerve cells communicated pain signals just as quickly as touch sensitive ones. They applied this technique to a group of 100 healthy participants.
The established canon was that in humans touch was signaled by fast-conducting, thickly myelinated afferents, and the pain was communicated by slow-conducting thinly myelinated or unmyelinated afferents. Myelin is a mixture of proteins and phospholipids that help nerves communicate signals more quickly. The new study concluded that pain actually travels just as rapidly as touch.
“It’s becoming evident that thickly myelinated nerve fibers contribute to the experience of pain when it has a mechanical cause. 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,” explained Nagi.
Twelve percent of the neurons that had a thick coat of myelin exhibited the same characteristics of nociceptors, in that they were able to detect and communicate potentially tissue-damaging events like pinching or stroking.