Scientists find nerves that respond only to soft touches

Neuroscientists have discovered what romantics have always known: The touch of a lover's hand is special.

Scientists announced last week that humans have a special set of nerves for feeling pleasure at a mother's caress or a lover's embrace.

These nerves are sensitive to the soft touch of fingers gliding over a forearm or a parent's soothing hand, but not to rough touches, jabs or pinches. Scientists speculate that the nerves may be designed to guide humans toward tenderness and nurture -- a theory bolstered by the fact that the nerves are wired to the same brain areas activated by romantic love and sexual arousal.

While these special nerves, which have thin fibers and send relatively slow signals to the brain, have been previously identified in animals and humans, their role had been unclear. Scientists had wondered about their purpose, especially because they do not work as efficiently as thick nerve fibers, which are also found in skin.

The new research, published in the current issue of Nature Neuroscience, indicates that while the thick fibers rapidly shoot electrical signals to the somatosensory cortex of the brain near the crown of the head and convey information about contact and pressure, the slow fibers are connected to the insular cortex deep inside the brain and convey the emotional context of the touching. Both sets of fibers fire together, and the brain combines information about physical contact with information about emotional context, melding them together into the richness of physical experience.

Feeling the love

A crucial reason nature may have endowed people with two different sets of nerves is that the slow fibers function from the earliest hours of life, perhaps even in the womb, while the fast fibers develop slowly after birth. Wondrously, newborn infants may be able to feel the love in a parent's touch before they can feel the touch itself.

Referring to studies showing that babies need physical contact and nurture, the group of scientists from Sweden and Canada who made the discovery wrote, "The profound importance of such a system for human well-being has long been suggested, at least since the classical study of baby monkeys who show affection for a surrogate mother in response to tactile comfort."

The nerve system continues to function throughout life, underscoring the continuing importance of such comfort. While the thicker nerve fibers that communicate contact information are more densely packed into areas like the palm, the thinner nerves are found on hairy areas of the skin, like the forearm.

"Their functional role is below the level of consciousness and has to do with the emotional aspects of touch -- like the pleasure of touch," said lead scientist Hakan Olausson, a neurophysiologist at the Sahlgrenska University Hospital in Goteborg, Sweden, in a telephone interview. "The fast fibers indicate when we are touched and how strong the touch is; these signal the fine aspects of touch."

Evidence about the functioning of the slow fiber nerve system was difficult to obtain because gentle touches also trigger the parallel nerve system. Researchers knew how to trigger just the thin nerve system in animals, but that didn't reveal much about pleasure.

An unusual patient

Olausson, Lamarre and a team of scientists from Sweden and Canada based their new report on studies of an unusual patient -- a 54-year-old woman from Montreal, dubbed G.L., who suffers from a disease that destroyed the nerve system that responds to the rougher touches.