BRITISH ASSOCIATION FESTIVAL OF SCIENCE:SCIENTISTS HAVE discovered a new form of touch that specifically imparts pleasure, one that connects to the emotional centres of the brain but unexpectedly uses the same type of skin nerve ending that transmits painful sensations.
The discovery shows that typical behaviours such as a mother cuddling her infant or a caress shared between partners has evolutionary significance, according to Prof Francis McGlone of Unilever RD at Liverpool University.
"Touch isn't just nice, it is of fundamental importance to our wellbeing," said Prof McGlone in a presentation on the importance of touch at the Festival of Science in Liverpool yesterday. The festival finishes later today.
Recent studies showed touch had much more than a passing effect on the person receiving the contact, he said. Premature babies used to be kept apart and untouched in incubators to reduce infection risks, unfortunately to their ultimate disadvantage.
All of these babies are now kept in regular physical touch with parents and hospital staff after findings that showed they had much better weight gain and improved immune systems if afforded this sensory contact.
Gentle stroking of the skin and light massage are also capable of altering a person's emotional state, the neuroscientist added and with colleagues in Sweden he has discovered why.
There are three main nerve fibre types for touch, temperature and pain; these are further subdivided into about 20 subtypes, he said. These tell you, for example, whether something is soft, rough, prickly, hot and so forth.
Some nerves, known as A- fibres, act very quickly to send instant messages to the brain to warn, for example, of pain, but others, called C-fibres, respond more slowly. The C-fibre group also include pain sensors and these provide the deep discomfort after a burn or toothache.
Prof McGlone and colleagues discovered, however, that C-fibres also respond to pleasant touch.
The researchers used electrodes inserted into nerve bundles to detect "traffic" towards the brain and found the greatest response from these C-fibre pleasure receptors occurred if the nerve endings were stroked. They developed a mechanical "stroking device" that could be set to deliver a fixed pressure and speed. They established that the strongest C-fibre response occurred when stroking speed was 3-4cm a second and pressure was equivalent to the apparent weight of 2g.
These tests were then conducted while subjects underwent MRI brain scans.
These showed that a response occurred in the brain's emotional centres. The C-fibres and touch "are fundamental to nurturing and caring", Prof McGlone said.
They also found however that stroking C-fibre pleasure sensors was capable of reducing pain felt by subjects exposed to a device that delivered specific levels of discomfort through heat.
Prof McGlone added that he believed that the spontaneous touching seen in humans and other primates had a strong evolutionary dimension.
"Evolution has developed these traits because they have some received value," he said.