New Layer of "Sensory Feedback" Discovered in the Skin

Recent research on two patients suffering from congenital insensitivity to pain has revealed that there may be an additional layer of "sensory feedback" in the skin that is responsible for providing tactile information.

Discovery of this additional feedback began when two patients visited lead study author David Bowsher, MD, Honorary Senior Research Fellow at the University of Liverpool's Pain Research Institute, for treatment for excessive sweating; it was soon discovered that the patients were largely unable to perceive anything with their skin.

"Although they had a few accidents over their lifetimes, what made these two patients unique was that they led normal lives," said Bowsher, who added that this may have been why the patients had not been diagnosed earlier. Most other patients with congenital insensitivity to pain have extremely dry skin, mutilate themselves accidentally, and are often severely mentally handicapped.

"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," Bowsher continued. "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."

Skin samples of the patients were then sent to the laboratory of senior author Frank Rice, PhD, neuroscience professor at Albany Medical College and leading authority on the nerve supply to the skin. Rice and fellow researchers from the Karolinska Institute in Sweden found that the skin samples lacked nerve endings usually associated with the ability to distinguish between different temperatures, different types of mechanical contact (such as vibrations from a cell phone) and painful stimuli. This finding led researchers to wonder how the patients had ever been able to feel anything.

"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 said. "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. Apparently, these unique individuals are able to 'feel things' through these remaining nerve endings. What we learned from these unusual individuals is that there's another level of sensory feedback that can give us conscious tactile information."

The team of researchers believes that this discovery may eventually enable physicians to better ascertain if a treatment is working or if the patient is even receiving the correct treatment. The study was also published in Pain.