Nerve fibers in the skin that transmit pleasure messages to the brain have been identified by U.S. and Swedish scientists, who said their finding may improve understanding of how touch sustains human relationships.
Along with identifying these "C-tactile" nerve fibers, the researchers also found that a person's skin must be stroked at a certain rate -- four to five centimeters per second -- to activate the pleasure sensation, BBC News reported.
If the stroke rate was faster or slower, the nerve fibers weren't activated, and the touch wasn't pleasurable, according to the study of 20 people. It also found that C-tactile fibers are only present on hairy skin and are not found on the hand. The findings were published in the journal Nature Neuroscience.
The preferred stroke rate is the same as that used by a mother to comfort a baby or by couples when they're showing affection, BBC News reported. These nerve fibers are part of the evolutionary mechanism that helps humans bond, said study author Professor Francis McGlone.
"Our primary impulse as humans is procreation, but there are some mechanisms in place that are associated with behavior and reward which are there to ensure relationships continue," McGlone said.