The human body may be equipped with a separate sensory system aside from the nerves that gives us the ability to touch and feel, according to a new study.
Most of us have millions of different types of nerve endings just beneath the skin that let us feel our surroundings. However, the once-hidden and recently discovered skin sense, found in two patients, is located throughout the blood vessels and sweat glands, and most of us don't even notice it's there.
"It's almost like hearing the subtle sound of a single instrument in the midst of a symphony," said senior author Frank Rice, a neuroscience professor at Albany Medical College in New York. "It is only when we shift focus away from the nerve endings associated with normal skin sensation that we can appreciate the sensation hidden in the background."
Our skin, the body's largest organ, seems to have some extraordinary qualities, as another recent study showed skin can hear.
The new finding, detailed in the Dec. 15 issue of the journal Pain, could help scientists to understand mysterious pain conditions such as migraine headaches and fibromyalgia. The study, and others by the team, was supported by the National Institutes of Health and several pharmaceutical companies.
The research team discovered the sensory system when studying two patients who were born with very little ability to feel pain — an extremely rare condition called congenital insensitivity to pain. Other individuals with this condition have excessively dry skin, often mutilate themselves accidentally and usually have severe mental handicaps, the researchers say.
It wasn't their pain-free lives that brought the patients into the lab, but rather excessive sweating.
"Curiously, our conventional tests with sensitive instruments revealed that all their skin sensation was severely impaired, including their response to different temperatures and mechanical contact," said study researcher Dr. David Bowsher, Honorary Senior Research Fellow at the University of Liverpool's Pain Research Institute.
"But, for all intents and purposes, they had adequate sensation for daily living and could tell what is warm and cold, what is touching them, and what is rough and smooth."
Bowsher took skin biopsies and sent them to Rice's lab for microscopic analyses of the nerve endings.
"Much to our surprise, the skin we received from England lacked all the nerve endings that we normally associated with skin sensation," Rice said. "So how were these individuals feeling anything?"
The answer: While the patients lacked the usual nerve endings in the skin, Rice and colleagues found sensory nerve endings on the small blood vessels and sweat glands embedded in their skin.
"Apparently, these unique individuals are able to 'feel things' through these remaining nerve endings," Rice said. "For many years, my colleagues and I have detected different types of nerve endings on tiny blood vessels and sweat glands, which we assumed were simply regulating blood flow and sweating."
Rice added, "We didn't think they could contribute to conscious sensation. However, while all the other sensory endings were missing in this unusual skin, the blood vessels and sweat glands still had the normal types of nerve endings."