NEW YORK (Reuters Health) - Researchers have zeroed in on the specific nerves that appear to communicate to the brain the positive emotions associated with touch.

Their findings are based on a 54-year-old woman who had lost the main touch nerves, or myelinated A fibers, throughout most of her body. A subset of nerves known as tactile C-fibers remained active, however. These nerves respond to slow stroking of the skin but not to stronger sensations, suggesting that they are not important for taking in tactile stimulation.

But, according to the study in an advance online publication of the September issue of Nature Neuroscience, they may play a key role in communicating emotional information.

A brain scan with functional MRI revealed that areas of the woman's brain involved in processing emotional information were triggered when researchers stroked her arm lightly with a paintbrush, despite the loss of her main touch nerves.

These areas were not activated in response to a stronger sensation on the same area of her arm, report Dr. Hakan Olausson from Sahlgrenska University in Goteborg, Sweden, and colleagues.

"I think our findings emphasize how important the emotional aspect of touch is," Olausson told Reuters Health. "We show here that we have a system of nerve fibers that primarily signal emotional aspects of touch to the brain."

He suggested that the same fibers might play a role in reducing the sensation of pain--in particular, chronic pain--because these fibers communicate feelings of well-being. Olausson is now testing this idea on a group of patients with spinal cord injuries.

SOURCE: Nature Neuroscience 2002;10.1038/nn896.

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