Researchers map the mechanisms behind affective touch

Skin-to-skin contact with slow strokes across the body, such as between a parent and a newborn child or between two adults, gives us a sense of pleasure and security. But why is this so and what role do sensory mechanisms have in making humans a social being?

These questions interest researchers around the world.

For more than 20 years, researchers at Sahlgrenska Academy at the Gothenburg University have been examining the neurological mechanisms behind touch, focusing on the C-tactile nerve fibers in our skin. These researchers have now shown that these nerve fibers are calibrated to respond to human touch.

In their latest study, the researchers inserted thin needles into the nerves of conscious subjects and, in this way, were able to "eavesdrop" on the nerve fibers’ signals. Their study shows that there is an optimum speed that causes the C-tactile fibers to react the strongest: when the stroking occurs at 1-10 cm per second.

Temperature also plays a role. Stroking with hot and cold temperatures results in lower activity, while skin-temperature stroking causes the greatest response.

"The positive benefits of a touch require more than just being touched by any soft object. The strongest sense of comfort and security requires the touch to occur between people, skin to skin," says Rochelle Ackerley, a researcher at Sahlgrenska Academy.

"In other words, it seems we have a system of nerve fibers finely tuned to respond to the force, speed and temperature of another person’s caressing stroke of the skin."

The researchers’ conclusion is that the C-tactile nerve fibers play an important role in creating affinity between people, especially between parents and a newborn.

"The C-tactile nerve fibers belong to the same family of nerve fibers that signal warning when we are subjected to pain. Both types of signals are probably processed in the same parts of our brain, and our results provide a large piece of the puzzle to understanding how the body’s sensory system works," says Helena Backlund Wasling, who led the study.

According to the researchers, the new results are significant for anyone working with people in need of touch, from newborns to the elderly.

In future studies the researchers will more closely map the nerve fiber mechanisms and study how our system of touch and feelings develop and change through life.

"International studies have shown that young children who suffer from lack of contact do not fully develop their nervous systems. Conversely, touch can be used as extra stimulus in premature babies to stimulate development of the nervous system," says Rochelle Ackerley.

"We wonder if the C-tactile nerve fibers work the same in newborns as in older people? Is affective touch as important for older people as it is for small children, and can we optimize the physical closeness that we know premature babies need?

Article Human C-tactile afferents are tuned to the temperature of a skin-stroking caress published in The Journal of Neuroscience on February 18.