When it comes to comfort or pleasure, nothing seems to quite match the human touch. Mothers, for instance, have always stroked their babies' heads to calm and soothe them. Now, scientists at Unilever's Port Sunlight laboratories in the UK have found a scientific basis for this.
Humans are hard wired for sensuality, with special "pleasure" nerves in the skin that respond to touch, the research has shown. The "C-fibre" nerves may be the reason why gentle massage feels so marvellous and a lover's fingertips make the skin tingle. When properly activated, the nerves send "feel good" signals to the brain.
But they only work when the skin is stroked at just the right speed, four to five cm per second. The 'C fibre' nerves usually transmit messages of pain but record pleasure when the skin is rubbed at this speed, according to the study carried out by scientists in Britain, Germany and the United States and published in the journal Nature Neuroscience. If rubbed too fast or too slow, and the nerves are not stimulated.
Scientists demonstrated the effect of C-fibres on volunteers using a "robotic tactile stimulator" - a mechanical arm fitted with soft brush. Sensually caressed by the robot, the volunteers produced C-fibre signals that could be recorded.
The nerves are found in "hairy" skin but notably absent in the palms of the hands. "We believe this could be Mother Nature's way of ensuring that mixed messages are not sent to the brain when it is in use as a functional tool," said Professor Francis McGlone, one of the scientists from the Unilever company's Port Sunlight laboratories in Wirral, Cheshire.
The authors wrote in their report, "These results are, to the best of our knowledge, the first demonstration of a relationship between positive hedonic sensation and coding the level of the peripheral afferent nerve, suggesting that C-tactile fibres contribute critically to pleasant touch."
McGlone said, "If you get a piece of grit in your eye, have a toothache, or bite your tongue, it hurts so much because there are more C fibres there. The research we have been doing is building evidence for another role of C fibres in the skin that are not pain receptors, but are pleasure receptors."
He said the findings appear to explain "the pleasantů aspects of touch we are all familiar with, such as when grooming or being cuddled".
The scientists say the study could help understand how touch sustains human relationships. There are some mechanisms in place that are associated with behaviour and reward which are there to ensure relationships continue, they said.
For many years, scientists have been trying to understand the mechanisms behind how the body experiences pain, and the nerves involved in conveying those messages to the brain. But the researchers involved in this work were looking to understand the opposite sensation - pleasure.
"Our primary impulse as humans is procreation, but there are some mechanisms in place that are associated with behaviour and reward which are there to ensure relationships continue," McGlone said