London, April 13 : What makes a mother's touch so comforting for her children? Well, scientists now have an answer to this question.

A team of experts from the Unilever company, the University of Gothenburg in Sweden, and the University of North Carolina have identified a class of nerve fibres in the skin which specifically send pleasure messages.

The researchers have found that people have to be stroked at a certain speed, 4-5cm per second, to activate the pleasure sensation.

They say that their findings may prove helpful in understanding how touch sustains human relationships.

During the study, the research team recorded nerve responses in 20 people, and tested how people responded to having their forearm skin stroked at a range of different speeds.

The researchers identified "C-tactile" nerve fibres as those stimulated when people said a touch had been pleasant.

They observed that the touch was not pleasurable, and the nerve fibres were not activated, when the stroke was faster or slower than the optimum speed.

The C-tactile nerve fibres are only present on hairy skin, and are not found on the hand, according to the experts.

"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," the BBC quoted lead researcher Professor Francis McGlone, now based at Unilever after an academic career where he carried out research into nerve response, as saying.

According to him, the speed at which people found arm-stroking pleasurable was the same as that which a mother uses to comfort a baby, or couples use to show affection.

He said that it was part of the evolutionary mechanism that sustained relationships between adults, or with children.

"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," he said.

A research article on this study has been published in the journal Nature Neuroscience. (ANI)