Nerve signals that tell the brain that we are being slowly stroked on the skin have their own specialised nerve fibres in the skin. This is shown by a new study from the Sahlgrenska Academy, University of Gothenburg, Sweden. The discovery may explain why touching the skin can relieve pain.
The specialised nerve fibres in the skin are called CT nerves (C-tactile) and they travel directly to the areas in the brain that are important in the emergence of feelings.
"Basically the signals that tell the brain that we are being stroked on the skin have their own direct route to the brain, and are not blocked even if the brain is receiving pain impulses from the same area. In fact it's more the opposite, that the stroking impulses are able to deaden the pain impulses," says Line Löken, postgraduate student in neurophysiology at the Sahlgrenska Academy.
The results are being published in the distinguished scientific journal, Nature Neuroscience. The research group examined a group of healthy subjects using a technique called microneurography.
"By inserting a thin electrode into a nerve in the forearm we can listen in on the nerve and pick up signals from one of the thousands of nerve fibres that make up a nerve," explains Associate Professor Håkan Olausson, who is leading the research group behind the discovery, together with Johan Wessberg.
Each individual nerve fibre is responsible for touch signals from roughly a square centimetre of skin. The research team used a specially-designed robot, which brushed over the exact area of skin for which a particular nerve fibre is responsible. The subjects were also asked to rate how pleasant or unpleasant they found the brushing.
"As the nerve signals that were sent in the CT nerves became more frequent, the subjects reported the experience as being increasingly pleasant. Of the skin nerves that we studied, it was only the CT nerves that had this strong link between the frequency of the signals and how pleasant it felt," says researcher Johan Wessberg.