Humans find gentle touches and strokes on the back and shoulder more pleasurable than strokes to the forearm and hand, according to new research on the effects of different types of touch on human emotions.
Researchers have linked the responses to different touches to the location of a group of nerves in the body. This led them to suggest it could be possible to create an 'emotional map' of the human body.
In mammals, nerves called C-tactile afferents (CTs) are used to detect feelings of gentle touches, and strongly respond to slow strokes, similar to a massage. In mice, these nerves are densest on the back and upper body, and there are much fewer on the lower limbs and feet.
Humans do not have CTs on the palms of their hands or the soles for their feet, but researchers did not know where exactly where they are located on the human body. If their location in the human body can be located, researchers say this would determines people's emotional responses to touch, and create an emotional body map.
To find out more about the impact of CTs, researchers from Liverpool John Moores University showed people 12 five-second videos. Each video clip showed an individual being touched on the back, shoulder, forearm, or palm at one of three speeds: static, slow and fast. Immediately after viewing each clip, researchers asked the people in the study to rate how pleasant they perceived the touch to be.
People rated touches on the back – where researchers think CTs are likely to be densely located – as most pleasant, and touches on the forearm, where they are likely to be sparse, as least pleasant.
Generally, the most pleasant touch was also associated with a slow-paced stroke. But on the palm, where these nerves have not been found, the speed of touch made no difference.
The research was presented this month at the Society for Neuroscience annual conference in Washington DC. Lead researcher Susannah Walker concluded: "Our results support the theory that a specialised system of nerves has evolved in mammals that signal the positive emotional value of gentle touch in human relations.
"We believe this system of nerves is essential because it provides the neurobiological basis for the formation and maintenance of social bonds and attachment relationships."
Touch plays a prominent role in intimate relationships and has important effects. For example, premature babies may benefit from daily stroking, and a lack of physical contact has been associated with poor outcomes in children at orphanages. In adults, social touch has been shown to promote trust and positive feelings towards other people.